Biceps

Thebicepsorbiceps brachii(Latin:musculus biceps brachii, "two-headed muscle of the arm") is a largemusclethat lies on the front of the upper arm between the shoulder and theelbow. Bothheads of the musclearise on thescapulaand join to form a singlemuscle bellywhich is attached to the upper forearm. While the long head of the biceps crosses both theshoulderand elbow joints, its main function is at the elbow where it flexes andsupinatesthe forearm.  Both these movements are used when opening a bottle with a corkscrew: first biceps screws in the cork (supination), then it pulls the cork out (flexion).
The biceps is one of three muscles in theanterior compartment of the upper arm, along with thebrachialis muscleand thecoracobrachialis muscle, with which the biceps shares a nerve supply.The biceps muscle has two heads, the short head and the long head, distinguished according to their origin at the coracoid process and supraglenoid tubercle of the scapula, respectively.From its origin on the glenoid, the long head remains tendinous as it passes through the shoulder joint and through theintertubercular grooveof thehumerus.Extending from its origin on the coracoid, the tendon of the short head runs adjacent to the tendon of thecoracobrachialis. Unlike the other muscles in the anterior compartment of the arm, the long head of the biceps muscle crosses two joints, the shoulder joint and the elbow joint.
Both heads of the biceps join in the middle upper arm to form a single muscle mass, usually near the insertion of thedeltoid, to form a common muscle belly;although several anatomic studies have demonstrated that the muscle bellies remain distinct structures without confluent fibers.As the muscle extendsdistally, the two heads rotate 90 degrees externally before inserting onto the radial tuberosity. The short head inserts distally on the tuberosity while the long head inserts proximally closer to the apex of the tuberosity.Thebicipital aponeurosis, also called the lacertus fibrosus, is a thick fascial band that organizes close to themusculotendinous junctionof the biceps and radiates over and inserts onto the ulnar part of theantebrachial fascia.
The tendon that attaches to the radial tuberosity is partially or completely surrounded by abursa, thebicipitoradial bursa, which ensures frictionless motion between the biceps tendon and the proximal radius duringpronationandsupinationof the forearm.
Two muscles lie underneath the biceps brachii. These are thecoracobrachialis muscle, which like the biceps attaches to the coracoid process of the scapula, and thebrachialis musclewhich connects to theulnaand along the mid-shaft of thehumerus. Besides those, thebrachioradialis muscleis adjacent to the biceps and also inserts on the radius bone, though more distally.
Traditionally described as a two-headed muscle, biceps brachii is one of the mostvariablemuscles of the human body and has a third head arising from thehumerusin 10% of cases (normal variation)—most commonly originating near the insertion of the coracobrachialis and joining the short head—but four, five, and even sevensupernumeraryheads have been reported in rare cases.
One study found a higher than expected number of female cadavers with a third head of biceps brachii, equal incidence between sides of the body, and uniform innervation by musculocutaneous nerve.
The distal biceps tendons are completely separated in 40% andbifurcatedin 25% of cases.
The biceps shares its nerve supply with the other two muscles of the anterior compartment. The muscles are supplied by themusculocutaneous nerve. Fibers of the fifth, sixth and seventhcervical nervesmake up the components of the musculocutaneous nerve which supply the biceps.
The blood supply of the biceps is thebrachial artery. The distal tendon of the biceps can be useful for palpating the brachial pulse, as the artery runs medial to the tendon in thecubital fossa.
The biceps works across three joints.The most important of these functions is to supinate the forearm and flex the elbow. Besides, the long head of biceps prevents the upward displacement of the head of the humerus.In more detail, the actions are, by joint:
Motor unitsin the lateral portion of the long head of the biceps are preferentially activated during elbow flexion, while motor units in the medial portionare preferentially activated during forearm supination.
The biceps are usually attributed as representative of strength within a variety of worldwide cultures.
The proximal tendons of the biceps brachii are commonly involved in pathological processes and are a frequent cause of anterior shoulder pain.Disorders of the distal biceps brachii tendon include insertional tendonitis and partial or complete tears of the tendon. Partial tears are usually characterized by pain and enlargement and abnormal contour of the tendon.Complete tears occur asavulsionof the tendinous portion of the biceps away from its insertion on the tuberosity of the radius, and is often accompanied by a palpable, audible "pop" and immediate pain and soft tissue swelling.
A soft-tissue mass is sometimes encountered in the anterior aspect of the arm, the so-called ReversePopeye deformity, which paradoxically leads to a decreased strength during flexion of the elbow and supination of the forearm.
Tears of the biceps brachii may occur during athletic activities, however avulsion injuries of the distal biceps tendon are frequently occupational in nature and sustained during forceful, eccentric contraction of the biceps muscle while lifting.
Treatment of a biceps tear depends on the severity of the injury.  In most cases, the muscle will heal over time with no corrective surgery. Applying cold pressure and using anti-inflammatory medications will ease pain and reduce swelling. More severe injuries require surgery and post-op physical therapy to regain strength and functionality in the muscle. Corrective surgeries of this nature are typically reserved for elite athletes who rely on a complete recovery.
The biceps can be strengthened usingweightandresistance training. Examples of well known biceps exercises are thechin-upandbiceps curl.
The biceps brachii muscle is the one that gave all muscles their name: it comes from theLatinmusculus, "little mouse", because the appearance of the flexed biceps resembles the back of a mouse.  The same phenomenon occurred inGreek, in which μῦς,mȳs, means both "mouse" and "muscle".
The termbiceps brachiiis a Latin phrase meaning "two-headed [muscle] of the arm", in reference to the fact that the muscle consists of two bundles of muscle, each with its own origin, sharing a common insertion point near the elbow joint. The properpluralform of theLatinadjectivebicepsisbicipites,a form not in general English use. Instead,bicepsis used in bothsingularand plural (i.e., when referring to both arms).
The English formbicep, attested from 1939, is aback formationderived from misinterpreting thesofbicepsas theEnglish pluralmarker-s.
Adriaan van den Spiegelcalled the biceps aPisciculus)due to its fusiform shape, which is why in the Italian-language medical literature it is sometimes calledil pescetto, "the small fish".
Leonardo da Vinciexpressed the original idea of the biceps acting as a supinator in a series of annotated drawings made between 1505 and 1510; in which the principle of the biceps as a supinator, as well as its role as a flexor to the elbow were devised. However, this function remained undiscovered by the medical community as da Vinci was not regarded as a teacher of anatomy, nor were his results publicly released. It was not until 1713 that this movement was re-discovered byWilliam Cheseldenand subsequently recorded for the medical community. It was rewritten several times by different authors wishing to present information to different audiences. The most notable recent expansion upon Cheselden's recordings was written byGuillaume Duchennein 1867, in a journal namedPhysiology of Motion. It remains one of the major references on supination action of the biceps brachii.
InNeanderthals, the radial bicipital tuberosities were larger than inmodern humans, which suggests they were probably able to use their biceps for supination over a wider range of pronation-supination.  It is possible that they relied more on their biceps for forceful supination without the assistance of thesupinator musclelike in modern humans, and thus that they used a different movement when throwing.
In the horse, the biceps' function is to extend the shoulder and flex the elbow.  It is composed of two short-fibred heads separated longitudinally by a thick internal tendon which stretches from the origin on the supraglenoid tubercle to the insertion on the medial radial tuberosity.  This tendon can withstand very large forces when the biceps is stretched.  From this internal tendon a strip of tendon, thelacertus fibrosus, connects the muscle with theextensor carpi radialis-- an important feature in the horse'sstay apparatus(through which the horse can rest and sleep whilst standing.)