A descriptive write-up on various bones and muscles of the human arm, and the role they play in functioning of this limb.

One of the most important constituents of the 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 bones and joints works in coordination with 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 and radius in upper and lower arms respectively.

Arm Muscles

There are various muscles in the arm which control various functions of this limb. Both, arm bones and muscles work in coordination with each other to makes various functions of the 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 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 these muscles are small in shape, they have a fascinating coordination between them which helps our hands perform several intricate functions. Studies have revealed that 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 a priority.