AskDefine | Define arm

Dictionary Definition



1 a human limb; technically the part of the superior limb between the shoulder and the elbow but commonly used to refer to the whole superior limb
2 any instrument or instrumentality used in fighting or hunting; "he was licensed to carry a weapon" [syn: weapon, weapon system]
3 an administrative division of some larger or more complex organization; "a branch of Congress" [syn: branch, subdivision]
4 any projection that is thought to resemble an arm; "the arm of the record player"; "an arm of the sea"; "a branch of the sewer" [syn: branch, limb]
5 the part of an armchair or sofa that supports the elbow and forearm of a seated person
6 the part of a garment that is attached at armhole and provides a cloth covering for the arm [syn: sleeve]


1 prepare oneself for a military confrontation; "The U.S. is girding for a conflict in the Middle East"; "troops are building up on the Iraqui border" [syn: build up, fortify, gird] [ant: disarm]
2 supply with arms; "The U.S. armed the freedom fighters in Afghanistan"

User Contributed Dictionary



Etymology 1

Middle English < Old English earm, from Germanic *armi- or *arma-, from PIE *ar-mo-, a suffixed form of *ar- 'to fit together'. Cognates to Avestan and Old Persian arma.


  1. The extended portion of the upper limb, from the shoulder to the wrist and sometimes including the hand.
    She stood with her right arm extended and her palm forward to indicate “Stop!”
  2. A long, narrow, more or less rigid part of an object extending from the main part or centre of the object, such as the arm of an armchair, a crane, a pair of spectacles or a pair of compasses.
    The robot arm reached out and placed the part on the assembly line.
  3. A bay or inlet off a main body of water.
    Shelburne Bay is an arm of Lake Champlain.
part of object
  • Albanian: krah
  • Finnish: sanka, käsinoja, varsi, haara, puomi, hiha
  • Greek: αρμός
  • Kurdish: destik, çembil
  • Norwegian: arm
  • Portuguese: braço
  • Russian: ручка
  • Scottish Gaelic: geug
  • Swedish: armstöd (of an armchair)
body of water
  • Finnish: haara
Derived terms


  1. In the context of "usually used in the plural}} A weapon.

Extensive Definition

In anatomy, an arm is one of the upper limbs of an animal. The term arm can also be used for analogous structures, such as one of the paired upper limbs of a four-legged animal, or the arms of an octopus. In the lexicon of human anatomy, the term arm refers specifically to the segment between the shoulder and the elbow. The segment between the elbow and wrist is the forearm. However, in colloquial speech the term arm often refers to the entire upper limb from shoulder to wrist.
In primates the arms are richly adapted for both climbing and for more skilled, manipulative tasks. The ball and socket shoulder joint allows for movement of the arms in a wide circular plane, while the presence of two forearm bones which can rotate around each other allows for additional range of motion at this level.

Anatomy of the human arm

The human arm contains 30 bones, joints, muscles, nerves, and blood vessels. Many of these muscles are used for everyday tasks.

Bony structure and joints

The humerus is the (upper) arm bone. It joins with the scapula above at the shoulder joint (or glenohumeral joint) and with the ulna and radius below at the elbow joint.

Elbow joint

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 300lbs.

Osteofascial compartments

The arm is divided by a fascial layer (known as lateral and medial intermuscular septa) separating the muscles into two osteofascial compartments:
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:
  • The large deltoid muscle 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 brachioradialis muscle originates in the arm but inserts into the forearm. This muscle is responsible for rotating the hand so its palm faces forward (supination).

Cubital fossa

The cubital fossa is clinically important for venepuncture and for blood pressure measurement. It is an imaginary triangle with borders being: The structures which smell through the cubital fossa are vital. The order from which they pass into the forearm are as follows, from medial to lateral:

Nervous supply

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 lesions or even transections in the nerve.
Other nerves passing through give no supply to the arm. These include:
  • The median nerve, nerve origin C5-T1, which is a branch of the lateral and medial cords of the brachial plexus. 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 forearm.
  • The ulnar nerve, origin C7-T1, is a continuation of the medial cord of the brachial plexus. This nerve passes in the same plane as the median nerve, between the biceps and triceps muscles. At the elbow, this nerve travels posterior to the medial epicondyle of the humerus. This means that condylar fractures can cause lesion to this nerve.

Blood supply and venous drainage


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.


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 basilic and the cephalic veins. 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.

Additional images

Image:Gray413_color.png|Cross-section through the middle of upper arm.
arm in Arabic: ذراع
arm in Catalan: Braç (anatomia)
arm in Welsh: Braich
arm in Danish: Arm
arm in German: Arm
arm in Spanish: Brazo
arm in Esperanto: Brako
arm in Basque: Beso
arm in French: Bras (segment de membre)
arm in Korean: 팔
arm in Indonesian: Lengan
arm in Italian: Braccio (anatomia)
arm in Latin: Brachium (anatomia)
arm in Lithuanian: Ranka
arm in Latvian: Roka
arm in Malagasy: Sandry
arm in Dutch: Arm (ledemaat)
arm in Japanese: 腕
arm in Polish: Ramię
arm in Portuguese: Braço
arm in Simple English: Arm
arm in Slovak: Kostra hornej končatiny
arm in Finnish: Käsivarsi
arm in Swedish: Arm
arm in Turkish: Kol
arm in Samogitian: Ronka
arm in Yiddish: ארעם

Synonyms, Antonyms and Related Words

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