Excitation contraction coupling is the process that leads to muscle contraction. This begins with an action potential arriving at the motor neuron which triggers the release of acetylcholine. The release of acetylcholine allows acetylcholine to diffuse into the sarcolemma and bind to receptors in the motor end plate. The motor end plate is a specialized region of the muscle fibers plasma region. The binding of acetycholine changes ion permeability which leads to a graded depolarization of the muscle plamsa membrane, this is the end plate potential. This series of events leads to the series of event in which muscle contration occurs.
A muscle twitch has three phases. The first phase is the latent phase in which time elapses between the generation of an action potential in a muscle cell and the beginning of the muscle contraction. The second phase is the contraction phase, this is where muscle contraction occurs. The cross bridge process that causes the overlapping of myosin and actin cause muscle contraction. The cross bridge cycle occurs in this second phase of a muscle twtich. The third phase is the relaxation phase, this is the peak tension of the muscle contraction until the end of muscle contraction. During this period, sarcomeres increase in length and the force generated decreases.
A skeletal muscle is able to produce tension, which is muscle force, when it recieves a nervous or an electrical stimualation. An increase in stimulation intensity leads to an increase in the number of active motor units. An increase in active motor units leads to an increase in muscle tension. The power of muscle contraction is related to the number of active motor units, so a muscle contraction with few active motor untis is not as strong as a muscle contraction with with many active motor units. More force means more active motor units which means more total force.
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