Ulnar Nerve

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Ulnar Nerve
Nerve Type	Mixed nerve
Origin	C8 and T1 from medial cord of Brachial Plexus
Major Branches	Dorsal sensory branch of the ulnar nerve (5-6cm proximal to ulnar styloid)
Sensory innervation	Palmar and dorsal sides of medial half of the fourth finger, entire fifth finger, and ulnar border of the hand.
Motor innervation	Flexor Carpi Ulnaris, Flexor Digitorum Profundus, Lumbricals, Opponens Digiti Minimi, Flexor Digiti Minimi, Abductor Digiti Minimi, Interossei, Adductor Pollicis

Motor Supply

All but five intrinsic hand muscles are innervated by the ulnar nerve. The remaining are innervated by the C8-T1 roots via the Median Nerve. The mnemonic AbOF can be used to remember which muscles are above the law in that they aren't innervated by the ulnar nerve: the abductor (Ab) and flexor (F) pollicis brevis, opponens pollicis (O), and lateral lumbricals (Law).

Clinical Relevance

Importantly, the ulnar nerve doesn't provide sensation to the medial forearm. That is innervated by the Medial Antebrachial Cutaneous Nerve. Therefore, an ulnar lesion at the elbow results in anaesthesia of the ulnar hand and fingers, but not the forearm.

Nerve compression in the Guyon canal results in anaesthesia of the ventral palm and fifth finger. Dorsal sensation is supplied by the dorsal sensory branch of the ulnar nerve.