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M01.03.024 Brachial Plexus
The brachial plexus is a vital network of nerves that innervates the skin and muscles of the upper limb. Understanding its anatomy is crucial for medical students and healthcare professionals. This article explores the brachial plexus’s formation, structure, and clinical relevance.
Formation of the Brachial Plexus
The anterior rami of spinal nerves C5, C6, C7, C8, and T1 form the Brachial plexus. It begins in the neck, traverses the axilla, and supplies the upper limb.
| Components | Details |
|---|---|
| Roots | Anterior rami of C5–T1 spinal nerves. |
| Trunks | Superior (C5–C6), Middle (C7), Inferior (C8–T1). |
| Divisions | Anterior and posterior divisions of each trunk. |
| Cords | Lateral, posterior, and medial (named relative to axillary artery). |
| Branches | Five major nerves and numerous minor branches. |
Anatomical Divisions of the Brachial Plexus
1. Roots
- Formed by the anterior rami of C5–T1 spinal nerves.
- Located between the anterior and medial scalene muscles.
- Responsible for initial nerve outflow from the spinal cord.
2. Trunks
- Located at the base of the neck:
- Superior Trunk: C5 and C6.
- Middle Trunk: Continuation of C7.
- Inferior Trunk: C8 and T1.
- Cross the posterior triangle of the neck.
3. Divisions
- Each trunk divides into:
- Anterior Division: Supplies flexor muscles.
- Posterior Division: Supplies extensor muscles.
- Pass into the axilla.
4. Cords
- Formed in the axilla by the recombination of divisions:
- Lateral Cord: Anterior divisions of the superior and middle trunks.
- Posterior Cord: All posterior divisions.
- Medial Cord: Anterior division of the inferior trunk.
5. Branches
The cords give rise to five major branches:
- Musculocutaneous Nerve (C5–C7)
- Axillary Nerve (C5–C6)
- Median Nerve (C6–T1)
- Radial Nerve (C5–T1)
- Ulnar Nerve (C8–T1)
| Nerve | Roots | Motor Functions | Sensory Functions |
|---|---|---|---|
| Musculocutaneous | C5–C7 | Biceps brachii, brachialis, coracobrachialis. | Lateral forearm. |
| Axillary | C5–C6 | Deltoid, teres minor. | Shoulder region (“regimental badge area”). |
| Median | C6–T1 | Most forearm flexors, thenar muscles. | Palmar hand, lateral 3.5 fingers. |
| Radial | C5–T1 | Triceps brachii, posterior forearm extensors. | Posterior arm, forearm, lateral hand. |
| Ulnar | C8–T1 | Intrinsic hand muscles (except thenar), flexor carpi ulnaris. | Medial 1.5 fingers, palm, and dorsum. |
Clinical Relevance
1. Upper Brachial Plexus Injury (Erb’s Palsy)
- Cause: Trauma to C5–C6 roots (e.g., during delivery).
- Nerves Affected: Musculocutaneous, axillary, suprascapular, and nerve to subclavius.
- Presentation: Limb hangs limply in the “waiter’s tip” position due to loss of shoulder abduction, lateral rotation, and elbow flexion.
2. Lower Brachial Plexus Injury (Klumpke’s Palsy)
- Cause: Trauma to C8–T1 roots.
- Nerves Affected: Ulnar and median nerves.
- Presentation: Claw hand deformity due to paralysis of lumbrical muscles.
| Type | Roots Affected | Clinical Features |
|---|---|---|
| Erb’s Palsy | C5–C6 | Waiter’s tip posture. |
| Klumpke’s Palsy | C8–T1 | Claw hand deformity. |
Dissection Insights
- Look for the characteristic “M” shape formed by:
- Musculocutaneous, median, and ulnar nerves.
- This landmark helps in identifying cords and branches.
Points to Remember
- Mnemonic for Plexus Divisions: Read That Damn Cadaver Book (Roots, Trunks, Divisions, Cords, Branches).
- Clinical Mnemonic for Erb’s Palsy: Waiter’s Tip.
- Landmark for Dissection: The “M” shape near the axillary artery.
- Functional Relevance: Each part of the plexus contributes to motor and sensory innervation.
Bibliography
- Moore, K. L., & Dalley, A. F. (2018). Clinically Oriented Anatomy. Wolters Kluwer.
- Drake, R. L., Vogl, W., & Mitchell, A. W. M. (2019). Gray’s Anatomy for Students. Elsevier.