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
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
Unconscious automatic control of visceral activities.
Autonomic Nervous System
Motor nervous system to visceral organs
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
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 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 Norepinephrine (NE), except on
adrenal medulla where it is Ach.
Located on superior pole of each kidney
Outer layer is cortex; central core = medulla
Adrenal medulla is a modified postganglionic
sympathetic ganglion that secretes epinephrine and
norepinephrine (80%/20%) when stimulated.
Adrenal cortex outer layer
Adrenal medulla inner core
Spinal nerves and paravertebral ganglia
White Ramus and Gray Ramus Communicans
White ramus communicans: All sympathetic
preganglionic neurons enter the paravertebral ganglion
chain via the white ramus communicans. They are
white because the nerves are myelinated.
Gray ramus communicans carry unmyelinated
postganglionic sympathetic nerves to peripheral
organs. They are gray because they are unmyelinated.
White Ramus and Gray Ramus
Sympathetic preganglionic neuron routes
Preganglionic neurons may do 1 of 3 things:
Enter the paravertebral ganglion at same level via
white ramus communicans and synapse there.
Enter paravertebral ganglion and either ascend or
descend to another level to synapse at that level.
Pass through the paravertebral ganglion via the white
ramus communicans and synapse in a prevertebral
Preganglionic neuron routes
Cranial/sacral origin; CN- III, VII, IX and X; S2-S4
Preganglionic neurons (myelinated)- relatively long
- synapse with postganglionic axons in ganglia
close to organs
- neurotransmitter is acetylcholine.
Postganglionic axons (unmyelinated)- relatively short
- neurotransmitter is acetylcholine
Distribution is more specific and less diffuse than
Ciliary ganglion → eye
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