Skeletal Muscle Contraction

Skeletal muscle is a voluntary and striated muscle that attaches to the skeleton to allow control over posture and movement. Each skeletal muscle consists of bundles of muscles fibers called fascicles. These fascicles are composed of many individual muscle fibers or muscle cells that can be up to several millimeters long. These muscle fibers are composed of myofibrils, which are organized into thick filaments, myosin, and thin filaments, actin. These filaments are organized into repeating structures called sarcomeres, which are the subunits of skeletal muscle. In order to generate force, these filaments must slide past one another (Widmaier 2011). Muscle fibers are innervated by motor neurons. A motor unit is a single motor neuron and all muscle fibers it innervates. Contraction occurs through a mechanism called excitation-contraction coupling when an action potential propagates down a motor neuron axon to initiate contraction. As the action potential then travels down these transverse tubules it opens ion channels, which releases calcium into the sarcoplasm. When this calcium is released, binding sites on the thin filaments become available that allow the thick filaments to bind and pull the thin filaments toward the center of the sarcomere, generating
This sensory neuron then relays this information to the central nervous system where afferent neurons synapse with interneurons which in turn synapse with efferent or motor neurons. This motor neuron then relays the information out of the brain to an effector. In this case, the effector is a skeletal muscle that causes the reflex response to occur. Reaction time is a measure of the time between when the stimulus is delivered and the response occurs. This speed can vary person-to-person depending on the speed of transmission of the signal from neuron to neuron, as well as the number of neurons involved (Widmaier