Arm
Encyclopedia
In human anatomy
, the arm is the part of the upper limb
between the shoulder and the elbow joints. In other animals, the term arm can also be used for analogous structures, such as one of the paired forelimb
s of a four-legged animal or the arms of cephalopods
. In anatomical usage, the term arm refers specifically to the segment between the shoulder and the elbow, while the segment between the elbow and wrist
is the forearm
. However, in common, literary, and historical usage, arm refers to the entire upper limb from shoulder to wrist. This article uses the former definition; see upper limb
for the wider definition.
In primates the arm is adapted for precise positioning of the hand
and thus assist in the hand's manipulative tasks. The ball and socket shoulder joint allows for movement of the arms in a wide circular plane, while the structure of the two forearm bones which can rotate around each other allows for additional range of motion at that level.
The humerus
is the bone of the arm. It joins with the scapula
above in the shoulder
at the glenohumeral joint
and with the ulna
and radius
below at the elbow
. The elbow joint is the hinge joint
between the distal end of the humerus and the proximal ends of the radius and ulna. The humerus cannot be broken easily. Its strength allows it to handle loading up to 300 lbs.
l layer (known as lateral and medial intermuscular septa) separating the muscles into two osteofascial compartments: the anterior
and the posterior compartments of the arm
. The fascia merges with the periosteum
(outer bone layer) of the humerus. The compartments contain muscles which are innervated by the same nerve and perform the same action.
Two other muscles are considered to be partially in the arm:
(colloquially known as the elbow pit) is clinically important for venepuncture and for blood pressure
measurement.
The musculocutaneous nerve
, from C5, C6, C7, is the main supplier of muscles of the anterior compartment. It originates from the lateral cord of the brachial plexus
of nerves. It pierces the coracobrachialis muscle and gives off branches to the muscle, as well as to brachialis and biceps brachii. It terminates as the anterior cutaneous nerve of the forearm.
The radial nerve
, which is from the fifth cervical spinal nerve to the first thoracic spinal nerve, originates as the continuation of the posterior cord of the brachial plexus. This nerve enters the lower triangular space (an imaginary space bounded by, amongst others, the shaft of the humerus and the triceps brachii) of the arm and lies deep to the triceps brachii. Here it travels with a deep artery of the arm (the profunda brachii
), which sits in the radial groove of the humerus. This fact is very important clinically as a fracture of the bone at the shaft of the bone here can cause lesion
s or even transections in the nerve.
Other nerves passing through give no supply to the arm. These include:
The main artery in the arm is the brachial artery
. This artery is a continuation of the axillary artery
. The point at which the axillary becomes the brachial is distal to the lower border of teres major. The brachial artery
gives off an important branch, the profunda brachii
(deep artery of the arm). This branching occurs just below the lower border of teres major.
The brachial artery continues to the cubital fossa
in the anterior compartment of the arm. It travels in a plane between the biceps
and triceps muscles, the same as the median nerve
and basilic vein
. It is accompanied by venae comitantes (accompanying veins). It gives branches to the muscles of the anterior compartment. The artery is in between the median nerve
and the tendon of the biceps muscle in the cubital fossa
. It then continues into the forearm
.
The profunda brachii travels through the lower triangular space with the radial nerve
. From here onwards it has an intimate relationship with the radial nerve. They are both found deep to the triceps muscle and are located on the spiral groove of the humerus
. Therefore fracture
of the bone may not only lead to lesion of the radial nerve
, but also haematoma of the internal structures of the arm. The artery then continues on to anastamose with the recurrent radial branch of the brachial artery
, providing a diffuse blood supply for the elbow joint.
and the cephalic vein
s. There is a connecting vein between the two, the median cubital vein
, which passes through the cubital fossa
and is clinically important for venepuncture (withdrawing blood).
The basilic vein travels on the medial side of the arm and terminates at the level of the seventh rib.
The cephalic vein travels on the lateral side of the arm and terminates as the axillary vein. It passes through the deltopectoral triangle, a space between the deltoid and the pectoralis major muscles.
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...
, the arm is the part of the upper limb
Upper limb
The upper limb or upper extremity is the region in an animal extending from the deltoid region to the hand, including the arm, axilla and shoulder.-Definition:...
between the shoulder and the elbow joints. In other animals, the term arm can also be used for analogous structures, such as one of the paired forelimb
Forelimb
A forelimb is an anterior limb on an animal's body. When referring to quadrupeds , the term foreleg is often instead used....
s of a four-legged animal or the arms of cephalopods
Cephalopod arm
A cephalopod arm is distinct from a tentacle, though the terms are often used interchangeably.Generally, cephalopod arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends. Octopuses have eight arms and no tentacles, while squid and cuttlefish...
. In anatomical usage, the term arm refers specifically to the segment between the shoulder and the elbow, while the segment between the elbow and wrist
Wrist
In human anatomy, the wrist is variously defined as 1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand;...
is the forearm
Forearm
-See also:*Forearm flexors*Forearm muscles...
