The brachial plexus is a complex network of nerves that originates in the neck and provides motor and sensory innervation to the upper limb, including the shoulder, arm, forearm, and hand. Its formation involves the lower four cervical nerves (C5-C8) and the first thoracic nerve (T1), with occasional contributions from C4 or T2.
Structure
- Roots: The brachial plexus originates from the ventral (anterior) rami of spinal nerves C5, C6, C7, C8, and T1. Sometimes there are contributions from C4 and T2 as well.
- Trunks: The roots combine to form three trunks: upper (formed by C5 and C6), middle (formed by C7), and lower (formed by C8 and T1).
- Divisions: Each trunk splits into an anterior and a posterior division. The anterior divisions supply the flexor compartments of the arm and forearm, whereas the posterior divisions supply the extensor compartments.
- Cords: The divisions converge to form three cords named for their relationship to the axillary artery: lateral, posterior, and medial.
- Major Branches: From these cords emanate the five major terminal branches:
- Musculocutaneous nerve
- Median nerve
- Ulnar nerve
- Radial nerve
- Axillary nerve
- Minor Branches: In addition, several smaller branches, like the dorsal scapular, long thoracic, and subscapular nerves, emerge at various points from the plexus to supply the shoulder girdle and chest wall.
Location
- Neck: The brachial plexus originates in the neck, between the anterior and middle scalene muscles.
- Clavicle: It courses laterally and downward, passing over the first rib and under the clavicle.
- Axilla: The plexus extends into the axillary region, where its major branches are given off to supply the upper limb.
- Relations: It is related to important structures like the axillary artery, subclavian artery, and vein, as well as several muscles of the neck and shoulder.
- Terminal Branching: The terminal branches of the brachial plexus continue down the arm and forearm to reach the hand.
Functions
The brachial plexus serves as a critical neural network for the upper limbs, providing both motor and sensory functions.
Motor Functions
- Shoulder Movement: The axillary nerve, originating from the brachial plexus, innervates the deltoid and teres minor muscles, allowing for arm abduction and some aspects of shoulder rotation.
- Arm Flexion and Extension: The musculocutaneous nerve controls arm flexion by innervating the biceps brachii and brachialis muscles. The radial nerve, in contrast, controls arm extension by supplying the triceps brachii.
- Forearm and Wrist Movement: The median and ulnar nerves are crucial for flexor muscle operation, facilitating flexion of the wrist and fingers. The radial nerve is vital for extensor muscle action, facilitating extension and supination of the wrist and fingers.
- Hand Function: The median, ulnar, and radial nerves allow for complex finger movements, facilitating grip and fine motor skills like pinching.
- Scapular Stabilization: The long thoracic and dorsal scapular nerves, minor branches of the brachial plexus, innervate muscles like the serratus anterior and rhomboids that stabilize the scapula during upper limb movements.
Sensory Functions
- Cutaneous Sensation: The brachial plexus contributes sensory fibers that supply the skin over the upper limb, shoulder, and part of the neck.
- Proprioception: Sensory fibers also provide proprioceptive feedback, allowing the brain to understand the spatial orientation of the upper limb, vital for coordinated movement.
- Pain and Temperature: The brachial plexus carries sensory signals for pain, temperature, and touch, contributing to reflex actions and conscious sensations.
Integrated Functions
- Coordinated Movement: The brachial plexus allows for the coordination of complex upper limb movements necessary for activities like eating, writing, and lifting objects.
- Defensive Mechanisms: Through its sensory fibers, the brachial plexus enables reflexive actions like pulling the hand away from a hot surface.
- Communication: The brachial plexus facilitates hand and finger movements, which are critical for non-verbal communication, such as gesturing.
Clinical significance
The brachial plexus holds significant clinical importance due to its essential role in upper limb function.
Diagnostic Importance
Trauma Assessment: In cases of traumatic injury to the shoulder or arm, such as motor vehicle accidents or sports injuries, assessment of brachial plexus integrity is crucial for determining treatment options and predicting outcomes.
Nerve Conduction Studies: Electromyography (EMG) and nerve conduction studies are commonly used to evaluate brachial plexus injuries and various neuropathies.
Clinical Conditions
- Brachial Plexus Injury: This can occur due to stretching, compression, or tearing of the plexus elements, often from trauma. Symptoms range from mild numbness to complete paralysis of the arm.
- Thoracic Outlet Syndrome: Compression of the brachial plexus near the neck and upper chest can cause symptoms like numbness, tingling, and weakness in the arm and hand.
- Erb’s Palsy: This condition usually occurs due to injury during childbirth and involves paralysis of the arm caused by damage primarily to the C5 and C6 roots of the brachial plexus.
Surgical Risks and Considerations
Shoulder and Arm Surgeries: Careful attention must be paid to the brachial plexus during surgeries involving the shoulder and arm to avoid nerve injury, which can lead to motor and sensory deficits.
Nerve Grafts and Transfers: In some cases of severe brachial plexus injury, surgical interventions like nerve grafts or nerve transfers are considered to restore function.
Therapeutic Implications
Pain Management: Understanding the anatomy of the brachial plexus is vital for targeted pain relief therapies, including nerve blocks or medications.
Physical Therapy: For mild to moderate brachial plexus injuries, physical therapy may improve function and promote nerve regeneration.
