Muscle Movement Report

The ability for muscles to contract and shorten to produce movement lies within its structure at a cellular level. The muscle organ is surrounded by a fibrous connective tissue called the epimysium, continuous to the perimysium, which separates the organ into small bundles called fascicles. Each fascicle can be further separated into muscle fibers by the endomysium. The plasma membrane of an individual muscle fiber is called the sarcolemma, which plays a major role in generating an action along the fiber. The contractile element of a muscle lies within the myofibril, a smaller component of the muscle fiber. Each myofibril contains thick and thin filaments made of actin, myosin, tropomyosin and troponin. The myosin molecule makes up the thick filaments and the head contains the actin and ATP binding site. The thin filament …show more content…
When a stimulus excites a motor neuron it stimulates the neuron to release ACh into the synaptic cleft of the NMJ. ACh binds to ACh receptors in the sarcolemma of the muscle fiber. This opens Na+ and K+ gated channels. 3 Na+ ions diffuses out of the sarcolemma, depolarizing the cell and once it reaches a threshold, Na+ channels close and K+ channels open allowing 2 K+ ions into the sarcolemma, repolarizing the muscle fiber to bring it back to its resting membrane potential. When the action potential is generated it travels down the sarcolemma reaching the T tubules that run along the terminal cisterin. The change in membrane potential causes Ca2+ channels in the terminal cisterin to open, allowing calcium ion to enter the cytosol. These calcium ion bind to troponin, once two calcium ions binds to troponin it moves the tropomyosin filament away from the myosin binding site on the actin filaments. The myosin heads of the thick filaments bind to the exposed myosin binding