Locomotion & Movement

Topic: Muscular System; Subtopic: Muscle Contraction Mechanism

Keyword Definitions:

• Actin: Protein forming thin filaments in muscle fibers, interacts with myosin for contraction.

• Myosin: Motor protein forming thick filaments, generates force during muscle contraction through cross-bridge cycling.

• Z-line: Structure at each end of sarcomere anchoring thin filaments and defining sarcomere boundaries.

• Sarcoplasmic Reticulum: Specialized endoplasmic reticulum in muscle storing and releasing calcium ions for contraction.

• Acetylcholine: Neurotransmitter released at neuromuscular junction to trigger muscle contraction, stored in vesicles, not sarcoplasmic reticulum.

• Calcium Binding Sites: Found on troponin in thin filaments, essential for initiating contraction, not on myosin cross-bridges.

• Thin Filament: Filament in muscle composed mainly of actin, troponin, and tropomyosin, responsible for sliding past thick filament.

• Thick Filament: Filament composed mainly of myosin, responsible for generating force through ATP-driven interactions with actin.

Lead Question - 2022 (Abroad)
Which of the following is correct statement ?
1. Actin and regulatory proteins are located in thin filament.
2. Z-lines anchor myosin (thick) filament to the ends of the sarcomere.
3. Sarcoplasmic reticulum stores acetylcholine.
4. Myosin cross bridges contain calcium binding sites.
Explanation: The correct answer is Actin and regulatory proteins are located in thin filament. In skeletal muscles, thin filaments are composed of actin along with regulatory proteins troponin and tropomyosin, which control contraction by exposing myosin-binding sites. Z-lines anchor thin filaments, not thick myosin filaments. Sarcoplasmic reticulum stores calcium, not acetylcholine. Calcium binds to troponin on thin filaments, not myosin cross-bridges. The sliding filament mechanism relies on ATP-driven interactions between actin (thin) and myosin (thick) filaments, regulated by calcium binding to troponin, ensuring coordinated contraction and relaxation cycles in skeletal muscles.

1. Single Correct Answer Type:
Which protein forms thick filaments in skeletal muscle?
1. Actin
2. Myosin
3. Troponin
4. Tropomyosin
Explanation: The correct answer is Myosin. Myosin molecules assemble into thick filaments in skeletal muscle sarcomeres. These filaments interact with actin thin filaments to generate contraction through ATP-powered cross-bridge cycling. Troponin and tropomyosin are regulatory proteins in thin filaments. Actin forms thin filaments and provides binding sites for myosin. This structure enables the sliding filament mechanism crucial for muscle contraction, making myosin essential for force generation in muscles and a key target in studies of muscle physiology and related disorders.

2. Single Correct Answer Type:
What is the main function of the sarcoplasmic reticulum in muscle fibers?
1. Store acetylcholine
2. Release calcium ions
3. Anchor thick filaments
4. Produce ATP
Explanation: The correct answer is Release calcium ions. The sarcoplasmic reticulum is a specialized endoplasmic reticulum in muscle cells that stores calcium ions. Upon stimulation by a nerve impulse, it releases calcium into the sarcoplasm, initiating contraction by binding to troponin on thin filaments. It does not store acetylcholine, anchor thick filaments, or produce ATP. Calcium release and reuptake regulate contraction and relaxation cycles, and proper functioning is essential for effective muscle contraction, excitation-contraction coupling, and overall muscle physiology.

3. Single Correct Answer Type:
Which structure anchors thin filaments in a sarcomere?
1. M-line
2. Z-line
3. Sarcoplasmic reticulum
4. T-tubules
Explanation: The correct answer is Z-line. Z-lines are boundaries of sarcomeres and anchor the thin filaments (actin) at each end. M-line anchors thick filaments (myosin). Sarcoplasmic reticulum stores calcium, while T-tubules transmit action potentials into the muscle fiber. Proper anchoring at Z-lines ensures sarcomere stability and allows efficient force transmission during contraction. Misalignment can cause impaired contraction, demonstrating the importance of Z-lines in structural integrity and function of skeletal muscles.

4. Single Correct Answer Type:
Where are calcium binding sites located in skeletal muscle?
1. Myosin cross-bridges
2. Troponin on thin filaments
3. Tropomyosin on thick filaments
4. Actin filaments
Explanation: The correct answer is Troponin on thin filaments. Calcium ions released from the sarcoplasmic reticulum bind to troponin, causing a conformational change that moves tropomyosin off myosin-binding sites on actin filaments. This allows myosin cross-bridges to bind actin, generating contraction. Myosin cross-bridges do not bind calcium. The precise location of calcium binding is essential for controlled contraction and relaxation cycles in skeletal muscles, forming a central mechanism in excitation-contraction coupling and proper muscular function.

5. Single Correct Answer Type:
Which protein regulates myosin binding to actin in skeletal muscle?
1. Myosin
2. Troponin
3. Tropomyosin
4. Both Troponin and Tropomyosin
Explanation: The correct answer is Both Troponin and Tropomyosin. Troponin binds calcium, causing tropomyosin to shift, exposing myosin-binding sites on actin. This regulation ensures that contraction occurs only when calcium levels rise. Myosin provides force but does not regulate binding. This coordinated interaction is essential for the sliding filament mechanism, enabling controlled muscle contraction and relaxation. Disruption can result in impaired muscle function and highlights the importance of regulatory proteins in skeletal muscle physiology.

6. Single Correct Answer Type:
Which molecule initiates muscle contraction by binding to troponin?
1. ATP
2. Acetylcholine
3. Calcium ions
4. ADP
Explanation: The correct answer is Calcium ions. Calcium released from the sarcoplasmic reticulum binds to troponin on thin filaments, inducing a conformational change that moves tropomyosin, exposing myosin-binding sites on actin. Acetylcholine triggers the action potential but does not directly bind troponin. ATP fuels myosin head movement, and ADP is a hydrolysis product. Calcium’s role is critical in excitation-contraction coupling, enabling the initiation of contraction at the molecular level and coordinating the precise timing of sarcomere shortening in skeletal muscles.

7. Assertion-Reason Type:
Assertion (A): Tropomyosin blocks myosin-binding sites on actin in resting muscle.
Reason (R): Troponin binds calcium ions to move tropomyosin and expose myosin-binding sites.
1. Both A and R are correct, and R is the correct explanation of A
2. Both A and R are correct, but R is not the correct explanation of A
3. A is correct, R is false
4. A is false, R is true
Explanation: Correct answer is Both A and R are correct, and R is the correct explanation of A. Tropomyosin covers myosin-binding sites in relaxed muscle. When calcium binds troponin, it induces a conformational change moving tropomyosin away, allowing myosin to attach to actin and generate contraction. This process underlies the regulation of skeletal muscle contraction and is essential for coordinated force generation during excitation-contraction coupling. The interplay between troponin, tropomyosin, calcium, and actin ensures precise control of muscle contraction.

8. Matching Type:
Match the structure with its function:
A. Z-line → (i) Store calcium
B. Sarcoplasmic reticulum → (ii) Anchor thin filaments

Topic: Human Muscular System
Subtopic: Muscular Disorders and Diseases

Keyword Definitions:

• Tetanus: A condition causing involuntary muscle contractions due to low calcium or bacterial toxins affecting motor neurons.

• Myasthenia gravis: An autoimmune disorder that weakens skeletal muscles by interfering with acetylcholine receptors.

• Muscular dystrophy: A genetic disorder causing progressive degeneration and weakening of muscles.

• Arthritis: Inflammation of one or more joints causing pain and stiffness, especially with age or autoimmune causes.

• Calcium ions (Ca²⁺): Essential for muscle contraction by binding to troponin, exposing binding sites for actin-myosin interaction.

Lead Question – 2022
Which of the following is a correct match for disease and its symptoms:
(1) Tetanus – high Ca²⁺ level causing rapid spasms
(2) Myasthenia gravis – Genetic disorder resulting in weakening and paralysis of skeletal muscle
(3) Muscular dystrophy – An autoimmune disorder causing progressive degeneration of skeletal muscle
(4) Arthritis – Inflamed joints

Explanation: Arthritis is a disorder characterized by inflammation of joints, causing swelling, stiffness, and pain. It is the correct match among the given options, while others describe wrong associations of cause and nature. Therefore, the correct answer is (4) Arthritis – Inflamed joints.

1. Which of the following is an autoimmune disorder affecting neuromuscular junctions?
(1) Myasthenia gravis
(2) Tetanus
(3) Muscular dystrophy
(4) Osteoarthritis
Explanation: Myasthenia gravis is an autoimmune disease that blocks acetylcholine receptors at neuromuscular junctions, causing muscle weakness. The correct answer is (1).

2. The genetic disorder resulting in progressive muscle degeneration is:
(1) Myasthenia gravis
(2) Muscular dystrophy
(3) Arthritis
(4) Gout
Explanation: Muscular dystrophy is caused by defective genes responsible for muscle structure and repair, leading to gradual muscle degeneration. The correct answer is (2).

3. Which of the following occurs due to sustained muscle contraction without relaxation?
(1) Muscle fatigue
(2) Muscle twitch
(3) Tetanus
(4) Cramp
Explanation: Tetanus occurs when muscle fibers remain contracted for a long duration due to continuous stimulation or bacterial toxin. The correct answer is (3).

4. Inflammation of joints leading to stiffness and pain is known as:
(1) Myalgia
(2) Osteoporosis
(3) Arthritis
(4) Rickets
Explanation: Arthritis is a condition characterized by joint inflammation and stiffness, often due to aging, autoimmune response, or infection. Hence, the correct answer is (3).

5. Which ion is essential for initiating muscle contraction?
(1) Sodium
(2) Potassium
(3) Calcium
(4) Magnesium
Explanation: Calcium ions play a crucial role in muscle contraction by binding to troponin, exposing actin binding sites for myosin cross-bridge formation. Hence, the correct answer is (3).

6. Which of the following is a bacterial disease affecting muscles?
(1) Tetanus
(2) Myasthenia gravis
(3) Arthritis
(4) Muscular dystrophy
Explanation: Tetanus is caused by Clostridium tetani, whose toxin affects motor neurons and causes continuous muscle spasms. Hence, the correct answer is (1).

7. Assertion (A): Myasthenia gravis is an autoimmune disorder affecting skeletal muscles.
Reason (R): It destroys acetylcholine receptors, reducing nerve impulse transmission.
(1) Both A and R are true and R explains A
(2) Both A and R are true but R does not explain A
(3) A is true but R is false
(4) A is false but R is true
Explanation: Both statements are true and the reason correctly explains the assertion, as receptor damage causes reduced muscle contraction. Hence, the correct answer is (1).

8. Match the following:
A. Tetanus — (i) Genetic muscle degeneration
B. Myasthenia gravis — (ii) Autoimmune disorder
C. Muscular dystrophy — (iii) Bacterial toxin
D. Arthritis — (iv) Joint inflammation
Options:
(1) A-(iii), B-(ii), C-(i), D-(iv)
(2) A-(i), B-(iii), C-(iv), D-(ii)
(3) A-(ii), B-(i), C-(iii), D-(iv)
(4) A-(iv), B-(ii), C-(i), D-(iii)
Explanation: Tetanus results from bacterial toxins, Myasthenia gravis is autoimmune, Muscular dystrophy is genetic, and Arthritis involves joint inflammation. Hence, the correct answer is (1).

9. Fill in the blank:
In Myasthenia gravis, _______ receptors are blocked by antibodies.
(1) Dopamine
(2) Serotonin
(3) Acetylcholine
(4) Epinephrine
Explanation: In Myasthenia gravis, acetylcholine receptors at neuromuscular junctions are blocked by autoantibodies, leading to muscle weakness. Hence, the correct answer is (3).

10. Choose the correct statements:
(1) Arthritis affects joints.
(2) Myasthenia gravis is bacterial.
(3) Muscular dystrophy is autoimmune.
(4) Tetanus is genetic.
Explanation: Arthritis causes joint inflammation, Myasthenia gravis is autoimmune, Muscular dystrophy is genetic, and Tetanus is bacterial. Hence, only statement (1) is correct.

Topic: Skeletal System and Bone Disorders
Subtopic: Osteoporosis and Hormonal Influence

Keyword Definitions:
• Osteoporosis: Condition characterized by decreased bone mass and increased fragility.
• Bone mass: The density and strength of bones.
• Fracture: Break or crack in a bone.
• Estrogen: Primary female sex hormone that helps maintain bone density.
• Calcium: Mineral essential for bone strength.
• Vitamin D: Vitamin necessary for calcium absorption in bones.
• Bone remodeling: Continuous process of bone formation and resorption.
• Osteoclast: Cell that breaks down bone tissue.
• Osteoblast: Cell that forms new bone.
• Hormonal imbalance: Disruption in hormone levels affecting body functions.

Lead Question (2022):
Given below are two statements: one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A): Osteoporosis is characterised by decreased bone mass and increased chances of fractures.
Reason (R): Common cause of osteoporosis is increased levels of estrogen.
(1) Both (A) and (R) are correct but (R) is not the correct explanation (A)
(2) (A) is correct but (R) is not correct
(3) (A) is not correct but (R) is correct
(4) Both (A) and (R) are correct and (R) is the correct explanation of (A)

Explanation: The correct answer is (2). Osteoporosis involves decreased bone mass, making bones fragile and more prone to fractures. However, increased estrogen does not cause osteoporosis; rather, decreased estrogen levels, especially after menopause, are a common cause. Hence, the assertion is correct, but the reason is incorrect.

