Chapter 16Chapter 16

The Autonomic Nervous The Autonomic Nervous SystemSystem

Sympathetic (Thoraco-lumbar) Sympathetic (Thoraco-lumbar) divisiondivision

Parasympathetic (Cranial-sacral) Parasympathetic (Cranial-sacral) divisiondivision

Somatic Motor Somatic Motor vsvs Visceral MotorVisceral Motor

Somatic motor is directed from cortical levels Somatic motor is directed from cortical levels to skeletal muscles and is voluntary.to skeletal muscles and is voluntary.

Visceral motor is directed from hypothalamus Visceral motor is directed from hypothalamus and midbrain and is involuntary, but has input and midbrain and is involuntary, but has input from cortex and thalamus.from cortex and thalamus.

Somatic lower motor neuron is in ventral horn Somatic lower motor neuron is in ventral horn of gray matter and neurotransmitter at of gray matter and neurotransmitter at skeletal muscle is Ach.skeletal muscle is Ach.

Visceral motor comes from cranial nerves or Visceral motor comes from cranial nerves or intermediolateral gray horn, involves 2 intermediolateral gray horn, involves 2 neurons and the neurotransmitter is either neurons and the neurotransmitter is either Ach or NE at either cardiac muscle, smooth Ach or NE at either cardiac muscle, smooth muscle or glands.muscle or glands.

Somatic motor vs Visceral Somatic motor vs Visceral motormotor

Visceral reflexesVisceral reflexes

Unconscious automatic control of Unconscious automatic control of visceral activities.visceral activities.

Autonomic Nervous Autonomic Nervous SystemSystem

Motor nervous system to visceral organsMotor nervous system to visceral organs Two divisions:Two divisions:

1.1. Sympathetic “Fight, Fright, or Flight” Sympathetic “Fight, Fright, or Flight”

-Derived from thoracic and lumbar -Derived from thoracic and lumbar spinal nervesspinal nerves

2.2. Parasympathetic “Rest, Digest, and Parasympathetic “Rest, Digest, and Reproduce”Reproduce”

-Derived from cranial and sacral nerves-Derived from cranial and sacral nerves

Sympathetic divisionSympathetic division Arise from Thoracic-Lumbar spinal nerves T1-L2Arise from Thoracic-Lumbar spinal nerves T1-L2 Preganglionic neuronsPreganglionic neurons (myelinated)- relatively (myelinated)- relatively

shortshort- Cell bodies are located in intermediolateral gray Cell bodies are located in intermediolateral gray

column of thoracic and lumbar vertebrae.column of thoracic and lumbar vertebrae.- Pregnaglionic neurons exit via ventral root → into Pregnaglionic neurons exit via ventral root → into

white ramus communicans → synapse with white ramus communicans → synapse with postganglionic axon in peripheral ganglion at same postganglionic axon in peripheral ganglion at same level or another level.level or another level.

- Neurotransmitter is acetylcholine.Neurotransmitter is acetylcholine. Postganglionic axonsPostganglionic axons (unmyelinated)- relatively (unmyelinated)- relatively

longlong-Cell bodies in peripheral ganglia extend to visceral -Cell bodies in peripheral ganglia extend to visceral

organsorgans Distribution is widespreadDistribution is widespread Neurotransmitter is norepinephrineNeurotransmitter is norepinephrine

Sympathetic divisionSympathetic division

Sympathetic gangliaSympathetic ganglia

Sympathetic postganglionic neuron arises Sympathetic postganglionic neuron arises from eitherfrom either::

Paravertebral sympathetic chain ganglia.Paravertebral sympathetic chain ganglia. Superior, middle or inferior cervical Superior, middle or inferior cervical

ganglion.ganglion. Coeliac ganglion Coeliac ganglion Superior and inferior mesenteric ganglionSuperior and inferior mesenteric ganglion Inferior hypogastric ganglionInferior hypogastric ganglion Neurotransmitter is Norepinephrine (NE), Neurotransmitter is Norepinephrine (NE),

except on adrenal medulla where it is Ach.except on adrenal medulla where it is Ach.

Adrenal glandsAdrenal glands

Located on superior pole of each kidneyLocated on superior pole of each kidney Outer layer is cortex; central core = Outer layer is cortex; central core =

medullamedulla Adrenal medulla is a modified Adrenal medulla is a modified

postganglionic sympathetic ganglion that postganglionic sympathetic ganglion that secretes epinephrine and norepinephrine secretes epinephrine and norepinephrine (80%/20%) when stimulated.(80%/20%) when stimulated.

Adrenal cortex outer layerAdrenal cortex outer layer Adrenal medulla inner coreAdrenal medulla inner core

Spinal nerves and Spinal nerves and paravertebralparavertebral gangliaganglia

White Ramus and Gray Ramus White Ramus and Gray Ramus CommunicansCommunicans

White ramus communicans: White ramus communicans: AllAll sympathetic preganglionic neurons enter sympathetic preganglionic neurons enter the paravertebral ganglion chain via the the paravertebral ganglion chain via the white ramus communicans. They are white ramus communicans. They are white because the nerves are myelinated.white because the nerves are myelinated.

