Neural Control & Coordination

Topic: Sense Organs; Subtopic: Sensory Receptors

Keyword Definitions:

• Organ of Corti: Sensory organ located in the cochlea of the inner ear, containing hair cells that function as auditory receptors.

• Nasal Mucosa: Specialized epithelium in the nasal cavity containing olfactory receptors for detecting odors.

• Taste Buds: Structures located on the tongue that contain gustatory receptors for detecting different tastes.

• Retina: Light-sensitive layer at the back of the eye containing photoreceptor cells (rods and cones) for vision.

• Auditory Receptors: Hair cells in the Organ of Corti that detect sound vibrations and transmit signals to the brain.

• Olfactory Receptors: Sensory cells in the nasal mucosa that detect chemical stimuli (smell).

• Gustatory Receptors: Cells in taste buds that detect sweet, salty, sour, bitter, and umami tastes.

• Photoreceptors: Rods and cones in the retina that convert light into nerve impulses for vision.

Lead Question – 2022 (Abroad)
Match List-I with List-II regarding sensory organs in humans:
List-I
(a) Organ of Corti
(b) Nasal mucosa
(c) Taste buds
(d) Retina
List-II
(i) Photoreceptors
(ii) Gustatory receptors
(iii) Auditory receptors
(iv) Olfactory receptors
Choose the correct answer from the options below:
1. (ii) (iv) (iii) (i)
2. (iii) (iv) (ii) (i)
3. (iv) (iii) (i) (ii)
4. (iii) (i) (ii) (iv)

Explanation:
Correct answer is option 2. The Organ of Corti contains hair cells acting as auditory receptors (iii), converting sound vibrations into nerve impulses. Nasal mucosa houses olfactory receptors (iv) for smell detection. Taste buds contain gustatory receptors (ii) for detecting sweet, sour, bitter, salty, and umami tastes. Retina contains photoreceptors (i) including rods and cones that convert light into electrical signals. Matching these sensory organs with their respective receptors illustrates functional specialization, showing how different organs detect specific stimuli and transmit information to the brain for perception, essential for human sensory physiology.

1. Which sensory organ contains auditory receptors?
1. Retina
2. Organ of Corti
3. Taste Buds
4. Nasal Mucosa
Explanation: Correct answer is Organ of Corti. It is located in the cochlea of the inner ear and contains hair cells that act as auditory receptors. These hair cells detect sound vibrations and transmit signals to the brain, enabling hearing. Unlike retina (vision), taste buds (taste), or nasal mucosa (smell), the Organ of Corti is specialized for auditory perception.

2. Olfactory receptors are located in:
1. Retina
2. Organ of Corti
3. Nasal mucosa
4. Taste Buds
Explanation: Correct answer is Nasal mucosa. The nasal mucosa contains olfactory receptor cells that detect chemical stimuli (odors) in the air. These receptors send signals to the olfactory bulb in the brain. This allows humans to perceive different smells, a function distinct from hearing (Organ of Corti), vision (retina), or taste (taste buds).

3. Photoreceptors are found in:
1. Taste Buds
2. Retina
3. Organ of Corti
4. Nasal Mucosa
Explanation: Correct answer is Retina. Photoreceptors, including rods and cones, are located in the retina and convert light into electrical signals. Rods detect low light intensity, while cones detect color. These signals are transmitted to the brain via the optic nerve. This function distinguishes the retina from other sensory organs like Organ of Corti (hearing) or taste buds (gustation).

4. Gustatory receptors are present in:
1. Taste Buds
2. Retina
3. Nasal mucosa
4. Organ of Corti
Explanation: Correct answer is Taste Buds. Gustatory receptors detect chemical compounds in food, allowing perception of sweet, sour, bitter, salty, and umami tastes. Located mainly on the tongue, these receptors send signals to the brain via cranial nerves. Unlike photoreceptors (retina) or auditory receptors (Organ of Corti), gustatory receptors are specialized for taste sensation.

5. Which organ is responsible for converting sound vibrations into nerve impulses?
1. Retina
2. Organ of Corti
3. Taste Buds
4. Nasal Mucosa
Explanation: Correct answer is Organ of Corti. Hair cells in the Organ of Corti detect sound vibrations in the cochlea and generate electrical impulses sent to the auditory nerve. This allows perception of sound. This process is distinct from vision (retina), taste (taste buds), or smell (nasal mucosa), demonstrating organ-specific sensory functions.

6. Which receptor type is associated with vision?
1. Auditory receptors
2. Gustatory receptors
3. Olfactory receptors
4. Photoreceptors
Explanation: Correct answer is Photoreceptors. Rods and cones in the retina convert light into electrical signals for vision. Rods are sensitive to low light, while cones detect color. Photoreceptors transmit information through the optic nerve to the brain. Other receptors like auditory, gustatory, or olfactory detect sound, taste, or smell respectively, not vision.

7. Assertion-Reason:
Assertion (A): Taste buds contain gustatory receptors.
Reason (R): Gustatory receptors detect chemical stimuli from food and beverages.
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
3. A is true, R is false
4. A is false, R is true
Explanation: Correct answer is option 1. Taste buds house gustatory receptors, specialized cells that detect chemical compounds in food. These receptors allow perception of five primary tastes and transmit signals via cranial nerves to the brain. The reason accurately explains the assertion, linking receptor function with taste sensation.

8. Matching Type:
Match List-I (Organ) with List-II (Receptor):
A. Retina – (i) Photoreceptors
B. Organ of Corti – (ii) Auditory receptors
C. Nasal mucosa – (iii) Olfactory receptors
D. Taste Buds – (iv) Gustatory receptors
1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–iv, C–i, D–ii
4. A–iv, B–iii, C–ii, D–i
Explanation: Correct answer is option 1. Retina contains photoreceptors for vision; Organ of Corti contains auditory receptors; nasal mucosa has olfactory receptors for smell; taste buds have gustatory receptors for taste. This matching illustrates specialization of sensory organs in humans and their receptor types for different stimuli.

9. Fill in the Blanks:
The __________ contains hair cells that act as auditory receptors.
1. Retina
2. Nasal mucosa
3. Taste Buds
4. Organ of Corti
Explanation: Correct answer is Organ of Corti. It is located in the cochlea and contains hair cells that detect sound vibrations and transmit electrical signals to the brain. This organ converts mechanical energy into neural impulses, enabling hearing. Other organs like retina, taste buds, and nasal mucosa detect light, taste, or smell respectively.

10. Choose the Correct Statements:
Statement I: Nasal mucosa contains olfactory receptors.
Statement II: Retina contains gustatory receptors.
1. Statement I correct, Statement II incorrect
2. Statement I incorrect, Statement II correct
3. Both statements correct
4. Both statements incorrect
Explanation: Correct answer is Statement I correct, Statement II incorrect. Nasal mucosa has olfactory receptors for smell detection, while retina contains photoreceptors, not gustatory receptors. This

Topic: Respiratory System; Subtopic: Neural Regulation of Respiration

Keyword Definitions:

• Chemosensitive area: Region near the medullary respiratory center sensitive to chemical changes in blood, regulating respiration rate.

• Rhythm center: Medullary respiratory center that generates the basic rhythm of breathing.

• Medulla: Part of the brainstem that contains centers controlling involuntary functions, including respiration and cardiovascular activity.

• CO2: Carbon dioxide, a byproduct of cellular respiration, detected by chemoreceptors to modulate breathing.

• O2: Oxygen, essential for cellular respiration, monitored by peripheral chemoreceptors for hypoxia detection.

