15.THE AUTONOMIC NERVOUS SYSTEM AND HOMEOSTASIS

15. THE AUTONOMIC NERVOUS SYSTEM

THE AUTONOMIC NERVOUS SYSTEM AND HOMEOSTASIS

• The autonomic nervous system contributes to homeostasis by responding to subconscious visceral sensations and exciting or inhibiting smooth muscle, cardiac muscle, and glands. 

As you learned in Chapter 12,

• the peripheral nervous system (PNS) includes cranial and spinal nerves 
• and is divided into 

1. a somatic nervous system (SNS),
2. autonomic nervous system (ANS), 
3. and enteric nervous system (ENS). 

• Like the somatic nervous system, the autonomic nervous system (ANS) operates via reflex arcs. 

• Structurally, the ANS includes 

1. autonomic sensory neurons, 
2. integrating centers in the CNS, 
3. and autonomic motor neurons. 

• A continual flow of nerve impulses from

 (1) autonomic sensory neurons in visceral organs and blood vessels propagate into 
(2) integrating centers in the central nervous system (CNS).
Then, impulses in (3) autonomic motor neurons propagate to various effector tissues, 

• thereby regulating the activity of smooth muscle, cardiac muscle, and many glands. 

• The ANS usually operates without conscious control. 

The system was originally named autonomic 

• because it was thought to function autonomously or in a self-governing manner, without control by the CNS.
• However, centers in the hypothalamus and brain stem do regulate ANS reflexes.

• In this chapter, we compare structural and functional features of the somatic and autonomic nervous systems. 
• Then we discuss the anatomy of the motor portion of the ANS 
• and compare the organization and actions of its two major parts, the sympathetic and parasympathetic divisions.