Gray ramus communicans carry Gray ramus communicans carry unmyelinated postganglionic sympathetic unmyelinated postganglionic sympathetic nerves to peripheral organs. They are nerves to peripheral organs. They are gray because they are unmyelinated.gray because they are unmyelinated.

White Ramus and Gray White Ramus and Gray Ramus CommunicansRamus Communicans

Sympathetic preganglionic Sympathetic preganglionic neuron routesneuron routes

Preganglionic neurons may do 1 of 3 things:Preganglionic neurons may do 1 of 3 things:

1.1. Enter the paravertebral ganglion at same Enter the paravertebral ganglion at same level via white ramus communicans and level via white ramus communicans and synapse there.synapse there.

2.2. Enter paravertebral ganglion and either Enter paravertebral ganglion and either ascend or descend to another level to ascend or descend to another level to synapse at that level.synapse at that level.

3.3. Pass through the paravertebral ganglion via Pass through the paravertebral ganglion via the white ramus communicans and synapse the white ramus communicans and synapse in a prevertebral ganglion.in a prevertebral ganglion.

Preganglionic neuron Preganglionic neuron routesroutes

Sympathetic gangliaSympathetic ganglia

Parasympathetic divisonParasympathetic divison Cranial/sacral origin; CN- III, VII, IX and X; Cranial/sacral origin; CN- III, VII, IX and X;

S2-S4S2-S4 Preganglionic neurons (myelinated)- Preganglionic neurons (myelinated)-

relatively longrelatively long

- synapse with postganglionic axons in - synapse with postganglionic axons in ganglia ganglia close to organsclose to organs

- neurotransmitter is acetylcholine.- neurotransmitter is acetylcholine. Postganglionic axons (unmyelinated)- Postganglionic axons (unmyelinated)-

relatively shortrelatively short- neurotransmitter is acetylcholine- neurotransmitter is acetylcholine

Distribution is more specific and less diffuse Distribution is more specific and less diffuse than sympatheticthan sympathetic

ParasympatheticParasympathetic

divisiondivision

Parasympathetic gangliaParasympathetic ganglia CN IIICN III = = Ciliary ganglion → eyeCiliary ganglion → eye CN VIICN VII = = Pterygopalatine and submandibular Pterygopalatine and submandibular

ganglion → eye and nasal mucosaganglion → eye and nasal mucosa CN IXCN IX == Otic ganglion → parotid salivary glandOtic ganglion → parotid salivary gland CN XCN X = = To ganglia on each organ (heart, To ganglia on each organ (heart,

lungs, lungs, stomach, pancreas, liver, spleen, small stomach, pancreas, liver, spleen, small and large intestine, rectum, kidneys and and large intestine, rectum, kidneys and urinary bladder).urinary bladder).

S2-S4S2-S4 = = To large intestine, rectum, genitalia, To large intestine, rectum, genitalia, ureters, and urinary bladderureters, and urinary bladder

Neurotransmitter is Ach at pre and postganglionic Neurotransmitter is Ach at pre and postganglionic synapsessynapses

Sympathetic vs Sympathetic vs ParasympatheticParasympathetic

Most organs have dual innervationMost organs have dual innervation In general the actions of one system opposes those In general the actions of one system opposes those

of the other. Ex. Eye; PS →constrict; Sym → dilationof the other. Ex. Eye; PS →constrict; Sym → dilation Both divisions are cooperative in salivary glandsBoth divisions are cooperative in salivary glands Predominant tone is parasympathetic in most Predominant tone is parasympathetic in most

organs.organs. Sym. tone exists solely in adrenal med., sweat Sym. tone exists solely in adrenal med., sweat

glands, piloerector muscles of skin, and many glands, piloerector muscles of skin, and many blood vessels.blood vessels.

Sympathetic distribution tends to be more diffuse Sympathetic distribution tends to be more diffuse whereas parasympathetic is more specific.whereas parasympathetic is more specific.

Overview of dualOverview of dual

innervation of innervation of

Sym vs Parasym.Sym vs Parasym.

SympatheticSympathetic vs vs ParasympatheticParasympathetic

Sympathetic vsSympathetic vs ParasympatheticParasympathetic

Autonomic Autonomic neurotransmittersneurotransmitters

All autonomic preganglionic synapsesAll autonomic preganglionic synapses have Achhave Ach as as the neurotransmitter (nicotinic receptors).the neurotransmitter (nicotinic receptors).

All postganglionic parasympathetic synapsesAll postganglionic parasympathetic synapses have have AchAch as the neurotransmitter (muscarinic receptors). as the neurotransmitter (muscarinic receptors).

Most postganglionic sympathetic synapses have NEMost postganglionic sympathetic synapses have NE as the neurotransmitter (adrenergic receptors).as the neurotransmitter (adrenergic receptors).

Sympathetic preganglionic neurotransmitter at Sympathetic preganglionic neurotransmitter at adrenal medulla is Achadrenal medulla is Ach (nicotinic receptor) → (nicotinic receptor) → release of Epi. and NE (80/20).release of Epi. and NE (80/20).

Sympathetic postganglionic neurotransmitter at Sympathetic postganglionic neurotransmitter at sweat glands is Achsweat glands is Ach (muscarinic receptors). (muscarinic receptors).

Autonomic Autonomic neurotransmittersneurotransmitters