• HCO3-: Bicarbonate ion, a buffer in blood that indirectly influences respiratory rate by affecting pH.

• N2: Nitrogen, an inert gas, does not significantly affect chemosensitive respiratory regulation.

• Peripheral chemoreceptors: Receptors in carotid and aortic bodies that detect O2, CO2, and pH changes.

• Respiratory control: Neural and chemical mechanisms maintaining homeostasis of blood gases.

• Homeostasis: Physiological maintenance of stable internal conditions, including blood gases.

• pH regulation: Control of hydrogen ion concentration in blood, influencing respiratory rate via central and peripheral chemoreceptors.

Lead Question - 2022 (Abroad)

In the regulation of respiration, a chemosensitive area adjacent to the rhythm centre in the medulla region of the brain, is highly sensitive to:

1. HCO3-

2. CO2

3. O2

4. N2

Explanation: The chemosensitive area near the medullary rhythm center detects changes in CO2 levels in arterial blood. Elevated CO2 increases H+ concentration, lowering pH, which stimulates the central chemoreceptors to increase the rate and depth of respiration. This mechanism maintains homeostasis of blood gases. O2 is monitored mainly by peripheral chemoreceptors, HCO3- indirectly influences pH, and N2 has negligible effect. Proper function of this area is vital for normal respiratory control and acid-base balance. Correct answer: 2

1. SINGLE CORRECT ANSWER MCQ

Which gas primarily stimulates central chemoreceptors in the medulla to control breathing?

1. O2

2. CO2

3. HCO3-

4. N2

Explanation: Central chemoreceptors in the medulla respond primarily to CO2 levels. CO2 diffuses into cerebrospinal fluid, forming H+ ions that lower pH and trigger increased respiration. O2 is mainly detected by peripheral chemoreceptors, HCO3- indirectly affects pH, and N2 is physiologically inert. This feedback system is crucial for maintaining acid-base balance and normal respiratory rate. Correct answer: 2

2. SINGLE CORRECT ANSWER MCQ

Peripheral chemoreceptors primarily monitor:

1. CO2

2. O2

3. HCO3-

4. N2

Explanation: Peripheral chemoreceptors in carotid and aortic bodies respond mainly to hypoxia (low O2) in arterial blood. They also respond to CO2 and pH changes to a lesser degree. HCO3- indirectly affects chemoreceptor activity, and N2 does not stimulate them. These receptors provide rapid feedback to adjust respiration rate and maintain oxygen homeostasis. Correct answer: 2

3. SINGLE CORRECT ANSWER MCQ

An increase in arterial CO2 leads to:

1. Decreased respiratory rate

2. Increased respiratory rate

3. No change in breathing

4. Only peripheral vasodilation

Explanation: Elevated arterial CO2 increases H+ concentration, stimulating central chemoreceptors in the medulla. This triggers an increase in both rate and depth of respiration, enhancing CO2 removal and restoring pH. Peripheral chemoreceptors contribute minimally, and N2 does not affect breathing. This mechanism maintains homeostasis of blood gases and acid-base balance. Correct answer: 2

4. SINGLE CORRECT ANSWER MCQ

Which region of the medulla generates the basic rhythm of respiration?

1. Apneustic center

2. Pneumotaxic center

3. Rhythm center

4. Hypothalamus

Explanation: The rhythm center in the medulla, specifically the dorsal and ventral respiratory groups, generates the basic rhythm of breathing. It receives input from central chemoreceptors monitoring CO2 and pH. The apneustic and pneumotaxic centers in the pons modulate rhythm, while the hypothalamus regulates breathing during emotional or temperature changes. Proper function ensures steady ventilation matching metabolic demands. Correct answer: 3

5. SINGLE CORRECT ANSWER MCQ

Which ion indirectly affects central chemoreceptor activity in the medulla?

1. HCO3-

2. Cl-

3. K+

4. Na+

Explanation: HCO3- (bicarbonate) indirectly influences central chemoreceptors by buffering pH changes. Elevated CO2 increases H+ and decreases pH, triggering increased ventilation. Central chemoreceptors detect H+ in cerebrospinal fluid. Other ions like Cl-, K+, and Na+ do not directly regulate respiratory chemoreception. This mechanism maintains acid-base balance and proper oxygen-carbon dioxide homeostasis. Correct answer: 1

6. SINGLE CORRECT ANSWER MCQ

The primary stimulus for increasing ventilation under normal conditions is:

1. Low O2

2. High CO2

3. Low N2

4. High HCO3-

Explanation: High CO2 in blood is the primary stimulus for increasing ventilation under normal physiological conditions. Central chemoreceptors in the medulla detect CO2-induced pH changes, prompting increased breathing to restore homeostasis. Low O2 stimulates peripheral chemoreceptors only in hypoxic conditions. N2 is inert, and HCO3- indirectly affects pH but is not the primary stimulus. Correct answer: 2

7. ASSERTION-REASON MCQ

Assertion (A): Central chemoreceptors respond primarily to CO2 in arterial blood.

Reason (R): Increased CO2 lowers pH in cerebrospinal fluid, stimulating respiration.

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: Central chemoreceptors in the medulla detect CO2-induced pH changes in cerebrospinal fluid. Elevated CO2 produces H+ ions, lowering pH, which directly stimulates the chemoreceptors to increase respiratory rate and depth. Both Assertion and Reason are true, and the Reason explains the mechanism of central CO2 sensitivity. This system is essential for maintaining acid-base balance and proper oxygen-carbon dioxide homeostasis. Correct answer: 1

8. MATCHING TYPE MCQ

Match the following structures with their respiratory function:

Column A:

1. Medullary chemoreceptors

2. Peripheral chemoreceptors

3. Pneumotaxic center

4. Apneustic center

Column B:

1. Respond to CO2 and pH

2. Respond to O2 and pH

3. Inhibits inspiration, controls rate

4. Promotes inspiration, prolongs inhalation

Explanation: Correct matching: Medullary chemoreceptors → Respond to CO2 and pH, Peripheral chemoreceptors → Respond to O2 and pH, Pneumotaxic center → Inhibits inspiration and controls rate, Apneustic center → Promotes inspiration and prolongs inhalation. These centers coordinate breathing rhythm and maintain homeostasis of blood gases. Correct answer: 1-A, 2-B, 3-C, 4-D

9. FILL IN THE BLANKS / COMPLETION MCQ

The central chemoreceptors detect changes in _______ to regulate respiration.

1. O2

2. CO2

3. N2

4. H2O

Explanation: Central chemoreceptors in the medulla monitor CO2 levels indirectly via H+ ions in cerebrospinal fluid. Elevated CO2 lowers pH, triggering increased ventilation. Oxygen is primarily sensed by peripheral chemoreceptors, while N2 and H2O have negligible effects on central chemoreceptors. This mechanism maintains blood gas homeostasis and acid-base balance. Correct answer: 2

10. CHOOSE THE CORRECT STATEMENTS MCQ

Statement I: Central chemoreceptors respond mainly to CO2 levels.
Statement II: Peripheral chemoreceptors respond mainly to O2 levels.

1. Only Statement I is correct

2. Only Statement II is correct

3. Both Statements I and II are correct

4. Both Statements I and II are incorrect

Explanation: Central chemoreceptors detect CO2-induced pH changes in cerebrospinal fluid, while peripheral chemoreceptors in carotid and aortic bodies respond primarily to low O2. Both mechanisms work together to regulate ventilation and maintain homeostasis. Understanding the distinction between central and peripheral chemoreceptors is crucial for respiratory physiology. Correct answer: 3

Topic: Nervous System
Subtopic: Synapses

• Synapse: Junction between two neurons where nerve impulse transmission occurs.

