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After studying this chapter, you should be able to:

  • Identify the location of the cell bodies and axonal trajectories of preganglionic and postganglionic sympathetic and parasympathetic neurons.

  • Identify the neurotransmitters and receptor types involved in neurotransmission within the autonomic nervous system and its target organs.

  • Describe how various drugs alter neurotransmitter synthesis, storage, release, and reuptake and receptor activation and blockade within the autonomic nervous system.

  • Describe the ways that the autonomic nervous system contributes to homeostasis.

  • Compare the overall functions of the parasympathetic and sympathetic nervous systems.

  • Compare and contrast the functions of sympathetic and parasympathetic nerves at targets where they act as functional antagonists, synergistically, and independently.

  • Identify the location of forebrain and brainstem neurons and sensory afferents that are involved in the control of the autonomic nervous system.

  • Identify examples of autonomic dysfunction due to primary damage within the autonomic nervous system or as a consequence of other pathologies.

  • Describe the composition and functions of the enteric nervous system.


The autonomic nervous system (ANS) is comprised of the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. The ANS is sometimes called the involuntary nervous system because it carries out its functions without requiring a conscious effort. It influences a wide array of physiological processes via its innervation of smooth muscle, cardiac muscle, and pacemaker cells, exocrine and endocrine glands, adipose tissue, liver cells, and lymphatic tissue. In fact, skeletal muscle is the only innervated part of the body that is not under the control of the ANS. The ultimate responsibility of the ANS is to maintain homeostasis despite perturbations exerted by the external and internal environments. Although survival may be possible without the ANS, the ability to adapt to environmental stressors and other challenges is severely compromised. The ANS also plays a role in the body’s response to an emotional experience. The importance of understanding the functions of the ANS is underscored by the fact that so many prescription and over-the-counter drugs exert their actions on elements of the ANS or its effector targets. Changes in autonomic activity contribute to many diseases (eg, hypertension, heart failure). Also, many neurologic disorders are associated with autonomic dysfunction (Clinical Box 13–1).

CLINICAL BOX 13–1 Multiple System Atrophy & Shy–Drager Syndrome

Multiple system atrophy (MSA) is a neurodegenerative disorder associated with autonomic failure due to loss of preganglionic autonomic neurons in the spinal cord and brainstem. In the absence of an autonomic nervous system, it is difficult to regulate body temperature, fluid and electrolyte balance, and blood pressure. In addition to these autonomic abnormalities, MSA presents with cerebellar, basal ganglia, locus coeruleus, inferior olivary nucleus, and pyramidal tract deficits. MSA is defined as “a sporadic, progressive, adult-onset disorder characterized by autonomic dysfunction, parkinsonism, and cerebellar ataxia in any combination.” Shy–Drager syndrome is a subtype of MSA in which autonomic failure dominates. The ...

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