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M01.03.026 Musculocutaneous Nerve
The musculocutaneous nerve is a major peripheral nerve of the upper limb, originating from the brachial plexus. This nerve plays a crucial role in the motor and sensory innervation of the arm and forearm.
| Feature | Details |
|---|---|
| Nerve Roots | C5–C7 |
| Motor Functions | Innervates muscles of the anterior compartment (coracobrachialis, biceps brachii, brachialis). |
| Sensory Functions | Provides sensation to the lateral forearm through the lateral cutaneous nerve. |
Anatomical Course
1. Origin and Path
- Origin: Terminal branch of the lateral cord of the brachial plexus (C5–C7).
- Emergence: Arises at the inferior border of the pectoralis minor.
2. Axilla
- Exits the axilla and pierces the coracobrachialis muscle near its humeral insertion.
- Supplies the coracobrachialis muscle at this point.
3. Arm
- Travels in the anterior compartment, lying:
- Superficial to the brachialis.
- Deep to the biceps brachii.
- Innervates the biceps brachii and brachialis muscles.
- Provides articular branches to the humerus and elbow.
4. Forearm
- Pierces the deep fascia lateral to the biceps tendon.
- Continues as the lateral cutaneous nerve of the forearm, providing sensory innervation to the lateral forearm.
Note: Variations in the nerve’s course are common. It may adhere to or exchange fibers with the median nerve or pass beneath the coracobrachialis.
Motor Functions
The musculocutaneous nerve innervates three muscles in the anterior compartment:
| Muscle | Function |
|---|---|
| Biceps brachii | Flexion at the elbow; supination of the forearm. |
| Brachialis | Primary flexor of the elbow. |
| Coracobrachialis | Flexion and adduction of the shoulder. |
Mnemonic:
- BBC – Biceps, Brachialis, Coracobrachialis
Sensory Functions
| Sensory Nerve | Area Supplied |
|---|---|
| Lateral cutaneous nerve | Skin of the anterolateral forearm. |
Path:
- Initially travels within the deep forearm.
- Pierces the deep fascia to become subcutaneous, located near the cephalic vein.
Clinical Relevance
1. Injury to the Musculocutaneous Nerve
Though rare due to its protective position in the axilla, the nerve can be injured by:
- Penetrating trauma (e.g., stab wounds).
- Iatrogenic damage (e.g., excessive retraction during surgeries).
| Effect | Details |
|---|---|
| Motor Impairment | Weak flexion at the shoulder and elbow. Weak supination. |
| Compensatory Muscles | Flexion: Pectoralis major (shoulder), brachioradialis (elbow). Supination: Brachioradialis. |
| Sensory Impairment | Loss of sensation over the lateral forearm. |
Points to Remember
- The musculocutaneous nerve arises from C5–C7 of the brachial plexus and is vital for upper limb movement and sensation.
- Motor Functions: Innervates coracobrachialis, biceps brachii, and brachialis.
- Sensory Functions: Provides sensation to the lateral forearm via the lateral cutaneous nerve.
- Injury to this nerve can lead to weakened arm movements but is compensated by other muscles.
References
TeachMeSeries Ltd, 2024