Ulnar nerve: The ulnar nerve is a comprehensive peripheral nerve of the upper limb. The ulnar collateral ligament of the elbow joint is in conjunction with the ulnar nerve. The nerve is the extensive unprotected nerve in the human body (unprotected by muscle or bone), so the injury is common.
The ulnar nerve is directly attached to the little finger, and the adjacent half of the ring finger, innervating the palmar side of these fingers, covering both front and back of the tips, perhaps as far back as the fingernail beds. This nerve can produce an electric shock-like sensation by striking the medial epicondyle of the humerus from posteriorly, or inferiorly among the elbow flexed.
Origin– Ulnar nerve comes from the medial cord of the brachial plexus (C8-T1)
Course of the Ulnar Nerve
After originating of the brachial plexus, the ulnar nerve drops down the medial side of the upper arm. At the elbow, it crosses posterior to the medial epicondyle of the humerus, entering the forearm. At the medial epicondyle, the ulnar nerve is simply palpable and vulnerable to injury.
In the forearm, the nerve penetrates the two heads of the flexor carpi ulnaris muscle and goes alongside the ulna. Three branches arise in the forearm:
Muscular branch: supplies some muscles in the anterior compartment of the forearm.
Palmar cutaneous branch: innervates the medial half of the palm of the skin.
Dorsal cutaneous branch: innervates the medial 1 and 1/2 fingers of the skin and the associated palm area.
At the wrist, the ulnar nerve goes superficially to the flexor retinaculum. It enters the hand via the ulnar canal (known as Guyon’s canal). In the hand, the ulnar nerve terminates by giving rise to superficial and deep branches.
Motor Functions of the Ulnar Nerve
The ulnar nerve supplies muscles in the anterior compartment of the forearm, and in the hand.
In the anterior compartment of the forearm, the muscular branch of the ulnar nerve supplies two muscles:
• Flexor carpi ulnaris
• Flexor digitorum profundus (medial half)
The intrinsic muscles of the hand are innervated by the deep branch of the ulnar nerve.
The hypothenar muscles are innervated by the ulnar nerve. It also innervates some other muscles of the hand:
• Adductor pollicis
• Medial two lumbricals
• Interossei of the hand
• Palmaris brevis
The other thenar muscles in the hand are innervated by the median nerve.
Sensory functions of the Ulnar Nerve
Innervates the anterior and posterior surfaces of the medial one and half fingers, and the associated palm area.
Three branches of the ulnar nerve are responsible for its cutaneous innervation.
Two branches arise in the forearm, and that travel into the hand:
• Dorsal cutaneous branch: Innervates the skin of the medial one and a half fingers, and the associated dorsal area of the hand.
• Palmar cutaneous branch: Innervates the skin of the medial half of the palm of the hand.
The last branch arises in the hand itself:
• Superficial branch – Innervates the palmar surface of the medial one and a half fingers.
Common Injuries of Ulnar Nerve
The most common place for compression of the nerve is the inside part of the elbow. Ulnar nerve compression at the elbow is called “cubital tunnel syndrome.”