Anatomy Review: the Ulnar Nerve
The ulnar nerve is composed of spinal contributions for C7, 8, T1, and is the continuation of the medial cord of the brachial plexus. The nerve provides motor input to most of the small muscles of the hand, to flexor carpi ulnaris, and to the ulnar (medial 2 slips) half of the flexor digitorum profundus. It also receives sensory feed back from the ulnar aspect of the hand.
Lying medial to the axillary and then to the brachial artery it continues distally to pierce the medial intermuscular septum midway along the arm. From here it runs anterior to the medial head of triceps, and comes to lie on the humerus in a groove between the medial epicondyle and olecranon (the cubital tunnel) where it gives off articular branches to the elbow. It enters the flexor compartment of the forearm between the heads of flexor carpi ulnaris.
In the flexor compartment it lies on flexor digitorum profundus under cover of flexor carpi ulnaris proximally. It supplies both of these muscles via muscular branches which it gives off near the elbow. The innervation of flexor digitorum profundus is variable, usually the ulnar nerve supplies the medial 2 slips but it may supply more or less.
Midway along the forearm it gives off a palmar cutaneous branch (C8) which continues distally on the ulnar artery, pierces deep fascia and provides sensory innervation to the ulnar part of the palm over the area of the pisiform.
About 5cm proximal to the wrist it gives off a dorsal branch which continues distally to the ulnar side of the dorsum of the wrist and hand before dividing into dorsal digital branches. The first dorsal digital nerve supplies the ulnar half of the dorsum of the little finger as far distally as the nail, the second supplies adjacent sides of the ring and little finger. Occasionally a third supplies adjacent sides of the ring and middle fingers.
More distally it comes to lie beneath deep fascia at the wrist, radially to flexor carpi ulnaris tendon and ulnarly to the ulnar artery. Piercing the deep fascia it continues distally superficial to the flexor retinaculum through Guyon’s canal to divide into superficial and deep terminal branches.
The superficial terminal branch continues distally deep to palmaris brevis which it innervates. It then divides into two palmar digital nerves; one to the ulnar half of the little finger and one (a common palmar digital nerve) to adjacent sides of little and ring fingers. The latter may send a small communicating branch to the median nerve.
The deep terminal branch passes between abductor digiti minimi and flexor digiti minimi together with the deep branch of the ulnar artery to pierce the opponens digiti minimi before coming to lie deep to the flexor tendons within the concavity of the deep palmar arterial arch. It gives motor branches to the hypothenar muscles, ulnar two (or more) lumbricals, palmar and dorsal interossei, adductor pollicis, and variably to opponens pollicis and flexor pollicis brevis. It also provides articular branches to the wrist and possibly to the carpus and carpometacarpal joints.
For some further reading on the Ulnar nerve and clinical conditions, here is an article written by Functional Anatomic Palpation Systems™ & Functional Range Release™ instructor Dr. John Saratisotis on Cubital tunnel syndrome: