Editing Muscular system

{{short description|Internal framework of the body}}
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{{Infobox anatomy
| Name        = Muscular system
| Latin       = systema musculare
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| Caption     = The human muscles, seen from the front, 19th century illustration
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The '''muscular system''' is an [[organ (anatomy)|organ system]] consisting of [[skeletal muscle|skeletal]], [[smooth muscle|smooth]], and [[cardiac muscle|cardiac]] muscle. It permits movement of the body, maintains posture, and circulates blood throughout the body.<ref name=":0">{{Cite book|title=Histology: a text and atlas: with correlated cell and molecular biology| vauthors = Ross MH, Wojciech P |date=2011|publisher=Wolters Kluwer/Lippincott Williams & Wilkins Health|isbn=9780781772006|edition=  6th|location=Philadelphia|oclc=548651322}}</ref> The muscular systems in [[vertebrate]]s are controlled through the [[nervous system]] although some muscles (such as the [[cardiac muscle]]) can be completely autonomous. Together with the [[Human skeleton|skeletal system]] in the human, it forms the [[musculoskeletal system]], which is responsible for the movement of the [[human body|body]].<ref>{{Cite book|title=Gray's anatomy : the anatomical basis of clinical practice| vauthors = Standring S, Gray H |isbn=9780702052309|edition=  Forty-first |location=[Philadelphia]|oclc=920806541|year = 2016}}</ref>

== Types ==
{{Main|Muscle tissue}}
[[File: Types Of Muscle.jpg|thumb|258x258px|Three distinct types of muscle (L to R): Smooth (non-striated) muscle in internal organs, cardiac or heart muscle, and skeletal muscle.]]
There are three distinct types of muscle: [[skeletal muscle]], [[cardiac muscle|cardiac or heart muscle]], and [[smooth muscle|smooth (non-striated) muscle]]. [[Muscle]]s provide strength, balance, posture, movement, and heat for the body to keep warm.<ref name=":1">{{Cite book|title=Junqueira's basic histology : text and atlas| vauthors = Mescher AL, Junqueira LC |isbn=9780071807203|edition=  Thirteenth |location=New York|oclc=854567882|date = 2013-02-22}}</ref>

There are more than 600 muscles in an adult male human body.<ref>{{cite web|url=https://www.uc.edu/content/dam/uc/ce/images/OLLI/Page%20Content/Muscular%20System%20s.pdf|title=THE MUSCULAR SYSTEM|website=www.uc.edu}}</ref> A kind of elastic tissue makes up each muscle, which consists of thousands, or tens of thousands, of small muscle fibers. Each fiber comprises many tiny strands called fibrils, impulses from nerve cells control the contraction of each muscle fiber.

=== Skeletal ===
{{Main|Skeletal muscle}}
{{See also|List of muscles of the human body}}

Skeletal muscle, is a type of [[striated muscle]], composed of [[muscle cell]]s, called [[Skeletal muscle#Skeletal muscle cells|muscle fibers]], which are in turn composed of [[myofibrils]]. Myofibrils are composed of [[sarcomere]]s, the basic building blocks of striated muscle tissue. Upon stimulation by an [[action potential]], skeletal muscles perform a coordinated contraction by shortening each sarcomere. The best proposed model for understanding contraction is the [[sliding filament model]] of muscle contraction. Within the sarcomere, [[actin]] and [[myosin]] fibers overlap in a contractile motion towards each other. Myosin filaments have club-shaped [[myosin head]]s that project toward the actin filaments,<ref name=":0" /><ref name=":1" /><ref name=":2">{{Cite book|title=Guyton and Hall textbook of medical physiology| vauthors = Hall JE, Guyton AC |year=2011 |isbn=9781416045748 |edition=  Twelfth |location=Philadelphia, Pa.|oclc=434319356}}</ref> and provide attachment points on binding sites for the actin filaments. The myosin heads move in a coordinated style; they swivel toward the center of the sarcomere, detach, and then reattach to the nearest active site of the actin filament. This is called a ratchet-type drive system.<ref name=":2" />

This process consumes large amounts of [[adenosine triphosphate]] (ATP), the energy source of the cell. ATP binds to the cross-bridges between myosin heads and actin filaments. The release of energy powers the swiveling of the myosin head. When ATP is used, it becomes [[adenosine diphosphate]] (ADP), and since muscles store little ATP, they must continuously replace the discharged   ADP with ATP. Muscle tissue also contains a stored supply of a fast-acting recharge chemical, [[creatine phosphate]], which when necessary can assist with the rapid regeneration of ADP into ATP.<ref name=":3">{{Cite book|title=Marks' basic medical biochemistry : a clinical approach| vauthors = Lieberman M, Peet A |isbn=9781496324818|edition=  Fifth|location=Philadelphia|oclc=981908072|year = 2018}}</ref>

[[Calcium ions]] are required for each cycle of the sarcomere. Calcium is released from the [[sarcoplasmic reticulum]] into the [[sarcomere]] when a muscle is stimulated to contract. This calcium uncovers the actin-binding sites. When the muscle no longer needs to contract, the calcium ions are pumped from the sarcomere and back into storage in the [[sarcoplasmic reticulum]].<ref name=":2"/>

