Editing Triceps (section)

{{Short description|Muscle on the back of the upper arm}}
{{Infobox muscle
| Name        = Triceps
| Latin       = musculus triceps brachii
| Image       = Triceps brachii.png
| Caption     = Triceps brachii seen from behind.
| Image2      = Triceps brachii muscle06.png
| Caption2    = Triceps brachii seen from behind. Three different colors represent three different bundles which compose triceps.{{legend|#FF0000|Long head.}}{{legend|#FFFF00|Lateral head.}}{{legend|#00FF00|Medial head.}}
| Origin      = '''Long head:''' [[infraglenoid tubercle of scapula]] <br />'''Lateral head:''' above the [[radial groove]]<br />'''Medial head:''' below the [[radial groove]]
| Insertion   = [[Olecranon]] process of [[ulna]]
| Blood       = [[Deep brachial artery]], [[posterior circumflex humeral artery]] (long head only)
| Nerve       = [[Radial nerve]]  
| Action      = [[Extension (kinesiology)|Extends]] [[forearm]], long head [[Extension (kinesiology)|extends, adducts arm]], [[Extension (kinesiology)|extends]] [[shoulder]]
| Antagonist  = [[Biceps brachii muscle]]
}}

The '''triceps''', or '''triceps brachii''' ([[Latin]] for "three-headed muscle of the arm"), is a large [[muscle]] on the [[ventral|back]] of the [[upper limb]] of many [[vertebrates]]. It consists of three parts: the medial, lateral, and long head. All three heads cross the elbow joint. However, the long head also crosses the shoulder joint. The triceps muscle contracts when the elbow is straightened and expands when the elbow is bent. The long head gets a further contraction when the arm is behind the torso due to how it crosses the shoulder joint. <ref>{{cite journal | doi=10.1249/JSR.0000000000000749 | title=Triceps Tendon Injuries | year=2020 | last1=Casadei | first1=Kyle | last2=Kiel | first2=John | last3=Freidl | first3=Michael | journal=Current Sports Medicine Reports | volume=19 | issue=9 | pages=367–372 | pmid=32925376 | s2cid=221567814 | doi-access=free }}</ref> It is the muscle principally responsible for [[Extension (kinesiology)|extension]] of the [[elbow joint]] (straightening of the arm).