These changes are the result of damage to which nerve ?
Describe the sensory distribution of this nerve in the hand and which muscles are supplied?
Along the course of this nerve, where is it most commonly damaged ?

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The ulnar nerve is derived from the medial cord of the brachial plexus, from nerve roots C8 and T1. It traverses down the upper arm medial to the axillary artery, over the medial head of the triceps and posterior to the medial epicondyle. In the forearm it passes between the two heads of the flexor carpi ulnaris and into Guyon's canal (between hamate bone and pisiform).

The motor supply are, in the forearm - flexor carpi ulnaris, half of flexor digitorum profundus (4th and 5th fingers). In the hand - hypothenar muscles, all interossei muscles, medial two lumbricals, adductor pollicis and deep head of flexor pollicis brevis.

The sensory distribution is over the palmar and dorsal aspects of the little finger and half of the ring finger. Note that the branch supplying the dorsal aspect arises in the forearm so loss of sensation in this area implies lesion proximal to the wrist.

The ulnar nerve are most commonly affected in these areas:

a) Brachial plexus, as a result of trauma or other lesions in this area
b) At the level of the medial epicondyle from local pressure, friction or stretching
c) Between the two heads of flexor carpi ulnaris distal to the elbow
d) Lacerations at wrist level
e) Ulnar tunnel syndrome, where the nerve passes through Guyon's canal