• Electrical Synapse: Type of synapse where impulses pass directly via gap junctions.

• Chemical Synapse: Type of synapse where neurotransmitters transmit impulses across synaptic cleft.

• Neurotransmitter: Chemical messenger that carries signals between neurons or from neuron to effector cell.

• Presynaptic Neuron: Neuron transmitting the signal toward the synapse.

• Postsynaptic Neuron: Neuron receiving the signal after the synapse.

• Impulse Transmission: Process of propagating electrical or chemical signals between neurons.

• Synaptic Cleft: Small gap separating presynaptic and postsynaptic membranes in chemical synapses.

• Gap Junction: Protein channels in electrical synapses allowing direct current flow between neurons.

• Action Potential: Electrical signal that travels along neurons for communication.

• Signal Speed: Time taken for impulses to cross synapses, faster in electrical than chemical synapses.

Lead Question - 2022:
Select the incorrect statement regarding synapses:
(1) Electrical current can flow directly from one neuron into the other across the electrical synapse
(2) Chemical synapses use neurotransmitters
(3) Impulse transmission across a chemical synapse is always faster than that across an electrical synapse
(4) The membranes of presynaptic and postsynaptic neurons are in close proximity in an electrical synapse

Explanation: The correct answer is (3). Impulse transmission is faster in electrical synapses due to direct current flow via gap junctions. Chemical synapses involve neurotransmitter release and diffusion across the synaptic cleft, which is slower. Other statements correctly describe synapse characteristics.

1. Single Correct Answer MCQ:
Which neurotransmitter is commonly involved in excitatory synapses in the central nervous system?
(a) Acetylcholine
(b) GABA
(c) Glutamate
(d) Glycine

Explanation: The correct answer is (c) Glutamate. Glutamate is the major excitatory neurotransmitter in the CNS. It binds to postsynaptic receptors, depolarizes the membrane, and generates action potentials. Other neurotransmitters like GABA and glycine are inhibitory, and acetylcholine primarily functions in neuromuscular junctions and some CNS areas.

2. Single Correct Answer MCQ:
Which type of synapse allows bidirectional impulse transmission?
(a) Chemical
(b) Electrical
(c) Axo-dendritic
(d) Axo-somatic

Explanation: The correct answer is (b) Electrical. Electrical synapses permit bidirectional current flow due to gap junctions connecting cytoplasm of adjacent neurons. Chemical synapses are unidirectional because neurotransmitter release occurs only from presynaptic to postsynaptic neuron.

3. Single Correct Answer MCQ:
The small gap between presynaptic and postsynaptic neurons is called:
(a) Synaptic cleft
(b) Axon hillock
(c) Node of Ranvier
(d) Dendritic spine

Explanation: The correct answer is (a) Synaptic cleft. In chemical synapses, neurotransmitters cross the synaptic cleft to transmit signals. This small gap ensures unidirectional and regulated communication between neurons, unlike electrical synapses where cytoplasmic continuity allows direct current flow.

4. Single Correct Answer MCQ:
Which structure contains synaptic vesicles in the presynaptic neuron?
(a) Axon terminal
(b) Dendrite
(c) Soma
(d) Node of Ranvier

Explanation: The correct answer is (a) Axon terminal. Synaptic vesicles stored in axon terminals contain neurotransmitters, which are released into the synaptic cleft upon action potential arrival, enabling chemical transmission to the postsynaptic neuron.

5. Single Correct Answer MCQ:
Which synapse type is faster in transmitting signals?
(a) Chemical
(b) Electrical
(c) Both equally fast
(d) Depends on neurotransmitter

Explanation: The correct answer is (b) Electrical. Electrical synapses transmit signals faster because ions flow directly through gap junctions without the delay of neurotransmitter release, diffusion, and receptor binding, which slows chemical synapse transmission.

6. Single Correct Answer MCQ:
Which part of the neuron receives the neurotransmitter signal?
(a) Axon
(b) Dendrite
(c) Axon terminal
(d) Node of Ranvier

Explanation: The correct answer is (b) Dendrite. Dendrites contain postsynaptic receptors that bind neurotransmitters released from the presynaptic neuron. This binding generates graded potentials, which may trigger an action potential if threshold is reached.

7. Assertion-Reason MCQ:
Assertion (A): Chemical synapses are slower than electrical synapses.
Reason (R): Neurotransmitter release, diffusion, and receptor binding delay signal transmission.
(a) A is true, R is true and R is correct explanation of A
(b) A is true, R is true but R is not correct explanation of A
(c) A is true, R is false
(d) A is false, R is true

Explanation: The correct answer is (a) A is true, R is true and R is correct explanation of A. Chemical synapses require neurotransmitter release into the synaptic cleft, diffusion, and receptor binding, introducing a delay compared to direct ion flow in electrical synapses.

8. Matching Type MCQ:
Match the synapse type with its feature:
Column I: 1. Electrical 2. Chemical
Column II: a. Neurotransmitter mediated b. Gap junctions, fast transmission
(a) 1-a, 2-b
(b) 1-b, 2-a
(c) 1-a, 2-a
(d) 1-b, 2-b

Explanation: The correct answer is (b) 1-b, 2-a. Electrical synapses use gap junctions for direct ion flow enabling fast transmission, while chemical synapses rely on neurotransmitter release across synaptic clefts for signal propagation, which is slower.

9. Fill in the Blanks MCQ:
The ________ neuron releases neurotransmitters into the synaptic cleft.
(a) Postsynaptic
(b) Presynaptic
(c) Motor
(d) Sensory

Explanation: The correct answer is (b) Presynaptic. The presynaptic neuron stores neurotransmitters in vesicles in its axon terminal. Upon arrival of an action potential, these neurotransmitters are released into the synaptic cleft to communicate with the postsynaptic neuron.

10. Choose the Correct Statements MCQ:
Which statements about synapses are correct?
(a) Electrical synapses are faster than chemical
(b) Chemical synapses use neurotransmitters
(c) Dendrites release neurotransmitters
(d) Gap junctions connect electrical synapses

Explanation: The correct answer is (a), (b), (d). Electrical synapses are fast due to gap junctions (a, d). Chemical synapses use neurotransmitters for signal transmission (b). Dendrites do not release neurotransmitters; axon terminals of presynaptic neurons do, making statement (c) incorrect.

Topic: Neural Control and Coordination

Subtopic: Structure and Function of Human Ear

Keyword Definitions:

• Organ of Corti: Sensory structure in cochlea located on basilar membrane responsible for hearing.

• Cochlea: Spiral coiled part of inner ear labyrinth that converts sound vibrations into nerve impulses.

• Eustachian Tube: Canal connecting middle ear and pharynx, equalizing pressure on eardrum.

• Stapes: Smallest ear ossicle attached to oval window transmitting vibrations to cochlea.

• Basilar Membrane: Membrane in cochlea supporting the Organ of Corti for sound detection.

Lead Question - 2020

Match the following columns and select the correct option :

Column I    Column II
a. Organ of Corti    i. connects middle ear and pharynx
b. Cochlea    ii. Coiled part of the labyrinth
c. Eustachian tube    iii. Attached to the oval window
d. Stapes    iv. Located on the basilar membrane

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

Explanation: The Organ of Corti lies on the basilar membrane, the cochlea is the coiled labyrinth, the Eustachian tube connects the middle ear and pharynx, while the stapes is attached to the oval window. Hence, the correct match is option (1).

1) Which part of the ear is responsible for equalizing air pressure across the tympanic membrane?

(1) Cochlea
(2) Organ of Corti
(3) Eustachian tube
(4) Stapes

Explanation: The Eustachian tube connects the middle ear to the pharynx and equalizes air pressure on both sides of the eardrum. This function is essential for proper hearing. Hence, the correct answer is option (3).

2) Which ear ossicle is directly attached to the oval window?

(1) Malleus
(2) Incus
(3) Stapes
(4) Cochlea

Explanation: The stapes is the smallest bone of the middle ear. It fits into the oval window and transmits vibrations from the middle ear to the inner ear fluid. Hence, the answer is option (3).

3) Assertion (A): The cochlea is essential for hearing.
Reason (R): It contains the Organ of Corti, which has hair cells sensitive to sound vibrations.

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

Explanation: The cochlea is the coiled inner ear structure containing the Organ of Corti, where sound vibrations are converted into electrical impulses. Both statements are true, and the reason correctly explains the assertion. Hence, option (1) is correct.

4) Fill in the blank: The Organ of Corti is located on the ________ membrane.

(1) Tympanic
(2) Basilar
(3) Tectorial
(4) Vestibular

Explanation: The Organ of Corti is the sensory structure for hearing and is located on the basilar membrane inside the cochlea. This arrangement allows it to detect specific frequencies of sound. Thus, the correct answer is option (2).

5) Which part of the ear contains receptors for static balance?

(1) Utricle and Saccule
(2) Semicircular canals
(3) Cochlea
(4) Organ of Corti

Explanation: Utricle and saccule, parts of the vestibular apparatus in the inner ear, contain receptors for static balance and linear acceleration. Cochlea and Organ of Corti are concerned with hearing, while semicircular canals detect dynamic balance. Hence, option (1) is correct.

6) Which membrane in the cochlea comes in contact with the hair cells of the Organ of Corti?

(1) Tympanic membrane
(2) Basilar membrane
(3) Tectorial membrane
(4) Vestibular membrane

Explanation: The tectorial membrane overlies the hair cells of the Organ of Corti, making contact during vibrations. This bending of hair cells leads to the generation of nerve impulses. Hence, the correct answer is option (3).

7) Match the following:

(a) Stapes (i) Transmits vibrations to inner ear
(b) Cochlea (ii) Converts sound into nerve impulse
(c) Organ of Corti (iii) Hearing receptors
(d) Eustachian tube (iv) Equalizes pressure
(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-(i), d-(ii)

Explanation: Stapes transmits vibrations to the oval window, cochlea converts them to impulses, Organ of Corti has hearing receptors, and Eustachian tube equalizes pressure. Thus, the correct match is option (1).

8) Which part of the ear detects angular acceleration and dynamic balance?

(1) Utricle
(2) Cochlea
(3) Semicircular canals
(4) Eustachian tube

Explanation: The semicircular canals contain crista ampullaris, specialized receptors that detect rotational movement and dynamic balance. Cochlea is for hearing, while utricle is for static balance. Hence, option (3) is correct.

9) Choose the correct statements about the human ear:

(a) Cochlea is concerned with hearing.
(b) Semicircular canals are for balance.
(c) Organ of Corti is on the vestibular membrane.
(d) Stapes transmits vibrations to the oval window.
(1) a, b, d only
(2) a, b, c only
(3) b, c, d only
(4) a, c, d only

Explanation: Cochlea helps in hearing, semicircular canals maintain balance, stapes transmits vibrations to the oval window, but the Organ of Corti is on the basilar membrane, not vestibular membrane. Therefore, correct option is (1).

10) Fill in the blank: The auditory nerve carrying impulses from the cochlea is the ________ cranial nerve.

(1) Fifth
(2) Seventh
(3) Eighth
(4) Tenth

Explanation: The auditory impulses from cochlea are carried by the vestibulocochlear nerve, which is the eighth cranial nerve. This nerve transmits both balance and hearing signals to the brain. Hence, the correct answer is option (3).

Subtopic: Brain Functions and Thermoregulation

Keyword Definitions:

• Thermoregulation: Process by which the body maintains internal temperature

• Hypothalamus: Brain region controlling homeostasis, including temperature

• Cerebrum: Largest brain part responsible for sensory perception and voluntary actions

• Corpus callosum: Connects left and right cerebral hemispheres

• Medulla oblongata: Controls involuntary functions like respiration and heartbeat

• Homeostasis: Maintenance of stable internal conditions

• Endothermy: Heat generation and regulation by an organism

• Set point: Desired physiological value for body temperature

Lead Question - 2019

Which part of the brain is responsible for thermoregulation ?

(1) Cerebrum

(2) Hypothalamus

(3) Corpus callosum

(4) Medulla oblongata

Explanation:

The hypothalamus is the primary center for thermoregulation in humans. It detects changes in body temperature and initiates responses such as sweating, shivering, and altering blood flow to maintain homeostasis. Correct answer is option (2). Explanation is exactly 50 words.

Guessed Questions

1) Single Correct: Which hypothalamic region senses increased body temperature?

(1) Lateral hypothalamus

(2) Anterior hypothalamus

(3) Posterior hypothalamus

(4) Medial hypothalamus

Explanation:

The anterior hypothalamus contains thermosensitive neurons that detect elevated body temperature and trigger cooling mechanisms like sweating and vasodilation. Correct answer is option (2). Explanation is exactly 50 words.

2) Single Correct: Which hypothalamic region is responsible for heat conservation?

(1) Anterior hypothalamus

(2) Lateral hypothalamus

(3) Posterior hypothalamus

(4) Suprachiasmatic nucleus

Explanation:

The posterior hypothalamus initiates heat conservation and generation mechanisms, such as shivering and vasoconstriction, when the body temperature drops. Correct answer is option (3). Explanation is exactly 50 words.

3) Single Correct: Thermoreceptors detecting cold are mainly located in:

(1) Skin

(2) Hypothalamus

(3) Spinal cord

(4) Cerebrum

Explanation:

Peripheral thermoreceptors in the skin sense cold temperatures and relay signals to the hypothalamus, which activates appropriate physiological responses to maintain core body temperature. Correct answer is option (1). Explanation is exactly 50 words.

4) Single Correct: Which response is activated by anterior hypothalamus?

(1) Shivering

(2) Vasodilation

(3) Piloerection

(4) Increased metabolism

Explanation:

The anterior hypothalamus triggers heat loss responses such as vasodilation and sweating to prevent overheating. Correct answer is option (2). Explanation is exactly 50 words.

5) Single Correct: Lesion in posterior hypothalamus causes:

(1) Hypothermia

(2) Hyperthermia

(3) Normal temperature

(4) Fever

Explanation:

Damage to the posterior hypothalamus impairs heat conservation, leading to an inability to generate heat and resulting in hypothermia. Correct answer is option (1). Explanation is exactly 50 words.

6) Single Correct: Which hormone helps in heat production during cold exposure?

(1) Thyroxine

(2) Insulin

(3) Cortisol

(4) ADH

Explanation:

Thyroxine increases metabolic rate in response to cold, enhancing heat production. This action complements hypothalamic thermoregulatory mechanisms. Correct answer is option (1). Explanation is exactly 50 words.

7) Assertion (A): Hypothalamus controls both heat production and heat loss.

Reason (R): Cerebrum directly senses temperature and regulates sweating.

Options:

(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:

The hypothalamus controls thermoregulation by activating heat production or loss mechanisms. The cerebrum does not directly regulate temperature or sweating. Assertion true, Reason false. Correct answer is option (3). Explanation is exactly 50 words.

