The lowest level of the central nervous system (CNS), anatomically and functionally, is the spinal cord. Continuous with the brainstem, it exits the skull through the foramen magnum. The spinal cord then passes through the vertebral canal of the vertebral column to the level of the first or second lumbar vertebrae. The spinal cord is divided into four anatomical regions: cervical, thoracic, lumbar, and sacral. These regions are named according to the vertebrae adjacent to them during embryonic development. Each region is subdivided into functional segments. A pair of spinal nerves extends from each segment (one nerve from the left side of the spinal cord and one nerve from the right ) and exits the CNS through the intervertebral foramina, or openings between adjacent vertebrae. There are a total of 31 pairs of spinal nerves:

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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