There are approximately 639 skeletal muscles in the human body.{{cn|date=February 2025}}

<gallery>
Image: Muscles anterior labeled.png|Skeletal muscles, viewed from the front
Image: Muscle posterior labeled.png|Skeletal muscles, viewed from the back
</gallery>

=== Cardiac ===
{{Main|Cardiac muscle}}
Heart muscle is striated muscle but is distinct from skeletal muscle because the [[muscle fibers]] are laterally connected. Furthermore, just as with smooth muscles, their movement is involuntary. Heart muscle is controlled by the [[sinus node]] influenced by the [[autonomic nervous system]].<ref name=":0" /><ref name=":1" />

=== Smooth ===
{{Main|Smooth muscle}}
Smooth muscle contraction is regulated by the autonomic [[nervous system]], [[hormone]]s, and local chemical signals, allowing for gradual and sustained contractions. This type of [[muscle tissue]] is also capable of adapting to different levels of stretch and tension, which is important for maintaining proper blood flow and the movement of materials through the [[Human digestive system|digestive system]].

== Physiology ==
=== Contraction ===
[[Neuromuscular junctions]] are the focal point where a [[motor neuron]] attaches to a muscle. [[Acetylcholine]], (a [[neurotransmitter]] used in skeletal muscle contraction) is released from the axon terminal of the nerve cell when an action potential reaches the microscopic junction called a [[synapse]]. A group of chemical messengers across the synapse and stimulate the formation of electrical changes, which are produced in the muscle cell when the acetylcholine binds to receptors on its surface. Calcium is released from its storage area in the cell's sarcoplasmic reticulum. An impulse from a nerve cell causes calcium release and brings about a single, short [[muscle contraction]] called a [[muscle twitch]]. If there is a problem at the neuromuscular junction, a very prolonged contraction may occur, such as the muscle contractions that result from [[tetanus]]. Also, a loss of function at the junction can produce [[paralysis]].<ref name=":2" />

Skeletal muscles are organized into hundreds of [[motor unit]]s, each of which involves a motor neuron, attached by a series of thin finger-like structures called [[Chemical synapse#Anatomy and physiology|axon terminals]]. These attach to and control discrete bundles of muscle fibers. A coordinated and fine-tuned response to a specific circumstance will involve controlling the precise number of motor units used. While individual muscle units' contract as a unit, the entire muscle can contract on a predetermined basis due to the structure of the motor unit. Motor unit coordination, balance, and control frequently come under the direction of the [[cerebellum]] of the brain. This allows for complex muscular coordination with little conscious effort, such as when one drives a car without thinking about the process.<ref name=":2" /><ref>{{Cite book|title=Neuroanatomy through clinical cases| vauthors = Blumenfeld H |date=2010 |publisher=Sinauer Associates |isbn=9780878930586|edition=  2nd|location=Sunderland, Mass.|oclc=473478856}}</ref>

=== Tendon ===
{{Main|Tendon}}
A tendon is a piece of connective tissue that connects a muscle to a bone.<ref>{{Cite web|url=https://medlineplus.gov/ency/imagepages/19089.htm|title=Tendon vs. ligament: MedlinePlus Medical Encyclopedia Image|website=medlineplus.gov}}</ref> When a muscle intercepts, it pulls against the skeleton to create movement. A tendon connects this muscle to a bone, making this function possible.

=== Aerobic and anaerobic muscle activity ===
At rest, the body produces the majority of its [[Adenosine triphosphate|ATP]] aerobically in the [[mitochondria]]<ref>{{cite book | vauthors = Abercrombie M, Hickman CJ, Johnson ML |date=1973 |title=A Dictionary of Biology |page=179 |location=Middlesex (England), Baltimore (U.S.A.), Ringwood (Australia) |publisher=Penguin Books |edition=  6th |series= Penguin reference books |oclc=943860 }}</ref> without producing [[lactic acid]] or other fatiguing byproducts. During exercise, the method of ATP production varies depending on the fitness of the individual as well as the duration and intensity of exercise. At lower activity levels, when exercise continues for a long duration (several minutes or longer), energy is produced aerobically by combining oxygen with [[carbohydrate]]s and [[fat]]s stored in the body.<ref name=":3" /><ref>{{cite journal | vauthors = Scott C | title = Misconceptions about Aerobic and Anaerobic Energy Expenditure | journal = Journal of the International Society of Sports Nutrition | volume = 2 | issue = 2 | pages = 32–37 | date = December 2005 | pmid = 18500953 | pmc = 2129144 | doi = 10.1186/1550-2783-2-2-32 | doi-access = free }}</ref>