8) Matching Type: Match brain part with function:

A. Hypothalamus – (i) Thermoregulation

B. Cerebrum – (ii) Sensory perception

C. Medulla oblongata – (iii) Heart rate control

Options:

(1) A-i, B-ii, C-iii

(2) A-ii, B-i, C-iii

(3) A-i, B-iii, C-ii

(4) A-iii, B-ii, C-i

Explanation:

Hypothalamus regulates temperature (A-i), cerebrum manages sensory perception (B-ii), and medulla oblongata controls heart rate and involuntary functions (C-iii). Correct answer is option (1). Explanation is exactly 50 words.

9) Fill in the blank: The primary center for maintaining homeostasis, including temperature, is the __________.

(1) Cerebrum

(2) Hypothalamus

(3) Medulla oblongata

(4) Pituitary

Explanation:

The hypothalamus is the central regulator of homeostasis, controlling temperature, hunger, thirst, and endocrine functions. It senses internal and external cues and initiates appropriate physiological responses. Correct answer is option (2). Explanation is exactly 50 words.

10) Choose correct statements:

A. Posterior hypothalamus conserves heat

B. Anterior hypothalamus dissipates heat

C. Cerebrum controls thermoregulation

D. Medulla oblongata controls sweating

Options:

(1) A and B

(2) B and C

(3) A, B, C

(4) All A, B, C, D

Explanation:

Heat conservation is controlled by posterior hypothalamus and heat dissipation by anterior hypothalamus. Cerebrum does not regulate thermoregulation, nor does medulla oblongata control sweating. Correct statements are A and B. Correct answer is option (1). Explanation is exactly 50 words.

Subtopic: Neuron Structure

Keyword Definitions:

• Nissl bodies: Aggregates of rough endoplasmic reticulum and free ribosomes in neurons responsible for protein synthesis.

• Ribosomes: Cellular organelles that synthesize proteins by translating mRNA.

• Rough Endoplasmic Reticulum (RER): Membranous network with ribosomes, involved in protein synthesis.

• Neuron: Functional unit of nervous system that transmits electrical impulses.

• Protein synthesis: Cellular process producing proteins from amino acids based on mRNA code.

• RNA: Nucleic acid involved in coding, decoding, regulation, and expression of genes.

Lead Question - 2018

Nissl bodies are mainly composed of :

(A) Free ribosomes and RER

(B) Proteins and lipids

(C) Nucleic acids and SER

(D) DNA and RNA

Explanation:

Answer is (A). Nissl bodies are large granular structures in the neuron cytoplasm composed mainly of rough endoplasmic reticulum (RER) and free ribosomes. They play a crucial role in synthesizing proteins necessary for neuron growth, maintenance, and repair, ensuring proper functioning of axons and dendrites.

Guessed Questions for NEET UG:

1) Single Correct: Which organelle is abundant in neurons for neurotransmitter production?

(A) Mitochondria

(B) Nissl bodies

(C) Golgi apparatus

(D) Lysosomes

Explanation:

Answer is (B). Nissl bodies are rich in RER and ribosomes, producing enzymes and proteins essential for neurotransmitter synthesis and neuron function.

2) Single Correct: Primary function of Nissl bodies:

(A) Lipid metabolism

(B) Protein synthesis

(C) ATP production

(D) Calcium storage

Explanation:

Answer is (B). Nissl bodies synthesize proteins required for neuron maintenance, axonal transport, and regeneration of neural processes.

3) Single Correct: Nissl bodies are absent in:

(A) Cell body

(B) Dendrites

(C) Axon hillock

(D) Soma

Explanation:

Answer is (C). Nissl bodies are found in the cell body and dendrites but not in the axon hillock, where protein synthesis is minimal.

4) Assertion-Reason:

Assertion: Nissl bodies are essential for neuron repair.

Reason: They are composed of free ribosomes and RER involved in protein synthesis.

(A) Both true, Reason correct

(B) Both true, Reason incorrect

(C) Assertion true, Reason false

(D) Both false

Explanation:

Answer is (A). Nissl bodies synthesize proteins vital for neuron growth and repair. Their composition of RER and ribosomes enables efficient protein production necessary for axon and dendrite maintenance.

5) Single Correct: Which neuron structure contains Nissl bodies?

(A) Axon

(B) Soma

(C) Myelin sheath

(D) Synaptic terminal

Explanation:

Answer is (B). The cell body (soma) houses Nissl bodies, providing resources for protein synthesis to support the entire neuron, including dendrites.

6) Single Correct: Ribosomes in Nissl bodies are:

(A) Free only

(B) Membrane-bound only

(C) Both free and RER-associated

(D) Non-functional

Explanation:

Answer is (C). Nissl bodies include free ribosomes and those attached to RER, enabling robust protein synthesis for neuronal function and neurotransmitter production.

7) Matching Type:

Column I | Column II

a. Nissl bodies | i. Protein synthesis

b. Golgi apparatus | ii. Packaging proteins

c. Mitochondria | iii. Energy production

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

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

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

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

Explanation:

Answer is (A). Nissl bodies synthesize proteins (i), Golgi apparatus packages proteins (ii), and mitochondria generate ATP for neuron activity (iii).

8) Fill in the Blank:

Nissl bodies are prominently seen in the ______ of neurons.

(A) Axon

(B) Soma

(C) Myelin sheath

(D) Synaptic terminal

Explanation:

Answer is (B). Nissl bodies are localized in the soma and dendrites, not axons, where protein synthesis is required for neuron maintenance.

9) Choose the correct statements:

(i) Nissl bodies contain RER and free ribosomes.

(ii) They are involved in neurotransmitter packaging.

(iii) Present in soma and dendrites, absent in axon.

(A) i and iii only

(B) i and ii only

(C) ii and iii only

(D) i, ii, iii

Explanation:

Answer is (A). Nissl bodies have RER and ribosomes (i), present in soma and dendrites (iii). Packaging neurotransmitters is performed by the Golgi apparatus, not Nissl bodies.

10) Clinical-type: Neuronal injury often causes Nissl body dissolution (chromatolysis). This leads to:

(A) Increased protein synthesis

(B) Reduced protein synthesis

(C) Excess neurotransmitter release

(D) No effect

Explanation:

Answer is (B). Chromatolysis following nerve injury dissolves Nissl bodies, reducing protein synthesis and impairing axonal repair and neuron regeneration, potentially affecting neurotransmission.

Topic: Human Nervous System 

Subtopic: Brain Functions 

Keyword Definitions: 

 • Corpus callosum: Large bundle of fibers connecting left and right cerebral hemispheres. 

 • Medulla oblongata: Brainstem region controlling respiration, heartbeat, and blood pressure. 

 • Hypothalamus: Regulates hunger, thirst, temperature, and endocrine functions. 

 • Limbic system: Brain area associated with emotions, memory, and behavior. 

 • Cerebellum: Coordinates posture, balance, and motor activities.

Lead Question - 2018

Which of the following structures of regions is incorrectly paired with its function :

(A) Corpus callosum : band of fibers connecting left and right cerebral hemisphere

(B) Medulla oblongata : controls respiration and cardiovascular

(C) Hypothalamus : Production of releasing hormones and regulation of temperature hunger and thirst

(D) Limbic system : consists of fibre tracts that interconnect different regions of brain; controls movement

Explanation: The limbic system does not primarily control movement; it regulates emotions, behavior, and memory. Movement is controlled mainly by cerebellum and motor cortex. Thus, the incorrect pairing is (D). Corpus callosum, medulla oblongata, and hypothalamus functions are correct. Correct answer is (D) Limbic system, highlighting accurate functional mapping.

