Brachial plexus

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Brachial plexus

The brachial plexus is a network of nerves that originate from the spinal cord in the neck and travel down the arm. It is responsible for the sensory and motor innervation of the upper limb. The brachial plexus is formed by the anterior rami of the lower four cervical nerves (C5-C8) and the first thoracic nerve (T1).

Anatomy

The brachial plexus is divided into five main parts: roots, trunks, divisions, cords, and branches.

Roots

The roots of the brachial plexus are the anterior rami of the spinal nerves C5, C6, C7, C8, and T1. These roots pass between the anterior scalene muscle and the middle scalene muscle.

Trunks

The roots combine to form three trunks:

• The upper trunk is formed by the union of the C5 and C6 roots.
• The middle trunk is a continuation of the C7 root.
• The lower trunk is formed by the union of the C8 and T1 roots.

Divisions

Each trunk then splits into an anterior division and a posterior division. These divisions will eventually give rise to the cords.

Cords

The divisions regroup to form three cords, named according to their position relative to the axillary artery:

• The lateral cord is formed by the anterior divisions of the upper and middle trunks.
• The posterior cord is formed by all three posterior divisions.
• The medial cord is formed by the anterior division of the lower trunk.

Branches

The cords give rise to the major nerves of the upper limb:

• The musculocutaneous nerve (from the lateral cord)
• The axillary nerve (from the posterior cord)
• The radial nerve (from the posterior cord)
• The median nerve (from both the lateral and medial cords)
• The ulnar nerve (from the medial cord)

Function

The brachial plexus is responsible for the motor and sensory innervation of the upper limb. It controls the muscles of the shoulder, arm, forearm, and hand, and provides sensation to the skin of these regions.

Clinical Significance

Injuries to the brachial plexus can result in loss of function and sensation in the upper limb. Common causes of brachial plexus injuries include trauma, such as from a motorcycle accident or a birth injury. Conditions such as brachial plexopathy and thoracic outlet syndrome can also affect the brachial plexus.

See Also

• Nervous system
• Peripheral nerve injury
• Neuroanatomy
• Upper limb anatomy