During activity that is higher in intensity, with possible duration decreasing as intensity increases, ATP production can switch to anaerobic pathways, such as the use of the [[Phosphocreatine|creatine phosphate]] and the phosphagen system or anaerobic [[glycolysis]]. Aerobic ATP production is biochemically much slower and can only be used for long-duration, low-intensity exercise, but produces no fatiguing waste products that cannot be removed immediately from the [[sarcomere]] and the body, and it results in a much greater number of ATP molecules per fat or carbohydrate molecule. Aerobic training allows the oxygen delivery system to be more efficient, allowing aerobic metabolism to begin quicker. Anaerobic ATP production produces ATP much faster and allows near-maximal intensity exercise, but also produces significant amounts of [[lactic acid]] which render high-intensity exercise unsustainable for more than several minutes. The phosphagen system is also anaerobic. It allows for the highest levels of exercise intensity, but intramuscular stores of [[phosphocreatine]] are very limited and can only provide energy for exercises lasting up to ten seconds. Recovery is very quick, with full creatine stores regenerated within five minutes.<ref name=":3" /><ref>{{cite journal | vauthors = Spriet LL | title = Anaerobic metabolism in human skeletal muscle during short-term, intense activity | journal = Canadian Journal of Physiology and Pharmacology | volume = 70 | issue = 1 | pages = 157–165 | date = January 1992 | pmid = 1581850 | doi = 10.1139/y92-023 }}</ref>

== Clinical significance ==
{{see also|Myopathy}}{{expand section|date=November 2017}}
Multiple diseases can affect the muscular system.

=== Muscular Dystrophy ===
[[File:Tipai.gif|alt=five body outlines, muscle areas outlines|thumb|Main areas of muscle weakness in different types of dystrophy]]
[[Muscular dystrophy]] is a group of disorders associated with progressive muscle weakness and loss of muscle mass. These disorders are caused by mutations in a person's genes.<ref>{{Cite web |last=CDC |date=2022-11-21 |title=What is Muscular Dystrophy? {{!}} CDC |url=https://www.cdc.gov/ncbddd/musculardystrophy/facts.html |access-date=2023-05-05 |website=Centers for Disease Control and Prevention |language=en-us}}</ref> The disease affects between 19.8 and 25.1 per 100,000 person-years globally.<ref>{{Cite journal |last1=Theadom |first1=Alice |last2=Rodrigues |first2=Miriam |last3=Roxburgh |first3=Richard |last4=Balalla |first4=Shiavnthi |last5=Higgins |first5=Chris |last6=Bhattacharjee |first6=Rohit |last7=Jones |first7=Kelly |last8=Krishnamurthi |first8=Rita |author-link8=Rita Krishnamurthi |last9=Feigin |first9=Valery |date=2014-12-16 |title=Prevalence of Muscular Dystrophies: A Systematic Literature Review |journal=Neuroepidemiology |volume=43 |issue=3–4 |pages=259–268 |doi=10.1159/000369343 |issn=0251-5350 |pmid=25532075 |s2cid=2426923 |doi-access=free|hdl=10292/13206 |hdl-access=free }}</ref>

There are more than 30 types of muscular dystrophy. Depending on the type, muscular dystrophy can affect the patient's heart and lungs, and/or their ability to move, walk, and perform daily activities. The most common types include:

* Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD)
* Myotonic dystrophy
* Limb-Girdle (LGMD)
* Facioscapulohumeral dystrophy (FSHD)
* Congenital dystrophy (CMD)
* Distal (DD)
* Oculopharyngeal dystrophy (OPMD)
* Emery-Dreifuss (EDMD)

== See also ==
* [[Major systems of the human body]]
* [[Intramuscular coordination]]

== References ==
{{Reflist|30em}}

== Further reading ==
{{refbegin}}
* {{cite journal | vauthors = Cartee GD, Hepple RT, Bamman MM, Zierath JR | title = Exercise Promotes Healthy Aging of Skeletal Muscle | journal = Cell Metabolism | volume = 23 | issue = 6 | pages = 1034–1047 | date = June 2016 | pmid = 27304505 | pmc = 5045036 | doi = 10.1016/j.cmet.2016.05.007 }}
* {{cite journal | vauthors = Murphy AC, Muldoon SF, Baker D, Lastowka A, Bennett B, Yang M, Bassett DS | title = Structure, function, and control of the human musculoskeletal network | journal = PLOS Biology | volume = 16 | issue = 1 | pages = e2002811 | date = January 2018 | pmid = 29346370 | pmc = 5773011 | doi = 10.1371/journal.pbio.2002811 | doi-access = free }}
{{refend}}

== External links ==
{{Wikibooks|Human Physiology|The Muscular System}}
{{Wikibooks|Anatomy and Physiology of Animals|Muscles}}
* {{cite web | title = Muscle | url = https://my.clevelandclinic.org/health/body/21887-muscle | work = Cleveland Clinic }}
* [https://web.archive.org/web/20060711193301/http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookMUSSKEL.html Online Muscle Tutorial]
* [http://www.getbodysmart.com/ap/muscularsystem/menu/menu.html GetBody Smart] Muscle system tutorials and quizzes
* [http://www.medbio.info/Horn/Time%206/muscle_metabolism_march_2007.htm MedBio.info] {{Webarchive|url=https://web.archive.org/web/20110205235216/http://www.medbio.info/Horn/Time%206/muscle_metabolism_march_2007.htm |date=2011-02-05 }}  Use and formation of ATP in muscle

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{{Human systems and organs}}
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[[Category:Muscular system| ]]