Subtopic: Cardiac Physiology
Keyword Definitions:
Poikilotherm: Organisms whose body temperature varies with the environment.
Coronary Circulation: Blood flow through vessels supplying the heart muscle.
Myogenic: Originating from the muscle itself, not nerve impulses.
Autoexcitable: Ability to generate spontaneous impulses.
Cardiac Muscle: Specialized muscle tissue forming the heart.
Depolarization: Loss of membrane potential leading to contraction.
Repolarization: Restoration of resting membrane potential.
Sinoatrial Node (SA Node): Pacemaker of the heart initiating impulses.
Atria: Upper chambers of the heart receiving blood.
Ventricles: Lower chambers pumping blood out of the heart.
Clinical Significance: Understanding heart activity helps in diagnosing cardiac disorders.
Lead Question - 2017
Frog’s heart when taken out of the body continues to beat for sometime. Select the best option from the following statements.
(a) Frog is a poikilotherm
(b) Frog does not have any coronary circulation
(c) Heart is “myogenic” in nature
(d) Heart is autoexcitable
Options:
(A) c and d
(B) Only c
(C) Only d
(D) a and b
Explanation: The frog’s heart continues beating outside the body because it is myogenic, meaning impulses originate from cardiac muscle itself, and autoexcitable, meaning it can spontaneously generate impulses without nerve stimulation. Therefore, both statements (c) and (d) are correct. Answer: A.
1. MCQ - Single Correct Answer
Which part of the human heart acts as the primary pacemaker?
(a) AV Node
(b) Purkinje Fibers
(c) SA Node
(d) Bundle of His
Explanation: The SA Node generates spontaneous impulses that initiate the heartbeat. It is located in the right atrium and sets the rhythm of cardiac contractions. Answer: c.
2. MCQ - Single Correct Answer
Which ion primarily initiates cardiac muscle contraction?
(a) Sodium
(b) Potassium
(c) Calcium
(d) Magnesium
Explanation: Calcium ions entering during the plateau phase trigger contraction by binding to troponin, enabling actin-myosin interaction. Sodium initiates depolarization, but calcium sustains contraction. Answer: c.
3. MCQ - Single Correct Answer (Clinical)
A patient shows irregular heartbeat due to SA node damage. Which condition is expected?
(a) Bradycardia
(b) Tachycardia
(c) Atrial Fibrillation
(d) Ventricular Hypertrophy
Explanation: Damage to the SA Node slows impulse generation, leading to bradycardia or slow heart rate. AV node may take over partially, but rhythm is irregular. Answer: a.
4. MCQ - Single Correct Answer
Which structure ensures unidirectional blood flow in the heart?
(a) SA Node
(b) AV Valves
(c) Purkinje Fibers
(d) Coronary Arteries
Explanation: AV Valves (tricuspid and mitral) prevent backflow from ventricles to atria, ensuring unidirectional flow during contractions. Valve closure produces the first heart sound. Answer: b.
5. MCQ - Single Correct Answer
Which is true regarding frog heart circulation?
(a) Double circulation
(b) Single circulation
(c) Pulmonary only
(d) Systemic only
Explanation: The frog heart exhibits double circulation with oxygenated and deoxygenated blood partially separated in a three-chambered heart. This supports both pulmonary and systemic circuits. Answer: a.
6. MCQ - Single Correct Answer (Clinical)
During heart block, which conduction pathway fails?
(a) SA Node
(b) AV Node
(c) Purkinje Fibers
(d) Sinoatrial Fibers
Explanation: In AV block, impulses fail to pass from atria to ventricles, delaying or stopping ventricular contraction. SA Node may remain functional but conduction is impaired. Answer: b.
7. MCQ - Assertion-Reason
Assertion (A): Cardiac muscle is myogenic.
Reason (R): Heart requires continuous nerve stimulation to beat.
(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
Explanation: Cardiac muscle is myogenic (A true) and beats without nerve stimulation, making reason false. Therefore, correct option is c. Answer: c.
8. MCQ - Matching Type
Match the following:
1. SA Node - (a) Impulse conduction to ventricles
2. AV Node - (b) Pacemaker
3. Purkinje Fibers - (c) Ventricular contraction
Options:
(A) 1-b, 2-a, 3-c
(B) 1-a, 2-b, 3-c
(C) 1-b, 2-c, 3-a
(D) 1-c, 2-a, 3-b
Explanation: SA Node is the pacemaker, AV Node conducts impulses to ventricles, and Purkinje fibers stimulate ventricular contraction. Correct matching: 1-b, 2-a, 3-c. Answer: A.
9. MCQ - Fill in the Blanks
The duration between two successive heartbeats is called __________.
(a) Cardiac Output
(b) Heart Rate
(c) Cardiac Cycle
(d) Stroke Volume
Explanation: The cardiac cycle is the complete sequence of atrial and ventricular contraction and relaxation between two successive heartbeats. It includes systole and diastole phases. Answer: c.
10. MCQ - Choose Correct Statements
Select correct statements about cardiac muscle:
1. It is striated
2. It is voluntary
3. Intercalated discs are present
4. Always requires nerve impulses
Options:
(A) 1 and 3
(B) 2 and 4
(C) 1, 2, and 3
(D) All 1,2,3,4
Explanation: Cardiac muscle is striated with intercalated discs for synchronized contraction. It is involuntary and myogenic, not requiring constant nerve impulses. Correct statements are 1 and 3. Answer: A.