51. The long plateau phase of the cardiac muscle action potential is due to a. m

Question

51. The long plateau phase of the cardiac muscle action potential is due to a. movement of fewer sodium ions across the cell membrane b. Ca channels remaining open e. increased membrane permeability to K d. increased membrane permeability to Na 52·The heart is innervated by nerves. a. parasympathetic b. sympathetic c. both parasympathetic and sympathetic d. somatomotor 53. In cardiac muscle, the fast depolarization phase of the action potential is the result of: a increased membrane permeability to Na b. increased membrane permeability to K c. decreased membrane permeability to Ca2 d. decreased membrane permeability to Na e. increased membrane permeability to CI 54. As a result of the long refractory period in the cardiac action potential, cardiac muscle cannot exhibit: a. tonus d. recruitment e. tetany b. treppe c. fatigue 55. Which of the following would be greater? a. the EDV when the heart rate is 150 beats/minute b. the EDV when the heart rate is 60 beats/minute 56. The term used to describe fluid collecting in the pericardial cavity that restricts the movement of the heart is known as: a. cardiac tamponade b. mitral valve prolapse c. pleural effusion d. cardiomyopathy e. pericarditis 57. The structure that permits blood flow from the right atrium to the left atrium in the fetal circulation is the: a. ligamentum arteriosum b. foramen ovale c. coronary sinus d. interatrial septum e. fossa ovalis 10

Explanation / Answer

Answers:

51. Option B; Calcium ion channels remains open

Explanation: Heart is made up of cardiac muscle fibers which do not fatigued at all. Like the other muscles; cardiac muscle fibers also undergoes action potential; that is a continuous state of contraction and relaxation is reported in these muscle fibers. The different events under the cardiac muscle action potential are as summarized below:

52. Option C; Both Parasympathetic and Sympathetic nerve fibers

Explanation: The rate of the heart beat is indirectly under the control of the autonomic nervous system. The cardiac centre lies in the medulla oblongata of the brain. It comprises of the cardio-inhibitor and the cardio-accelerator parts. Cardio inhibitor decreases the heart beat rate and is connected to the heart by the parasympathetic nerve fibers. Whereas cardio accelerator accelerates the heart beat rate and it is connected to the heart via the sympathetic nerve fibers.

53. Option A; Increased permeability to the Na+

Explanation: For each and every muscle; the contraction and relaxation events can electro physiologically be categorized into the following groups:

Resting state; inside negative and outside positive. That is the cells are considered to be electrically polarized. This is due to the movement of three sodium ions out of the cell and import of only two potassium ions occurs at an expense of an ATP molecule. That is now the extracellular milieu of the cell becomes rich in the sodium ions.

Depolarized state: In this state the sodium ions starts to move inside the cell through the sodium ion channels. Thus the polarity of the cell gets reversed; that is the inside of the cell becomes positive and the outside becomes negative.

54. Option E

Explanation: Refractory period is defined as the gap between the depolarization of one cycle to that of the depolarization of the other cycle. In this period the complete emptying of the ventricles takes place before the initiation of the next systolic/contraction phase. Cardiac muscles have a long refractory phase which is marked by the condition that they would be unable to generate the tetanic state of the heart.

Tetany is referred to as the condition wherein the muscular spasms are experienced due to the deficiency of the calcium ions. Since in heart there is a continuous supply of the calcium ions made during the plateau phase; there is no such phase which is experienced and likewise cardiac muscles do not get fatigued anytime.

55. Option A

Explanation: EDV stands for End diastolic Volume. It is defined as the amount of the blood in the ventricles (right and left) during their diastolic phase that is their relaxations; marked by the pumping of blood to different body parts through them.

If the end diastolic volume is high; then according to the Frank-Starling law of the working of the heart; it is supposed to increase the pre work load on the heart too and likewise heart would need to contract and relax faster; hence the heart beat increases.

56. Option A; Cardiac Tamponade

Explanation: Cardiac tamponade is also known as the pericardial tamponade. It is marked by the compression and thus loss in functioning of the heart due to the build up and accumulation of fluid in the pericardium ; that is the covering to the heart. The condition is marked by symptoms including the shortness in the breath, cough formation, general weakness and many others.

57.

Option B; Foramane Ovale

Explanation: Human heart is made up of four chambers out of which there are two atria and two ventricles. Right atrium and ventricle are separated from each other by tricuspid valves whereas left atrium and ventricles are separated from each other by bicuspid valves. Likewise, in the right atrium; adjoining the interatrial septum to that of the left atrium; an oval depression is present named Fosa Ovalis. It actually marks the position of an opening; Foramen ovale present between the two atria in the fetus; however in adults it is marked by a depression.

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