Anatomy of the Brachial Plexus

Anatomy of the Brachial Plexus

• The brachial plexus is a network of nerves formed by the ventral rami of the lower four cervical and first thoracic spinal nerves (C5, C6, C7, C8, and T1). It has minimal contribution from C4 to T2.
• The brachial plexus involves four main components: roots, trunks, divisions, and cords.
• Roots: Five roots, composed of the anterior primary rami of C5-T1 spinal nerves; located in the neck, behind the anterior scalene muscle.
• Trunks: Three trunks are formed by the fusion of the roots: Upper trunk (C5 and C6), Middle trunk (C7), and Lower trunk (C8 and T1) . They are located in the neck, between the anterior and middle scalene muscles.
• Divisions: Each trunk divides into anterior and posterior divisions, located behind the clavicle.
• Cords: The anterior and posterior divisions of the trunks unite to form three cords: Lateral cord, Medial cord, and Posterior cord situated in the axilla.

Branches of the Brachial Plexus

• From roots: Long thoracic nerve (C5, C6, C7) innervating the serratus anterior muscle; dorsal scapular nerve (C5) innervating the rhomboids. Additional branches supply the scalenus muscles and longus colli (C5, C6, C7, C8). There's also a contribution to the phrenic nerve (C5).
• From trunks: Suprascapular nerve (C5 and C6) and nerve to subclavius (C5 and C6).
• From cords:
  • Lateral cord: Lateral pectoral nerve (C5, C6, C7), lateral root of the median nerve (C5, C6, C7), and musculocutaneous nerve (C5, C6, C7).
  • Medial cord: Medial pectoral nerve (C8 and T1), medial cutaneous nerve of the arm (T1), medial cutaneous nerve of the forearm (C8 and T1), medial root of the median nerve (C8 and T1), and ulnar nerve (C7, C8, and T1).
  • Posterior cord: Radial nerve (C5, C6, C7, C8, and T1), axillary nerve (C5 and C6), thoracodorsal nerve (C6, C7, and C8), upper subscapular nerve (C5 and C6), and lower subscapular nerve (C5 and C6).

Applied Anatomy

• Erb's point: The region where the upper trunk of the brachial plexus is formed at the junction of the C5 and C6 nerve roots. This area is also where the suprascapular and nerve to the subclavius and also where the trunk divides into anterior and posterior divisions.
• Erb's paralysis (upper plexus injury): Caused by excessive stretching of the upper plexus, often during a fall or birth injury. Characterized by adduction of the arm, medial rotation of the arm, extension of the elbow, and pronation of forearm (policeman's tip hand)
• Klumpke's paralysis (lower plexus injury): Caused by hyperabduction of the arm (e.g., fall, certain deliveries). Characterized by claw hand due to paralysis of the flexor muscles of the wrist and fingers (C6, C7, and C8). It also involves loss of sensation along the medial border of the forearm and hand (T1) and sometimes includes Horner's syndrome.

Additional Details

• Surgical approaches to the axilla (armpit) may involve risk to intercostobrachial nerve, long thoracic nerve, thoracodorsal nerve, and thoracodorsal artery when the axillary lymph nodes are removed in breast cancer surgery.