The brachial plexus is a network of nerves that supplies the shoulder, arm, forearm, and hand. It carries motor signals to muscles and sensory signals from the upper limb to the central nervous system.
Understanding brachial plexus anatomy is important for MBBS students and FMGE aspirants because injuries to different parts of this nerve network produce characteristic patterns of muscle weakness and sensory loss.
What Is the Brachial Plexus?
The brachial plexus is formed by the anterior rami of spinal nerves C5, C6, C7, C8, and T1. It provides most of the motor and sensory innervation to the upper limb.
Formation of the Brachial Plexus
The brachial plexus is divided into five main parts:
- Roots: C5, C6, C7, C8, and T1.
- Trunks: Upper, middle, and lower.
- Divisions: Three anterior and three posterior divisions.
- Cords: Lateral, posterior, and medial.
- Terminal branches: Musculocutaneous, axillary, radial, median, and ulnar nerves.
Easy memory trick: Remember R-T-D-C-B: Roots, Trunks, Divisions, Cords, and Branches.
1. Roots of the Brachial Plexus
The roots are formed by the anterior rami of C5–T1.
Important branches arising from the roots include:
- Dorsal scapular nerve: Mainly C5; supplies the rhomboid muscles and contributes to the nerve supply of levator scapulae.
- Long thoracic nerve: C5–C7; supplies the serratus anterior muscle.
Clinical importance: Injury to the long thoracic nerve can cause winging of the scapula.
2. Trunks of the Brachial Plexus
The roots unite to form three trunks:
- Upper trunk: C5 and C6.
- Middle trunk: C7.
- Lower trunk: C8 and T1.
The upper trunk is commonly involved in Erb palsy, while the lower trunk is classically involved in Klumpke palsy.
3. Divisions of the Brachial Plexus
Each trunk divides into an anterior and a posterior division, giving a total of six divisions.
In general, anterior divisions contribute to nerves supplying the anterior compartments of the upper limb, while posterior divisions contribute to nerves supplying the posterior compartments.
4. Cords of the Brachial Plexus
The cords are named according to their relationship to the second part of the axillary artery.
- Lateral cord: Formed by the anterior divisions of the upper and middle trunks.
- Medial cord: Formed by the anterior division of the lower trunk.
- Posterior cord: Formed by the posterior divisions of all three trunks.
5. Terminal Branches of the Brachial Plexus
| Nerve | Main function |
|---|---|
| Musculocutaneous nerve | Elbow flexion through the anterior arm muscles. |
| Axillary nerve | Deltoid function and shoulder abduction, especially from 15° to 90°. |
| Radial nerve | Extension of the elbow, wrist, and fingers. |
| Median nerve | Many forearm flexor functions and thumb opposition. |
| Ulnar nerve | Most intrinsic muscles of the hand. |
Clinical Anatomy of the Brachial Plexus
Erb Palsy
Erb palsy classically results from injury to the upper trunk of the brachial plexus, mainly C5–C6.
- It may occur due to excessive separation of the head and shoulder.
- The characteristic posture is called the waiter's tip position.
- Shoulder abduction, lateral rotation, elbow flexion, and supination may be impaired.
Klumpke Palsy
Klumpke palsy classically involves the lower trunk, mainly C8–T1.
- It may result from excessive upward traction on the upper limb.
- Intrinsic hand muscle weakness may produce a claw-hand deformity.
- Horner syndrome may occur when sympathetic pathways associated with T1 are involved.
Winged Scapula
Injury to the long thoracic nerve weakens the serratus anterior muscle. This can cause the medial border of the scapula to become prominent, particularly when the patient pushes against a wall.
High-Yield FMGE Revision Points
- The brachial plexus is formed by C5–T1.
- The upper trunk is formed by C5–C6.
- The middle trunk is formed by C7.
- The lower trunk is formed by C8–T1.
- Erb palsy involves the upper trunk.
- Klumpke palsy involves the lower trunk.
- Long thoracic nerve injury causes winging of the scapula.
- Axillary nerve injury can cause deltoid weakness and impaired shoulder abduction.
Practice MCQs on the Brachial Plexus
1. The brachial plexus is formed by which spinal nerve roots?
A. C1–C4
B. C5–T1
C. T1–T5
D. C3–C7
Answer: B. C5–T1
2. Erb palsy most commonly involves which part of the brachial plexus?
A. Lower trunk
B. Medial cord
C. Upper trunk
D. Posterior cord
Answer: C. Upper trunk
3. Injury to which nerve commonly causes winging of the scapula?
A. Axillary nerve
B. Long thoracic nerve
C. Radial nerve
D. Musculocutaneous nerve
Answer: B. Long thoracic nerve
4. The cords of the brachial plexus are named in relation to which structure?
A. Clavicle
B. Subclavian vein
C. Axillary artery
D. Humerus
Answer: C. Axillary artery
5. Klumpke palsy classically affects which roots?
A. C5–C6
B. C5–C7
C. C8–T1
D. C3–C4
Answer: C. C8–T1
Frequently Asked Questions
What are the five roots of the brachial plexus?
The five roots are C5, C6, C7, C8, and T1.
Which part of the brachial plexus is affected in Erb palsy?
Erb palsy classically affects the upper trunk, mainly C5–C6.
Which nerve injury causes winging of the scapula?
Injury to the long thoracic nerve can weaken the serratus anterior and cause winging of the scapula.
Why is the brachial plexus important in clinical practice?
Understanding its anatomy helps clinicians localize nerve injuries based on muscle weakness, sensory loss, and other clinical findings.
Conclusion
The brachial plexus is an important nerve network supplying most of the upper limb. Learning its roots, trunks, divisions, cords, and branches makes it easier to understand common nerve injuries and prepare for MBBS and FMGE examinations.
Medical Disclaimer: The information provided in this article is strictly for educational, study, and exam-preparation purposes. It does not constitute professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for clinical decisions.