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Triceps brachii
Triceps brachii
Details
Origin	long head: scapula lateral head: posterior humerus medial head: posterior humerus
Insertion	olecranon process of ulna
Artery	deep brachial artery
Nerve	radial nerve
Actions	extends forearm, caput longum adducts shoulder
Antagonist	Biceps brachii muscle
Identifiers
Latin	musculus triceps brachii
TA98	A04.6.02.019
TA2	2471
FMA	37688
Anatomical terms of muscle

The triceps brachii (Latin for "three-headed" [muscle] of the arm) is the large muscle on the back of the human upper limb. It is the muscle principally responsible for extension of the elbow joint (i.e. straightening of the arm). Though a similarly-named muscle, the triceps surae, is found on the lower leg, the triceps brachii is commonly called simply the "triceps".

Terminology

The proper plural form of the adjective triceps is tricipes, a form not in general use; instead, triceps is used in both singular and plural (i.e., when referring to both arms). The form tricep [sic], though common even in professional contexts, is incorrect. The error may derive from a mistaken belief that triceps is a plural noun (rather than a singular adjective), since English typically forms its plurals with the addition of the letter s to the end of a word stem.

Origin and insertion

The three heads have the following names and origins:

• The "Long head": infraglenoid tubercle of the scapula
• The "Lateral head": posterior shaft of the humerus, lateral and superior to the radial (spiral) groove.
• The "Medial head": posterior shaft of the humerus, medial and inferior to the radial (spiral) groove.

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.)

Many mammals have a fourth head, the "Accessory head", which lies between the Lateral and Medial heads. In humans, the Anconeus is sometimes loosely called "the fourth head of the triceps brachii".

Actions

The triceps is an extensor muscle of the elbow joint, and is an antagonist of the biceps and brachialis muscles. It can also fixate the elbow joint when the forearm and hand are used for fine movements, e.g., when writing.

The triceps accounts for approximately 70 percent of the upper arm's muscle mass.

Training

The triceps can be worked through either isolation or compound elbow extension movements, and can contract statically to keep the arm straightened against resistance.

Isolation movements include cable push-downs, "skull-crushers", and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the push up, bench press (flat, incline or decline), military press and dips. Using a closer grip stabilizes the arm allowing more weight to be used, so the triceps can be worked harder without assistance from the pectorals or deltoids.

Static contraction movements include pullovers, straight-arm pulldowns, and bent-over lateral raises, which are also used to build the deltoids and latissimus dorsi.

Elbow extension is important to many athletic activities. As the biceps is often worked more for aesthetic purposes, this is usually a mistake for fitness training. While it is important to maintain a balance between the biceps and triceps for postural & effective movement purposes, what the balance should be and how to measure it is a conflicted area. Pushing and pulling movements on the same plane are often used to measure this ratio.

Additional images

• 
  Left humerus. Posterior view.
• 
  Bones of left forearm. Posterior aspect.
• 
  Cross-section through the middle of upper arm.
• 
  Posterior surface of the forearm. Superficial muscles.
• 
  The scapular and circumflex arteries.
• 
  The axillary artery and its branches.
• 
  The brachial artery.
• 
  The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front.
• 
  Suprascapular and axillary nerves of right side, seen from behind.
• 
  The suprascapular, axillary, and radial nerves.

See also

• Triceps reflex

External links

• Template:MuscleLoyola
• Illustration: tricepsbrachii from The Department of Radiology at the University of Washington
• . GPnotebook https://www.gpnotebook.co.uk/simplepage.cfm?ID=751829070. {{cite web}}: Missing or empty |title= (help)
• Anatomy photo:06:11-0100 at the SUNY Downstate Medical Center
• Photo at Ithaca College
• Template:Exrx