Spinal Nerves

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton, Kim Jackson and Ahmed M Diab  

Introduction

Formation of spinal nerve from roots of spinal cord

Spinal nerves are mixed nerves that send motor, sensory, and autonomic signals between the CNS and the body, and belong to the peripheral nervous system (PNS).

Humans have 31 left–right pairs of spinal nerves, each roughly corresponding to a segment of the vertebral column: eight cervical spinal nerve pairs, 12 thoracic pairs , five lumbar pairs, five sacral pairs, and one coccygeal pair.

The spinal nerves have a variable course, horizontal in the cervical region and increasingly oblique in an inferolateral direction as the spinal cord descends (due of the growth discordance between the spinal cord and the spine).

Spinal nerves can be impacted by a variety injuries, and cause pain, weakness, or decreased sensation. eg A nerve entrapment occurs when there is pressure or compression of a spinal nerve, and it is the most common spinal nerve disorder; a nerve can be lacerated resulting in cessation of function.

Anatomy

Cervical vertebra, spinal nerve.

Each spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord.

1. The dorsal roots carry afferent sensory axons
2. The ventral roots carry efferent motor axons.

The spinal nerve emerges from the spinal column through in the intervertebral foramen between adjacent vertebrae, where it is surrounded by the dura mater.

Each spinal nerve is a mixed nerve that contains afferent and efferent, somatic and autonomic fibers.

Rami

Spinal Nerve

Once outside the vertebral column, the nerve divides divides.

1. The Dorsal Ramus contains nerves that serve the dorsal portions of the trunk carrying visceral motor, somatic motor, and somatic sensory information to and from the skin and muscles of the back.
2. The Ventral Ramus contains nerves that serve the remaining ventral parts of the trunk and the upper and lower limbs carrying visceral motor, somatic motor, and sensory information to and from the ventrolateral body surface, structures in the body wall, and the limbs.

The meningeal branches branch from the spinal nerve to re-enter the intervertebral foramen to innervating the ligaments, dura, blood vessels, intervertebral discs, facet joints, and periosteum of the vertebrae.

Plexi

The spinal nerves form within a few centimeters of the spine on each side. Some groups of spinal nerves merge with each other to form a large plexus. Some spinal nerves divide into smaller branches, without forming a plexus.

A plexus is a group of nerves that combine with each other. There are five main plexi formed by the spinal nerves:

1. Cervical Plexus
2. Brachial Plexus
3. Lumbar Plexus
4. Sacral Plexus
5. Coccygeal Plexus: Composed of the merging of nerves S4 through Co1, this plexus supplies motor and sensory control of the genitalia and the muscles that control defecation.

Physiotherapy Relevance

Disc Herniation

Spinal nerves can be affected by a number of conditions. These situations can cause pain, sensory changes, and/or weakness. eg:

• Disc Herniation
• Herpes Zoster (Shingles)
• Guilliane Barre Disease
• Trauma eg falls, whiplash
• Multiple Sclerosis