Weak (non-threshold) stimulation is known as subliminal or inadequate stimulation. Because, it fails to produce any response. But when the number of such subliminal stimuli are applied repeatedly they may give rise to response due to the summation effect. Summation is possible only when the second stimuli are given after the refractory period of the first stimulus. Cause-The effects of inadequate stimuli are completely fused to produce a single stronger adequate stimulus and this adequate sti1nulus causes contraction of the muscle.

A skeletal muscle is a type of muscle that is attached to the bones. These muscles have alternate dark and light striations and are called striated muscles. The control of the skeletal muscles is under the control of the will of an individual. Thus, they are also called voluntary muscles. These muscles are made up of thick filaments called myosin and thin filaments called actin. The alternate arrangement of these filaments given a striated appearance to the myofibril. Along with actin and myosin proteins, tropomyosin and troponin are also present. Troponin is a component of thin actin filaments along with actin and tropomyosin.