Guessed MCQs:

1. Single Correct Answer:
Which hormone deficiency is a major cause of osteoporosis in postmenopausal women?
(a) Testosterone
(b) Estrogen
(c) Progesterone
(d) Cortisol
Explanation: The correct answer is (b). Decreased estrogen levels after menopause reduce bone density, leading to osteoporosis and higher fracture risk.

2. Single Correct Answer:
Which cell type is primarily responsible for bone resorption in osteoporosis?
(a) Osteoblast
(b) Osteocyte
(c) Osteoclast
(d) Chondrocyte
Explanation: The correct answer is (c). Osteoclasts break down bone tissue, and excessive activity relative to osteoblasts leads to decreased bone mass in osteoporosis.

3. Single Correct Answer:
Which nutrient deficiency worsens osteoporosis?
(a) Vitamin C
(b) Calcium
(c) Iron
(d) Vitamin K
Explanation: The correct answer is (b). Calcium deficiency reduces bone mineral density, aggravating osteoporosis and increasing susceptibility to fractures.

4. Assertion-Reason MCQ:
Assertion (A): Postmenopausal women are at higher risk of osteoporosis.
Reason (R): Decreased estrogen levels accelerate bone loss.
(a) Both A and R are correct and R explains A
(b) Both A and R are correct but R does not explain A
(c) A is correct, R is incorrect
(d) A is incorrect, R is correct
Explanation: The correct answer is (a). After menopause, estrogen levels drop, accelerating bone resorption by osteoclasts, increasing osteoporosis risk.

5. Single Correct Answer:
Which of the following is a preventive measure for osteoporosis?
(a) Weight-bearing exercises
(b) Smoking
(c) Excess alcohol
(d) Sedentary lifestyle
Explanation: The correct answer is (a). Weight-bearing exercises stimulate bone formation and increase bone density, helping prevent osteoporosis.

6. Single Correct Answer:
Which vitamin is essential for calcium absorption and bone health?
(a) Vitamin A
(b) Vitamin D
(c) Vitamin C
(d) Vitamin K
Explanation: The correct answer is (b). Vitamin D facilitates calcium absorption in the gut, maintaining bone mineral density and preventing osteoporosis.

7. Matching Type:
Match the following:
Column A
1. Osteoblast
2. Osteoclast
3. Calcium
4. Estrogen
Column B
A. Promotes bone formation
B. Breaks down bone
C. Mineral essential for bones
D. Hormone that maintains bone density
Options:
(a) 1-A, 2-B, 3-C, 4-D
(b) 1-B, 2-A, 3-D, 4-C
(c) 1-A, 2-B, 3-D, 4-C
(d) 1-B, 2-A, 3-C, 4-D
Explanation: The correct answer is (a). Osteoblast forms bone (1-A), osteoclast breaks bone (2-B), calcium is essential mineral (3-C), estrogen maintains bone density (4-D).

8. Fill in the Blanks:
Osteoporosis is characterized by decreased _______ and increased risk of _______.
(a) Bone mass, fractures
(b) Muscle mass, injuries
(c) Bone mass, infections
(d) Cartilage, fractures
Explanation: The correct answer is (a). Osteoporosis reduces bone mass and increases fragility, making bones prone to fractures, especially in elderly individuals.

9. Single Correct Answer:
Which lifestyle factor aggravates osteoporosis?
(a) Balanced diet
(b) Regular exercise
(c) Smoking
(d) Sunlight exposure
Explanation: The correct answer is (c). Smoking accelerates bone loss and reduces estrogen levels, increasing osteoporosis risk and fracture susceptibility.

10. Choose the correct statements:
(a) Osteoporosis involves decreased bone mass
(b) Decreased estrogen levels increase osteoporosis risk
(c) High calcium and vitamin D intake prevent osteoporosis
(d) Osteoporosis is caused by increased estrogen
Explanation: The correct answer is (a), (b), and (c). Osteoporosis results from decreased bone mass, aggravated by low estrogen, and can be mitigated with calcium and vitamin D intake.

Topic: Skeletal System
Subtopic: Vertebral Column and Joints

Keyword Definitions:
• Vertebral Column: Series of bones (vertebrae) forming the backbone and protecting the spinal cord.
• Cartilage: Flexible connective tissue found between bones providing cushioning and reducing friction.
• Areolar Tissue: Loose connective tissue supporting organs and blood vessels.
• Smooth Muscle: Involuntary muscle found in internal organs controlling movements.
• Intercalated Discs: Specialized junctions between cardiac muscle cells for synchronized contraction.
• Joint: Site where two or more bones meet enabling movement.
• Disc (Intervertebral): Fibrocartilaginous structure between vertebrae absorbing shocks.
• Ligament: Fibrous tissue connecting bones and stabilizing joints.
• Spinal Cord: Nervous tissue transmitting signals between brain and body.
• Vertebra: Individual bones forming the vertebral column.

Lead Question (2022):
Which of the following is present between the adjacent bones of the vertebral column?
(1) Cartilage
(2) Areolar tissue
(3) Smooth muscle
(4) Intercalated discs

Explanation: The correct answer is (1). Cartilage, specifically fibrocartilage forming intervertebral discs, is located between adjacent vertebrae. It acts as a cushion, absorbs shocks, allows slight movement, and prevents friction between bones, thus maintaining flexibility and strength of the vertebral column.

Guessed MCQs:

1. Single Correct Answer:
Which connective tissue cushions joints and absorbs shocks?
(a) Cartilage
(b) Ligament
(c) Areolar tissue
(d) Tendon
Explanation: The correct answer is (a). Cartilage, especially fibrocartilage, acts as a cushion in joints and between vertebrae, reducing friction, absorbing shocks, and allowing smooth movement of bones, thus maintaining structural integrity of the skeletal system.

2. Single Correct Answer:
Which type of cartilage is present in intervertebral discs?
(a) Fibrocartilage
(b) Hyaline
(c) Elastic
(d) Articular
Explanation: The correct answer is (a). Fibrocartilage, strong and resilient, forms intervertebral discs between vertebrae, providing cushioning, flexibility, and resistance to compression, helping maintain proper posture and spinal integrity.

3. Assertion-Reason MCQ:
Assertion (A): Intervertebral discs contain fibrocartilage.
Reason (R): Fibrocartilage provides cushioning and absorbs mechanical stress.
(a) Both A and R are correct, R explains A
(b) Both A and R are correct, R does not explain A
(c) A is correct, R is false
(d) A is false, R is true
Explanation: The correct answer is (a). Intervertebral discs are made of fibrocartilage, which cushions vertebrae, absorbs shocks, and allows flexibility. This tissue ensures stability and prevents damage to the vertebral column during movement.

4. Matching Type MCQ:
Match the tissue with its location:
A. Cartilage – (i) Between vertebrae
B. Areolar tissue – (ii) Under skin and around organs
C. Smooth muscle – (iii) Walls of internal organs
D. Intercalated discs – (iv) Heart muscle
Options:
1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–iv, C–ii, D–i
4. A–iv, B–iii, C–ii, D–i
Explanation: The correct answer is (1). Cartilage cushions vertebrae, areolar tissue supports organs, smooth muscle is found in organ walls, and intercalated discs connect cardiac muscle cells for coordinated heart contractions.

5. Single Correct Answer:
What connects bones and stabilizes joints?
(a) Ligaments
(b) Tendons
(c) Cartilage
(d) Areolar tissue
Explanation: The correct answer is (a). Ligaments are strong fibrous connective tissues that connect bones, stabilizing joints and preventing excessive movement, complementing cartilage that cushions bones at joints.

6. Single Correct Answer:
Which structure in vertebrae allows slight movement while maintaining stability?
(a) Intervertebral disc
(b) Tendon
(c) Smooth muscle
(d) Areolar tissue
Explanation: The correct answer is (a). Intervertebral discs, made of fibrocartilage, provide cushioning and slight flexibility, enabling movement of vertebrae while preventing friction and absorbing mechanical stress.

7. Fill in the Blanks:
The intervertebral ________ is made of fibrocartilage and absorbs shocks between vertebrae.
(a) disc
(b) ligament
(c) tendon
(d) muscle
Explanation: The correct answer is (a). Intervertebral discs, consisting of fibrocartilage, cushion the vertebrae, absorb mechanical shocks, and permit limited movement, ensuring spinal stability and protecting the spinal cord.

8. Single Correct Answer:
Which tissue type is not present between vertebrae?
(a) Smooth muscle
(b) Cartilage
(c) Fibrocartilage
(d) Nucleus pulposus
Explanation: The correct answer is (a). Smooth muscle is absent between vertebrae; instead, intervertebral discs with fibrocartilage and a gelatinous nucleus pulposus provide cushioning and shock absorption.

9. Single Correct Answer:
Which part of intervertebral disc acts as a shock absorber?
(a) Nucleus pulposus
(b) Ligament
(c) Tendon
(d) Articular cartilage
Explanation: The correct answer is (a). The nucleus pulposus, the gelatinous core of the intervertebral disc, distributes pressure evenly and absorbs mechanical shocks between adjacent vertebrae.

10. Choose the correct statements:
(a) Intervertebral discs are fibrocartilaginous.
(b) Cartilage prevents friction between bones.
(c) Smooth muscles are present between vertebrae.
(d) Ligaments connect and stabilize bones.
Options:
1. a, b, d only
2. a and c only
3. b and c only
4. All statements
Explanation: The correct answer is (1). Intervertebral discs are fibrocartilaginous, cartilage prevents bone friction, and ligaments stabilize joints. Smooth muscles are not present between vertebrae, so statement (c) is incorrect.

Topic: Human Skeletal System
Subtopic: Types of Bones and Joints

Keyword Definitions:

• Scapula: A large triangular flat bone of the shoulder girdle.

• Cranium: Part of the skull protecting the brain, joined by fibrous joints.

• Sternum: Flat bone in the thoracic region where ribs attach anteriorly.

• Vertebral column: Bony structure made of vertebrae, connected by cartilaginous joints.

• Flat bone: Bone type providing protection and muscle attachment, e.g., sternum.

• Fibrous joints: Immovable joints connected by dense connective tissue.

• Cartilaginous joints: Slightly movable joints connected by cartilage, e.g., vertebrae.

• Axial skeleton: Skeleton including skull, vertebral column, ribs, and sternum.

• Appendicular skeleton: Bones of limbs and girdles connecting them to axial skeleton.

• Bone classification: Bones classified into long, short, flat, and irregular types.

• Joint: Point of articulation between bones enabling movement or stability.

Lead Question - 2021

Match List - I with List - II
List - I  List - II
(a) Scapula  (i) Cartilaginous joints
(b) Cranium  (ii) Flat bone
(c) Sternum  (iii) Fibrous joints
(d) Vertebral column  (iv) Triangular flat bone
Choose the correct answer from the options given below
(1) (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
(2) (a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)
(3) (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
(4) (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)

Explanation: Scapula is a triangular flat bone (a-iv). Cranium bones are joined by fibrous joints (b-iii). Sternum is a flat bone (c-ii). Vertebral column has cartilaginous joints (d-i). Therefore, the correct matching is (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i). Correct answer is option (3).

1. Single Correct Answer:
Which of the following is a flat bone?
(1) Femur
(2) Sternum
(3) Radius
(4) Humerus
Explanation: Sternum is a flat bone forming the anterior part of the thoracic cage. Femur and humerus are long bones, radius is also a long bone. Correct answer is option (2).

2. Single Correct Answer:
Fibrous joints are found in:
(1) Knee
(2) Skull sutures
(3) Vertebrae
(4) Shoulder
Explanation: Fibrous joints are immovable and found in skull sutures where bones are tightly joined by connective tissue. Knee and shoulder have synovial joints, vertebrae have cartilaginous joints. Correct answer is option (2).

3. Single Correct Answer:
Vertebral column joints are mainly:
(1) Fibrous
(2) Cartilaginous
(3) Synovial
(4) Ball and socket
Explanation: Vertebrae are joined by cartilaginous joints allowing slight movement and providing flexibility with stability. Fibrous joints are immovable, synovial joints allow free movement, ball and socket is a type of synovial joint. Correct answer is option (2).

4. Single Correct Answer:
Scapula articulates with:
(1) Sternum
(2) Humerus
(3) Vertebral column
(4) Ribs
Explanation: Scapula articulates with the humerus at the glenoid cavity forming the shoulder joint. It does not directly articulate with sternum, vertebral column, or ribs. Correct answer is option (2).

5. Single Correct Answer:
Which type of skeleton includes scapula?
(1) Axial skeleton
(2) Appendicular skeleton
(3) Both
(4) None
Explanation: Scapula belongs to the appendicular skeleton, forming the shoulder girdle that connects arms to axial skeleton. Axial skeleton includes skull, vertebral column, sternum, and ribs. Correct answer is option (2).

