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Related Subjects: |Radial Nerve |Median Nerve |Ulnar Nerve |Musculocutaneous nerve |Axillary nerve |Brachial plexus |Dermatomes

Overview of the Brachial Plexus

The brachial plexus is a complex network of nerves that originates from the spinal cord in the neck and provides motor and sensory innervation to the shoulder, arm, forearm, and hand.

Anatomy of the Brachial Plexus

• Roots:
  • Formed by the anterior rami of spinal nerves C5, C6, C7, C8, and T1.
• Trunks:
  • Upper Trunk: Formed by the union of the C5 and C6 roots.
  • Middle Trunk: Continuation of the C7 root.
  • Lower Trunk: Formed by the union of the C8 and T1 roots.
• Divisions:
  • Each trunk splits into an anterior and a posterior division.
• Cords:
  • Formed by the recombination of the anterior and posterior divisions.
    • Lateral Cord: Formed by the anterior divisions of the upper and middle trunks.
    • Posterior Cord: Formed by the posterior divisions of all three trunks.
    • Medial Cord: Formed by the anterior division of the lower trunk.
• Terminal Branches:
  • Musculocutaneous Nerve: Arises from the lateral cord; innervates the biceps brachii, brachialis, and coracobrachialis muscles.
  • Axillary Nerve: Arises from the posterior cord; innervates the deltoid and teres minor muscles.
  • Radial Nerve: Arises from the posterior cord; innervates the triceps brachii and the extensor muscles of the forearm and hand.
  • Median Nerve: Formed from contributions of the lateral and medial cords; innervates most of the flexor muscles of the forearm and some muscles of the hand.
  • Ulnar Nerve: Arises from the medial cord; innervates the flexor carpi ulnaris, part of the flexor digitorum profundus, and most of the intrinsic hand muscles.

Functions of the Brachial Plexus

• Motor Innervation:
  • Provides motor innervation to the muscles of the shoulder, arm, forearm, and hand.
• Sensory Innervation:
  • Provides sensory innervation to the skin of the shoulder, arm, forearm, and hand.

Clinical Relevance

• Brachial Plexus Injuries:
  • Can result from trauma, compression, or stretching of the nerves.
  • Erb's Palsy: Injury to the upper trunk (C5-C6); causes weakness in the shoulder and upper arm muscles.
  • Klumpke's Palsy: Injury to the lower trunk (C8-T1); affects muscles of the forearm and hand, leading to claw hand deformity.
• Thoracic Outlet Syndrome:
  • Compression of the brachial plexus nerves and/or blood vessels as they pass through the thoracic outlet.
  • Symptoms: Pain, numbness, and weakness in the arm and hand.
• Winged Scapula:
  • Caused by damage to the long thoracic nerve, a branch of the brachial plexus that innervates the serratus anterior muscle.
  • Results in the protrusion of the scapula from the back, especially when pushing against resistance.
• Carpal Tunnel Syndrome:
  • Compression of the median nerve within the carpal tunnel.
  • Symptoms: Numbness, tingling, and weakness in the hand, particularly affecting the thumb, index, and middle fingers.

Diagnostic Techniques

• Physical Examination:
  • Assessment of motor function and sensation in the upper limb.
• Electromyography (EMG) and Nerve Conduction Studies:
  • Evaluate the electrical activity of muscles and the speed of nerve conduction.
• Imaging Studies:
  • Magnetic Resonance Imaging (MRI) and ultrasound can visualize the brachial plexus and identify structural abnormalities.

Summary

The brachial plexus is a complex network of nerves that provides motor and sensory innervation to the upper limb. It consists of roots, trunks, divisions, cords, and terminal branches. Understanding its anatomy and functions is crucial for diagnosing and managing conditions related to nerve injuries and compressions.