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
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 ...
and join to form a single
muscle belly
Anatomical terminology is used to uniquely describe aspects of skeletal muscle, cardiac muscle, and smooth muscle such as their actions, structure, size, and location.
Types
There are three types of muscle tissue in the body: skeletal, smooth, ...
which is attached to the upper forearm. While the biceps crosses both the
shoulder
The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder mak ...
and elbow joints, its main function is at the elbow where it flexes the forearm and
supinates the 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
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 ...
).
Structure
The biceps is one of three muscles in the
anterior compartment of the upper arm, along with the
brachialis muscle
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 p ...
and the
coracobrachialis muscle
The coracobrachialis muscle is the smallest of the three muscles that attach to the coracoid process of the scapula. (The other two muscles are pectoralis minor and the short head of the biceps brachii.) It is situated at the upper and medial part ...
, 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 the
intertubercular groove
The bicipital groove (intertubercular groove, sulcus intertubercularis) is a deep groove on the humerus that separates the greater tubercle from the lesser tubercle. It allows for the long tendon of the biceps brachii muscle to pass.
Structure ...
of the
humerus.
Extending from its origin on the coracoid, the tendon of the short head runs adjacent to the tendon of the
coracobrachialis
The coracobrachialis muscle is the smallest of the three muscles that attach to the coracoid process of the scapula. (The other two muscles are pectoralis minor and the short head of the biceps brachii.) It is situated at the upper and medial part ...
as the conjoint tendon. Unlike the other muscles in the anterior compartment of the arm, 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 the
deltoid 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 extends
distally
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
, 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.
The
bicipital aponeurosis
The bicipital aponeurosis (also known as lacertus fibrosus) is a broad aponeurosis of the biceps brachii, which is located in the cubital fossa of the elbow. It separates superficial from deep structures in much of the fossa.
Structure
The bicip ...
, also called the lacertus fibrosus, is a thick fascial band that organizes close to the
musculotendinous junction
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 muscle ...
of the biceps and radiates over and inserts onto the ulnar part of the
antebrachial fascia
The antebrachial fascia (antibrachial fascia or deep fascia of forearm) continuous above with the brachial fascia, is a dense, membranous investment, which forms a general sheath for the muscles in this region; it is attached, behind, to the olec ...
.
The tendon that attaches to the radial tuberosity is partially or completely surrounded by a
bursa, the
bicipitoradial bursa, which ensures frictionless motion between the biceps tendon and the proximal radius during pronation and supination of the forearm.
Two muscles lie underneath the biceps brachii. These are the
coracobrachialis muscle
The coracobrachialis muscle is the smallest of the three muscles that attach to the coracoid process of the scapula. (The other two muscles are pectoralis minor and the short head of the biceps brachii.) It is situated at the upper and medial part ...
, which like the biceps attaches to the coracoid process of the scapula, and the
brachialis muscle
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 p ...
which connects to 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 ...
and along the mid-shaft of the
humerus. Besides those, the
brachioradialis muscle
The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm. It is attached to the distal styloid process of the radius by wa ...
is adjacent to the biceps and also inserts on the radius bone, though more distally.
File:Flexión del brazo.png, Biceps and triceps
The triceps, or triceps brachii (Latin for "three-headed muscle of the arm"), is a large muscle on the back of the upper limb of many vertebrates. It consists of 3 parts: the medial, lateral, and long head. It is the muscle principally responsibl ...
.
File:Animation triceps biceps.gif, Movement of biceps and triceps when arm is flexing
File:Kelly Lynn bicep flex 2.jpg, The split line between the long and short heads
Variation
Traditionally described as a two-headed muscle, biceps brachii is one of the most
variable
Variable may refer to:
* Variable (computer science), a symbolic name associated with a value and whose associated value may be changed
* Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...
muscles of the human body and has a third head arising from the
humerus in 10% of cases (normal variation)—most commonly originating near the insertion of the coracobrachialis and joining the short head—but four, five, and even seven
supernumerary
Supernumerary means "exceeding the usual number".
