Arm Bones and Muscles

One of the most important constituent in human anatomy, the arm plays a vital role in various body functions. The term 'arm' is more often used to refer to the entire limb, starting from the shoulder to the wrist. However, in the medical field, the term 'arm' is technically used to refer to the upper limb, from the shoulder to the elbow joint. The remaining part, from the elbow joint to the wrist, is referred to as the 'forearm'.

Arm Bones

A look at the anatomy of the human hand shows that the entire arm has 3 bones in each arm, one in the upper arm (arm - extending from the shoulder to the elbow joint) and two in the lower arm (forearm - extending from the elbow joint to the wrist). These pairs of arm bones and joints works in coordination with the various muscles in the arms to execute the daily functions we perform. Now let's have a detailed look at each of these bones.

Humerus
The humerus is a long bone located in the upper arm, which extends from the shoulder to the elbow joint. It technically connects the scapula (flat triangular shoulder bone) to the lower arm. The humerus is further divided into three zones

• Upper extremity of humerus.
• Body of humerus.
• Lower extremity of humerus.

Radius
The radius is one of the two pairs of bones in the lower arm or forearm. It basically runs from the lateral side of the elbow to the thumb side of the wrist. The long, prism shaped bone tends to join the capitulum of the humerus in the upper arm, and connects the elbow to the forearm. Like the humerus, the radius is also divided into three zones.

• Upper extremity of radius.
• Body of radius.
• Lower extremity of radius.

Ulna
The ulna is another long bone located in the forearm of the individual, precisely placed at the medial side of the forearm, running parallel to the radius, to the wrist. The ulna articulates the humerus as well as the radius in upper and lower arms respectively.

Arm Muscles

There are various muscles in the arm which control the various functions of this limb. Both arm bones and muscles work in coordination with each other to makes various functions of the human hand possible. Basically, the muscles of the arm assist the bones in executing the following functions

• Bend or flex the elbow.
• Extend or straighten the elbow.
• Supinate or rotate the palm up.
• Pronate or rotate the palm down.
• Abduct or take the fingers and the wrist away from the midline of the body.
• Adduct or bring the fingers and wrist closer to the midline of the body.

The tables given below will tell you the function of each of the muscles in the arm.

Muscles in the Upper Arm

Muscle Name	Function
Coracobrachialis	Adducts humerus
Biceps brachii	Flexes elbow and supinates forearm
Brachialis	Flexion at elbow joint
Triceps brachii	Extends forearm, caput longum adducts shoulder
Anconeus triceps	Assists triceps in extension of the forearm

Muscles in the Lower Arm

Muscle Name	Function
Pronator teres	Pronation of forearm, flexes elbow
Palmaris longus	Wrist flexor
Flexor carpi radialis	Flexion and abduction at wrist
Flexor carpi ulnaris	Flexion of wrist
Flexor digitorum superficialis	Flexor of fingers
Pronator quadratus	Pronates the forearm
Flexor digitorum profundus	Flex hand, interphalangeal joints
Flexor pollicis longus	Flexion of the thumb
Extensor digitorum	Extension of hand and fingers
Extensor digiti minimi	Extends the little finger at all joints
Extensor carpi ulnaris	Extends and adducts the wrist
Brachioradialis	Flexion of forearm
Extensor carpi radialis longus	Extensor at the wrist joint, abducts the hand at the wrist
Extensor carpi radialis brevis	Extensor and abductor of the hand at the wrist joint
Supinator	Supinates forearm
Extensor indicis	Extends index finger, wrist
Abductor pollicis	Longus abduction, extension of thumb
Extensor pollicis brevis	Extension of thumb at metacarpophalangeal joint
Extensor pollicis longus	Extension of the thumb

Although the muscles which make up the human arm are small in shape, they have a fascinating coordination between them, which helps our hands perform several intricate functions. Studies have revealed that the arm bones and muscle growth is inter-related and therefore one has to ensure that the exercises which facilitate the strengthening of arm bones and muscle building, are given first priority.