13) Which ion is responsible for the depolarization phase of myocardial contract
ID: 3507228 • Letter: 1
Question
13) Which ion is responsible for the depolarization phase of myocardial contractile cells a. Ca+2 b. Na+ c. K+ d. Mg+ e. Cl- 14) The depolarization phase of autorythmic cardiac cells is caused by the opening of a. Funny channels b. Potassium channel:s c. Sodium channels d. Calcium channels e. G-coupled gated channels 15) Which of the following describes the steps of the conduction of the heart 1) SA nodes 2) Bundle of HIS 3) Purkinje fibers 4) AV nodes 5) Right and left branch a. 1, 2,3,4,5 b. 1,4, 2, 5, 3 c. 1, 4, 3, 5, 2 d. 4, 1, 2,5, 3 e. 4, 1, 3, 2,5 16) When both the atria and ventricles are relaxing: which valves are open? a. Tricuspids b. Bicuspids c. Pulmonary d. Aortic e. AV valves 17) Which wave from an ECG is related to atrial systole a. P-wave b. Q-R wave c. R-S wave d. T-wave e. QRS waveExplanation / Answer
13. Cardiac muscle cells are of two types: myocardial contractile cells and myocardial conducting cells. The myocardial cells are present in the atria and ventricles. They conduct impulses and cause the contraction required for pumping blood in the body. They require an action potential for contraction. The opening of voltage gated fast sodium channels occurs in response to voltage changes. This results in the rapid influx of sodium ions into the cell, leading to depolarization.
Initially the resting membrane potential is -90 mV. Opening of gap junction causes influx of sodium and calcium ions that reduced the membrane potential to -85 mV. This causes the voltage gates sodium channels to open. Sodium ions enter the cell, making the interior of the cell more positive. The membrane potential is now to +25 mV causing depolarization.
Right answer is b. Na+.
14. Autorythmic cells spontaneously generate their own action potential. They have three types of channels- sodium channels, fast calcium channels and potassium channels.
Initially there is a mall influx of sodium ions and reduced efflux of potassium ions that reduces the resting membrane potential of -60 mV to -40 mV. This opens the fast calcium channels that allow influx of calcium ions into the cells. As a result, these is depolarization of the membrane. The membrane potential is now +10 mV.
Right answer is d. calcium channels.
15. Cardiac conduction system follows five steps:
i) There is contraction of sinoatrial node that causes generation of nerve impulses. These impulses travel through throughout the walls of heart. As a result, there is contraction of atria.
ii) The impulses from the SA node reach the atrioventricular (AV) node. Here, they are delayed for one tenth of a second. The atria contract and their contents are emptied into ventricles. The ventricles are now filled with blood.
iii) The bundle of His now receives the nerve impulse and splits into right and left branches. The nerve impulses now reach the left and right ventricles from the center of the heart.
iv) The bundle at base of heart will form Purkinje fibers. When the nerve impulses reach these Purkinje fibers, they induce muscle contraction of ventricles. As a result, blood is pumped to lungs and aorta.
Right sequence is SA node, AV node, Bundle of His, right and left branches and Purkinje fibers.
Right answer is b. 1, 4, 2, 5 and 3.
16. In the first diastole, atria and ventricles relax. The atrioventricular (AV) valve open and deoxygenated blood passes through the inferior vena capa. This blood now flows into right atrium. The tricuspid and the mitral valve allow blood to flow into the ventricles. Impulses from SA node travel to the AV node. This causes both atria to contract and empty contents into the right ventricle.
Right answer is e. AV valves.
17. Depolarization induced by the SA node action potential causes the atria to contract. Blood flows into the ventricles. This is known as atrial systole. Atrial contraction is represented by the P wave in ECG. It is followed by the QRS complex. First 1/3 part of P wave is the right atrial contraction while the last 1/3rd part is the left atrial contraction. The region in between is the combination of the two.
Right choice is a. P wave.
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