Editing Triceps (section)

== Structure ==

* The long head arises from the [[infraglenoid tubercle]] of the [[scapula]]. It extends distally anterior to the [[Teres minor muscle|teres minor]] and posterior to the [[Teres major muscle|teres major]].<ref name="Platzer-156">{{cite book | year = 2004 | first = Werner | last = Platzer | name-list-style = vanc | title = Color Atlas of Human Anatomy, Vol. 1: Locomotor System | publisher = [[Thieme Medical Publishers|Thieme]] | isbn = 3-13-533305-1<!---US: 1-58890-159-9---> | edition   = 5th }}</ref>

* The medial head arises proximally in the [[humerus]], just inferior to the [[Radial sulcus|groove of the radial nerve]]; from the dorsal (back) surface of the humerus; from the [[Medial intermuscular septum of arm|medial intermuscular septum]]; and its distal part also arises from the [[Lateral intermuscular septum of arm|lateral intermuscular septum]]. The medial head is mostly covered by the lateral and long heads and is only visible distally on the humerus.<ref name="Platzer-156" />

* The lateral head arises from the dorsal surface of the humerus, lateral and proximal to the [[Radial sulcus|groove of the radial nerve]], from the [[greater tubercle]] down to the region of the lateral intermuscular septum.<ref name="Platzer-156" />

[[File:Slide9B.JPG|thumb|right|[[Horizontal section]] of upper arm. Triceps muscle is shown in green text|378x378px]]

Each of the three fascicles has its own motorneuron subnucleus in the motor column in the spinal cord. The medial head is formed predominantly by small type I fibers and motor units, the lateral head of large type IIb fibers and motor units, and the long head of a mixture of fiber types and motor units.<ref name="Lucas"/><ref>See the article "[[Skeletal striated muscle]]" for a discussion of type I and type II muscle fibers.</ref> It has been suggested that each fascicle "may be considered an independent muscle with specific functional roles."<ref name="Lucas"/>

The fibers converge to a single tendon to insert onto the [[olecranon]] process of the [[ulna]] (though some research indicates that there may be more than one tendon)<ref>{{cite journal | vauthors = Madsen M, Marx RG, Millett PJ, Rodeo SA, Sperling JW, Warren RF | title = Surgical anatomy of the triceps brachii tendon: anatomical study and clinical correlation | journal = The American Journal of Sports Medicine | volume = 34 | issue = 11 | pages = 1839–43 | date = November 2006 | pmid = 16735585 | doi = 10.1177/0363546506288752 | s2cid = 11671310 }}</ref> and to the posterior wall of the capsule of the elbow joint where [[Synovial bursa|bursae]] (cushion sacks) are often found. Parts of the common tendon radiate into the [[Deep fascia|fascia]] of the forearm and can almost cover the [[anconeus muscle]].<ref name="Platzer-156" />
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===Innervation===
All three heads of the triceps brachii are classically believed to be innervated by the [[radial nerve]].<ref>{{cite journal | vauthors = Bekler H, Wolfe VM, Rosenwasser MP | title = A cadaveric study of ulnar nerve innervation of the medial head of triceps brachii | journal = Clinical Orthopaedics and Related Research | volume = 467 | issue = 1 | pages = 235–8 | date = January 2009 | pmid = 18850256 | pmc = 2600974 | doi = 10.1007/s11999-008-0535-6 }}</ref> However, more recent studies observed that in around 14% of individuals, the long head of the triceps brachii was innervated by the [[axillary nerve]], and in 3% it received dual innervation from both the radial nerve and axillary nerve.<ref>{{Cite journal |last1=Wade |first1=Michael D. |last2=McDowell |first2=Arthur R. |last3=Ziermann |first3=Janine M. |date=2018 |title=Innervation of the Long Head of the Triceps Brachii in Humans-A Fresh Look: INNERVATION OF THE LONG HEAD OF THE TRICEPS BRACHII |url=https://onlinelibrary.wiley.com/doi/10.1002/ar.23741 |journal=The Anatomical Record |language=en |volume=301 |issue=3 |pages=473–483 |doi=10.1002/ar.23741|pmid=29418118 |s2cid=3676096 |doi-access=free }}</ref><ref>{{Cite journal |last1=Erhardt |first1=Alexandra J. |last2=Futterman |first2=Bennett |date=2017-01-01 |title=Variations in the Innervation of the Long Head of the Triceps Brachii: A Cadaveric Investigation |url=https://doi.org/10.1007/s11999-016-5146-z |journal=Clinical Orthopaedics and Related Research |language=en |volume=475 |issue=1 |pages=247–250 |doi=10.1007/s11999-016-5146-z |issn=1528-1132 |pmc=5174069 |pmid=27830483}}</ref>

===Variation===
A [[Tendon|tendinous]] arch is frequently the origin of the long head and the tendon of [[Latissimus dorsi muscle|latissimus dorsi]]. In rare cases, the long head can originate from the lateral margin of the scapula and from the capsule of the shoulder joint.<ref name="Platzer-156" />