Muscle Contraction Essay

Muscle contraction is made possible when an action potential is propagated from a motor neuron to a muscle fiber. This occurs at the neuromuscular junction, where the neuron innervates the muscle fiber. One nerve can innervate thousands of muscle fibers, allowing for an entire muscle to contract. At each neuromuscular junction, muscle tissue (an excitable tissue) is able to receive an electrical signal from the motor neuron and propagate it further. As the electrical signal reaches the terminal end of the motor neuron, it passes into a region of the nerve called the motor end plate. This is a pocket formed around the end of a motor neuron by the sarcolemma, or the cell membrane of a muscle cell. Each motor end plate is mitochondria-dense because a lot of energy is needed for the release and re-uptake of the neurotransmitter acetylcholine. Once acetylcholine crosses the …show more content…
This helps to successfully create and propagate an action potential. Once an action potential is generated, the muscle must convert an electrical signal into a motor movement in a process called excitation-contraction coupling. This is made possible with calcium ions. The action potential travels along the muscle membrane and down into an infolding of the sarcolemma called a t-tubule, which is close in proximity to the sarcoplasmic reticulum (SR). The SR is a membranous network that can store and transport calcium ions. Once the action potential reaches the SR, the SR releases its stored calcium ions into the cytoplasm of the muscle cell called the sarcoplasm. Once in the sarcoplasm, calcium ions can easily bind to the protein troponin located on an actin filament, which causes a shift in the thread-like protein tropomyosin. This ultimately exposes the active sites on the actin filament, allowing the contractile filaments actin and myosin to form a