6. Single Correct Answer:
Which joint allows free movement in multiple directions?
(1) Hinge joint
(2) Fibrous joint
(3) Ball and socket joint
(4) Cartilaginous joint
Explanation: Ball and socket joints allow free movement in all directions, such as shoulder and hip joints. Hinge joints allow unidirectional movement, fibrous joints are immovable, cartilaginous allow slight movement. Correct answer is option (3).

7. Assertion-Reason:
Assertion (A): Sternum is a flat bone.
Reason (R): Flat bones provide protection to organs and surface for muscle attachment.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true
Explanation: Sternum is a flat bone that protects the heart and lungs and provides muscle attachment. The reason correctly explains the assertion. Correct answer is option (1).

8. Matching Type:
Match the bone with its classification:
(a) Femur - 1. Long bone
(b) Sternum - 2. Flat bone
(c) Vertebra - 3. Irregular bone
(d) Patella - 4. Sesamoid bone
Options:
(1) a-1, b-2, c-3, d-4
(2) a-2, b-3, c-1, d-4
(3) a-1, b-4, c-2, d-3
(4) a-3, b-1, c-4, d-2
Explanation: Femur is a long bone, sternum a flat bone, vertebra irregular bone, patella sesamoid bone. Correct answer is option (1).

9. Fill in the Blank:
The immovable joints of the skull are called _____.
(1) Sutures
(2) Cartilage
(3) Synovial joints
(4) Ligaments
Explanation: Immovable joints of the skull are fibrous joints known as sutures, tightly binding bones. Correct answer is option (1).

10. Choose the correct statements:
(a) Vertebrae are connected by cartilaginous joints.
(b) Scapula is part of axial skeleton.
(c) Sternum is a flat bone.
(d) Cranium joints are fibrous.
Options:
(1) a, b, c
(2) a, c, d
(3) b, c, d
(4) a, b, d
Explanation: Vertebrae have cartilaginous joints (a), scapula belongs to appendicular not axial skeleton (b false), sternum is flat (c), cranium joints are fibrous (d). Correct statements are (a, c, d). Correct answer is option (2).

Topic: Muscle Contraction
Subtopic: Sliding Filament Theory

Keyword Definitions:

• H-zone: Central part of sarcomere containing only thick filaments, disappears during contraction.

• A-band: Dark band of sarcomere, length remains constant during contraction.

• I-band: Light band consisting of thin filaments, narrows during contraction.

• Z-line: Boundary of sarcomere where actin filaments are anchored.

• Myosin: Motor protein that hydrolyzes ATP to power muscle contraction.

• ATP hydrolysis: Energy-releasing reaction providing force for cross-bridge cycling.

• Sarcomere: Functional unit of myofibril between two Z-lines.

• Sliding filament theory: Explains contraction by sliding of actin over myosin filaments.

• Cross-bridge cycle: Attachment, pivoting, and detachment of myosin heads from actin.

• Actin: Thin filament protein that interacts with myosin during contraction.

• Muscle contraction: Process of shortening muscle fibers through actin-myosin interaction.

Lead Question - 2021

During muscular contraction which of the following events occur?
(a) 'H' zone disappears
(b) 'A' band widens
(c) 'I' band reduces in width
(d) Myosin hydrolyzes ATP, releasing the ADP and Pi
(e) Z-lines attached to actins are pulled inwards
Choose the correct answer from the options given below.
(1) (a), (b), (c), (d) only
(2) (b), (c), (d), (e) only
(3) (b), (d), (e), (a) only
(4) (a), (c), (d), (e) only

Explanation: During contraction, H-zone disappears, I-band shortens, myosin hydrolyzes ATP for energy, and Z-lines are pulled inward. A-band length remains constant, not widened. Therefore, correct combination is (a), (c), (d), and (e). Correct answer is option (4).

1. Single Correct Answer:
Which band remains unchanged during muscle contraction?
(1) I-band
(2) H-zone
(3) A-band
(4) Z-line
Explanation: The A-band corresponds to the length of thick filaments and remains unchanged during contraction. I-band shortens, H-zone disappears, and Z-lines move closer. Correct answer is option (3).

2. Single Correct Answer:
Which molecule provides direct energy for muscle contraction?
(1) ADP
(2) ATP
(3) Creatine
(4) Glucose
Explanation: ATP directly powers muscle contraction by hydrolysis through myosin heads. ADP, creatine, and glucose are indirectly involved but do not directly supply energy for contraction. Correct answer is option (2).

3. Single Correct Answer:
Cross-bridge cycle involves binding of:
(1) Actin with tropomyosin
(2) Myosin head with actin
(3) ATP with troponin
(4) Calcium with ATP
Explanation: Cross-bridge formation occurs when the myosin head attaches to the actin filament, powered by ATP hydrolysis. Other options are unrelated to the cycle. Correct answer is option (2).

4. Single Correct Answer:
Which ion regulates binding of actin and myosin?
(1) Sodium
(2) Potassium
(3) Calcium
(4) Magnesium
Explanation: Calcium binds to troponin, causing tropomyosin to move away and expose actin-binding sites, enabling myosin to bind. This regulation is essential for contraction. Correct answer is option (3).

5. Single Correct Answer:
During contraction, Z-lines:
(1) Move closer together
(2) Move farther apart
(3) Remain unchanged
(4) Disappear completely
Explanation: Z-lines are pulled inward during contraction as actin filaments slide over myosin, reducing sarcomere length. They do not remain unchanged or disappear. Correct answer is option (1).

6. Single Correct Answer:
ATP is hydrolyzed by:
(1) Actin filament
(2) Troponin
(3) Myosin head
(4) Tropomyosin
Explanation: Myosin head contains ATPase activity that hydrolyzes ATP into ADP and Pi, releasing energy for contraction. Actin, troponin, and tropomyosin lack ATPase activity. Correct answer is option (3).

7. Assertion-Reason:
Assertion (A): I-band shortens during muscle contraction.
Reason (R): Actin filaments slide inward over myosin.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true
Explanation: I-band shortens as actin filaments slide inward during contraction, reducing the zone of only thin filaments. The reason directly explains the assertion. Correct answer is option (1).

8. Matching Type:
Match the structure with its change during contraction:
(a) H-zone - 1. Disappears
(b) I-band - 2. Shortens
(c) A-band - 3. Remains constant
(d) Z-lines - 4. Move closer
Options:
(1) a-1, b-2, c-3, d-4
(2) a-2, b-1, c-4, d-3
(3) a-4, b-3, c-2, d-1
(4) a-3, b-2, c-1, d-4
Explanation: H-zone disappears (a-1), I-band shortens (b-2), A-band remains constant (c-3), and Z-lines move closer (d-4). Correct answer is option (1).

9. Fill in the Blank:
During contraction, the _____ zone disappears.
(1) I-band
(2) A-band
(3) H-zone
(4) Z-line
Explanation: The H-zone disappears during contraction as actin filaments slide into the central region of the sarcomere, overlapping myosin completely. Correct answer is option (3).

10. Choose the correct statements:
(a) A-band length changes
(b) H-zone disappears
(c) Z-lines move inward
(d) I-band shortens
Options:
(1) a, b, c
(2) b, c, d
(3) a, c, d
(4) b, d only
Explanation: A-band remains unchanged, while H-zone disappears, I-band shortens, and Z-lines move inward during contraction. Therefore, correct statements are (b, c, d). Correct answer is option (2).

Subtopic: Muscular Disorders

• Autoimmune disorder: Disease where the immune system attacks the body’s own cells.

• Neuromuscular junction: Synapse between motor neuron and skeletal muscle fiber.

• Myasthenia gravis: Autoimmune disorder causing weakness due to impaired transmission at neuromuscular junction.

• Muscular dystrophy: Genetic disorder leading to progressive muscle degeneration.

• Gout: Disorder due to uric acid crystal deposition in joints.

• Arthritis: Inflammation of joints causing pain and stiffness.

• Acetylcholine: Neurotransmitter essential for nerve impulse transmission at neuromuscular junction.

• Fatigue: Decreased ability of muscle to generate force.

• Paralysis: Loss of muscle function due to nerve or muscle defect.

• Autoantibodies: Antibodies that mistakenly target self-antigens.

• Acetylcholine receptor: Protein at muscle membrane necessary for nerve-muscle communication.

Lead Question - 2021

Chronic autoimmune disorder affecting neuromuscular junction leading to fatigue, weakening and paralysis of skeletal muscle is called as:
Options:
(1) Muscular dystrophy
(2) Myasthenia gravis
(3) Gout
(4) Arthritis

Explanation: The autoimmune disease Myasthenia gravis targets acetylcholine receptors at neuromuscular junction, impairing nerve-muscle communication. This results in muscle fatigue, weakness, and sometimes paralysis. It differs from muscular dystrophy, gout, and arthritis, which have different causes. Answer: Myasthenia gravis.

1. Single Correct Answer MCQ: Which neurotransmitter is affected in Myasthenia gravis?
Options:
A. Dopamine
B. Acetylcholine
C. Serotonin
D. GABA

Explanation: In Myasthenia gravis, acetylcholine receptors are blocked by autoantibodies, preventing proper nerve-muscle transmission. Answer: Acetylcholine.

2. Single Correct Answer MCQ: Muscular dystrophy primarily arises due to:
Options:
A. Autoimmunity
B. Genetic defects
C. Viral infections
D. Vitamin deficiency

Explanation: Muscular dystrophy is a genetic disorder, usually linked to dystrophin gene defects, causing progressive muscle wasting. Answer: Genetic defects.

3. Single Correct Answer MCQ: Which enzyme increases in blood due to arthritis-related inflammation?
Options:
A. Lipase
B. Uricase
C. Cyclooxygenase
D. Amylase

Explanation: In arthritis, inflammation involves cyclooxygenase enzymes, which promote prostaglandin production causing joint pain and stiffness. Answer: Cyclooxygenase.

4. Single Correct Answer MCQ: Which disorder is caused by uric acid crystal deposition?
Options:
A. Arthritis
B. Gout
C. Myasthenia gravis
D. Muscular dystrophy

Explanation: Gout results from uric acid crystal deposition in joints, leading to intense pain and swelling. Answer: Gout.

5. Single Correct Answer MCQ: Which immune component causes receptor destruction in Myasthenia gravis?
Options:
A. Autoantibodies
B. Cytokines
C. Complement proteins
D. T cells only

Explanation: In Myasthenia gravis, autoantibodies attack acetylcholine receptors, disrupting neuromuscular communication and weakening skeletal muscles. Answer: Autoantibodies.

6. Single Correct Answer MCQ: Which symptom is most specific for Myasthenia gravis?
Options:
A. Joint pain
B. Progressive muscle fatigue
C. Involuntary tremors
D. High uric acid

Explanation: The hallmark of Myasthenia gravis is progressive muscle fatigue that worsens with activity and improves with rest. Answer: Progressive muscle fatigue.

7. Assertion-Reason MCQ:
Assertion (A): Myasthenia gravis is an autoimmune disorder.
Reason (R): It is caused by genetic deletion of dystrophin gene.
Options:
A. Both A and R true, R explains A
B. Both A and R true, R not correct explanation
C. A true, R false
D. A false, R true

Explanation: Myasthenia gravis is autoimmune, but dystrophin deletion relates to muscular dystrophy, not this disorder. Answer: A true, R false.

8. Matching Type MCQ:
List I: a. Myasthenia gravis b. Gout c. Muscular dystrophy d. Arthritis
List II: i. Autoimmune fatigue ii. Uric acid deposition iii. Genetic muscle wasting iv. Joint inflammation
Options:
A. a-i, b-ii, c-iii, d-iv
B. a-ii, b-iii, c-iv, d-i
C. a-iii, b-i, c-iv, d-ii
D. a-iv, b-iii, c-i, d-ii

Explanation: Myasthenia gravis = autoimmune fatigue, Gout = uric acid deposition, Muscular dystrophy = genetic muscle wasting, Arthritis = joint inflammation. Answer: a-i, b-ii, c-iii, d-iv.

9. Fill in the Blanks MCQ: Chronic autoimmune neuromuscular disorder characterized by fatigue and weakness is _______.
Options:
A. Arthritis
B. Muscular dystrophy
C. Myasthenia gravis
D. Gout

Explanation: Myasthenia gravis causes fatigue and weakness due to autoimmune attack on acetylcholine receptors at neuromuscular junction. Answer: Myasthenia gravis.

10. Choose the correct statements MCQ:
Options:
A. Myasthenia gravis is autoimmune
B. Muscular dystrophy is genetic
C. Gout is due to uric acid deposition
D. Arthritis always arises from uric acid crystals
Select:
1. A, B, C
2. A, C, D
3. A, B, D
4. B, C, D

Explanation: Myasthenia gravis = autoimmune, Muscular dystrophy = genetic, Gout = uric acid deposition. Arthritis may have other causes like autoimmune inflammation, not always uric acid. Correct set: A, B, C. Answer: Option 1.

Topic: Skeletal System

Subtopic: Bone Structure

• Hollow bones: Bones with internal cavities, reducing weight and aiding flight.

• Pneumatic bones: Air-filled bones connected to respiratory system in birds.

• Hemidactylus: A genus of geckos, terrestrial lizard with solid bones.

• Macropus: Marsupial, kangaroo, with strong solid bones for hopping.

• Ornithorhynchus: Platypus, semi-aquatic mammal with solid bones.