. However, in common, literary, and historical usage, arm refers to the entire upper limb from shoulder to wrist. This article uses the former definition; see upper limb
Upper limb
The upper limb or upper extremity is the region in an animal extending from the deltoid region to the hand, including the arm, axilla and shoulder.-Definition:...
for the wider definition.
In primates the arm is adapted for precise positioning of the hand
Hand
A hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...
and thus assist in the hand's manipulative tasks. The ball and socket shoulder joint allows for movement of the arms in a wide circular plane, while the structure of the two forearm bones which can rotate around each other allows for additional range of motion at that level.
Skeleton
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
is the bone of the arm. It joins with the scapula
Scapula
In anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
above in the shoulder
Shoulder
The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...
at the glenohumeral joint
Glenohumeral joint
The glenohumeral joint, or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula and the head of the humerus...
and with the ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
and radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
below at the elbow
Elbow
The human elbow is the region surrounding the elbow-joint—the ginglymus or hinge joint in the middle of the arm. Three bones form the elbow joint: the humerus of the upper arm, and the paired radius and ulna of the forearm....
. The elbow joint is the hinge joint
Hinge joint
A hinge joint is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane—backward and forward—the extent of motion at the same time being considerable....
between the distal end of the humerus and the proximal ends of the radius and ulna. The humerus cannot be broken easily. Its strength allows it to handle loading up to 300 lbs.
Muscles
The arm is divided by a fasciaFascia
A fascia is a layer of fibrous tissue that permeates the human body. A fascia is a connective tissue that surrounds muscles, groups of muscles, blood vessels, and nerves, binding those structures together in much the same manner as plastic wrap can be used to hold the contents of sandwiches...
l layer (known as lateral and medial intermuscular septa) separating the muscles into two osteofascial compartments: the anterior
Anterior compartment of the arm
The anterior compartment of the arm is known as the "flexor compartment" as flexion is its main action.The muscles contained therein are the biceps brachii, brachialis, and coracobrachialis....
and the posterior compartments of the arm
Posterior compartment of the arm
The posterior compartment of the arm is an anatomic compartment which contains muscles which are all supplied by the radial nerve. This compartment is also known as the "extensor compartment", extension being its main action.-Contents:...
. The fascia merges with the periosteum
Periosteum
Periosteum is a membrane that lines the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of all bones....
(outer bone layer) of the humerus. The compartments contain muscles which are innervated by the same nerve and perform the same action.
Two other muscles are considered to be partially in the arm:
- The large deltoid muscleDeltoid muscleIn human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the central...
is considered to have part of its body in the anterior compartment. This muscle is the main abductor muscle of the upper limb and extends over the shoulder. - The brachioradialisBrachioradialisBrachioradialis is a muscle of the forearm that acts to flex the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm...
muscle originates in the arm but inserts into the forearm. This muscle is responsible for rotating the hand so its palm faces forward (supinationSupinationSupination is a position of either the forearm or foot; in the forearm when the palm faces anteriorly, or faces up . Supination in the foot occurs when a person appears "bow-legged" with their weight supported primarily on the anterior of their feet.The hand is supine in the anatomical position...
).
Nerve and blood supply
The cubital fossaCubital fossa
The cubital fossa is the triangular area on the anterior view of the elbow of a human or other hominid animal. It is colloquially known as the "elbow pit".-Boundaries:...
(colloquially known as the elbow pit) is clinically important for venepuncture and for blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
measurement.
Innervation
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.-Path:...
, from C5, C6, C7, is the main supplier of muscles of the anterior compartment. It originates from the lateral cord of the brachial plexus
Brachial plexus
The brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...
of nerves. It pierces the coracobrachialis muscle and gives off branches to the muscle, as well as to brachialis and biceps brachii. It terminates as the anterior cutaneous nerve of the forearm.
The radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...
, which is from the fifth cervical spinal nerve to the first thoracic spinal nerve, originates as the continuation of the posterior cord of the brachial plexus. This nerve enters the lower triangular space (an imaginary space bounded by, amongst others, the shaft of the humerus and the triceps brachii) of the arm and lies deep to the triceps brachii. Here it travels with a deep artery of the arm (the profunda brachii
Profunda brachii
The arteria profunda brachii is a large vessel which arises from the lateral and posterior part of the brachial artery, just below the lower border of the Teres major.-Course:...
), which sits in the radial groove of the humerus. This fact is very important clinically as a fracture of the bone at the shaft of the bone here can cause lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s or even transections in the nerve.
Other nerves passing through give no supply to the arm. These include:
- The median nerveMedian nerveThe median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....
, nerve origin C5-T1, which is a branch of the lateral and medial cords of the brachial plexusBrachial plexusThe brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...
. This nerve continues in the arm, travelling in a plane between the biceps and triceps muscles. At the cubital fossa, this nerve is deep to the pronator teres muscle and is the most medial structure in the fossa. The nerve passes into the forearmForearm-See also:*Forearm flexors*Forearm muscles...
