Triceps brachii muscle

From Wikipedia, the free encyclopedia
Jump to: navigation, search

The triceps brachii muscle is a muscle on the back of the upper arm. There are three parts that each come from different places at the top of the arm and join together at the elbow. It straightens the arm. The name is Latin for "three-headed muscle in the arm".

Structure[change | change source]

The triceps brachii has three heads. They are: the long head, medial (inside) head, and the lateral (outside) head.The long head comes from the shoulderblade. It goes down the arm between teres minor muscle and teres major muscle.[1]

Horizontal section of upper arm. Triceps muscle shown with green writing

The medial head and lateral heads comes from the humerus (upper arm bone).[1]

The medial head is mostly made of small, slow muscle fibers and motor units. The lateral head is mostly made of large, fast fibers and motor units. The long head is made of a mixture of fiber types and motor units.[2] Some scientists think that each of the three parts can be thought of as separate muscles.[2]

The fibers join to a single tendon to attach to the ulna bone. Some research found that there might be more than one tendon.[3]

Nerve supply[change | change source]

Scientists used to think that all three heads of the triceps brachii got nerve signals from the radial nerve.[4] However, a study found that, in 20 cadaveric (dead) bodies and 15 live people, the long head actually got nerve signals from part of the axillary nerve in every case.[5]

Function[change | change source]

The triceps straightens the elbow pulls against the biceps and brachialis muscles. It can also hold the elbow in place when the forearm and hand are used for small movements, like writing.The long head might be used when the same force is needed for a long time, or to help control shoulder and elbow movement. The lateral head is used when a lot of force is needed at once, while the medial part is used for more careful movement.[2]

The long head also moves shoulder joint, bringing the arm backwards or inwards.[1]

Training[change | change source]

Triceps training

The triceps can be trained by itself or together with other muscles by straightening the elbow or keeping it straight while holding something.

Name[change | change source]

The name triceps brachii is Latin for three-headed. It is called this because there are three parts of the muscle. The triceps brachii is commonly just called the triceps.

The plural of triceps used to be tricipites, but now people usually say triceps to mean both singular and plural.

Animals[change | change source]

In horses, the long head is about 84% of the weight of the triceps, the lateral head is about 15%, and the medial head is about 3%.[6]

Many mammals, like dogs, cows, and pigs, have a fourth triceps head, called the accessory head. It is between the lateral and medial heads.[2]

Additional images[change | change source]

References[change | change source]

  1. 1.0 1.1 1.2 Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1. 
  2. 2.0 2.1 2.2 2.3 Lucas-Osma, AM; Collazos-Castro, JE. (2009). "Compartmentalization in the triceps brachii motoneuron nucleus and its relation to muscle architecture". J Comp Neurol 516 (3): 226–39. doi:10.1002/cne.22123. PMID 19598170.
  3. Nigel del a rosa die porte madretis (2006). "Surgical anatomy of the triceps brachii tendon: anatomical study and clinical correlation". Am J Sports Med 34 (11): 1839–43. doi:10.1177/0363546506288752. PMID 16735585.
  4. Bekler H, Wolfe VM, Rosenwasser MP (2009). "A Cadaveric Study of Ulnar Nerve Innervation of the Medial Head of Triceps Brachii". Clin Orthop Relat Res 467 (1): 235–238. doi:10.1007/s11999-008-0535-6. PMC 2600974. PMID 18850256.
  5. de Se`ze MP, Rezzouk J, de Se`ze M, Uzel M, Lavignolle B, Midy D, Durandeau A (2004). "Does the motor branch of the long head of the triceps brachii arise from the radial nerve?". Surg Radiol Anat 26 (6): 459–461. doi:10.1007/s00276-004-0253-z. PMID 15365769.
  6. Watson, JC; Wilson, AM. (2007). "Muscle architecture of biceps brachii, triceps brachii and supraspinatus in the horse". J Anat. 210 (1): 32–40. doi:10.1111/j.1469-7580.2006.00669.x. PMC 2100266. PMID 17229281.

Other websites[change | change source]