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Triceps brachii
Triceps brachii.png
Triceps brachii
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Muscles on the dorsum of the scapula, and the Triceps brachii.
Latin musculus triceps brachii
Gray's subject #124 444
Origin long head: infraglenoid tubercle of scapula
lateral head: posterior humerus
medial head: posterior humerus
Insertion    olecranon process of ulna
Artery deep brachial artery (Profunda brachii)
Nerve radial nerve
Actions extends forearm, caput longum adducts shoulder
Antagonist Biceps brachii muscle

The triceps brachii muscle (Latin for "three-headed" muscle of the arm, it is called a three headed muscle because there are three bundles of muscle, each of different origin, joining together at the elbow) 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".

Contents

Terminology

Historically, in a now-extinct dialect of English, the plural form of the adjective triceps was tricipes, a form not in general use today, instead triceps is used in both singular and plural (i.e., when referring to both arms).

Origin and insertion

The three heads have the following names and origins:

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.)[1]

In the horse, 84%, 15%, and 3% of the total muscle weight correspond to the long, lateral, and medial heads.[2]

Many mammals such as dogs, cows, and pigs have a fourth head, the "Accessory head", which lies between the Lateral and Medial heads.[3] In humans, the Anconeus is sometimes loosely called "the fourth head of the triceps brachii".

Each of the three fascicle has its own motorneuron subnucleus in the motor column in the spinal cord. The medial head being formed predominantly by small type I fibers and motor units, the lateral fascicle of large type IIb fibers and motor units and the long head of a mixture of fiber types and motor units.[3] It has been suggested that each fascicle "may be considered an independent muscle with specific functional roles".[3]

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. It has been suggested that the long head fascicle is employed when sustained force generation is demanded, or when there is a need for a synergistic control of the shoulder and elbow or both. The lateral head is used for movements requiring occasional high-intensity force, while the medial fascicle enables more precise, low-force movements.[3]

The triceps accounts for approximately 60 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, lying triceps extensions and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the push up, bench press, close grip bench press (flat, incline or decline), military press and dips. A closer grip targets the triceps more than wider grip movements.

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 and 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

See also

References

  1. ^ Madsen M, Marx R, Millett P, Rodeo S, Sperling J, Warren R (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.  
  2. ^ Watson JC, Wilson AM. (2007). Muscle architecture of biceps brachii, triceps brachii and supraspinatus in the horse. J Anat. 210(1):32-40. PMID 17229281
  3. ^ a b c d 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. PMID 19598170 doi:10.1002/cne.22123

External links

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