• Neophron: A vulture species with hollow and pneumatic long bones.

• Long bones: Bones longer than wide, supporting weight and movement.

• Avian adaptations: Hollow bones reduce weight for flight efficiency.

• Vertebrates: Animals with backbone, having varied skeletal structures.

• Osteology: Study of bones and their morphology.

• Pneumatization: Process of air-filling in bones of birds.

Lead Question - 2021

Which one of the following organisms bears hollow and pneumatic long bones?

(1) Hemidactylus
(2) Macropus
(3) Ornithorhynchus
(4) Neophron

Explanation: Neophron, a vulture, has hollow and pneumatic long bones. These adaptations reduce weight for flight, connecting the bones with the respiratory system. Hemidactylus, Macropus, and Ornithorhynchus have solid bones for terrestrial or aquatic locomotion. Answer: Neophron.

1. Single Correct Answer MCQ: Hollow bones are characteristic of which class of animals?
Options:
A. Mammals
B. Amphibians
C. Birds
D. Reptiles

Explanation: Birds possess hollow bones to reduce weight and aid flight. Mammals, reptiles, and amphibians generally have solid bones. Answer: Birds.

2. Single Correct Answer MCQ: Pneumatic bones are connected to which system?
Options:
A. Circulatory
B. Respiratory
C. Digestive
D. Nervous

Explanation: Pneumatic bones in birds are air-filled and connected to the respiratory system, helping efficient respiration during flight. Other systems are unrelated. Answer: Respiratory.

3. Single Correct Answer MCQ: Which of the following has solid bones for terrestrial locomotion?
Options:
A. Neophron
B. Hemidactylus
C. Eagle
D. Pigeon

Explanation: Hemidactylus is a terrestrial gecko with solid bones supporting ground movement. Neophron, eagle, and pigeon have hollow bones for flight. Answer: Hemidactylus.

4. Single Correct Answer MCQ: Long bones are primarily adapted for:
Options:
A. Flight
B. Weight support and movement
C. Digestion
D. Respiration

Explanation: Long bones provide mechanical support and enable movement. In birds, they are hollow, but in terrestrial vertebrates, they mainly support weight. Answer: Weight support and movement.

5. Single Correct Answer MCQ: Pneumatization in bones is most commonly seen in:
Options:
A. Reptiles
B. Birds
C. Amphibians
D. Mammals

Explanation: Pneumatization refers to air-filled bones seen in birds, facilitating flight by reducing skeletal weight. Other classes lack this adaptation. Answer: Birds.

6. Single Correct Answer MCQ: Which bone type reduces overall body weight in flying animals?
Options:
A. Short bones
B. Long solid bones
C. Hollow bones
D. Irregular bones

Explanation: Hollow bones in birds and flying reptiles reduce skeletal weight, aiding flight efficiency. Solid and irregular bones do not provide this adaptation. Answer: Hollow bones.

7. Assertion-Reason MCQ:
Assertion (A): Neophron has pneumatic bones.
Reason (R): Hollow bones store fat for energy.
Options:
A. Both A and R true, R correct explanation
B. Both A and R true, R not correct explanation
C. A true, R false
D. A false, R true

Explanation: Neophron has pneumatic bones to reduce weight and aid flight. They do not store fat; that function is unrelated. Assertion true, reason false. Answer: A true, R false.

8. Matching Type MCQ:
List I: a. Neophron b. Macropus c. Ornithorhynchus d. Hemidactylus
List II: i. Hollow bones ii. Solid hopping bones iii. Solid aquatic bones iv. Solid terrestrial bones
Options:
A. a-i, b-ii, c-iii, d-iv
B. a-ii, b-i, c-iii, d-iv
C. a-iv, b-ii, c-i, d-iii
D. a-i, b-iv, c-ii, d-iii

Explanation: Neophron = hollow bones, Macropus = solid hopping bones, Ornithorhynchus = solid aquatic bones, Hemidactylus = solid terrestrial bones. Answer: a-i, b-ii, c-iii, d-iv.

9. Fill in the Blanks MCQ: Hollow and pneumatic bones are an adaptation for _______.
Options:
A. Swimming
B. Flight
C. Burrowing
D. Running

Explanation: Hollow and pneumatic bones reduce weight, aiding flight in birds. Swimming, burrowing, or running animals usually have solid bones. Answer: Flight.

10. Choose the correct statements MCQ:
Options:
A. Hollow bones occur in Neophron
B. Macropus has pneumatic bones
C. Hemidactylus has solid bones
D. Ornithorhynchus has solid bones
Select:
1. A, B
2. A, C, D
3. B, C
4. All of the above

Explanation: Neophron has hollow bones. Macropus has solid hopping bones. Hemidactylus has solid terrestrial bones. Ornithorhynchus has solid aquatic bones. Correct statements are A, C, D. Answer: A, C, D.

Subtopic: Skeletal Disorders and Muscular Diseases

Keyword Definitions:

• Gout: A metabolic disorder caused by accumulation of uric acid crystals in joints, leading to inflammation and pain.

• Osteoporosis: A skeletal disorder characterized by decreased bone density, often due to hormonal imbalance like low estrogen levels.

• Tetany: A condition marked by muscle spasms due to low calcium ion concentration in blood.

• Muscular dystrophy: A group of inherited genetic disorders causing progressive muscle weakness and degeneration.

• Autoimmune disorder: A condition where the immune system mistakenly attacks the body's own cells and tissues.

• Arthritis: Inflammation of joints causing pain, stiffness and reduced mobility.

• Rickets: A childhood bone disorder due to vitamin D deficiency leading to weak and deformed bones.

• Myasthenia Gravis: An autoimmune neuromuscular disorder causing weakness of skeletal muscles.

• Scoliosis: Abnormal lateral curvature of the spine affecting posture.

• Osteomalacia: Softening of bones in adults due to defective mineralization, often linked to vitamin D deficiency.

Lead Question - 2020 (COVID Reexam)

Match the following columns and select the correct option:

Column - I    Column - II
(a) Gout                 (i) Decreased levels of estrogen
(b) Osteoporosis    (ii) Low ions in the blood
(c) Tetany                (iii) Accumulation of uric acid crystals
(d) Muscular dystrophy   (iv) Autoimmune disorder
                                                      (v) Genetic disorder

1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(iii), (b)-(i), (c)-(ii), (d)-(v)
3. (a)-(iv), (b)-(v), (c)-(i), (d)-(ii)
4. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Explanation:
The correct answer is option 2. Gout results from uric acid accumulation, osteoporosis is linked to decreased estrogen, tetany occurs due to hypocalcemia (low ions), and muscular dystrophy is a genetic disorder. These matches explain underlying causes of different skeletal and muscular conditions, helping to differentiate them clinically and conceptually.

1. Which vitamin deficiency is directly associated with rickets?

1. Vitamin A
2. Vitamin D
3. Vitamin K
4. Vitamin B12

Explanation:
The correct answer is Vitamin D. Rickets results from impaired bone mineralization due to deficiency of vitamin D, calcium or phosphate. It is common in children exposed to poor sunlight. Supplementation of vitamin D and calcium helps prevent and treat the condition, ensuring proper skeletal development and prevention of deformities.

2. Which of the following is an autoimmune disorder affecting skeletal muscles?

1. Myasthenia gravis
2. Osteoporosis
3. Gout
4. Rickets

Explanation:
The correct answer is Myasthenia gravis. It is caused when antibodies block or destroy acetylcholine receptors at neuromuscular junctions. This prevents effective muscle contraction, leading to weakness. The condition demonstrates how autoimmune reactions disrupt normal physiology and must be differentiated from metabolic or genetic skeletal disorders during diagnosis and management.

3. Osteomalacia occurs in adults due to deficiency of:

1. Vitamin B complex
2. Vitamin D
3. Vitamin K
4. Vitamin A

Explanation:
The correct answer is Vitamin D. Osteomalacia is the adult counterpart of rickets. It is caused by defective mineralization of bone matrix due to vitamin D deficiency. Patients experience bone pain, muscle weakness, and fractures. This highlights the importance of sunlight exposure and dietary supplementation for maintaining bone health across all ages.

4. Which joint disease is most commonly associated with aging?

1. Osteoarthritis
2. Rickets
3. Gout
4. Scoliosis

Explanation:
The correct answer is Osteoarthritis. It is the most common degenerative joint disease, caused by progressive wear and tear of cartilage. It leads to stiffness, joint pain, and reduced flexibility. Unlike autoimmune arthritis, osteoarthritis is primarily age-related, making lifestyle modification and physiotherapy important aspects of its management in elderly patients.

5. Scoliosis refers to:

1. Forward bending of spine
2. Lateral curvature of spine
3. Backward bending of spine
4. Inflammation of vertebrae

Explanation:
The correct answer is Lateral curvature of spine. Scoliosis can appear during growth spurts, especially in adolescence. It causes uneven shoulders, posture changes and sometimes respiratory difficulties in severe cases. Identifying scoliosis early allows bracing or corrective measures to prevent progression, distinguishing it from kyphosis or lordosis which are different curvatures.

6. Which of the following is a genetic disorder affecting muscle proteins?

1. Muscular dystrophy
2. Osteomalacia
3. Tetany
4. Rickets

Explanation:
The correct answer is Muscular dystrophy. It is caused by mutations in genes responsible for muscle proteins like dystrophin. Patients show progressive weakness, difficulty in mobility, and muscle wasting. Being a genetic condition, there is no permanent cure, but supportive therapies help improve quality of life and slow down progression of symptoms.

7. Assertion–Reason Question:

Assertion (A): Osteoporosis is common in postmenopausal women.
Reason (R): Estrogen deficiency accelerates bone resorption.

1. Both A and R are true, R is the correct explanation.
2. Both A and R are true, R is not the correct explanation.
3. A is true, R is false.
4. A is false, R is true.

Explanation:
The correct answer is option 1. Osteoporosis in postmenopausal women is primarily due to estrogen deficiency. Estrogen normally inhibits bone resorption by osteoclasts. Its decline after menopause leads to increased bone loss, making the condition a common health issue among elderly women, with higher fracture risk compared to men.

8. Matching Type:

Match the following disorders with their causes:
(a) Arthritis – (i) Autoimmune disorder
(b) Osteomalacia – (ii) Vitamin D deficiency
(c) Gout – (iii) Uric acid crystals
(d) Myasthenia gravis – (iv) Autoantibodies

1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
3. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
4. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

Explanation:
The correct answer is option 1. Arthritis is often autoimmune, osteomalacia arises from vitamin D deficiency, gout is due to uric acid crystals, and myasthenia gravis results from autoantibodies against neuromuscular junction receptors. Understanding these mechanisms is crucial for clinical differentiation and therapeutic targeting of skeletal and neuromuscular diseases.

9. Fill in the Blank:

__________ is the childhood skeletal disorder caused by vitamin D deficiency.

1. Osteoporosis
2. Arthritis
3. Rickets
4. Tetany

Explanation:
The correct answer is Rickets. It is seen in children with inadequate sunlight exposure or poor vitamin D intake. Bones become soft, weak, and deformed due to defective mineralization. Recognizing this condition early enables preventive measures, distinguishing it from osteomalacia which occurs in adults due to similar deficiency.

10. Choose the Correct Statements:

1. Gout is due to uric acid deposition.
2. Osteoporosis occurs mainly due to high estrogen levels.
3. Tetany arises from hypocalcemia.
4. Muscular dystrophy is genetic in nature.

Options:
(a) 1, 2 and 3
(b) 1, 3 and 4
(c) 2 and 3
(d) 1 and 2 only

Explanation:
The correct answer is option (b). Gout is indeed due to uric acid crystals. Tetany is linked with hypocalcemia, and muscular dystrophy is genetic. Osteoporosis occurs due to estrogen deficiency, not excess. Such differentiation helps in accurate diagnosis and targeted treatment of musculoskeletal disorders affecting patients in clinical practice.

Topic: Skeletal System

Subtopic: Bones of Thorax and Shoulder Girdle

• Floating Ribs: Ribs that do not connect to the sternum and are free at their anterior ends.

• Acromion: Bony projection of scapula forming the highest point of the shoulder and connecting with the clavicle.

• Scapula: Shoulder blade; a flat bone connecting the humerus with the clavicle and supporting upper limb movements.

• Glenoid cavity: Shallow depression in scapula articulating with head of humerus to form shoulder joint.

• Clavicle: Collarbone connecting scapula to sternum, supporting shoulder movements.

• Humerus: Bone of upper arm connecting scapula to elbow joint.

• Sternum: Breastbone in the middle of thorax to which most ribs attach.

• Thorax: Part of the body enclosed by ribs, sternum, and vertebrae, protecting heart and lungs.

• Rib cage: Bony structure made of ribs and sternum enclosing thoracic organs.

• Articulation: Joint or connection between two bones allowing movement.

• Shoulder girdle: Bones (scapula and clavicle) connecting upper limb to axial skeleton.

