The triceps, or triceps brachii (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

for "three-headed muscle of the arm"), is a large

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

on the

back The human back, also called the dorsum, is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck. It is the surface of the body opposite from the chest and the abdomen. The vertebral column runs ...

of the

upper limb The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shou ...

of many

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

. It consists of 3 parts: the medial, lateral, and long head. It is the muscle principally responsible for

extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * Ext ...

of the

elbow joint The elbow is the region between the arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and the media ...

(straightening of the arm).

Structure

The long head arises from the

infraglenoid tubercle The infraglenoid tubercle is the part of the scapula from which the long head of the triceps brachii muscle originates. The infraglenoid tubercle is a tubercle located on the lateral part of the scapula, inferior to (below) the glenoid cavity. T ...

of the

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...

. It extends distally anterior to the

teres minor The teres minor (Latin ''teres'' meaning 'rounded') is a narrow, elongated muscle of the rotator cuff. The muscle originates from the lateral border and adjacent posterior surface of the corresponding right or left scapula and inserts at both the ...

and posterior to the

teres major The teres major muscle is a muscle of the upper limb. It attaches to the scapula and the humerus and is one of the seven scapulohumeral muscles. It is a thick but somewhat flattened muscle. The teres major muscle (from Latin ''teres'', meaning ...

The medial head arises proximally in the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a r ...

, just inferior to the groove of the radial nerve; from the dorsal (back) surface of the humerus; from the medial intermuscular septum; and its distal part also arises from the lateral intermuscular septum. The medial head is mostly covered by the lateral and long heads, and is only visible distally on the humerus. The lateral head arises from the dorsal surface of the humerus, lateral and proximal to the groove of the radial nerve, from the greater tubercle down to the region of the lateral intermuscular septum. 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. It has been suggested that each fascicle "may be considered an independent muscle with specific functional roles." The fibers converge to a single tendon to insert onto the

olecranon The olecranon (, ), is a large, thick, curved bony eminence of the ulna, a long bone in the forearm that projects behind the elbow. It forms the most pointed portion of the elbow and is opposite to the cubital fossa or elbow pit. The olecranon ...

process of the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

(though some research indicates that there may be more than one tendon) and to the posterior wall of the capsule of the elbow joint where bursae (cushion sacks) are often found. Parts of the common tendon radiates into the

fascia A fascia (; plural fasciae or fascias; adjective fascial; from Latin: "band") is a band or sheet of connective tissue, primarily collagen, beneath the skin that attaches to, stabilizes, encloses, and separates muscles and other internal organs ...

of the forearm and can almost cover the

anconeus muscle The anconeus muscle (or anconaeus/anconæus) is a small muscle on the posterior aspect of the elbow joint. Some consider anconeus to be a continuation of the triceps brachii muscle. Some sources consider it to be part of the posterior compart ...

Innervation

All three heads of the triceps brachii are classically believed to be innervated by the

radial nerve The radial nerve is a nerve in the human body that supplies the posterior portion of the upper limb. It innervates the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial comp ...

. However, more recent studies observed that in around 14% of individuals the long head of the triceps brachii was innervated by the

axillary nerve The axillary nerve or the circumflex nerve is a nerve of the human body, that originates from the brachial plexus ( upper trunk, posterior division, posterior cord) at the level of the axilla (armpit) and carries nerve fibers from C5 and C6. Th ...

, and in 3% it received dual innervation from both the radial nerve and axillary nerve.

Variation

A tendinous arch is frequently the origin of the long head and the tendon of

latissimus dorsi The latissimus dorsi () is a large, flat muscle on the back that stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline. The word latissimus dorsi (plural: ''latissimi dorsorum'') comes from ...

. In rare cases, the long head can originate from the lateral margin of the scapula and from the capsule of the shoulder joint.

Function

The triceps is an

extensor In anatomy, extension is a movement of a joint that increases the angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extendin ...

muscle of the elbow joint and an antagonist of the

biceps The biceps or biceps brachii ( la, musculus biceps brachii, "two-headed muscle of the arm") is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join ...

and

brachialis The brachialis (brachialis anticus), also known as the Teichmann muscle, is a muscle in the upper arm that flexes the elbow. It lies deeper than the biceps brachii, and makes up part of the floor of the region known as the cubital fossa (elbow ...

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. With its origin on the scapula, the long head also acts on the shoulder joint and is also involved in retroversion and

adduction Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...

of the arm. It helps stabilise the shoulder joint at the top of the

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 Lying triceps extensions, also known as skull crushers and French extensions or French presses, are a strength exercise used in many different forms of strength training. Lying triceps extensions are one of the most stimulating exercises to the ...

and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the

push up The push-up (sometimes called a press-up in British English) is a common calisthenics exercise beginning from the prone position. By raising and lowering the body using the arms, push-ups exercise the pectoral muscles, triceps, and anterio ...

bench press The bench press, or chest press, is a weight training exercise in which the trainee presses a weight upwards while lying on a weight training bench. Although the bench press is a full-body exercise, the muscles primarily used are the pectorali ...

, close grip bench press (flat, incline or decline),

military press The overhead press is an upper-body weight training exercise in which the trainee presses a weight overhead while seated or standing. It is mainly used to develop the anterior deltoid muscles of the shoulder. The standing version was once a compon ...

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

. Ruptures of the triceps muscle are rare, and typically only occur in anabolic steroid users.

Clinical significance

The triceps reflex, elicited by hitting the triceps, is often used to test the function of the nerves of the arm. This tests spinal nerves C6 and C7, predominantly C7.

History

Etymology

It is sometimes called a three-headed muscle (Latin literally three-headed, ''tri'' - three, and ''ceps'', from ''caput'' - head), because there are three bundles of muscles, each of different origins, joining at the elbow. Though a similarly named muscle, the

triceps surae The triceps surae consists of two muscles located at the calf – the two-headed gastrocnemius and the soleus. These muscles both insert into the calcaneus, the bone of the heel of the human foot, and form the major part of the muscle of the p ...

, is found on the

lower leg The human leg, in the general word sense, is the entire lower limb of the human body, including the foot, thigh or sometimes even the hip or gluteal region. However, the definition in human anatomy refers only to the section of the lower limb e ...

, the triceps brachii is commonly called the triceps. Historically, the plural form of ''triceps'' was ''tricipites'', a form not in general use today; instead, ''triceps'' is both

singular Singular may refer to: * Singular, the grammatical number that denotes a unit quantity, as opposed to the plural and other forms * Singular homology * SINGULAR, an open source Computer Algebra System (CAS) * Singular or sounder, a group of boar ...

and

plural The plural (sometimes list of glossing abbreviations, abbreviated pl., pl, or ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a noun typically denotes a quantity greater than the ...

(i.e., when referring to both arms).

Animals

In the horse, 84%, 15%, and 3% of the total triceps muscle weight correspond to the long, lateral and medial heads, respectively. Many mammals, such as dogs, cattle, and pigs, have a fourth head, the accessory head. It lies between the lateral and medial heads. In humans, the anconeus is sometimes loosely called "the fourth head of the triceps brachii".

Additional images

File:Triceps brachii muscle - animation02.gif, Animation. Close up. File:Triceps brachii muscle10.png, Still image. Anterior view. File:Gray412.png, Muscles on the dorsum of the scapula, and the Triceps brachii. File:Animation triceps biceps.gif, Movement of biceps and triceps when arm is flexing

References

External links

* * {{Authority control Elbow extensors Muscles of the upper limb Shoulder extensors

Structure

Innervation

Variation

Function

Training

Clinical significance

History

Etymology

Animals

Additional images

See also

References

External links