Supernumerary may also refer to:
* Supernumerary actor, a performer in a film, television show, or stage production who has no role or purpose other than to appear in the background, more commonl ...
heads 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% and
bifurcated in 25% of cases.
Nerve supply
The biceps shares its nerve supply with the other two muscles of the anterior compartment. The muscles are supplied by the
musculocutaneous nerve
The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the pectoralis major, its fibers being derived from C5, C6 and C7.
Structure
The musculocutaneous nerve arises from the lateral cor ...
. Fibers of the fifth, sixth and seventh
cervical nerves
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
make up the components of the musculocutaneous nerve which supply the biceps.
Blood supply
The blood supply of the biceps is the
brachial artery. The distal tendon of the biceps can be useful for palpating the brachial pulse, as the artery runs medial to the tendon in the
cubital fossa
The cubital fossa, chelidon, or elbow pit, is the triangular area on the anterior side of the upper limb between the arm and forearm of a human or other hominid animals. It lies anteriorly to the elbow (Latin ) when in standard anatomical position ...
.
Function
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:
*
Proximal radioulnar joint
The proximal radioulnar articulation, also known as the proximal radioulnar joint (PRUJ), is a synovial pivot joint between the circumference of the head of the radius and the ring formed by the radial notch of the ulna and the annular ligament ...
of the elbow – The biceps brachii functions as a powerful supinator of the forearm, i.e. it turns the palm upwards. This action, which is aided by the
supinator muscle, requires the
humeroulnar joint of the elbow to be at least partially flexed. If the humeroulnar joint, is fully extended, supination is then primarily carried out by the supinator muscle. The biceps is a particularly powerful supinator of the forearm due to the distal attachment of the muscle at the radial tuberosity, on the opposite side of the bone from the supinator muscle. When flexed, the biceps effectively pulls the radius back into its neutral supinated position in concert with the supinator muscle.
*
Humeroulnar joint of the elbow – The biceps brachii also functions as an important flexor of the forearm, particularly when the forearm is supinated.
Functionally, this action is performed when lifting an object, such as a bag of groceries or when performing a
biceps curl The term "biceps curl" refers to any of a number of weight training exercises that primarily targets the biceps brachii muscle. It may be performed using a barbell, dumbbell, resistance band, or other equipment.
Overview
The biceps curl mainly ...
. When the forearm is in
pronation (the palm faces the ground), the brachialis,
brachioradialis
The brachioradialis is a muscle of the forearm that flexes the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm. It is attached to the distal styloid process of the radius by ...
, and supinator function to flex the forearm, with minimal contribution from the biceps brachii. It is also important to note that regardless of forearm position, (supinated, pronated, or neutral) the force exerted by the biceps brachii remains the same; however, the brachioradialis has a much greater change in exertion depending on position than the biceps during concentric contractions. That is, the biceps can only exert so much force, and as forearm position changes, other muscles must compensate.
*
Glenohumeral joint
The shoulder joint (or glenohumeral joint from Greek ''glene'', eyeball, + -''oid'', 'form of', + Latin ''humerus'', shoulder) is structurally classified as a synovial ball-and-socket joint and functionally as a diarthrosis and multiaxial joint ...
(shoulder joint) – Several weaker functions occur at the glenohumeral joint. The biceps brachii weakly assists in forward flexion of the shoulder joint (bringing the arm forward and upwards). It may also contribute to
abduction (bringing the arm out to the side) when the arm is externally (or laterally) rotated. The short head of the biceps brachii also assists with horizontal
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 ...
(bringing the arm across the body) when the arm is internally (or medially) rotated. Finally, the short head of the biceps brachii, due to its attachment to 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 ...
(or shoulder blade), assists with stabilization of the shoulder joint when a heavy weight is carried in the arm. The tendon of the long head of the biceps also assists in holding the head of the humerus in the glenoid cavity.