Lead Question (2020): Match the following columns and select the correct option :

Columns - I  Columns - II
(a) Floating Ribs  (i) Located between second and seventh ribs
(b) Acromion  (ii) Head of the Humerus
(c) Scapula  (iii) Clavicle
(d) Glenoid cavity  (iv) Do not connect with the sternum

1. a-iii, b-ii, c-iv, d-i

2. a-iv, b-iii, c-i, d-ii

3. a-ii, b-iv, c-i, d-iii

4. a-i, b-iii, c-ii, d-iv

Explanation: The correct answer is 2. Floating ribs are those that do not connect to the sternum (a-iv). Acromion is the bony projection connecting with clavicle (b-iii). Scapula is located between second and seventh ribs (c-i). Glenoid cavity articulates with the head of humerus (d-ii), forming the shoulder joint.

Guessed MCQs:

1. Question 1: Which rib is called a floating rib?
   A. First rib
   B. Last two ribs
   C. Third rib
   D. All true ribs
   Explanation: The correct answer is B. The 11th and 12th ribs are floating ribs as they do not attach anteriorly to the sternum, providing flexibility and protection without direct sternum articulation.

2. Question 2: Acromion connects with:
   A. Humerus
   B. Scapula
   C. Clavicle
   D. Sternum
   Explanation: The correct answer is C. Acromion is a bony projection of scapula that articulates with the clavicle, forming the acromioclavicular joint essential for shoulder movement.

3. Question 3: Glenoid cavity articulates with:
   A. Radius
   B. Ulna
   C. Humerus
   D. Clavicle
   Explanation: The correct answer is C. Glenoid cavity of scapula forms the socket for the head of humerus, allowing ball-and-socket movement at the shoulder joint.

4. Question 4: Scapula is located:
   A. Between first and fifth ribs
   B. Between second and seventh ribs
   C. Behind sternum
   D. On clavicle
   Explanation: The correct answer is B. The scapula is a flat bone situated on the posterior thoracic wall between second and seventh ribs, providing attachment for muscles and articulation with humerus.

5. Question 5: Floating ribs are different from true ribs because:
   A. They are longer
   B. They lack anterior attachment to sternum
   C. They are fused
   D. They are part of scapula
   Explanation: The correct answer is B. Floating ribs (11th and 12th) do not connect to the sternum anteriorly, unlike true ribs which attach directly to the sternum.

6. Question 6: Clavicle connects:
   A. Sternum to humerus
   B. Sternum to scapula
   C. Humerus to scapula
   D. Scapula to ribs
   Explanation: The correct answer is B. Clavicle or collarbone connects scapula to sternum, providing support and enabling shoulder mobility.

7. Question 7: Assertion-Reason:
   Assertion (A): Floating ribs do not attach to sternum.
   Reason (R): They articulate with vertebrae only.
   A. Both A and R are true, R is correct explanation
   B. Both A and R are true, R is not correct explanation
   C. A true, R false
   D. A false, R true
   Explanation: The correct answer is A. Floating ribs are free anteriorly and attach only to vertebrae posteriorly, which explains why they do not connect with the sternum.

8. Question 8: Matching Type: Match bones with features:
   i. Scapula - A. Articulates with humerus
   ii. Clavicle - B. Connects scapula to sternum
   iii. Floating rib - C. Does not connect to sternum
   iv. Acromion - D. Bony projection connecting clavicle
   Choices:
   A. i-A, ii-B, iii-C, iv-D
   B. i-B, ii-A, iii-D, iv-C
   C. i-C, ii-D, iii-A, iv-B
   D. i-D, ii-C, iii-B, iv-A
   Explanation: The correct answer is A. Scapula articulates with humerus (i-A), clavicle connects scapula to sternum (ii-B), floating ribs do not connect to sternum (iii-C), and acromion is projection connecting clavicle (iv-D).

9. Question 9: Fill in the Blanks: The ________ cavity of scapula articulates with the head of humerus.
   A. Acromion
   B. Glenoid
   C. Coracoid
   D. Clavicular
   Explanation: The correct answer is B. The glenoid cavity forms the socket of the shoulder joint, allowing articulation with the head of the humerus for wide range of movements.

10. Question 10: Choose the correct statements:
    i. Floating ribs do not connect to sternum
    ii. Acromion connects with clavicle
    iii. Scapula lies between second and seventh ribs
    iv. Glenoid cavity articulates with clavicle
    A. i, ii, iii
    B. ii, iii, iv
    C. i, iii, iv
    D. i, ii, iii, iv
    Explanation: The correct answer is A. Floating ribs are free anteriorly (i), acromion articulates with clavicle (ii), scapula lies between second and seventh ribs (iii). Glenoid cavity articulates with humerus, not clavicle.

Topic: Thoracic Cage

Subtopic: Ribs and Sternum Articulation

Keyword Definitions:

• Vertebrosternal ribs: Ribs that attach directly to the sternum via costal cartilage.

• Vertebrochondral ribs: Ribs indirectly connected to the sternum through cartilage of superior ribs.

• Vertebral ribs: Ribs not connected to the sternum; also called floating ribs.

• Sternum: Flat bone forming the anterior midline of the thorax.

• Hyaline cartilage: Flexible cartilage present at the anterior ends of ribs for articulation.

• Thoracic vertebrae: 12 vertebrae forming the posterior attachment of ribs.

Lead Question (September 2019):

Select the correct option:
(1) 8th, 9th and 10th pairs of ribs articulate directly with the sternum.
(2) 11th and 12th pairs of ribs are connected to the sternum with the help of hyaline cartilage.
(3) Each rib is a flat thin bone and all the ribs are connected dorsally to the thoracic vertebrae and ventrally to the sternum.
(4) There are seven pairs of vertebrosternal, three pairs of vertebrochondral and two pairs of vertebral ribs.

Explanation: The correct answer is (4). The human thoracic cage has 12 pairs of ribs: 7 vertebrosternal, 3 vertebrochondral, and 2 vertebral ribs. Dorsally all ribs attach to thoracic vertebrae; anterior connection varies. NEET UG tests detailed knowledge of thoracic skeletal anatomy.

1) Which ribs are floating ribs?
(1) 1st and 2nd
(2) 11th and 12th
(3) 8th and 9th
(4) 5th and 6th

Explanation: The correct answer is (2) 11th and 12th pairs. Floating ribs are not connected anteriorly to the sternum. NEET UG evaluates understanding of thoracic cage rib classification.

2) How many vertebrochondral ribs are there?
(1) 2
(2) 3
(3) 7
(4) 5

Explanation: The correct answer is (2) 3. Vertebrochondral ribs (8th, 9th, 10th) attach indirectly to sternum through superior rib cartilage. NEET UG may ask rib articulation details.

3) Characteristics of ribs include:
(1) Flat and thin bones
(2) Connected dorsally to thoracic vertebrae
(3) Ventral attachment varies
(4) All of the above

Explanation: The correct answer is (4). Ribs are flat, thin, dorsally attached to thoracic vertebrae, ventral connection differs. NEET UG tests structural details of thoracic cage bones.

4) Vertebrosternal ribs are:
(1) 8th, 9th, 10th
(2) 11th, 12th
(3) 1st to 7th
(4) 2nd to 9th

Explanation: The correct answer is (3) 1st to 7th ribs. They connect directly to the sternum via costal cartilage. NEET UG may test classification of ribs by anterior attachment.

5) Hyaline cartilage is found in:
(1) Floating ribs
(2) Vertebrochondral ribs
(3) Vertebrosternal ribs
(4) All ribs

Explanation: The correct answer is (2). Vertebrochondral ribs use hyaline cartilage to attach indirectly to sternum. NEET UG tests knowledge of rib-sternum connections.

6) Dorsal attachment of ribs is always to:
(1) Lumbar vertebrae
(2) Thoracic vertebrae
(3) Sacrum
(4) Cervical vertebrae

Explanation: The correct answer is (2) Thoracic vertebrae. All ribs dorsally articulate with thoracic vertebrae. NEET UG tests skeletal anatomy of thorax.

7) Assertion-Reason Type:
Assertion (A): The 8th rib attaches indirectly to the sternum.
Reason (R): It is a vertebrochondral rib connecting via superior rib cartilage.
(1) A true, R true, R correct explanation
(2) A true, R true, R not explanation
(3) A true, R false
(4) A false, R true

Explanation: The correct answer is (1). The 8th rib is vertebrochondral and connects indirectly to sternum via cartilage. NEET UG tests correlation between rib type and attachment.

8) Matching Type:
Match rib type with characteristic:
(a) Vertebrosternal - (i) 1st to 7th, direct sternum
(b) Vertebrochondral - (ii) 8th to 10th, indirect sternum
(c) Vertebral ribs - (iii) 11th, 12th, no sternum
Options:
(1) a-i, b-ii, c-iii
(2) a-ii, b-i, c-iii
(3) a-iii, b-ii, c-i
(4) a-i, b-iii, c-ii

Explanation: The correct answer is (1). Vertebrosternal: 1–7, direct sternum; vertebrochondral: 8–10, indirect; vertebral: 11–12, floating. NEET UG tests classification of rib types.

9) Fill in the blanks:
The 11th and 12th pairs of ribs are called ______.
(1) Vertebrosternal
(2) Vertebrochondral
(3) Vertebral
(4) Floating

Explanation: The correct answer is (3) Vertebral ribs, also called floating ribs. NEET UG evaluates knowledge of rib classification and terminology.

10) Choose the correct statements:
(1) First 7 ribs are vertebrosternal
(2) 8th to 10th ribs are vertebrochondral
(3) 11th and 12th ribs are floating
(4) All ribs directly connect to sternum
Options:
(1) 1, 2, 3
(2) 1, 3, 4
(3) 2, 3, 4
(4) 1, 2, 4

Explanation: The correct answer is (1) 1, 2, 3. Only first 7 ribs attach directly; 8–10 indirectly; 11–12 floating. NEET UG examines rib classification and anterior attachment patterns.

Topic: Muscular Disorders
Subtopic: Inherited and Acquired Muscle Diseases

Keyword Definitions

• Tetany: Condition due to low calcium levels causing muscle spasms.

• Muscular dystrophy: Inherited disorder leading to progressive muscle weakness.

• Myasthenia gravis: Autoimmune neuromuscular disease causing muscle fatigue.

• Botulism: Paralytic disease caused by toxin from Clostridium botulinum.

• Inherited disorder: Disease transmitted genetically from parents to offspring.

Lead Question - 2019

Which of the following muscular disorders is inherited?

(1) Tetany
(2) Muscular dystrophy
(3) Myasthenia gravis
(4) Botulism

Explanation: Muscular dystrophy is an inherited genetic disorder characterized by progressive weakness and degeneration of skeletal muscles. Unlike tetany, myasthenia gravis, or botulism which are acquired conditions, muscular dystrophy runs in families. The correct answer is (2) Muscular dystrophy. It is most commonly linked to defective dystrophin gene on the X chromosome.

1) Guessed Question

Duchenne muscular dystrophy is caused due to mutations in

(1) Dystrophin gene
(2) Actin gene
(3) Troponin gene
(4) Myosin gene

Explanation: Duchenne muscular dystrophy is the most severe form of muscular dystrophy, caused by mutations in the dystrophin gene located on the X chromosome. This protein provides structural stability to muscle fibers. Hence, the correct answer is (1) Dystrophin gene. Absence of dystrophin leads to progressive muscle degeneration and weakness.

2) Guessed Question

Myasthenia gravis occurs due to defect in

(1) Neuromuscular junction
(2) Sarcomere formation
(3) Calcium storage
(4) ATP synthesis

Explanation: Myasthenia gravis is an autoimmune disorder where antibodies block acetylcholine receptors at neuromuscular junctions. This prevents proper nerve impulse transmission to muscles, causing weakness and fatigue. The correct answer is (1) Neuromuscular junction. Treatment includes anticholinesterase drugs and immunosuppressive therapy to improve neuromuscular transmission.

3) Guessed Question

Botulism results from

(1) Autoimmune reaction
(2) Calcium deficiency
(3) Bacterial toxin
(4) Gene mutation

Explanation: Botulism is a rare but serious condition caused by toxins produced by the bacterium Clostridium botulinum. The toxin blocks acetylcholine release at synapses, leading to muscle paralysis. Thus, the correct answer is (3) Bacterial toxin. Proper food preservation prevents botulism outbreaks, especially in canned or fermented products.

4) Guessed Question

Tetany is caused due to

(1) Low magnesium
(2) Low calcium
(3) Low sodium
(4) High potassium

Explanation: Tetany occurs when blood calcium levels drop below normal, leading to increased excitability of nerves and involuntary muscle spasms. This condition may occur in hypoparathyroidism. Therefore, the correct answer is (2) Low calcium. Calcium plays a vital role in stabilizing nerve and muscle cell membranes, preventing hyperexcitability.

5) Guessed Question

Which muscular disorder is autoimmune in nature?

(1) Tetany
(2) Muscular dystrophy
(3) Myasthenia gravis
(4) Botulism

Explanation: Myasthenia gravis is an autoimmune disease caused by antibodies against acetylcholine receptors. This reduces signal transmission, leading to muscle weakness. The correct answer is (3) Myasthenia gravis. Unlike muscular dystrophy which is inherited, myasthenia gravis develops due to immune system malfunction targeting neuromuscular junction receptors.

6) Guessed Question

Which muscular disorder is caused by defective gene inheritance?

