Central Nervous System Spinal Cord

The spinal cord lies within the bony vertebral column (Figure 8-36). It is a slender cylinder of soft tissue about as big around as the little finger. The central butterfly-shaped area (in cross section) of gray matter

PART TWO Biological Control Systems

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

II. Biological Control Systems

8. Neural Control Mechanisms

PART TWO Biological Control Systems

© The McGraw-Hill Companies, 2001

Gray matter

I Long neural pathways

Multineuronal pathways

Reticular formation

FIGURE 8-35

Long neural pathways and multineuronal (multisynaptic) pathways and their relationship to the reticular formation.

Dorsal horn

White matter

Spinal cord

Spinal nerve

Gray matter

Dorsal horn

White matter

Spinal cord

Spinal nerve

Dorsal Root Ganglion Function

Dorsal root ganglion

Ventral root

Dorsal root ganglion

Ventral root

Vertebra

FIGURE 8-36

Section of the spinal cord, ventral view. The arrows indicate the direction of transmission of neural activity. %

is composed of interneurons, the cell bodies and dendrites of efferent neurons, the entering fibers of afferent neurons, and glial cells. It is called gray matter because there are more cells than myelinated fibers, and the cells appear gray.

The gray matter is surrounded by white matter, which consists of groups of myelinated axons of in-terneurons. These groups of axons, called fiber tracts or pathways, run longitudinally through the cord, some descending to relay information from the brain to the spinal cord, others ascending to transmit information to the brain. Pathways also transmit information between different levels of the spinal cord.

Groups of afferent fibers that enter the spinal cord from the peripheral nerves enter on the dorsal side of the cord (the side nearest the back of the body) via the dorsal roots (Figure 8-36). Small bumps on the dorsal roots, the dorsal root ganglia, contain the cell bodies of the afferent neurons. The axons of efferent neurons leave the spinal cord on the ventral side (nearest the front surface of the body) via the ventral roots. A short distance from the cord, the dorsal and ventral roots from the same level combine to form a spinal nerve, one on each side of the spinal cord. The 31 pairs of spinal nerves are designated by the four vertebral levels: from which they exit: cervical, thoracic, lumbar, and sacral (Figure 8-37).

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • ghenet
    What is the bump in the dorsal root?
    6 years ago

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