Autonomic Nervous System

Chapter 16
The Autonomic Nervous System
Sympathetic (Thoraco-lumbar) division
Parasympathetic (Cranial-sacral) division

Somatic Motor vs Visceral Motor

Somatic motor is directed from cortical levels to skeletal muscles and is voluntary.
Visceral motor is directed from hypothalamus and midbrain and is involuntary, but has input from cortex and thalamus.
Somatic lower motor neuron is in ventral horn of gray matter and neurotransmitter at skeletal muscle is Ach.
Visceral motor comes from cranial nerves or intermediolateral gray horn, involves 2 neurons and the neurotransmitter is either Ach or NE at either cardiac muscle, smooth muscle or glands.

Somatic motor vs Visceral motor

Visceral reflexes

Unconscious automatic control of visceral activities.

Increased BP

HR decreases

Autonomic Nervous System
Motor nervous system to visceral organs

Two divisions:
1. Sympathetic “Fight, Fright, or Flight”
-Derived from thoracic and lumbar spinal nerves
2. Parasympathetic “Rest, Digest, and Reproduce”
-Derived from cranial and sacral nerves


Sympathetic division

Arise from Thoracic-Lumbar spinal nerves T1-L2
Preganglionic neurons (myelinated)- relatively short


Cell bodies are located in intermediolateral gray column of thoracic and lumbar vertebrae.
Pregnaglionic neurons exit via ventral root → into white ramus communicans → synapse with postganglionic axon in peripheral ganglion at same level or another level.
Neurotransmitter is acetylcholine.

Postganglionic axons (unmyelinated)- relatively long
-Cell bodies in peripheral ganglia extend to visceral organs
■ Distribution is widespread
■ Neurotransmitter is norepinephrine

Sympathetic division

Sympathetic ganglia
Sympathetic postganglionic neuron arises from either:
■ Paravertebral sympathetic chain ganglia.
■ Superior, middle or inferior cervical ganglion.
■ Coeliac ganglion
■ Superior and inferior mesenteric ganglion
■ Inferior hypogastric ganglion
■ Neurotransmitter is

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