Formation and Structure

The brachial plexus is formed by the anterior rami of spinal nerves C5 to T1. These nerves emerge from the spinal cord and pass through the neck, axilla, and into the arm. The plexus is organized into five key components:

1. Roots: C5, C6, C7, C8, and T1.

2. Trunks: The roots combine to form three trunks:

   • Superior (C5 and C6)

   • Middle (C7)

   • Inferior (C8 and T1)

3. Divisions: Each trunk splits into an anterior and posterior division.

4. Cords: The divisions regroup to form three cords, named based on their position relative to the axillary artery:

   • Lateral

   • Posterior

   • Medial

5. Branches: The cords give rise to the terminal branches, which include:

   • Musculocutaneous nerve

   • Axillary nerve

   • Radial nerve

   • Median nerve

   • Ulnar nerve

Function

The brachial plexus supplies:

• Motor innervation: To the muscles of the shoulder, arm, forearm, and hand.

• Sensory innervation: To the skin of the shoulder and upper limb.

• Autonomic fibers: For vasomotor, pilomotor, and sudomotor functions.

Clinical Relevance

Injuries to the brachial plexus can result in significant functional impairments. Common conditions include:

• Erb's Palsy: Caused by injury to the upper trunk (C5-C6), leading to weakness in shoulder abduction, external rotation, and elbow flexion.

• Klumpke's Palsy: Results from injury to the lower trunk (C8-T1), affecting hand and wrist movements and potentially causing Horner's syndrome.

• Winged Scapula: Due to damage to the long thoracic nerve, leading to paralysis of the serratus anterior muscle.