29. The longest refractory period is in the action potential of a: A. Neuron C.

Question

29. The longest refractory period is in the action potential of a:

A.       Neuron                             C.       Skeletal muscle cell

B.       Smooth muscle cell D.       Cardiac muscle cell

30. Which of the following is the correct sequence of contraction for the heart?

A.       Simultaneous contraction of right atria and right ventricle followed by simultaneous contraction of left atria and left ventricle

B.       Right atrium followed by right ventricle followed by left atrium followed by left ventricle

C.       Right atrium followed by left atrium followed by right ventricle followed by left ventricle

D.       Simultaneous contraction of both atria followed by simultaneous contraction of both ventricles

31. Which of the following is the most numerous cell in the blood?

A.       Basophil                 C. Erythrocyte

B.       Leukocyte               D. Platelet

32. If you were to extract the protein molecules from the A-band, which of the following molecules would be found in the extract?

A.       myosin                             D.       troponin

B.       actin                                 E.        all of the preceding

C.       tropomyosin

Explanation / Answer

29.A) The refractory period in neuron lasts from 2-3milliseconds.Action potential is in three phases, The phases are depolarization, repolarization and absolute and relative refractory periods.

B). In skeletal muscle cell, the refractory period is short, 1-2ms

C).In smooth muscle cell it is short compared to cardiac muscle cell

D).Hence cardiac muscle cell has the longest refractory period (250ms), with absolute and relative refractory periods.It preventing wave summation, fatigue and tetanic contractions which would cause the heart to stop pumping rythmically.

30.B is the correct sequence of contraction of the heart.

Blood enters the heart through two large veins, the inferior and superior vena cava emptying oxygen poor blood from the body into the right atrium of the heart. As the atrium contracys, blood flows from your right atrium into your right ventricle through the open tricuspid valve

31).C is the correct answer

Erythrocytes or red blood cells are the most numerous cell in the blood. There are around 4.5- 5.5millions per mL which is of d highest range.

Platelet ranges from 1,40,000- 4,00,000 per mL

White blood cells ranges from 5000-10000 per mL which include basophils, neutrophils and lymphocytes.

32).E is the correct answer.

Actin filaments are major component of the I band and extends into the A band

Myosin , the thick filaments are bipolar and extends throughout the A band.

Normally the head of myosin molecules present in myosin filaments has a strong tendency to get attached with the active site of f actin. However in relaxed condition, the active site of f actin is covered by the tropomyosin, therefore the myosin head cannot combine with actin. Large number of calcium ions bind with troponin C.The loading of tropnin C with calcium ions produces changes in position of tropnin molecule.

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