(1) Botulism
(2) Myasthenia gravis
(3) Tetany
(4) Muscular dystrophy

Explanation: Muscular dystrophy arises due to mutations in genes responsible for muscle protein structure, mainly dystrophin. This genetic defect is passed down from parents. Hence, the correct answer is (4) Muscular dystrophy. It highlights the hereditary nature of the disorder, differentiating it from acquired muscular diseases.

7) Assertion-Reason MCQ

Assertion: Muscular dystrophy is an inherited muscular disorder.
Reason: It occurs due to defective dystrophin gene.

(1) Both Assertion and Reason are true, and Reason is the correct explanation
(2) Both Assertion and Reason are true, but Reason is not the correct explanation
(3) Assertion is true but Reason is false
(4) Assertion is false but Reason is true

Explanation: Muscular dystrophy is indeed inherited, and the absence or mutation of dystrophin gene is the cause. Therefore, both assertion and reason are true, and the reason explains the assertion. The correct answer is (1). This shows the genetic basis of muscular dystrophy linked to defective dystrophin production.

8) Matching Type MCQ

Match the muscular disorder with its cause:

A. Tetany → 1. Low calcium
B. Muscular dystrophy → 2. Dystrophin gene mutation
C. Myasthenia gravis → 3. Autoimmune disease
D. Botulism → 4. Bacterial toxin

(1) A-1, B-2, C-3, D-4
(2) A-2, B-3, C-1, D-4
(3) A-3, B-1, C-4, D-2
(4) A-4, B-1, C-2, D-3

Explanation: Tetany is due to low calcium, muscular dystrophy due to dystrophin mutation, myasthenia gravis due to autoimmunity, and botulism due to bacterial toxin. Hence the correct answer is (1) A-1, B-2, C-3, D-4. This mapping illustrates the diverse origins of muscular disorders.

9) Fill in the Blanks MCQ

Duchenne muscular dystrophy is linked to the ______ chromosome.

(1) X
(2) Y
(3) 21st
(4) 18th

Explanation: Duchenne muscular dystrophy is inherited in an X-linked recessive pattern, affecting mostly males. The dystrophin gene responsible lies on the X chromosome. Hence, the correct answer is (1) X. Female carriers usually do not show severe symptoms, but they can pass the defective gene to offspring.

10) Choose the Correct Statements MCQ

Choose the correct statements regarding muscular disorders:
(a) Tetany is due to low calcium
(b) Muscular dystrophy is inherited
(c) Myasthenia gravis is autoimmune
(d) Botulism is genetic

(1) (a), (b), and (c)
(2) (b), (c), and (d)
(3) (a) and (d)
(4) (a) and (b)

Explanation: Tetany occurs due to low calcium, muscular dystrophy is inherited, and myasthenia gravis is autoimmune. Botulism, however, is caused by bacterial toxin, not genetics. Hence, the correct statements are (a), (b), and (c). Correct answer is (1). This highlights the differences between inherited and acquired muscular disorders.

Topic: Muscular System

Subtopic: Skeletal Muscle Contraction

Keyword Definitions:

• Calcium: A divalent cation essential for muscle contraction, neurotransmission, and bone structure.

• Skeletal muscle: Striated voluntary muscles attached to bones that enable movement.

• Troponin: Regulatory protein on actin filaments that binds calcium to initiate contraction.

• Actin: Thin filament protein in muscle fibers involved in contraction.

• Myosin: Thick filament motor protein responsible for sliding along actin during contraction.

• Cross-bridge: Interaction between myosin heads and actin filaments enabling contraction.

Lead Question - 2018

Calcium is important in skeletal muscle contraction because it :

(A) prevents the formation of bonds between the myosin cross bridges and the actin filament

(B) binds to troponin to remove the masking of active sites on actin for myosin

(C) detaches the myosin head from the actin filament

(D) activates the myosin ATPase by binding to it

Explanation:

Answer is (B). Calcium ions bind to troponin, inducing conformational changes that shift tropomyosin and expose active sites on actin. This exposure allows myosin cross bridges to attach to actin filaments, initiating skeletal muscle contraction. Without calcium, active sites remain masked, preventing contraction.

Guessed Questions for NEET UG:

1) Single Correct: Which ion triggers the release of neurotransmitters at the neuromuscular junction?

(A) Sodium

(B) Calcium

(C) Potassium

(D) Chloride

Explanation:

Answer is (B). Calcium influx into the presynaptic terminal triggers exocytosis of acetylcholine vesicles, enabling transmission of the nerve impulse to skeletal muscle fibers.

2) Single Correct: Tropomyosin in skeletal muscle:

(A) Binds calcium

(B) Covers active sites on actin

(C) Hydrolyzes ATP

(D) Forms cross bridges

Explanation:

Answer is (B). Tropomyosin blocks myosin-binding sites on actin in resting muscle. Calcium binding to troponin shifts tropomyosin, allowing cross-bridge formation and contraction.

3) Single Correct: During contraction, myosin heads:

(A) Remain stationary

(B) Attach and pull actin filaments

(C) Bind calcium

(D) Bind tropomyosin

Explanation:

Answer is (B). Myosin heads cyclically attach to actin, pivot, and pull thin filaments toward the sarcomere center, powered by ATP hydrolysis, producing muscle shortening.

4) Assertion-Reason:

Assertion: Calcium is essential for muscle contraction.

Reason: It binds to tropomyosin and moves it out of the way.

(A) Both true, Reason correct

(B) Both true, Reason incorrect

(C) Assertion true, Reason false

(D) Both false

Explanation:

Answer is (C). Calcium binds to troponin, not tropomyosin directly, which then moves tropomyosin to expose actin active sites, enabling myosin attachment and contraction.

5) Single Correct: Which protein directly interacts with calcium during contraction?

(A) Actin

(B) Myosin

(C) Troponin

(D) Tropomyosin

Explanation:

Answer is (C). Troponin binds calcium ions, causing conformational changes that shift tropomyosin and expose actin sites for myosin cross-bridge attachment.

6) Single Correct: ATP in skeletal muscle contraction:

(A) Binds actin

(B) Powers myosin head movement

(C) Binds calcium

(D) Binds troponin

Explanation:

Answer is (B). ATP binds myosin, hydrolysis provides energy for the power stroke, and detachment of myosin heads from actin, enabling repeated contraction cycles.

7) Matching Type:

Column I | Column II

a. Actin | i. Binds calcium

b. Troponin | ii. Thin filament

c. Myosin | iii. Thick filament

(A) a-ii, b-i, c-iii

(B) a-iii, b-i, c-ii

(C) a-i, b-iii, c-ii

(D) a-ii, b-iii, c-i

Explanation:

Answer is (A). Actin: thin filament (ii), Troponin: binds calcium (i), Myosin: thick filament (iii). Proper protein interactions are essential for contraction.

8) Fill in the Blank:

Calcium binds to ________ to initiate skeletal muscle contraction.

(A) Tropomyosin

(B) Troponin

(C) Actin

(D) Myosin

Explanation:

Answer is (B). Troponin binding with calcium causes tropomyosin movement, exposing actin active sites for myosin attachment and triggering contraction.

9) Choose the correct statements:

(i) Calcium ions are stored in the sarcoplasmic reticulum.

(ii) Calcium binding to troponin exposes actin sites.

(iii) Calcium directly hydrolyzes ATP.

(A) i and ii only

(B) ii and iii only

(C) i and iii only

(D) i, ii, iii

Explanation:

Answer is (A). Calcium is stored in the sarcoplasmic reticulum and binds troponin to expose actin. It does not hydrolyze ATP directly; ATP hydrolysis occurs at myosin heads.

10) Clinical-type: A patient has hypocalcemia. Which effect is expected in skeletal muscles?

(A) Enhanced contraction

(B) Reduced contraction

(C) No effect

(D) Continuous contraction

Explanation:

Answer is (B). Low calcium reduces binding to troponin, preventing tropomyosin movement. Consequently, actin sites remain masked, and skeletal muscle contraction is impaired, causing weakness or tetany.

Subtopic: Skeletal System - Joints

Keyword Definitions:

Pivot Joint: Synovial joint allowing rotational movement around a single axis.

Atlas: First cervical vertebra supporting the skull.

Axis: Second cervical vertebra with odontoid process enabling rotation.

Saddle Joint: Synovial joint allowing movement in two planes.

Fibrous Joint: Joint connected by fibrous tissue, mostly immovable.

Cartilaginous Joint: Joint connected by cartilage with limited movement.

Synovial Joint: Freely movable joint with synovial fluid.

Odontoid Process: Projection of axis around which atlas rotates.

Rotational Movement: Movement around a central axis.

Clinical Significance: Injuries to atlanto-axial joint can impair head rotation and cause neurological issues.

Joint Disorders: Conditions like arthritis or dislocation can affect mobility and stability.

Lead Question - 2017

The pivot joint between atlas and axis is a type of:

(A) saddle joint

(B) Fibrous joint

(C) Cartilaginous joint

(D) Synovial joint

Explanation: The joint between atlas and axis is a pivot synovial joint allowing rotational movement of the head. Atlas rotates around the odontoid process of axis. It is freely movable, making it a synovial joint, not fibrous, cartilaginous, or saddle. Correct answer: D.

1. MCQ - Single Correct Answer

Which movement is allowed by the atlanto-axial joint?

(a) Flexion only

(b) Rotation of head

(c) Abduction

(d) Extension only

Explanation: The pivot joint between atlas and axis permits rotation of the head on a vertical axis. Flexion, extension, or abduction are limited at this joint. This rotation allows shaking the head side to side. Correct answer: b.

2. MCQ - Single Correct Answer

The odontoid process is part of which vertebra?

(a) Atlas

(b) Axis

(c) Cervical 3

(d) Thoracic 1

Explanation: The odontoid process, or dens, is a projection of the axis (C2) vertebra. The atlas rotates around it, forming a pivot joint. Atlas is C1 without dens, cervical 3 and thoracic vertebrae are not involved in pivot rotation. Correct answer: b.

3. MCQ - Single Correct Answer (Clinical)

Fracture of the odontoid process affects:

(a) Shoulder rotation

(b) Head rotation

(c) Wrist movement

(d) Knee extension

Explanation: A fracture of the odontoid process disrupts the pivot joint, impairing head rotation. It can lead to spinal cord injury with neurological deficits. Shoulder, wrist, or knee movement is not directly affected. Correct answer: b.

4. MCQ - Single Correct Answer

Which type of synovial joint is the atlanto-axial joint?

(a) Ball and socket

(b) Hinge

(c) Pivot

(d) Saddle

Explanation: The atlanto-axial joint is a pivot synovial joint, allowing rotation around a single axis. Ball and socket allow multi-directional movement, hinge allows flexion-extension, and saddle permits movement in two planes. Correct answer: c.

5. MCQ - Single Correct Answer

Atlas articulates superiorly with:

(a) Occipital condyles

(b) Axis

(c) Thoracic vertebrae

(d) Sacrum

Explanation: The atlas (C1) articulates superiorly with occipital condyles of the skull, allowing nodding movements. Inferiorly, it articulates with axis for rotation. Thoracic vertebrae and sacrum are unrelated to this joint. Correct answer: a.

6. MCQ - Single Correct Answer (Clinical)

Atlanto-axial subluxation is commonly associated with which condition?

(a) Osteoporosis

(b) Rheumatoid arthritis

(c) Hip dysplasia

(d) Scoliosis

Explanation: Rheumatoid arthritis can affect ligaments of the atlanto-axial joint, leading to subluxation and risk of spinal cord compression. Osteoporosis affects bones generally, hip dysplasia affects hip joint, scoliosis affects spinal curvature. Correct answer: b.

7. MCQ - Assertion-Reason

Assertion (A): Atlanto-axial joint is a pivot joint.

Reason (R): It allows rotational movement of the head.

(a) Both A and R true, R correct explanation

(b) Both A and R true, R not correct explanation

(c) A true, R false

(d) A false, R true

Explanation: The atlanto-axial joint is indeed a pivot joint, allowing rotation of the head around the odontoid process. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer: a.

8. MCQ - Matching Type

Match joint type with example:

1. Pivot - (a) Elbow

2. Hinge - (b) Atlanto-axial

3. Ball and socket - (c) Shoulder

Options:

(A) 1-b, 2-a, 3-c

(B) 1-a, 2-b, 3-c

(C) 1-c, 2-a, 3-b

(D) 1-b, 2-c, 3-a

Explanation: Pivot joint: atlanto-axial; Hinge: elbow; Ball and socket: shoulder. Correct matching: 1-b, 2-a, 3-c. Answer: A.

9. MCQ - Fill in the Blanks

The atlas rotates around the __________ of axis.

(a) Odontoid process

(b) Spinous process

(c) Transverse process

(d) Vertebral body

Explanation: The atlas rotates around the odontoid process (dens) of axis, forming a pivot joint. This allows lateral rotation of the head. Spinous and transverse processes or vertebral body are not rotation points. Correct answer: a.

10. MCQ - Choose Correct Statements

Select correct statements about atlanto-axial joint:

1. Pivot synovial joint

2. Allows head rotation

3. Located between atlas and axis

4. Limited movement in all directions

Options:

(A) 1, 2, and 3

(B) 1 and 4

(C) 2 and 3 only

(D) All 1,2,3,4

Explanation: The atlanto-axial joint is a pivot synovial joint, located between atlas and axis, permitting head rotation. It does not allow multi-directional movement. Correct statements: 1, 2, and 3. Answer: A. 

