MCQ Snacks - (Free trial) - Physiology

1. Which of the following is true for the excitation-contraction coupling of all muscle types (skeletal, cardiac, and smooth)?

An action potential causes calcium levels in the cytosol to increase

Calcium binds to troponin

Thick and thin filaments slide past each other

A & c

During excitation-contraction coupling in all muscle types, an action potential is generated, which causes calcium levels in the cytosol to increase. This increase in calcium levels then leads to the binding of calcium to troponin, resulting in the exposure of binding sites on actin. Subsequently, the thick and thin filaments slide past each other, leading to muscle contraction. Therefore, both options "a" (an action potential causes calcium levels in the cytosol to increase) and "c" (thick and thin filaments slide past each other) are true for the excitation-contraction coupling of all muscle types.

Explanation

During excitation-contraction coupling in all muscle types, an action potential is generated, which causes calcium levels in the cytosol to increase. This increase in calcium levels then leads to the binding of calcium to troponin, resulting in the exposure of binding sites on actin. Subsequently, the thick and thin filaments slide past each other, leading to muscle contraction. Therefore, both options "a" (an action potential causes calcium levels in the cytosol to increase) and "c" (thick and thin filaments slide past each other) are true for the excitation-contraction coupling of all muscle types.

2. ln isometric exercise all are increased except :

Heart rate

Cardiac output

Mean arterial pressure

Systemic vascular resistance

In isometric exercise, the muscles contract without any change in length, which leads to an increase in blood pressure. As a result, mean arterial pressure, cardiac output, and heart rate all increase. However, systemic vascular resistance refers to the resistance to blood flow in the blood vessels, and in isometric exercise, it remains unchanged or may even decrease due to vasodilation. Therefore, all the options except systemic vascular resistance increase during isometric exercise.

Explanation

In isometric exercise, the muscles contract without any change in length, which leads to an increase in blood pressure. As a result, mean arterial pressure, cardiac output, and heart rate all increase. However, systemic vascular resistance refers to the resistance to blood flow in the blood vessels, and in isometric exercise, it remains unchanged or may even decrease due to vasodilation. Therefore, all the options except systemic vascular resistance increase during isometric exercise.

3. Which of the following is true about fourth heart sound 'S4' :

Can be heard by the unaided ear

Frequency is greater than 20 Hz

Heard during ventricular filling phase

Heard during ventricular ejection phase

S4 is heard during the last rapid filling phase of cardiac cycle.

Explanation

S4 is heard during the last rapid filling phase of cardiac cycle.

4. Broca's area is concerned with:

Word formation

Comprehension

Repetition

Reading

Broca's area is the motor speech area concerned with word formation.

Explanation

Broca's area is the motor speech area concerned with word formation.

5. Which of the following hormone is not secreted by the kidney:

Renin

Angiotensin I

Erythropoietin

1, 25 Dihydroxycholecalciferol

Angiotensin I is formed by action of Renin (secreted by kidney) on Angiotensinogen (secreted by liver).

Explanation

Angiotensin I is formed by action of Renin (secreted by kidney) on Angiotensinogen (secreted by liver).

6. Increase in threshold level of a nerve on application of a slowly rising sub-threshold stimulus is known as:

Adaptation

Accomodation

Refractoriness

Electrotonus

Accommodation refers to the increase in threshold level of a nerve when a slowly rising sub-threshold stimulus is applied. This phenomenon allows the nerve to adapt to the gradually increasing stimulus and eventually reach its threshold level, resulting in an action potential. This process is important for the nerve to properly respond to varying levels of stimuli and maintain its sensitivity.

Explanation

Accommodation refers to the increase in threshold level of a nerve when a slowly rising sub-threshold stimulus is applied. This phenomenon allows the nerve to adapt to the gradually increasing stimulus and eventually reach its threshold level, resulting in an action potential. This process is important for the nerve to properly respond to varying levels of stimuli and maintain its sensitivity.

7. Pulmonary circulation differs from systemic circulation

Pulmonary vasodilation in hypoxia

Pulmonary vasoconstriction in hypoxia

Decreased blood volume during systole

Increased basal vasoconstrictor tone

In hypoxia, the body's response is to constrict the blood vessels in the lungs, known as pulmonary vasoconstriction. This helps to redirect blood flow to areas of the lungs that are better oxygenated, improving the efficiency of gas exchange. This is in contrast to systemic circulation, where vasodilation occurs in response to hypoxia to increase blood flow to tissues and organs.

Explanation

In hypoxia, the body's response is to constrict the blood vessels in the lungs, known as pulmonary vasoconstriction. This helps to redirect blood flow to areas of the lungs that are better oxygenated, improving the efficiency of gas exchange. This is in contrast to systemic circulation, where vasodilation occurs in response to hypoxia to increase blood flow to tissues and organs.

8. When a muscle cell is relaxed and intracellular ATP levels are normal, a crossbridge will remain in which of the following states?

Bound to actin and in the low-energy form

Bound to actin and in the high-energy form

In the high-energy form, with ADP and Pi bound to it

In the high-energy form, with ATP bound to it

When a muscle cell is relaxed and intracellular ATP levels are normal, a crossbridge will remain in the high-energy form with ADP and Pi (inorganic phosphate) bound to it. This is because during muscle contraction, ATP is hydrolyzed into ADP and Pi, releasing energy that is used to power the movement of the crossbridge. In the relaxed state, the crossbridge is still bound to actin but is in the high-energy form, ready to undergo the power stroke and generate force when the muscle is stimulated to contract.

Explanation

When a muscle cell is relaxed and intracellular ATP levels are normal, a crossbridge will remain in the high-energy form with ADP and Pi (inorganic phosphate) bound to it. This is because during muscle contraction, ATP is hydrolyzed into ADP and Pi, releasing energy that is used to power the movement of the crossbridge. In the relaxed state, the crossbridge is still bound to actin but is in the high-energy form, ready to undergo the power stroke and generate force when the muscle is stimulated to contract.