Question

question is worth. the he 1. Contraction of individual muscle fibers is an "all-or-none phenomenon. How, then, can the force of Contraction of an intact muscle be changed? bLvKNCR eases tod Pie50 yarates he Fua affeetco E Ca a. Cardiac muscle cells have an extremely long refractory period. What is happening at the cellular en acsslevel to cause this long refractory period? b. How is the long refractory period useful? dischange their sensitivity to a particular hormone?

Answer 1

Ans 1) The muscle contraction is controlled by certain force and the muscles are present in a particular state which is taken care by the force of the intact muscle. The force of contraction can be changed with help of myofilaments of the sarcomere. With the contraction of the sarcomere, there are cross bridges formed between myosin and actin head. This leads to the sliding of the thin filaments over the thick filaments as there is movement of the actin. The contraction of the muscle is its ability to shorten and the force is changed by sliding of the thin filaments over the thick filaments.

Ans 2) a) It is important for the cardiac muscle cells that the refractory period is long so that the heart is able to enter the titanic contraction or summation. During this the muscle receives the stimuli and due to its rapid stimulation, there is no chance for the muscle to relax. At the cellular level due to the longer refractory period, it allows the stimulus to be sent briefly and hence the number of action potential sent out per minutes at cellular level is limited.

Ans b) The long refractory period of cardiac muscle cell is important because it helps the heart to undergo tetanic contraction as well as summation with rapid stimulation of the muscles. With such rapid stimulation, there is continuous stimuli and hence contraction of the heart. With long refractory period, it helps in limiting the action potential which is important for the heart cells.