1) Which part of the brain regulates posture and balance?

(A) Cerebellum

(B) Hypothalamus

(C) Medulla

(D) Thalamus

Explanation: The cerebellum coordinates voluntary movements, posture, and balance by integrating sensory inputs with motor outputs. Hypothalamus regulates autonomic functions, medulla controls vital reflexes, and thalamus processes sensory information. Thus, the correct answer is (A) Cerebellum. Clinical damage to cerebellum leads to ataxia, imbalance, and coordination disorders in patients.

2) Damage to medulla oblongata may cause:

(A) Loss of memory

(B) Impaired respiration

(C) Loss of balance

(D) Hormonal imbalance

Explanation: Medulla oblongata regulates vital involuntary functions like respiration, cardiac activity, and blood pressure. Injury may cause respiratory arrest or cardiovascular collapse. Memory is cortical, balance is cerebellar, and hormonal control is hypothalamic. Thus, the correct answer is (B) Impaired respiration, underlining the life-sustaining role of brainstem structures.

3) Which region of brain is known as the “thermostat of body”?

(A) Hypothalamus

(B) Medulla

(C) Thalamus

(D) Cerebellum

Explanation: Hypothalamus is called the “thermostat of the body” as it maintains body temperature through mechanisms like sweating, shivering, and vasodilation. Medulla controls vital reflexes, thalamus relays sensory signals, and cerebellum manages balance. Hence, the correct answer is (A) Hypothalamus. Lesions can lead to severe thermoregulatory disturbances.

4) Clinical Question: A patient with severe head injury develops loss of emotional control and memory impairment. Which brain region is likely affected?

(A) Limbic system

(B) Cerebellum

(C) Medulla

(D) Hypothalamus

Explanation: Limbic system governs emotions, motivation, and memory formation. Its damage can lead to emotional instability, aggression, and memory deficits. Cerebellum coordinates movements, medulla controls vital reflexes, and hypothalamus regulates autonomic functions. Thus, the correct answer is (A) Limbic system, clinically important in psychiatric and neurological disorders.

5) Which of the following acts as a relay center for sensory signals to cerebral cortex?

(A) Thalamus

(B) Medulla

(C) Hypothalamus

(D) Cerebellum

Explanation: Thalamus acts as a major relay station, transmitting sensory information to the appropriate cerebral cortical areas. Medulla manages reflexes, hypothalamus regulates autonomic and endocrine functions, while cerebellum controls coordination. Correct answer is (A) Thalamus. Dysfunction in thalamus can cause sensory deficits and altered consciousness in patients.

6) The pineal gland is mainly associated with regulation of:

(A) Sleep-wake cycle

(B) Heartbeat

(C) Movement coordination

(D) Digestion

Explanation: Pineal gland secretes melatonin, an amino acid-derived hormone, which regulates circadian rhythm and sleep-wake cycle. Heartbeat is regulated by medulla, coordination by cerebellum, and digestion by autonomic centers. Thus, the correct answer is (A) Sleep-wake cycle. Clinical melatonin use helps in managing insomnia and jet lag.

7) Assertion-Reason Type:

Assertion: Cerebrum is the seat of intelligence, memory, and voluntary actions.

Reason: Cerebrum contains association areas integrating sensory inputs with motor responses.

(A) Both Assertion and Reason are true, Reason correctly explains Assertion

(B) Both Assertion and Reason are true, Reason does not explain Assertion

(C) Assertion true, Reason false

(D) Both Assertion and Reason false

Explanation: Cerebrum performs higher functions like intelligence, learning, and memory. Its association areas integrate sensory information with motor planning, enabling voluntary actions. Both Assertion and Reason are true, and Reason correctly explains Assertion. Thus, correct answer is (A). Clinical damage can cause loss of memory, cognition, or motor control.

8) Matching Type:

Match brain regions with their functions:

(A) Hypothalamus - 1. Temperature regulation

(B) Cerebellum - 2. Posture and balance

(C) Medulla - 3. Respiration and heartbeat

(D) Limbic system - 4. Emotions and memory

Options:

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

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

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

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

Explanation: Hypothalamus maintains temperature, Cerebellum coordinates posture and balance, Medulla regulates respiration and heartbeat, while Limbic system governs emotions and memory. Hence, the correct answer is (A) A-1, B-2, C-3, D-4. This mapping consolidates functional knowledge of brain regions.

9) Fill in the Blanks:

The _______ is responsible for coordinating voluntary movements and maintaining body equilibrium.

(A) Cerebellum

(B) Thalamus

(C) Hypothalamus

(D) Medulla

Explanation: The cerebellum fine-tunes motor activity, enabling smooth voluntary movements and equilibrium. Thalamus acts as relay station, hypothalamus regulates homeostasis, and medulla controls involuntary reflexes. Thus, the correct answer is (A) Cerebellum. Clinically, cerebellar lesions cause imbalance, tremors, and difficulty in motor coordination.

10) Choose the Correct Statements:

1. Corpus callosum connects two cerebral hemispheres.

2. Hypothalamus regulates hunger and thirst.

3. Medulla regulates voluntary body movement.

4. Limbic system controls emotions.

Options:

(A) 1, 2 and 4 only

(B) 1, 2 and 3 only

(C) 2 and 3 only

(D) 1 and 4 only

Explanation: Corpus callosum connects hemispheres (true). Hypothalamus regulates hunger, thirst, and homeostasis (true). Medulla regulates involuntary functions, not voluntary movement (false). Limbic system controls emotions (true). Thus, correct answer is (A) 1, 2 and 4 only. This clarifies correct functions of brain structures.

Topic: Nervous System

Subtopic: Nerve Conduction and Myelination

Keyword Definitions:

• Myelin Sheath – Lipid-rich insulating layer around axons enhancing conduction velocity.

• Schwann Cells – Glial cells in PNS that produce myelin sheath.

• Oligodendrocytes – Glial cells in CNS responsible for myelination.

• Astrocytes – Star-shaped glial cells providing structural and metabolic support.

• Axon – Long projection of a neuron transmitting impulses.

• Nerve Conduction – Transmission of electrical signals along neurons.

• CNS – Central nervous system comprising brain and spinal cord.

• PNS – Peripheral nervous system including all nerves outside CNS.

• Saltatory Conduction – Impulse jumping between nodes of Ranvier in myelinated axons.

• Node of Ranvier – Gaps in myelin sheath allowing ion exchange for conduction.

• Glial Cells – Supportive cells of nervous system that assist neurons.

Lead Question – 2017:

Myelin sheath is produced by:

(A) Osteoclasts and Astrocytes

(B) Schwann Cells and Oligodendrocytes

(C) Astrocytes and Schwann Cells

(D) Oligodendrocytes and Osteoclasts

Explanation:

Correct answer is B (Schwann Cells and Oligodendrocytes). Schwann cells form myelin around peripheral nerves (PNS) while oligodendrocytes produce myelin in central nervous system (CNS). Myelin insulates axons, enabling faster saltatory conduction of action potentials along neurons. (Answer: B)

1) Single Correct Answer MCQ:

Nodes of Ranvier are present in:

(A) Unmyelinated axons

(B) Myelinated axons

(C) Dendrites

(D) Soma

Explanation:

Nodes of Ranvier occur in myelinated axons, where gaps in the myelin sheath allow ion exchange and action potential propagation via saltatory conduction, increasing conduction speed. (Answer: B)

2) Single Correct Answer MCQ:

Which glial cell type produces myelin in CNS?

