The Autonomic Nervous System

The autonomic nervous system (ANS) is the division of the nervous system that controls the involuntary actions of muscles and glands (Fig. 17-6). The ANS itself has two divisions: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system motivates our response to stress, the so-called "fight-or-flight" response. It increases heart rate and respiration rate, stimulates the adrenal gland, and delivers more blood to skeletal muscles. The parasympathetic system returns the body to a steady state and stimulates maintenance activities, such as digestion of food. Most organs are controlled by both systems and, in general, the two systems have opposite effects on a given organ.

Brain

Brain stem

Cervical enlargement

Spinal cord

Lumbar-

enlargement

Brain

Brain stem

Spinal cord

Lumbar-

enlargement

Sacral Reflex Arc

Lumbar nerves

Sacral nerves (S1-5)

Coccygeal nerve

Lumbar nerves

Sacral nerves (S1-5)

Coccygeal nerve

FIGURE 17-4. Spinal cord from the side, showing the divisions of the spinal nerves.

Cervical Enlargement Spinal Cord
FIGURE 17-5. Cross-section of the spinal cord and pathway of impulses in a reflex arc.

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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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