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M01.03.029 Ulnar Nerve
The ulnar nerve is a major peripheral nerve of the upper limb. It originates from the brachial plexus and plays crucial roles in the motor and sensory functions of the forearm and hand.
Key Features
- Spinal Roots: C8–T1
- Motor Functions:
- Two muscles in the anterior forearm:
- Flexor carpi ulnaris
- Medial half of flexor digitorum Profundus
- Most intrinsic hand muscles (excluding thenar muscles and lateral lumbricals)
- Two muscles in the anterior forearm:
- Sensory Functions:
- Medial one and a half fingers and associated palm
Anatomical Course
| Region | Path | Branches |
|---|---|---|
| Axilla | Continuation of the medial cord of the brachial plexus | None |
| Arm | Descends medial to the brachial artery; penetrates medial fascial septum; enters posterior arm | Articular branch (elbow joint) |
| Forearm | Passes through flexor carpi ulnaris; travels alongside the ulna | Muscular, palmar cutaneous, dorsal cutaneous |
| Wrist & Hand | Passes superficial to flexor retinaculum; enters via Guyon’s canal | Superficial and deep branches |
Motor Functions
| Region | Muscles Innervated | Function |
|---|---|---|
| Anterior Forearm | – Flexor carpi ulnaris | Wrist flexion and adduction |
| – Medial half of flexor digitorum profundus | Flexes 4th and 5th digits at DIP joints | |
| Hand (Intrinsic) | – Hypothenar muscles | Movement of the little finger |
| – Medial two lumbricals | Flex MCP and extend IP joints (4th, 5th digits) | |
| – Adductor pollicis | Thumb adduction | |
| – Palmar and dorsal interossei | Finger abduction and adduction | |
| – Palmaris brevis (superficial branch) | Wrinkles skin of hypothenar eminence |
Sensory Functions
| Branch | Region Innervated |
|---|---|
| Palmar cutaneous | Medial half of palm |
| Dorsal cutaneous | Dorsal surface of medial 1.5 fingers and corresponding hand |
| Superficial branch | Palmar surface of medial 1.5 fingers |
Clinical Relevance
Froment’s Sign
- Test: Patient holds paper between thumb and index finger.
- Positive Sign: Flexion of thumb’s interphalangeal joint due to adductor pollicis paralysis.
Ulnar Nerve Palsy
Damage at the Elbow
| Mechanism of Injury | Trauma (e.g., medial epicondyle fracture, cubital tunnel compression) |
|---|---|
| Motor Impairment | – Weak wrist flexion/abduction |
| Sensory Loss | Entire ulnar nerve sensory distribution |
Damage at the Wrist
| Mechanism of Injury | Lacerations at the anterior wrist |
|---|---|
| Motor Impairment | – Weakness in intrinsic hand muscles |
| Sensory Loss | Palmar sensory loss; dorsal sensory spared |
Points to Remember
- The ulnar nerve originates from C8-T1 roots of the brachial plexus.
- It innervates most intrinsic hand muscles and provides sensation to the medial hand.
- Common clinical conditions include ulnar nerve palsy and compression syndromes (e.g., cubital tunnel).
- Froment’s sign is a diagnostic test for ulnar nerve dysfunction.
Bibliography
- TeachMeSeries Ltd. “Anatomy of the Ulnar Nerve.” 2024.
- Gray’s Anatomy for Students, 4th Edition, Elsevier.
- Moore, K.L., Dalley, A.F., & Agur, A.M.R. Clinically Oriented Anatomy, 7th Edition.