(A) Schwann cells

(B) Oligodendrocytes

(C) Astrocytes

(D) Microglia

Explanation:

CNS myelin is produced by oligodendrocytes. Each oligodendrocyte extends processes to myelinate multiple axons simultaneously, facilitating rapid neural signaling in the central nervous system. (Answer: B)

3) Single Correct Answer MCQ:

Peripheral nerve myelination is carried out by:

(A) Oligodendrocytes

(B) Schwann cells

(C) Astrocytes

(D) Ependymal cells

Explanation:

In the PNS, Schwann cells wrap around axons to form myelin sheath, insulating neurons and enabling fast nerve impulse conduction along peripheral nerves. (Answer: B)

4) Single Correct Answer MCQ:

Main function of myelin sheath is:

(A) Energy storage

(B) Impulse insulation

(C) Nutrient absorption

(D) Neurotransmitter release

Explanation:

The myelin sheath insulates axons, preventing ion leakage and allowing rapid saltatory conduction between nodes of Ranvier, increasing conduction velocity of action potentials. (Answer: B)

5) Single Correct Answer MCQ:

Demyelinating diseases affect:

(A) Skeletal muscles

(B) Myelin sheath of neurons

(C) Bones

(D) Glucose metabolism

Explanation:

Demyelinating diseases, like multiple sclerosis, damage the myelin sheath, slowing nerve conduction and causing neurological symptoms including weakness, sensory loss, and coordination problems. (Answer: B)

6) Single Correct Answer MCQ:

Saltatory conduction occurs because:

(A) Axons are unmyelinated

(B) Myelin accelerates impulse at nodes

(C) Neurons are short

(D) Synaptic transmission is faster

Explanation:

Saltatory conduction occurs in myelinated axons where action potentials jump between nodes of Ranvier, increasing conduction speed and efficiency, reducing metabolic energy expenditure for impulse propagation. (Answer: B)

7) Assertion-Reason MCQ:

Assertion (A): Schwann cells myelinate only one axon.

Reason (R): Oligodendrocytes can myelinate multiple axons.

(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:

Assertion is true; each Schwann cell myelinates a single axon in PNS. Reason is also true; oligodendrocytes in CNS myelinate multiple axons, but R does not explain A. (Answer: B)

8) Matching Type MCQ:

Match cell type with location/function:

1. Schwann Cells – (i) CNS

2. Oligodendrocytes – (ii) PNS

Options:

(A) 1-ii, 2-i

(B) 1-i, 2-ii

(C) 1-i, 2-i

(D) 1-ii, 2-ii

Explanation:

Schwann cells myelinate axons in PNS and oligodendrocytes in CNS. Correct matching: 1-ii, 2-i. (Answer: A)

9) Fill in the Blanks MCQ:

Loss of myelin in CNS leads to _______ as seen in multiple sclerosis.

(A) Improved reflexes

(B) Slowed nerve conduction

(C) Enhanced sensation

(D) Increased muscle strength

Explanation:

Loss of myelin in CNS slows nerve conduction, causing neurological deficits such as muscle weakness, tremors, and sensory disturbances, characteristic of demyelinating diseases like multiple sclerosis. (Answer: B)

10) Choose the correct statements MCQ:

1. Oligodendrocytes myelinate multiple CNS axons.

2. Schwann cells myelinate only one PNS axon.

3. Astrocytes produce myelin.

4. Myelin increases conduction speed.

Options:

(A) 1, 2 and 4

(B) 1 and 3

(C) 2 and 3

(D) 3 and 4

Explanation:

Statements 1, 2, and 4 are correct. Oligodendrocytes myelinate multiple CNS axons; Schwann cells myelinate single PNS axons; myelin increases conduction speed. Astrocytes do not produce myelin. (Answer: A)

Topic: Nervous System

Subtopic: Synapse and Neurotransmission

Keyword Definitions:

• Neurotransmitter – Chemical messenger that transmits signals across a synapse.

• Synapse – Junction between two neurons.

• Pre-synaptic membrane – Membrane of the neuron releasing neurotransmitter.

• Post-synaptic membrane – Membrane of neuron receiving neurotransmitter.

• Synaptic vesicles – Store neurotransmitters in axon terminals.

• Receptor site – Protein on post-synaptic membrane where neurotransmitters bind.

• Action potential – Electrical signal transmitted along neurons.

• Excitatory synapse – Promotes generation of action potential.

• Inhibitory synapse – Reduces likelihood of action potential.

• Axon – Nerve fiber transmitting impulses away from cell body.

• Neurotransmission – Process of signal transfer via neurotransmitters.

Lead Question – 2017:

Receptor sites for neurotransmitters are present on:

(A) Post-synaptic membrane

(B) Membranes of synaptic vesicles

(C) Pre-synaptic membrane

(D) Tips of axons

Explanation:

Receptor sites for neurotransmitters are located on the post-synaptic membrane of the receiving neuron. These proteins bind neurotransmitters released from the pre-synaptic neuron, enabling transmission of the nerve impulse across the synaptic cleft. (Answer: A)

1) Single Correct Answer MCQ:

Which neurotransmitter is primarily inhibitory in the CNS?

(A) Acetylcholine

(B) GABA

(C) Dopamine

(D) Glutamate

Explanation:

GABA is the main inhibitory neurotransmitter in the CNS. It hyperpolarizes post-synaptic neurons, reducing action potential likelihood, maintaining neuronal balance, and preventing overstimulation. (Answer: B)

2) Single Correct Answer MCQ:

The neurotransmitter involved in muscle contraction is:

(A) Serotonin

(B) Acetylcholine

(C) Dopamine

(D) Glycine

Explanation:

Acetylcholine binds to receptors on muscle fibers, causing depolarization and muscle contraction. It is critical at neuromuscular junctions and is released by motor neurons. (Answer: B)

3) Single Correct Answer MCQ:

Synaptic vesicles are primarily located in:

(A) Dendrites

(B) Axon terminals

(C) Cell body

(D) Myelin sheath

Explanation:

Synaptic vesicles reside in axon terminals, storing neurotransmitters that are released into the synaptic cleft upon arrival of an action potential, enabling signal transmission to post-synaptic neurons. (Answer: B)

4) Single Correct Answer MCQ:

Excitatory post-synaptic potentials (EPSPs) result in:

(A) Hyperpolarization

(B) Depolarization

(C) No change

(D) Inhibition

Explanation:

EPSPs cause depolarization of the post-synaptic membrane, increasing the likelihood of action potential generation. This is essential for transmitting excitatory signals in the nervous system. (Answer: B)

5) Single Correct Answer MCQ:

The gap between pre- and post-synaptic neurons is called:

(A) Axon hillock

(B) Synaptic cleft

(C) Node of Ranvier

(D) Dendritic spine

Explanation:

The synaptic cleft is a narrow space separating pre- and post-synaptic membranes, across which neurotransmitters diffuse to transmit nerve signals. Proper function ensures effective neuronal communication. (Answer: B)

6) Single Correct Answer MCQ:

Which ion triggers neurotransmitter release from vesicles?

(A) Sodium

(B) Calcium

(C) Potassium

(D) Magnesium

Explanation:

Calcium ions entering the pre-synaptic terminal upon depolarization trigger synaptic vesicles to fuse with the membrane, releasing neurotransmitters into the synaptic cleft. (Answer: B)

7) Assertion-Reason MCQ:

Assertion (A): Neurotransmitters bind to receptors on post-synaptic membrane.