Motor units in the lateral portion of the long head of the biceps are preferentially activated during elbow flexion, while motor units in the medial portion are preferentially activated during forearm supination.
The biceps are usually attributed as representative of strength within a variety of worldwide cultures.
Clinical significance
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 as avulsion of 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 Reverse Popeye deformity, which paradoxically leads to a decreased strength during flexion of the elbow and supination of the forearm.
Tendon rupture
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.
Training
The biceps can be strengthened using
weight
In science and engineering, the weight of an object is the force acting on the object due to gravity.
Some standard textbooks define weight as a vector quantity, the gravitational force acting on the object. Others define weight as a scalar qua ...
and
resistance training
Strength training or resistance training involves the performance of physical exercises that are designed to improve strength and endurance. It is often associated with the lifting of weights. It can also incorporate a variety of training te ...
. Examples of well known biceps exercises are the
chin-up
A pull-up is an upper-body strength exercise. The pull-up is a closed-chain movement where the body is suspended by the hands, gripping a bar or other implement at a distance typically wider than shoulder-width, and pulled up. As this happens, ...
and
biceps curl The term "biceps curl" refers to any of a number of weight training exercises that primarily targets the biceps brachii muscle. It may be performed using a barbell, dumbbell, resistance band, or other equipment.
Overview
The biceps curl mainly ...
.
Etymology and grammar
The biceps brachii muscle is the one that gave all muscles their name: it comes from the
Latin
Latin (, or , ) is a classical language belonging to the 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 the power of the ...
''musculus'', "little mouse", because the appearance of the flexed biceps resembles the back of a mouse. The same phenomenon occurred in
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
, in which μῦς, ''mȳs'', means both "mouse" and "muscle".
The term ''biceps brachii'' is a Latin phrase meaning "two-headed
uscleof 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 proper
plural
The plural (sometimes abbreviated pl., pl, or ), in many languages, is one of the values of the grammatical category of number. The plural of a noun typically denotes a quantity greater than the default quantity represented by that noun. This de ...
form of the
Latin
Latin (, or , ) is a classical language belonging to the 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 the power of the ...
adjective
In linguistics, an adjective (abbreviated ) is a word that generally modifies a noun or noun phrase or describes its referent. Its semantic role is to change information given by the noun.
Traditionally, adjectives were considered one of the ma ...
''biceps'' is ''bicipites'', a form not in general English use. Instead, ''biceps'' is used in 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 (i.e., when referring to both arms).
The English form ', attested from 1939, is a
back formation
In etymology, back-formation is the process or result of creating a new word via inflection, typically by removing or substituting actual or supposed affixes from a lexical item, in a way that expands the number of lexemes associated with the ...
derived from misinterpreting the ''s'' of ''biceps'' as the
English plural
English nouns are inflected for grammatical number, meaning that, if they are of the countable type, they generally have different forms for singular and plural. This article discusses the variety of ways in which English plural nouns are formed ...
marker ''-s''.
History
Leonardo da Vinci
Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially res ...
expressed 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 by
William Cheselden and 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 by
Guillaume Duchenne
Guillaume-Benjamin-Amand Duchenne (de Boulogne) (September 17, 1806 in Boulogne-sur-Mer – September 15, 1875 in Paris) was a French neurologist who revived Galvani's research and greatly advanced the science of electrophysiology. The era of m ...
in 1867, in a journal named ''Physiology of Motion''. To this day it remains one of the major references on supination action of the biceps brachii.
Other species
Neanderthals
In
Neanderthal
Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While the ...
s, the radial bicipital tuberosities were larger than in
modern 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 the
supinator muscle like in modern humans, and thus that they used a different movement when throwing.
Horses
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, the ''lacertus fibrosus'', connects the muscle with the
extensor carpi radialis -- an important feature in the horse's
stay apparatus (through which the horse can rest and sleep whilst standing.)
References
External links
*
{{Authority control
Elbow flexors
Forearm supinators
Muscles of the upper limb
Shoulder flexors