# What is the composition and central connections of the spinal nerves?

Gray’s Anatomy (1918) describes the composition and central connections of the spinal nerves as follows: The typical spinal nerve consists of at least four types of fibers, the somatic sensory, sympathetic afferent or sensory, somatic motor and sympathetic efferent or preganglionic.

## What it means

- The typical spinal nerve consists of at least four types of fibers, the somatic sensory, sympathetic afferent or sensory, somatic motor and sympathetic efferent or preganglionic.
- The somatic sensory fibers, afferent fibers, arise from cells in the spinal ganglia and are found in all the spinal nerves, except occasionally the first cervical, and conduct impulses of pain, touch and temperature from the surface of the body through the posterior roots to the spinal cord and impulses of muscle sense, tendon sense and joint sense from the deeper structures.
- The sympathetic afferent fibers, conduct sensory impulses from the viscera through the rami communicantes and posterior roots to the spinal cord. They are probably limited to the white rami connected with the spinal nerves in two groups, viz., the first thoracic to the second lumbar and the second sacral to the fourth sacral nerves.
- The somatic motor fibers, efferent fibers, arise from cells in the anterior column of the spinal cord and pass out through the anterior roots to the voluntary muscles. The sympathetic efferent fibers, probably arise from cells in the lateral column or the base of the anterior column and emerge through the anterior roots and white rami communicantes.
- These are preganglionic fibers which end in various sympathetic ganglia from which postganglionic fibers conduct the motor impulses to the smooth muscles of the viscera and vessels and secretory impulses to the glands. These fibers are also limited to two regions, the first thoracic to the second lumbar and the second sacral to the fourth sacral nerves.
- The afferent fibers which pass into the spinal cord establish various types of connections, some within the cord itself for spinal reflexes, others for reflexes connected with higher centers in the brain, while still others conduct impulses of conscious sensation by a series of neurons to the cerebral cortex.

## Sources

- [Gray's Anatomy of the Human Body (1918)](https://www.bartleby.com/lit-hub/anatomy-of-the-human-body/4d-composition-and-central-connections-of-the-spinal-nerves/)

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