Autonomic Nervous System

& certain glands
Structures involved
general visceral afferent neurons
general visceral efferent neurons
integration

center within the brain
Receives input from limbic system and other regions of the cerebrum

muscle
one neuron connects CNS to organ
Autonomic nervous system
unconsciously perceived visceral

sensations
involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion
two neurons needed to connect CNS to organ
preganglionic and postganglionic neurons

pathway
Somatic NS pathway only contains one neuron.

cord
axon is myelinated type B fiber that extends to

autonomic ganglion




Postganglionic neuron
cell body lies outside the CNS in an autonomic ganglion
axon is unmyelinated type C fiber that terminates in a visceral effector

slows down organ
Sympathetic NS increases heart rate
Parasympathetic NS decreases heart

rate

and first 2 lumbar segments of spinal cord

Parasympathetic (craniosacral) division
preganglionic

cell bodies in nuclei of 4 cranial nerves and the sacral spinal cord

ganglia near large blood vessel in gut
celiac
superior mesenteric
inferior mesenteric
Parasympathetic

Ganglia
terminal ganglia in wall of organ

communicantes
white ramus = myelinated = preganglionic fibers
gray ramus = unmyelinated

= postganglionic fibers
Postganglionic cell bodies
sympathetic chain ganglia along the spinal column
prevertebral ganglia at a distance from spinal cord
celiac ganglion
superior mesenteric ganglion
inferior mesenteric ganglion

chain & out spinal n
Collateral ganglion route
out splanchnic n to

collateral ganglion

glands, arrector pili mm., blood vessels to skin & skeletal

mm.
Thoracic & cranial plexuses supply:
heart, lungs,esophagus & thoracic blood vessels
plexus around carotid artery to head structures
Splanchnic nerves to prevertebral ganglia supply:
GI tract from stomach to rectum, urinary & reproductive organs

many postganglionic cells
Mass activation due to divergence
multiple target organs
fight or

flight response explained
Adrenal gland
modified cluster of postganglionic cell bodies that release epinephrine & norepinephrine into blood

nerve nuclei in brainstem
S2 to S4 spinal cord
Postganglionic

cell bodies very near or in the wall of the target organ in a terminal ganglia

constrictor muscle inside eyeball
Facial nerve
pterygopalatine and submandibular ganglions
supply tears, salivary

& nasal secretions
Glossopharyngeal
otic ganglion supplies parotid salivary gland
Vagus nerve
many brs supply heart, pulmonary and GI tract as far as the midpoint of the colon

on terminal ganglia in walls of target organs
Innervate smooth muscle

and glands in colon, ureters, bladder & reproductive organs

the neurotransmitter released

Adrenergic


Cholinergic

postganglionic neurons

Action: Excites or inhibits depending upon receptor type and

organ involved

Receptor:
Nicotinic receptors are found on dendrites & cell bodies of autonomic NS cells and at NMJ
Muscarinic receptors are found on plasma membranes of all parasympathetic effectors

Excites or inhibits organs depending on receptors

Receptor:
Alpha1 and Beta1 receptors

produce excitation
Alpha2 and Beta2 receptors cause inhibition
Beta3 receptors (brown fat) increase thermogenesis
NE lingers at the synapse until enzymatically inactivated by monoamine oxidase (MAO) or catechol-O-methyltransferase (COMT)

glands, adrenal medulla, arrector pili mm & many blood vessels

controlled by regulation of the “tone” of the sympathetic system

Most body organs receive dual innervation
innervation by both sympathetic & parasympathetic
Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels

or emotional stress -- “E situations”
emergency, embarrassment, excitement, exercise
Alarm

reaction = flight or fight response
dilation of pupils
increase of heart rate, force of contraction & BP
decrease in blood flow to nonessential organs
increase in blood flow to skeletal & cardiac muscle
airways dilate & respiratory rate increases
blood glucose level increase
Long lasting due to lingering of NE in synaptic gap and release of norepinephrine by the adrenal gland

energy during times of rest
Normally dominate over sympathetic impulses
SLUDD type

responses = salivation, lacrimation, urination, digestion & defecation
3 “decreases”--- decreased HR, diameter of airways and diameter of pupil
Paradoxical fear when there is no escape route or no way to win
causes massive activation of parasympathetic division
loss of control over urination and defecation

Bladder
UT: Kidney
UT: Urinary Bladder
Repro: Sex Organs
Sympathetic

Increase HR
Constriction

Dilation











Ejaculation
Parasympathetic






Increase motility

Glycogenesis

Contraction

Diuresis

Contraction/ urination

Erection










Repro: Sex

Organs

Components of that reflex arc:
sensory receptor
sensory neuron
integrating center
pre & postganglionic

motor neurons
visceral effectors
Unconscious sensations and responses
changes in blood pressure, digestive functions etc
filling & emptying of bladder or defecation

center is in lower regions of the brain
Hypothalamus is major

control center
input: emotions and visceral sensory information
smell, taste, temperature, osmolarity of blood, etc
output: to nuclei in brainstem and spinal cord
posterior & lateral portions control sympathetic NS
increase heart rate, inhibition GI tract, increase temperature
anterior & medial portions control parasympathetic NS
decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility

cord injury above T6
Certain sensory impulses trigger mass stimulation of

sympathetic nerves below the injury
Result
vasoconstriction which elevates blood pressure
parasympathetic NS tries to compensate by slowing heart rate & dilating blood vessels above the injury
pounding headaches, sweating warm skin above the injury and cool dry skin below
can cause seizures, strokes & heart attacka