Body movements in many biological species are strictly under the voluntary.
Motor units within skeletal muscle consist of a.
single motor neuron and all of the muscle fibers it innervates (UNT, 2010).
All-or-nothing responses of muscle fibers are triggered autonomously at.
their own specific threshold creating a graded response.
During excitation of skeletal muscle, acetylcholine (Ach) is released from.
the axon terminal of a motor neuron at the neuromuscular junction (NMJ) in.
response to an action potential (AP). The sarcolemma, or plasma membrane,.
of a muscle fiber is located on the opposing side of the synaptic cleft of.
the NMJ. Ach diffuses across the synaptic cleft and binds to specific.
receptors on the sarcolemma, opening sodium channels (UNT, 2010). If the.
influx of sodium causes a sufficient depolarization an AP is generated in.
the sarcolemma. .
Specialized transverse tubule (T tubule) invaginations.
conduct the AP directly to the sarcoplasmic reticulum (SR) triggering.
calcium channels to open and release calcium into the sarcoplasm. The.
hypothesis that ionic calcium might play a role in linking membrane.
potential and contraction was suggested by Lewis V. Heilibrunn, as early as.
1930 (Burggren et al., 1978). The discharged calcium initiates the.
formation of cross bridges between actin and myosin by binding to troponin.
That reaction causes a conformational change that shifts the position of.
tropomyosin, exposing active sites on actin (UNT, 2010). Myosin heads.
"cock" preparing to bind to the exposed active site by splitting ADP to.
ATP. The formation of a cross bridge is then completed once the myosin head.
binds to the newly exposed active site on actin.
The total time it takes a stimulus to conduct an excitation and form cross.
bridges for contraction is known as the latent period. The latent period.
provides a driving force behind shortening of sarcomeres and its mechanical.
manipulation contributes to the force of a contraction.