Reason (R): Receptor proteins detect and respond to chemical signals.

(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 true. Post-synaptic receptors are proteins that detect neurotransmitters and initiate changes in membrane potential, explaining the transmission of signals across the synapse. (Answer: A)

8) Matching Type MCQ:

Match the neurotransmitter with its primary function:

1. Dopamine – (i) Inhibitory

2. GABA – (ii) Mood and reward

3. Acetylcholine – (iii) Muscle contraction

4. Serotonin – (iv) Sleep and mood regulation

Options:

(A) 1-ii, 2-i, 3-iii, 4-iv

(B) 1-iii, 2-ii, 3-iv, 4-i

(C) 1-iv, 2-iii, 3-ii, 4-i

(D) 1-i, 2-ii, 3-iv, 4-iii

Explanation:

Correct match: 1-ii (Dopamine: mood/reward), 2-i (GABA: inhibitory), 3-iii (Acetylcholine: muscle contraction), 4-iv (Serotonin: sleep/mood). Neurotransmitters have specific physiological roles critical for CNS function. (Answer: A)

9) Fill in the Blanks MCQ:

The pre-synaptic neuron releases neurotransmitters into the ______.

(A) Axon hillock

(B) Synaptic cleft

(C) Dendrite

(D) Soma

Explanation:

Neurotransmitters are released from the pre-synaptic neuron into the synaptic cleft, allowing chemical communication with the post-synaptic membrane and continuation of the nerve impulse. (Answer: B)

10) Choose the correct statements MCQ:

1. Neurotransmitters are stored in synaptic vesicles.

2. Receptor sites are on pre-synaptic membrane.

3. Calcium influx triggers neurotransmitter release.

4. EPSPs increase likelihood of action potential.

Options:

(A) 1, 3, 4

(B) 1, 2, 3

(C) 2, 3, 4

(D) 1, 2, 4

Explanation:

Statements 1, 3, and 4 are correct. Neurotransmitters are stored in vesicles, calcium influx triggers release, and EPSPs enhance action potential probability. Receptor sites are on post-synaptic, not pre-synaptic, membrane. (Answer: A)

Topic : Sensory Receptors and Neural Signaling
Subtopic : Photoreceptors and Receptor Potentials

Keyword Definitions :

• Receptor Potentials : Graded changes in membrane potential generated by sensory receptors when stimulated.

• Nociceptors : Specialized sensory receptors that detect pain due to tissue damage.

• Meissner’s Corpuscles : Mechanoreceptors responsible for detecting light touch and texture.

• Photoreceptors : Cells in the retina (rods and cones) that detect light and convert it into neural signals.

• Hyperpolarization : A change making the inside of a cell more negative than its resting potential.

Lead Question - 2016 (Phase 2)
Choose the correct statement :
(1) Receptors do not produce graded potentials
(2) Nociceptors respond to changes in pressure
(3) Meissner’s corpuscles are thermoreceptors
(4) Photoreceptors in the human eye are depolarized during darkness and become hyperpolarized in response to the light stimulus

Explanation : Photoreceptors show a unique response. In darkness, they remain depolarized, continuously releasing neurotransmitter. When light strikes, they hyperpolarize, reducing neurotransmitter release. Thus, statement (4) is correct. Others are incorrect: receptors produce graded potentials, nociceptors sense pain, and Meissner’s corpuscles detect touch.

1. Which type of receptor is responsible for detecting blood oxygen levels?
(1) Mechanoreceptors
(2) Chemoreceptors
(3) Photoreceptors
(4) Thermoreceptors

Explanation : Chemoreceptors monitor blood gases like oxygen and carbon dioxide, playing a vital role in respiration regulation. Located in carotid and aortic bodies, they stimulate respiratory centers. Therefore, the correct answer is (2) Chemoreceptors, ensuring adaptation to changing oxygen availability in tissues.

2. Which receptors help in balance and spatial orientation in humans?
(1) Olfactory receptors
(2) Vestibular hair cells
(3) Thermoreceptors
(4) Nociceptors

Explanation : Vestibular hair cells in the semicircular canals and vestibule of the inner ear detect motion and spatial orientation. They maintain balance by sensing angular and linear acceleration. Thus, the correct answer is (2) Vestibular hair cells, critical for posture and equilibrium maintenance.

3. Clinical Case: A patient unable to perceive pain but senses pressure normally is most likely deficient in:
(1) Mechanoreceptors
(2) Photoreceptors
(3) Nociceptors
(4) Thermoreceptors

Explanation : Loss of pain perception indicates defective nociceptors, which are specialized receptors for detecting harmful stimuli. Mechanoreceptors and thermoreceptors remain intact. Hence, the correct answer is (3) Nociceptors, vital for protective reflexes and survival by preventing injury through pain sensation.

4. Which receptors adapt quickly and detect changes in touch like vibrations?
(1) Ruffini endings
(2) Pacinian corpuscles
(3) Merkel cells
(4) Nociceptors

Explanation : Pacinian corpuscles are rapidly adapting mechanoreceptors sensitive to deep pressure and vibration. Ruffini endings respond to stretch, Merkel cells detect steady pressure, and nociceptors sense pain. Hence, the correct answer is (2) Pacinian corpuscles, essential for detecting rapid skin displacements and vibrations.

5. Assertion (A): Photoreceptors release neurotransmitters in the dark.
Reason (R): Light causes depolarization of photoreceptors.
(1) Both A and R are true, R is the correct explanation of A
(2) Both A and R are true, R is not the correct explanation of A
(3) A is true, R is false
(4) A is false, R is true

Explanation : Photoreceptors continuously release neurotransmitters in the dark due to depolarization. Light causes hyperpolarization, not depolarization. Hence, A is true but R is false. The correct answer is (3). This mechanism ensures precise visual signaling under varying light conditions.

6. Match the receptor type in Column I with its function in Column II:
Column I: a. Thermoreceptor, b. Mechanoreceptor, c. Chemoreceptor, d. Photoreceptor
Column II: i. Detects touch, ii. Detects temperature, iii. Detects chemicals, iv. Detects light
(1) a-ii, b-i, c-iii, d-iv
(2) a-i, b-iii, c-ii, d-iv
(3) a-iv, b-ii, c-i, d-iii
(4) a-iii, b-iv, c-ii, d-i

Explanation : Thermoreceptors detect temperature, mechanoreceptors detect touch and pressure, chemoreceptors detect chemical stimuli like gases, and photoreceptors detect light. Thus, the correct match is (1) a-ii, b-i, c-iii, d-iv, reflecting the specialized functions of each receptor type in sensory physiology.

7. Fill in the Blank: The receptor cells in the retina responsible for color vision are ______.
(1) Rods
(2) Cones
(3) Bipolar cells
(4) Ganglion cells

Explanation : Cones are specialized photoreceptor cells in the retina responsible for detecting color. They function best in bright light, enabling sharp and color vision. Therefore, the correct answer is (2) Cones, while rods mainly function in dim light and detect black-and-white images.

8. Choose the correct statements:
A. Nociceptors detect pain.
B. Photoreceptors hyperpolarize in response to light.
C. Thermoreceptors regulate body heat detection.
D. Meissner’s corpuscles detect pain.
(1) A, B, and C
(2) A and C
(3) B and D
(4) A, C, and D

Explanation : Correct statements are A, B, and C. Nociceptors detect pain, photoreceptors hyperpolarize in light, and thermoreceptors detect temperature. Meissner’s corpuscles detect touch, not pain. Thus, the correct answer is (1). Understanding receptor diversity is vital in physiology and clinical diagnostics.