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Spinal Nerves

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notes

link with arm nerves, leg nerves, bodily senses

Introduction

There are 31 sets of spinal nerves that enter and leave the spinal cord between vertebrae. These provide the majority of communication between the brain and the body - the other means being cranial nerves and hormones. The spinal nerves are classified as follows, depending on their level:

8 cervical nerves
12 thoracic nerves
5 lumbar nerves
5 sacral nerves
1 coccygeal nerve

Composition

Spinal nerves meet the spinal cord as sensory information enters through the dorsal root and motor/autonomic information leaves through the ventral root.

Dorsal Root

main article: bodily senses

The dorsal root contains sensory axons, both from somatic and visceral receptors. These pseudounipolar neurons have their bodies in the dorsal root ganglia. Visceral neurons extend through paravertebral ganglia and white ramus communicantes.

The medial bundle contains large, myelinated fibres (Aα and Aβ) for proprioreceptors and fine touch. These typically enter and ascend ipsilaterally through the dorsal finiculus.

The lateral bundle contains smaller Aδ and C fibres for generally nociception and temperature. These enter and synapse in the dorsal horn substantia gelatinosa.

Ventral Root

main article: motor control

The ventral root is the site of exit of from the spinal cord following synapse of upper motor neurons of the corticospinal tract.

Lower alpha motor neuron axons are distributed peripherally to skeletal muscle.

Autonomic outflow, originating from the lateral horn, leaves the ventral root but leaves the spinal nerve through the white ramus communicantes and enters the paravertebral ganglia, where they can ascend or descend, or synpase.

Axons can leave through the splanchnic nerves and join the pre-vertebral ganglia. They can also leave the gray ramus communicantes to rejoin spinal nerves and innervate blood vessels, glands, hairs.

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