Autonomic Nervous System ANS

-is a set of efferent pathways from the central nervous system (CNS) that innervates and regulates smooth muscle, cardiac muscle, and glands.

- is distinct from the somatic nervous system, which innervates skeletal muscle.

- has three divisions: sympathetic, parasympathetic, and enteric (the enteric division is discussed in Chapter 6).

A. Organization of the ANS (Table 2-1 and Figure 2-1)

1. Synapses between neurons are made in the autonomic ganglia.

Table 2-1. Organization of the Autonomic Nervous System

Characteristic

Sympathetic

Parasympathetic

Somatic*

Origin of preganglionic nerve

Nuclei of spinal cord segments T1-T12; Ll-L3 (thoracolumbar)

Nuclei of cranial nerves III, VII, IX, and X; spinal cord segments S2-S4 (craniosacral)

Length of preganglionic nerve axon

Short

Long

Neurotransmitter in ganglion

ACh

ACh

Receptor type in ganglion

Nicotinic

Nicotinic

Length of postganglionic nerve axon

Long

Short

Effector organ

Smooth and cardiac muscle; glands

Smooth and cardiac muscle; glands

Skeletal muscle

Neurotransmitter in effector organ

Norepinephrine (except sweat glands, which use ACh)

ACh

ACh (synapse is neuromuscular junction)

Receptor type in effector organ

<*ii «2, ßi. and ß2

Muscarinic

Nicotinic

•Somatic nervous system has been included for comparison. ACh = acetylcholine.

•Somatic nervous system has been included for comparison. ACh = acetylcholine.

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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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