Frog Muscle Physiology
2) What was the smallest voltage required to produce max contraction? What proportion of the muscle fibers in the muscle do you think were contracting to produce this maximal response?
Muscle fibers act in response to isolated stimuli in an all or none fashion. However, a muscle organ, such as the gastrocnemius muscle, is composed of many individual muscle fibers. It is known that all of the fibers in a muscle do not have the same threshold and that a stimulus applied to a muscle does not necessarily excite all the fiber in it. As the intensity (voltage) of the stimulus is increased above the threshold, more fibers are stimulated and the response becomes greater. In due course, however, stimulus intensity (voltage) is attained further than which the response is constant. This stimulus, called the maximal stimulus marks the point where all of the fibers in the muscle are stimulated and responding all-or-none. By varying the number motor units (groups of muscle fibers innervated by a singe somatic motor neuron) contracting at a given time, the amount of tension generated by the whole muscle can vary. As stimulus strength is being increased, progressively more muscle fibers reach their thresholds and contract. Thus, the change in tension is due to the number of contracting muscle fibers. Stimuli below the minimum strength required to trigger any of the muscle fibers to reach threshold and go through an action potential (i.e., subthreshold stimuli) will not cause any contraction in the muscle. In conclusion, when stimulus strength is increased above a certain level (maximal) no further increase in tension occurs, as all muscle fibers in the muscle are contracting.
HUMAN MUSCLE PHYSIOLOGY
5.) Why does varying the stimulus strength affect the twitch force?
Stimulus intensity (voltage) is attained further than which the response is constant. This stimulus, called the maximal stimulus marks the point where all of the fibers in the