Editing Muscle cell (section)

==Function==
===Muscle contraction in striated muscle===
{{Main|Muscle contraction}}
[[File:Sliding Filament Mechanism Diagram.pdf|thumb| ]]

====Skeletal muscle contraction====
When [[Muscle contraction|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<sup>2+</sup>.<ref name="courses.washington.edu">{{cite web|title=Structure, and Function of Skeletal Muscles|url=http://courses.washington.edu/conj/motor/musclereview.htm|website=courses.washington.edu|access-date=13 February 2015|url-status=live|archive-url=https://web.archive.org/web/20150215092857/http://courses.washington.edu/conj/motor/musclereview.htm|archive-date=15 February 2015}}</ref>

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]].<ref>{{cite web|title=Muscle Fiber Excitation|url=http://courses.washington.edu/conj/bess/muscle/musclexcitation.html|website=courses.washington.edu|publisher=University of Washington|access-date=11 February 2015|url-status=live|archive-url=https://web.archive.org/web/20150227010858/http://courses.washington.edu/conj/bess/muscle/musclexcitation.html|archive-date=27 February 2015}}</ref>

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.<ref name=ziser>{{cite web|last1=Ziser|first1=Stephen|title=Muscle Cell Anatomy & Function|url=http://www.austincc.edu/sziser/Biol%202404/2404LecNotes/2404LNExII/Muscle%20Physiology.pdf|website=www.austincc.edu|access-date=12 February 2015|url-status=live|archive-url=https://web.archive.org/web/20150923181106/http://www.austincc.edu/sziser/Biol%202404/2404LecNotes/2404LNExII/Muscle%20Physiology.pdf|archive-date=23 September 2015}}</ref>

When the action potential reaches the sarcoplasmic reticulum it triggers the release of Ca<sup>2+</sup> from the Ca<sup>2+</sup> channels. The Ca<sup>2+</sup> 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<sup>2+</sup> 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.<ref name=ziser />

There are four main [[Muscle contraction#Types|types of muscle contraction]]: isometric, isotonic, eccentric and concentric.<ref name="Gash">{{cite web |last1=Gash |first1=Matthew C. |last2=Kandle |first2=Patricia F. |last3=Murray |first3=Ian V. |last4=Varacallo |first4=Matthew |title=Physiology, Muscle Contraction |url=https://www.ncbi.nlm.nih.gov/books/NBK537140/ |website=StatPearls |publisher=StatPearls Publishing |date=2024}}</ref>  [[Isometric contraction]]s are skeletal muscle contractions that do not cause movement of the muscle. and [[isotonic contraction]]s are skeletal muscle contractions that do cause movement. [[Eccentric training|Eccentric contraction]] is when a muscle moves under a load. Concentric contraction is when a muscle shortens and generates force.

====Cardiac muscle contraction====
{{See also|Bowditch effect}}
Specialized [[cardiomyocytes]] in the [[sinoatrial node]] generate electrical impulses that control the [[heart]] rate.  These electrical impulses coordinate contraction throughout the remaining heart muscle via the [[electrical conduction system of the heart]].  Sinoatrial node activity is modulated, in turn, by nerve fibers of both the [[Sympathetic nervous system|sympathetic]] and [[Parasympathetic nervous system|parasympathetic]] nervous systems.  These systems act to increase and decrease, respectively, the rate of production of electrical impulses by the sinoatrial node.