Topic: Skeletal System

Subtopic: Ribs and Sternum

Keyword Definitions:

• Ribs – Curved bones forming the thoracic cage, protecting thoracic organs.

• True ribs – Ribs that attach directly to the sternum via costal cartilage.

• False ribs – Ribs indirectly attached or not attached to sternum.

• Floating ribs – Last two pairs of ribs not attached ventrally.

• Vertebral column – Spine providing dorsal attachment for ribs.

• Sternum – Breastbone where true ribs attach ventrally.

• Thoracic cage – Skeleton of thorax including ribs, sternum, vertebrae.

• Costal cartilage – Hyaline cartilage connecting ribs to sternum.

• Dorsal – Back side of the body.

• Ventral – Front side of the body.

Lead Question – 2017:

Out of ‘X’ pairs of ribs in humans only ‘Y’ pairs are true ribs. Select the option that correctly represents values of X and Y and provides their explanation:

(A) X = 24, Y = 12 True ribs are dorsally attached to vertebral column but are free on ventral side

(B) X = 12, Y = 7 True ribs are attached dorsally to vertebral column and ventrally to the sternum

(C) X = 12, Y = 5 True ribs are attached dorsally to vertebral column and sternum on the two ends

(D) X = 24, Y = 7 True ribs are dorsally attached to vertebral column but are free on ventral side

Explanation:

Humans have 12 pairs of ribs (X = 12), of which the first seven pairs (Y = 7) are true ribs that attach dorsally to vertebrae and ventrally to the sternum through costal cartilage. The remaining five pairs are false or floating ribs. Hence, correct answer is (B). (Answer: B)

1) Single Correct Answer MCQ:

Which ribs are called floating ribs?

(A) 1st and 2nd pairs

(B) 11th and 12th pairs

(C) 7th pair

(D) 5th and 6th pairs

Explanation:

Floating ribs (11th and 12th pairs) are not attached ventrally to the sternum, providing protection to lower organs but allowing flexibility. (Answer: B)

2) Single Correct Answer MCQ:

Costal cartilage connects ribs to:

(A) Vertebrae

(B) Sternum

(C) Scapula

(D) Clavicle

Explanation:

True ribs connect to the sternum ventrally through costal cartilage, while dorsally they attach to vertebrae. (Answer: B)

3) Single Correct Answer MCQ:

Which statement is correct regarding false ribs?

(A) Attach directly to sternum

(B) Attach indirectly or not at all to sternum

(C) Always float freely

(D) None of the above

Explanation:

False ribs (8th–12th pairs) are indirectly attached or free ventrally, with the last two pairs being floating ribs. (Answer: B)

4) Single Correct Answer MCQ:

Total number of ribs in a human adult is:

(A) 24

(B) 12

(C) 14

(D) 20

Explanation:

Humans have 12 pairs of ribs, totaling 24 individual ribs forming the thoracic cage. (Answer: A)

5) Single Correct Answer MCQ:

True ribs are also called:

(A) Vertebral ribs

(B) Sternal ribs

(C) Floating ribs

(D) False ribs

Explanation:

True ribs are sternal ribs as they attach directly to the sternum via costal cartilage. (Answer: B)

6) Single Correct Answer MCQ:

Which rib pair is attached dorsally to vertebrae but ventrally free?

(A) 1st pair

(B) 7th pair

(C) 11th pair

(D) 5th pair

Explanation:

Floating ribs (11th pair) are dorsally attached to vertebrae but ventrally free, allowing movement and protection of lower abdominal organs. (Answer: C)

7) Assertion-Reason MCQ:

Assertion (A): True ribs are attached to both vertebrae and sternum.

Reason (R): True ribs support and protect thoracic organs.

(A) Both A and R true, R explains A

(B) Both A and R true, R does not explain A

(C) A true, R false

(D) A false, R true

Explanation:

Both A and R are correct. True ribs are connected dorsally and ventrally, providing protection to heart and lungs. (Answer: A)

8) Matching Type MCQ:

Match:

1. True ribs – (i) Direct attachment to sternum

2. False ribs – (ii) Indirect or no attachment

3. Floating ribs – (iii) Last two pairs

Options:

(A) 1-i, 2-ii, 3-iii

(B) 1-ii, 2-i, 3-iii

(C) 1-i, 2-iii, 3-ii

(D) 1-iii, 2-i, 3-ii

Explanation:

Correct matching: 1-i (true ribs attach directly), 2-ii (false ribs indirect/no), 3-iii (floating ribs are last two pairs). (Answer: A)

9) Fill in the Blanks MCQ:

The thoracic cage consists of ______ pairs of ribs.

(A) 10

(B) 12

(C) 14

(D) 7

Explanation:

The human thoracic cage has 12 pairs of ribs, forming a protective cage for thoracic organs. (Answer: B)

10) Choose the correct statements MCQ:

1. True ribs are 1–7 pairs

2. False ribs are 8–12 pairs

3. Floating ribs are part of true ribs

4. All ribs attach to sternum ventrally

Options:

(A) 1, 2

(B) 1, 3

(C) 2, 4

(D) 1, 4

Explanation:

Statements 1 and 2 are correct. Floating ribs are not part of true ribs, and not all ribs attach to sternum. True ribs are 1–7; false ribs 8–12, with 11th–12th floating. (Answer: A)

Topic: Locomotion and Movement
Subtopic: Skeletal Disorders

Keyword Definitions:

• Osteoporosis: A skeletal disorder marked by low bone mass and fragile bones.

• Estrogen: A hormone essential for bone health; its deficiency accelerates bone loss.

• Uric Acid: Waste product; excess causes gout, not osteoporosis.

• Neuromuscular Junction: Site where nerves communicate with muscles.

• Calcium Ions (Ca++): Vital for bone mineralization and muscle contraction.

• Skeletal System: Framework of bones providing support, protection, and movement.

Lead Question - 2016 (Phase 2)
Osteoporosis, an age- related disease of skeletal system, may occur due to :
(1) accumulation of uric acid leading to inflammation of joints
(2) immune disorder affecting neuromuscular junction leading to fatigue
(3) high concentration of Ca++ and Na+
(4) decreased level of estrogen

Explanation: Osteoporosis is characterized by fragile bones due to reduced bone mass. It often occurs in postmenopausal women because estrogen levels drop, reducing calcium deposition in bones. Correct answer is (4) decreased level of estrogen. Estrogen maintains bone density, and its deficiency accelerates bone resorption leading to osteoporosis.

1. A 65-year-old woman presents with frequent fractures after minor falls. Which hormone deficiency is most likely responsible?
(1) Estrogen
(2) Progesterone
(3) Cortisol
(4) Testosterone

Explanation: Postmenopausal women often develop osteoporosis due to estrogen deficiency, leading to weak bones and increased fracture risk. Correct answer is (1) Estrogen. Progesterone and testosterone have limited skeletal roles, while cortisol excess leads to osteoporosis but not in typical age-related cases.

2. Which vitamin is most essential for intestinal absorption of calcium?
(1) Vitamin A
(2) Vitamin D
(3) Vitamin K
(4) Vitamin E

Explanation: Vitamin D promotes intestinal absorption of calcium and phosphate, essential for bone mineralization. Its deficiency causes rickets in children and osteomalacia in adults. Correct answer is (2) Vitamin D. Vitamin A and K help bone remodeling, but absorption depends on Vitamin D.

3. Which bone cells are responsible for bone resorption in osteoporosis?
(1) Osteoblasts
(2) Osteoclasts
(3) Chondrocytes
(4) Fibroblasts

Explanation: Osteoclasts are bone-resorbing cells that break down bone tissue. In osteoporosis, osteoclastic activity exceeds osteoblastic formation, leading to reduced bone density. Correct answer is (2) Osteoclasts. Osteoblasts form bone, while chondrocytes and fibroblasts serve other functions.

4. Assertion-Reason: Assertion: Osteoporosis risk increases in postmenopausal women. Reason: Decreased estrogen enhances osteoclastic activity.
(1) Both A and R true, R explains A
(2) Both A and R true, R not explanation
(3) A true, R false
(4) A false, R true

Explanation: Estrogen deficiency in menopause leads to enhanced osteoclastic activity, weakening bones and increasing fracture risk. Correct answer is (1) Both A and R are true, and R explains A. Hence, estrogen directly maintains bone density by suppressing resorption.

5. A patient with osteoporosis is given bisphosphonates. These drugs primarily act by:
(1) Inhibiting osteoblast activity
(2) Stimulating calcium absorption
(3) Inhibiting osteoclast activity
(4) Increasing vitamin D levels

Explanation: Bisphosphonates inhibit osteoclast activity, reducing bone resorption and slowing bone loss in osteoporosis patients. Correct answer is (3) Inhibiting osteoclast activity. They do not directly affect osteoblasts, vitamin D, or absorption, but indirectly improve bone mineral density.

6. Which of the following is a clinical feature of osteoporosis?
(1) Bone pain and fractures
(2) Muscle cramps
(3) Swollen joints
(4) Nerve palsy

Explanation: Osteoporosis typically presents with bone pain, fractures after minor trauma, and spinal deformities like kyphosis. Correct answer is (1) Bone pain and fractures. Muscle cramps are due to electrolyte imbalance, swollen joints suggest arthritis, and nerve palsy is neurological.

7. Matching Type: Match the hormone with its role in bone health:
A. Estrogen
B. Parathyroid hormone
C. Calcitonin
D. Vitamin D
(i) Increases calcium absorption
(ii) Inhibits osteoclasts
(iii) Promotes bone resorption
(iv) Maintains bone density
(1) A-iv, B-iii, C-ii, D-i
(2) A-ii, B-i, C-iv, D-iii
(3) A-iii, B-iv, C-i, D-ii
(4) A-iv, B-ii, C-iii, D-i

Explanation: Estrogen maintains bone density, PTH promotes bone resorption, Calcitonin inhibits osteoclasts, and Vitamin D increases calcium absorption. Correct answer is (1) A-iv, B-iii, C-ii, D-i. Together, they regulate calcium balance and bone homeostasis.

8. Fill in the Blank: __________ deficiency accelerates osteoporosis in elderly women.
(1) Testosterone
(2) Estrogen
(3) Progesterone
(4) Thyroxine

Explanation: Estrogen deficiency after menopause accelerates bone resorption, increasing the risk of osteoporosis in women. Correct answer is (2) Estrogen. Testosterone, progesterone, and thyroxine play secondary roles but estrogen is the critical hormone for skeletal health in females.

9. Which diagnostic test is most commonly used to detect osteoporosis?
(1) X-ray
(2) DEXA scan
(3) MRI
(4) Ultrasound

Explanation: DEXA (Dual Energy X-ray Absorptiometry) scan is the gold standard for measuring bone mineral density and diagnosing osteoporosis. Correct answer is (2) DEXA scan. X-rays detect only advanced cases, while MRI and ultrasound are not standard diagnostic methods for osteoporosis.

10. Choose the correct statements about osteoporosis:
(1) It causes weak and brittle bones
(2) Estrogen deficiency increases risk
(3) Calcium and Vitamin D supplementation helps
(4) Uric acid accumulation is the cause
(A) 1, 2, 3 only
(B) 2, 3, 4 only
(C) 1 and 4 only
(D) All four

Explanation: Osteoporosis causes weak bones, worsened by estrogen deficiency. Calcium and Vitamin D supplementation reduces risk. Uric acid accumulation causes gout, not osteoporosis. Correct answer is (A) 1, 2, 3 only. Thus, lifestyle modification and early detection are crucial for prevention.

Topic : Muscle Contraction
Subtopic : Role of Calcium in Cross-Bridge Formation

Keyword Definitions :

• Actin : Thin filament protein in muscle fibers that interacts with myosin for contraction.

• Myosin : Thick filament protein with heads that bind actin to form cross-bridges during contraction.

• Tropomyosin : Regulatory protein that blocks active sites on actin in a relaxed muscle.

• Troponin : Protein complex that binds calcium, shifting tropomyosin to expose actin binding sites.

• Calcium Ion (Ca²⁺) : Ion that initiates muscle contraction by unmasking active sites on actin filaments.

Lead Question - 2016 (Phase 2)
Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction :
(1) Potassium
(2) Calcium
(3) Magnesium
(4) Sodium

Explanation : Calcium ions bind to troponin, causing a conformational shift that moves tropomyosin away from actin’s active sites. This unmasking allows myosin heads to form cross-bridges with actin filaments. Thus, the correct answer is (2) Calcium, crucial for excitation-contraction coupling in skeletal muscle physiology.

1. Which molecule directly provides energy for cross-bridge cycling during muscle contraction?
(1) ATP
(2) ADP
(3) Creatine phosphate
(4) Glucose

Explanation : ATP is the immediate source of energy for cross-bridge cycling. Hydrolysis of ATP energizes myosin heads, enabling attachment, power stroke, and detachment from actin filaments. Hence, the correct answer is (1) ATP, making it essential for repeated muscle contractions and relaxation.