. - The ulnar nerveUlnar nerveIn human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...
, origin C8-T1, is a continuation of the medial cord of the brachial plexusBrachial plexusThe brachial plexus is a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots...
. This nerve passes in the same plane as the median nerveMedian nerveThe median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....
, between the biceps and triceps muscles. At the elbow, this nerve travels posterior to the medial epicondyle of the humerus. This means that condylar fractureFractureA fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
s can cause lesion to this nerve.
Arteries
Brachial artery
The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...
. This artery is a continuation of the axillary artery
Axillary artery
In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla and the upper limb...
. The point at which the axillary becomes the brachial is distal to the lower border of teres major. The brachial artery
Brachial artery
The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...
gives off an important branch, the profunda brachii
Profunda brachii
The arteria profunda brachii is a large vessel which arises from the lateral and posterior part of the brachial artery, just below the lower border of the Teres major.-Course:...
(deep artery of the arm). This branching occurs just below the lower border of teres major.
The brachial artery continues to the cubital fossa
Cubital fossa
The cubital fossa is the triangular area on the anterior view of the elbow of a human or other hominid animal. It is colloquially known as the "elbow pit".-Boundaries:...
in the anterior compartment of the arm. It travels in a plane between the biceps
Biceps
Biceps may refer to:*Biceps brachii muscle, a muscle located on the inside of the upper arm*Biceps femoris muscle, one of the hamstring muscles of the back of each thigh*Biceps , a point in a metrical pattern...
and triceps muscles, the same as the median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....
and basilic vein
Basilic vein
In human anatomy, the basilic vein is a large superficial vein of the upper limb that helps drain parts of hand and forearm. It originates on the medial side of the dorsal venous network of the hand, and it travels up the base of the forearm and arm...
. It is accompanied by venae comitantes (accompanying veins). It gives branches to the muscles of the anterior compartment. The artery is in between the median nerve
Median nerve
The median nerve is a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus....
and the tendon of the biceps muscle in the cubital fossa
Cubital fossa
The cubital fossa is the triangular area on the anterior view of the elbow of a human or other hominid animal. It is colloquially known as the "elbow pit".-Boundaries:...
. It then continues into the forearm
Forearm
-See also:*Forearm flexors*Forearm muscles...
.
The profunda brachii travels through the lower triangular space with the radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...
. From here onwards it has an intimate relationship with the radial nerve. They are both found deep to the triceps muscle and are located on the spiral groove of the humerus
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
. Therefore fracture
Fracture
A fracture is the separation of an object or material into two, or more, pieces under the action of stress.The word fracture is often applied to bones of living creatures , or to crystals or crystalline materials, such as gemstones or metal...
of the bone may not only lead to lesion of the radial nerve
Radial nerve
The radial nerve is a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin.It...
, but also haematoma of the internal structures of the arm. The artery then continues on to anastamose with the recurrent radial branch of the brachial artery
Brachial artery
The brachial artery is the major blood vessel of the arm.It is the continuation of the axillary artery beyond the lower margin of teres major muscle. It continues down the ventral surface of the arm until it reaches the cubital fossa at the elbow. It then divides into the radial and ulnar arteries...
, providing a diffuse blood supply for the elbow joint.
Veins
The veins of the arm carry blood from the extremities of the limb, as well as drain the arm itself. The two main veins are the basilicBasilic vein
In human anatomy, the basilic vein is a large superficial vein of the upper limb that helps drain parts of hand and forearm. It originates on the medial side of the dorsal venous network of the hand, and it travels up the base of the forearm and arm...
and the cephalic vein
Cephalic vein
In human anatomy, the cephalic vein is a superficial vein of the upper limb.It communicates with the basilic vein via the median cubital vein at the elbow and is located in the superficial fascia along the anterolateral surface of the biceps brachii muscle.Superiorly the cephalic vein passes...
s. There is a connecting vein between the two, the median cubital vein
Median cubital vein
In human anatomy, the median cubital vein is a superficial vein of the upper limb. It connects the basilic and cephalic vein and is often used for venipuncture . It lies in the cubital fossa superficial to the bicipital aponeurosis.There exists a fair amount of variation of the median cubital vein...
, which passes through the cubital fossa
Cubital fossa
The cubital fossa is the triangular area on the anterior view of the elbow of a human or other hominid animal. It is colloquially known as the "elbow pit".-Boundaries:...
and is clinically important for venepuncture (withdrawing blood).
The basilic vein travels on the medial side of the arm and terminates at the level of the seventh rib.
The cephalic vein travels on the lateral side of the arm and terminates as the axillary vein. It passes through the deltopectoral triangle, a space between the deltoid and the pectoralis major muscles.
See also
- Anatomical terms of locationAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
- Anthropometry of the upper arm
- Humerus fractureHumerus fractureA humerus fracture can be classified by the location of the humerus involved: the upper end, the shaft, or the lower end.Certain lesions are commonly associated with fractures to specific areas of the humerus. At the upper end, the surgical neck of the humerus and anatomical neck of humerus can...