Muscle Twitch and Muscle Tension - Motor unit size and force

muscle contraction depends on the activity of groups of muscle cells a group of muscle cells controlled by a single neuron is defined as a motor unit when a stimulus of sufficient intensity is applied to a muscle through a single neuron all the cells in the motor unit respond by producing a single contraction called a muscle twitch the

muscle twitch which consists of several phases can be recorded in a tracing called a Maya gram immediately after stimulation there is a very brief period where no contraction is observed this is the latent period although contraction is not evident during the latent period the muscle is not inactive calcium ions are flowing out of the

sarcoplasmic reticulum cross-bridges are forming and elastic components of the muscle are being stretched the first discernible force of the muscle initiates the contraction period when the muscle reaches its greatest point of contraction it enters the relaxation period motor unit size varies among different muscles muscles involved in fine control such as those that move the

fingers have small motor units postural muscles or those that move large body parts such as the quadriceps have large motor units the amount of twitch contraction force depends on the size of the motor unit large motor units contain more cells and can therefore produce more tension and a greater contraction force