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PinkMonkey Online Study Guide-Biology

23.2 The Autonomic Nervous System

The central nervous system controls almost all voluntary activities of the animal. The autonomic nervous system controls automatic activities which are free of will (involuntary such as heart beat, breathing, peristalsis etc.) Thus, this system deals with the internal environment of the body (homeostasis). The autonomic nervous system is connected with the central nervous system and is divided into two parts. (1) Sympathetic nervous system and (2) Parasympathetic nervous system. The main structural and functional similarities and differences are given in the following table.

  Sympathetic Nervous System   Parasympathetic Nervous System
1 Contains nerve fibers on which there is no voluntary control. (Involuntary nerve fibers.) 1 ---------- same ----------
2 Nerve fibers emerge from the brain or spinal cord. 2 ---------- same ----------
3 The final nerve fibers supplying organ do not have thick myelin sheath, thus sometimes called non-myelinated fiber. 3 ---------- same ----------
4 The ganglia lie close to the vertebrae/spinal cord. 4 The ganglia are embedded in the wall of effector itself.
5 Pre-ganglionic fibers are short. 5 Pre-ganglionic fibers are long.
6 Post-ganglionic fibers are long. 6 Post-ganglionic fibers are short.
7 Sympathetic fibers are generally activatory. (i.e. increase rate of heart beat.) 7 Parasympathetic fibers are generally inhibitory (i.e. decreases rate of heart beat).
8 Functions antagonistic to para-sympathetic fibers. 8 Functions antagonistic to sympathetic fibers..
9 Terminals of post-ganglionic fibers secrete adrenaline or epinephrin (adrenergic fibers). 9 Terminals of post ganglionic fibers release acteylcholine (cholinergic fibers.)


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Table of Contents


23.0 Introduction
23.1 Central nervous system
23.2 The automatic nervous system
23.3 Receptors and effects
23.4 Reflex action - mechanism of nervous action

Chapter 24





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