Muscle cell
Skeletal muscle contraction

When contracting, thin and thick filaments slide concerning each other by using adenosine triphosphate. This pulls the Z discs closer together in a process called the sliding filament mechanism. The contraction of all the sarcomeres results in the contraction of the whole muscle fiber. This contraction of the myocyte is triggered by the action potential over the cell membrane of the myocyte. The action potential uses transverse tubules to get from the surface to the interior of the myocyte, which is continuous within the cell membrane.Sarcoplasmic reticula are membranous bags that transverse tubules touch but remain separate from. These wrap themselves around each sarcomere and are filled with Ca.

Excitation of a myocyte causes depolarization at its synapses, the neuromuscular junctions, which triggers an action potential. With a singular neuromuscular junction, each muscle fiber receives input from just one somatic efferent neuron. Action potential in a somatic efferent neuron causes the release of the neurotransmitter acetylcholine.

When the acetylcholine is released it diffuses across the synapse and binds to a receptor on the sarcolemma, a term unique to muscle cells that refers to the cell membrane. This initiates an impulse that travels across the sarcolemma.

When the action potential reaches the sarcoplasmic reticulum it triggers the release of Ca from the Ca channels. The Ca flows from the sarcoplasmic reticulum into the sarcomere with both of its filaments. This causes the filaments to start sliding and the sarcomeres to become shorter. This requires a large amount of ATP, as it is used in both the attachment and release of every myosin head. Very quickly Ca is actively transported back into the sarcoplasmic reticulum, which blocks the interaction between the thin and thick filament. This in turn causes the muscle cell to relax.

There are four main types of muscle contraction: isometric, isotonic, eccentric and concentric. Isometric contractions are skeletal muscle contractions that do not cause movement of the muscle. and isotonic contractions are skeletal muscle contractions that do cause movement. Eccentric contraction is when a muscle moves under a load. Concentric contraction is when a muscle shortens and generates force.
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