17.23: Spinal Nerves: Plexus I
Nerve plexuses are networks of interlacing nerves that serve as communication hubs to distribute and organize nerve action across various body regions. The nerve plexuses are organized into the cervical plexus located in the neck region, brachial plexus in the shoulder area, lumbar plexus found in the lower back, sacral plexus situated in the pelvis, and coccygeal plexus located in the coccygeal region.
The Cervical Plexus
The cervical plexus, formed by the anterior rami of the first four cervical spinal nerves (C1-C4), and partially the fifth cervical spinal nerve (C5), is situated in the neck region. This plexus innervates the skin and muscles of the head, neck, and shoulders, facilitating both sensory and motor functions.
- • Motor Innervation: The phrenic nerve is a primary motor nerve emerging from the cervical plexus. It innervates the diaphragm and is essential in controlling the respiratory process. Without the proper function of this nerve, breathing would be significantly impaired.
Other motor components of the cervical plexus include the ansa cervicalis and segmental branches. The ansa cervicalis innervates some infrahyoid muscles, aiding in swallowing and speech. The segmental branches supply motor fibers to the deep muscles of the neck, contributing to the stability and movement of the head.
- • Sensory Innervation: The cervical plexus also comprises four primary sensory nerves: the lesser occipital, great auricular, transverse cervical, and supraclavicular nerves. These nerves provide sensation to the skin of the neck, ear area, and parts of the shoulder and chest, ensuring sensory input from these regions reaches the central nervous system.
The Brachial Plexus
The brachial plexus extends from the neck into the axilla and is formed by the anterior rami of the fifth to eighth cervical nerves (C5-C8) and the first thoracic nerve (T1). This plexus supplies the shoulder and upper limbs, orchestrating a wide range of movements and sensory functions. The brachial plexus gives rise to five significant nerves:
- • Axillary Nerve: This innervates the deltoid and teres minor muscles, enabling shoulder abduction and playing a role in the sensation of the shoulder area.
- • Musculocutaneous Nerve: This nerve supplies the flexor muscles in the front of the arm, facilitating elbow flexion, and provides sensory information from the lateral forearm.
- • Radial Nerve: By innervating the muscles on the posterior aspect of the upper limb, this nerve supports elbow extension, wrist and finger extension, and thumb abduction. It also conveys sensory input from the posterior arm and hand.
- • Median Nerve: This nerve is primarily responsible for flexing the wrist and fingers, along with thumb opposition. It also carries sensory information from the palmar aspect of the hand.
- • Ulnar Nerve: The intricate movements of the fingers and wrist are controlled by this nerve. It provides sensation to the little finger and part of the ring finger, highlighting its importance in grip and hand movements.
