Forearm Anatomy

The forearm is the region of the upper limb between the elbow and the wrist. It contains two bones, the radius and the ulna, which run parallel to each other.

Bones of the forearm

The radius is located on the thumb side of the forearm, while the ulna is located on the little finger side. The bones of the forearm are connected by a group of muscles, tendons, and ligaments that allow for movement of the hand and wrist.

Muscles in the forearm

The muscles of the forearm are divided into two groups: the flexors and the extensors.

The flexor muscles are located on the medial (inner) side of the forearm and are responsible for bending the wrist and fingers. The main flexor muscles in the forearm are the flexor carpi radialis, the flexor carpi ulnaris, the palmaris longus, and the pronator teres.

The extensor muscles are located on the lateral (outer) side of the forearm and are responsible for straightening the wrist and fingers. The main extensor muscles in the forearm are the brachioradialis, the extensor carpi radialis, the extensor carpi ulnaris, and the supinator.

The brachioradialis muscle is a flexor muscle that runs along the lateral side of the forearm and is responsible for the extension and supination of the forearm.

The pronator teres muscle is located on the medial side of the forearm and is responsible for pronation of the forearm.

The supinator muscle is located on the lateral side of the forearm and is responsible for supination of the forearm, the action of rotating the hand so the palm faces upward.

All these muscles are interconnected and work together to control the movement and position of the hand and wrist.

Nerves in the forearm

The nerves that innervate the forearm are the median nerve and the ulnar nerve.

The median nerve is a mixed nerve that originates from the cervical spine and runs down the arm, through the elbow, and into the forearm. It provides motor innervation to the flexor muscles of the forearm, as well as some of the muscles of the hand, such as the thenar eminence (the fleshy area at the base of the thumb) and the first two lumbricals (muscles in the hand that bend the fingers at the metacarpophalangeal joints). It also provides sensory innervation to the palmar surface of the thumb, index finger, middle finger, and half of the ring finger.

The ulnar nerve is also a mixed nerve that originates from the cervical spine and runs down the arm, through the elbow, and into the forearm. It provides motor innervation to the intrinsic muscles of the hand, such as the interossei (muscles between the fingers) and the hypothenar eminence (the fleshy area at the base of the little finger), as well as the flexor carpi ulnaris muscle in the forearm. It also provides sensory innervation to the skin over the medial (inner) side of the hand and fingers, as well as the palmar surface of the little finger and half of the ring finger.

Both the median and ulnar nerves are important for the function of the hand, providing both motor and sensory innervation to the muscles and skin of the forearm and hand. Damage or injury to either of these nerves can result in weakness or loss of sensation in the affected areas

What are the compartments of the forearm?

The forearm is divided into two compartments, the anterior compartment and the posterior compartment.

The anterior compartment of the forearm contains the muscles that flex the wrist and fingers, as well as the median nerve and the radial artery. The muscles in this compartment include the flexor carpi radialis, the palmaris longus, the flexor digitorum superficialis, and the flexor carpi ulnaris.

The posterior compartment of the forearm contains the muscles that extend the wrist and fingers, as well as the ulnar nerve and the deep branch of the radial artery. The muscles in this compartment include the brachioradialis, the extensor carpi radialis, the extensor digitorum, and the extensor carpi ulnaris.

The compartments are separated by the interosseous membrane, a fibrous sheet of connective tissue that runs between the radius and ulna, and are enclosed by the deep fascia, a layer of connective tissue that surrounds the muscles.

The compartments of the forearm are important for the functional movement of the hand, the anterior compartment muscles are responsible for the flexion of the wrist and fingers and the posterior compartment muscles are responsible for the extension of the wrist and fingers. Injuries or conditions that affect the muscles or nerves in these compartments can lead to weakness or loss of function in the hand and wrist.

If you want to learn more about the forearm complex, check out this science journal article.