2. Clinical Case: A patient with severe muscle weakness is suspected of myasthenia gravis. This condition is caused by autoantibodies against:
(1) Actin
(2) Acetylcholine receptors
(3) Troponin
(4) Myosin

Explanation : Myasthenia gravis is an autoimmune disorder where antibodies block or destroy acetylcholine receptors at the neuromuscular junction. This prevents efficient transmission of nerve impulses to muscles. Therefore, the correct answer is (2) Acetylcholine receptors, leading to progressive weakness and fatigue.

3. Which structure stores calcium ions in skeletal muscle fibers?
(1) Golgi apparatus
(2) Sarcoplasmic reticulum
(3) Mitochondria
(4) Lysosomes

Explanation : The sarcoplasmic reticulum serves as the calcium storage organelle in muscle fibers. Upon stimulation, it releases calcium ions into the cytoplasm to initiate contraction. Hence, the correct answer is (2) Sarcoplasmic reticulum, essential for rapid contraction and relaxation cycles in muscles.

4. During the power stroke of muscle contraction, which event occurs?
(1) Myosin head binds ATP
(2) Myosin head pulls actin filament inward
(3) Calcium is pumped back into the sarcoplasmic reticulum
(4) Troponin detaches from actin

Explanation : During the power stroke, the energized myosin head pivots and pulls the actin filament toward the center of the sarcomere, generating force. This step shortens the muscle fiber. Thus, the correct answer is (2) Myosin head pulls actin filament inward.

5. Assertion (A): Rigor mortis occurs after death due to lack of ATP.
Reason (R): ATP is required for detachment of myosin heads from actin filaments.
(1) Both A and R are true, R is correct explanation of A
(2) Both A and R are true, R is not correct explanation of A
(3) A is true, R is false
(4) A is false, R is true

Explanation : After death, ATP production ceases. Without ATP, myosin heads remain bound to actin, leading to rigidity known as rigor mortis. Thus, both A and R are true, and R correctly explains A. The correct answer is (1).

6. Match the muscle structure in Column I with its function in Column II:
a. Actin - i. Thick filament
b. Myosin - ii. Thin filament
c. Sarcomere - iii. Functional unit of contraction
d. Tropomyosin - iv. Blocks actin binding sites
(1) a-ii, b-i, c-iii, d-iv
(2) a-i, b-ii, c-iv, d-iii
(3) a-iii, b-iv, c-ii, d-i
(4) a-iv, b-iii, c-i, d-ii

Explanation : Actin forms the thin filament, myosin forms the thick filament, sarcomere is the functional unit of contraction, and tropomyosin blocks actin sites in resting muscles. Hence, the correct match is (1) a-ii, b-i, c-iii, d-iv, ensuring proper contraction regulation.

7. Fill in the Blank: The neurotransmitter released at the neuromuscular junction is ______.
(1) Dopamine
(2) Acetylcholine
(3) Serotonin
(4) Noradrenaline

Explanation : Acetylcholine is released by motor neurons at neuromuscular junctions. It binds to receptors on the muscle fiber, triggering depolarization and subsequent contraction. Therefore, the correct answer is (2) Acetylcholine, a vital neurotransmitter for skeletal muscle activation.

8. Choose the correct statements:
A. Calcium ions are stored in the sarcoplasmic reticulum.
B. Myosin heads require ATP for detachment.
C. Tropomyosin exposes actin binding sites when bound to calcium.
D. Actin is a thick filament.
(1) A, B, and C
(2) A and D
(3) B and C only
(4) A, C, and D

Explanation : Statements A and B are correct. Calcium is stored in the sarcoplasmic reticulum, and ATP is required for detachment of myosin. However, it is troponin, not tropomyosin, that binds calcium. Actin is thin, not thick. Thus, the correct answer is (1).

Chapter: Animal Physiology

Topic: Locomotion and Movement

Subtopic: Biomechanics of Animal Movement

Keyword Definitions:

• Metabolic Rate: The rate at which an organism converts energy from food into usable energy for cellular processes.

• Oxygen Requirement: The amount of oxygen an organism needs to sustain its metabolic activities.

• Muscle Efficiency: The ability of muscles to convert chemical energy into mechanical work during movement.

• Body Weight: The mass of an animal which affects the energy required for movement.

• Uphill Locomotion: Movement against gravity, typically requiring more energy in large animals.

2016 (Phase 1)

Lead Question: It is much easier for a small animal to run uphill than for a large animal, because:

• (1) It is easier to carry a small body weight.

• (2) Smaller animals have a higher metabolic rate.

• (3) Small animals have a lower O2 requirement.

• (4) The efficiency of muscles in large animals is less than in small animals.

Answer & Explanation: The correct answer is (1). Small animals have lower body mass, requiring less energy to overcome gravity when running uphill. This makes uphill movement energetically more efficient for small animals than for large ones, which have higher body weight and energy requirements, making uphill locomotion more difficult and demanding for them.

Single Correct Answer MCQ: Which of the following is a major factor making uphill movement easier for small animals?

• (1) Low oxygen consumption

• (2) Higher metabolic rate

• (3) Lower body weight

• (4) Higher muscle efficiency

Answer & Explanation: The correct answer is (3). Small animals have lower body weight, which reduces the energy needed to lift themselves uphill. Energy cost of locomotion depends significantly on body weight, making small animals more efficient during uphill movement. Metabolic rate or muscle efficiency plays a lesser role compared to body mass in this context.

Assertion-Reason MCQ:

Assertion (A): Small animals can run uphill more easily than large animals.

Reason (R): Small body weight reduces the energy needed for uphill locomotion.

• (1) Both A and R are true, and R is correct explanation of A.

• (2) Both A and R are true, but R is not correct explanation of A.

• (3) A is true, but R is false.

• (4) A is false, but R is true.

Answer & Explanation: The correct answer is (1). The small body weight of small animals reduces the energy required to overcome gravity when moving uphill. This makes uphill locomotion easier compared to large animals whose greater mass requires significantly more energy for the same movement.

Matching Type MCQ: Match Term to Definition:

A. Metabolic rate          1. Energy use per unit time

B. Muscle efficiency      2. Conversion of chemical to mechanical energy

C. Body weight            3. Mass of an animal

D. Oxygen requirement     4. Oxygen needed for metabolism

• (1) A-1, B-2, C-3, D-4

• (2) A-4, B-3, C-2, D-1

• (3) A-2, B-1, C-4, D-3

• (4) A-3, B-4, C-1, D-2

Answer & Explanation: The correct answer is (1). Metabolic rate refers to energy use per unit time. Muscle efficiency refers to conversion of chemical energy into mechanical work. Body weight indicates the mass of the animal. Oxygen requirement refers to the oxygen needed to sustain metabolism during activity.

Fill in the Blanks / Completion MCQ: The primary reason small animals run uphill more easily is their __________.

• (1) higher metabolic rate

• (2) lower body weight

• (3) better muscle efficiency

• (4) lower oxygen requirement

Answer & Explanation: The correct answer is (2). Small animals have lower body weight compared to large animals. This reduces the energy cost to overcome gravity when moving uphill, making them more efficient. Other factors like metabolic rate or oxygen requirement play a secondary role in this specific context.

Choose the correct statements MCQ:

• 1. Small animals require less energy for uphill movement.

• 2. Large animals have higher muscle efficiency.

• 3. Metabolic rate has no role in uphill locomotion.

• 4. Oxygen requirement depends on body size.

• (1) 1 and 4 only

• (2) 2 and 3 only

• (3) 1, 3, and 4 only

• (4) 1, 2, and 4 only

Answer & Explanation: The correct answer is (1). Small animals need less energy for uphill movement due to lower body weight. Oxygen requirement scales with body size. Muscle efficiency does not significantly differ in this context, and metabolic rate has a role but is not the main reason.

Keywords:

• Muscle contraction: Shortening of muscle fibers resulting in movement.

• Sustained contraction: Continuous contraction over a period of time.

• Spasm: Involuntary, sudden muscle contraction.

• Fatigue: Temporary decline in muscle performance due to prolonged activity.

• Tetanus: Continuous, sustained contraction of muscles without relaxation between stimuli.

• Tonus: Continuous partial contraction of muscles at rest.

• Stimulus: A signal triggering muscle contraction.

• Neuromuscular junction: Connection between motor neuron and muscle fiber.

• Calcium ions: Ions responsible for muscle contraction by interacting with troponin-tropomyosin complex.

• ATP: Energy source required for muscle contraction and relaxation.

• Myosin-actin interaction: Molecular mechanism underlying muscle contraction.

Chapter: Muscle Physiology

Topic: Muscle Contraction

Subtopic: Types of Muscle Contraction

Lead Question - 2016 (Phase 1): Lack of relaxation between successive stimuli in sustained muscle contraction is known as :

(1) Spasm
(2) Fatigue
(3) Tetanus
(4) Tonus

Answer: 3

Explanation: Tetanus refers to continuous muscle contraction without relaxation due to repeated stimuli. Unlike spasm or tonus, tetanus results from rapid stimuli summating the muscle response. This is physiologically important for sustained actions but may cause cramping in clinical conditions.

1. Single Correct Answer MCQ: Which ion triggers muscle contraction?

(A) Sodium
(B) Potassium
(C) Calcium
(D) Chloride

Answer: C

Explanation: Calcium ions are released from the sarcoplasmic reticulum and bind to troponin, initiating actin-myosin interaction and muscle contraction. Sodium and potassium mainly propagate action potentials, not directly trigger contraction.

2. Single Correct Answer MCQ: Fatigue in muscles occurs due to:

(A) Excess ATP
(B) Lactic acid accumulation
(C) High calcium concentration
(D) Continuous tetanus

Answer: B

Explanation: Muscle fatigue occurs due to lactic acid accumulation, depletion of energy stores, and ionic imbalances. This leads to reduced force production and temporary inability of muscles to sustain contraction.

3. Single Correct Answer MCQ: Partial continuous contraction in resting muscles is called:

(A) Spasm
(B) Tonus
(C) Tetanus
(D) Fatigue

Answer: B

Explanation: Muscle tonus is a low-level, continuous contraction present in resting muscles, maintaining posture and readiness for action. It differs from tetanus or spasm.

4. Single Correct Answer MCQ: A sudden involuntary muscle contraction is termed:

(A) Fatigue
(B) Tetanus
(C) Spasm
(D) Tonus

Answer: C

Explanation: Spasm is an involuntary, brief, sudden contraction of muscles. It may occur due to electrolyte imbalance, nerve irritation, or injury.

5. Single Correct Answer MCQ: Energy for muscle contraction is primarily supplied by:

(A) DNA
(B) ATP
(C) RNA
(D) Glucose only

Answer: B

Explanation: ATP is the direct energy source for actin-myosin cross-bridge cycling. Glucose and other substrates generate ATP via metabolism, but ATP is the immediate energy currency for contraction and relaxation.

6. Single Correct Answer MCQ: Summation of muscle contractions leading to sustained tension is called:

(A) Tetanus
(B) Fatigue
(C) Tonus
(D) Spasm

Answer: A

Explanation: Tetanus occurs when multiple stimuli rapidly follow one another, producing a sustained contraction without relaxation. This demonstrates temporal summation of muscle action potentials.

7. Assertion-Reason MCQ:
Assertion (A): Tetanus is continuous muscle contraction without relaxation.
Reason (R): Rapid successive stimuli prevent muscle fiber from relaxing completely.

(A) Both A and R are true, R is correct explanation of A
(B) Both A and R are true, R is NOT correct explanation of A
(C) A is true, R is false
(D) A is false, R is true

Answer: A

Explanation: Tetanus occurs when high-frequency stimuli summate, preventing relaxation. This leads to sustained maximal contraction, which is physiologically used for prolonged muscular activities.

8. Matching Type MCQ: Match type of contraction with description:

1. Spasm   A. Partial contraction at rest
2. Tonus   B. Involuntary sudden contraction
3. Tetanus   C. Sustained contraction without relaxation
4. Fatigue   D. Reduced ability to contract after prolonged activity

(A) 1-B, 2-A, 3-C, 4-D
(B) 1-A, 2-B, 3-D, 4-C
(C) 1-C, 2-D, 3-B, 4-A
(D) 1-D, 2-C, 3-B, 4-A

Answer: A

Explanation: Spasm is sudden contraction, tonus is partial contraction at rest, tetanus is sustained contraction, and fatigue reduces force after prolonged activity.

9. Fill in the Blanks: Continuous contraction without relaxation is called ________, while reduced muscle force after prolonged activity is termed ________.

(A) Tetanus; Fatigue
(B) Tonus; Spasm
(C) Spasm; Tetanus
(D) Fatigue; Tetanus

Answer: A

Explanation: Tetanus is sustained contraction due to repeated stimuli. Fatigue is the decline in muscle force after prolonged activity, often due to metabolic byproducts and energy depletion.

10. Choose the Correct Statements:
(A) Tetanus results from rapid successive stimuli.
(B) Spasm is involuntary muscle contraction.
(C) Fatigue is a sustained contraction without relaxation.
(D) Tonus maintains posture at rest.

(1) A, B, D
(2) A, C
(3) B, C
(4) All are correct

Answer: 1

Explanation: Statements A, B, and D are correct. Fatigue is not sustained contraction; it refers to decreased force after prolonged activity. Tetanus, not fatigue, is sustained contraction.