What causes the variation of the measurements for the periods (latent, contraction, relaxation periods) for the different twitches?
Motor neurons that are located in the motor cortex of the brainstem or the spinal cord innervate skeletal muscle fibers. They are also called alpha motor neurons. A motor neuron along with all muscle fibers it innervates form a motor unit.
An action potential that is transmitted by motor neurons causes contraction of all of the muscle fibers associated with it.
The muscle twitch is a contraction generated by a single
action potential. A single muscle twitch has three periods namely, the latent period, or lag phase, the contraction phase, and the relaxation phase.
The latent period is a short delay which lasts 1-2 ms. The action potential is being generated along the sarcolemma and calcium ions are released from the SR.
During the contraction phase, the calcium ions in the sarcoplasm are bound to troponin, tropomyosin is moved from actin-binding sites, cross-bridges created, and sarcomeres are actively shortening to produce tension.
During the relaxation phase, the tension decreases as contraction stops. Calcium ions are moved from the sarcoplasm into the SR and formation of cross-bridge halts, and the muscle fibers are returned to their resting state.
Trending now
This is a popular solution!
Step by step
Solved in 3 steps
