Transcript Document

THE AUTONOMIC NERVOUS SYSTEM
• Innervates smooth muscle, cardiac muscle
and glands
• Helps to maintain homeostasis
• Also called the involuntary or visceral motor
system
THE AUTONOMIC NERVOUS SYSTEM
• Regulation
– By brainstem, spinal cord, hypothalamus
and parts of the cerebrum
AUTONOMIC GANGLIA AND CIRCUITS
• The motor units of the ANS consist of two neurons:
– Preganglionic Neuron
• Cell body is in the CNS
• Synapses with another neuron before reaching the
effector
• The synapse occurs in an autonomic ganglion outside
the CNS
• (The somatic motor unit consists of one neuron with its
cell body in the CNS and its axon extending to the
effector)
– Postganglionic Neuron
• Extends from the autonomic ganglion in the PNS to the
effector
AUTONOMIC GANGLIA AND CIRCIUTS
CNS
PNS
Effector
THE AUTONOMIC NERVOUS SYSTEM
DIVISIONS OF THE ANS:
The Sympathetic System (see table 14.4)
• Fight or flight system activated in emergency
situations
• Effects:
– Increases heart rate
– Dilates bronchial tubes and pupils
– Constricts blood vessels
– Stimulates secretion of epinephrine and
norepinephrine from the adrenal gland
– Stimulates sweat glands
– Inhibits digestion
– Aids in ejaculation in males
THE SYMPATHETIC SYSTEM
• Neurons
– Emerge through the ventral roots
of spinal nerves T1 through L2
(thoracolumabar outflow)
THE SYMPATHETIC SYSTEM
• Preganglionic Sympathetic
Neurons
– Preganglionic bodies are
in the lateral horns of the
spinal cord at the T1
through L2 levels
– Preganglionic
sympathetic axons are
short
– Preganglionic fibers pass
through the ventral root
into the white rami
communicantes
THE SYMPATHETIC SYSTEM
• Preganglionic Sympathetic
Neurons
– Preganglionic
sympathetic neurons
synapse with a
postganglionic neuron in
the paravertebral chain
ganglia
• Paravertebral chain
ganglia run lateral to the
spinal cord on both
sides
• There are 22 to 23 pair of
paravertebral ganglia on
both sides of the
vertebral column
THE SYMPATHETIC SYSTEM
• Preganglionic
Sympathetic Neurons
– Preganglionic fibers
may ascend or
descend within the
chain to synapse
within a ganglion at a
different level
– Some sympathetic
preganglionic fibers
pass through the
chain ganglion
without synapsing
• These are called
sympathetic
splanchnic nerves
THE SYMPATHETIC SYSTEM
• Preganglionic
Sympathetic Neurons
– Sympathetic
splanchnic nerves
synapse in ganglia
anterior to the
vertebral column (near
the aorta)
– These ganglia are
called prevertebral or
collateral ganglia
– Sympathetic
splanchnics innervate
smooth muscles of the
abdominal and pelvic
viscera and their blood
vessels
THE SYMPATHETIC SYSTEM
• Postganglionic
Sympathetic Neurons
– Post ganglionic
sympathetic axons are
long
– Post ganglionic
sympathetic neurons
exit the paravertebral
ganglia via the gray
rami communicantes
(unmyelinated) and reenter the spinal nerve
– From here they
continue on to the
effector (viscera, blood
vessels, sweat glands)
THE SYMPATHETIC SYSTEM
• All sympathetic preganglionic neurons release acetylcholine
as a neurotransmitter (cholinergic)
• Sympathetic postganglionic neurons release norepinephrine
(adrenergic) with the exception of neurons to blood vessels
and sweat glands (cholinergic)
THE SYMPATHETIC SYSTEM
• Adrenal Medulla
– Preganglionic sympathetic neurons innervate the
adrenal medulla
– Cause release of epinephrine and norepinephrine into
the bloodstream
– Has the same effect as the sympathetic system only
lasts 5 to 10 times longer
THE SYMPATHETIC SYSTEM
• Norepinephrine & Epinephrine
– Norepinephrine and epinephrine both have
similar effects on the body
– Epinephrine has a greater effect on cardiac
stimulation, raising B.P. and increasing
metabolic rate
– Both are secreted by the adrenal medulla in
response to sympathetic stimulation
– Same effect as stimulating organs via
sympathetic nerves only lasts 5 to 10 times
longer
THE PARASYMPATHETIC SYSTEM
• Effects:
– Constricts the pupils and bronchi
– Restores gland and digestive system
activity
– Slows heartrate
THE PARASYMPATHETIC SYSTEM
• Neurons:
– Emerge with the
cranial nerves (III, VII,
IX and X)
– Some emerge with the
sacral spinal nerves
– Craniosacral outflow
Neuron cell bodies for
the fibers traveling
with cranial nerves are
in the brainstem
Cell bodies for the
fibers traveling with
the sacral spinal
nerves are in the
lateral gray horns of
spinal levels S2-S4
C.N. III
C.N. VII
C.N. IX
C.N. X
THE PARASYMPATHETIC SYSTEM
• Preganglionic Parasympathetic
Neurons
– Preganglionic neurons are
long
– Preganglionic neurons travel
from the CNS almost all the
way to the effector before
synapsing with a
postganglionic neuron
THE PARASYMPATHETIC SYSTEM
• Postganglionic
Parasympathetic Neurons
– Postganglionic
parasympathetic neurons are
short
– Postganglionic neurons
synapse with preganglionics
on or near the effector organ
in terminal ganglia
(collectively called
intramural ganglia)
– Postganglionic neurons
travel from the terminal
ganglia to the effector cells
THE PARASYMPATHETIC SYSTEM
• Cranial Outflow
– With C.N. III, VII, IX and
X
– Preganglionic fibers
travel with each cranial
nerve
– Postganglionic fibers
for C.N. III, VII and IX
travel with C.N. X for
distribution to the face
 Vagus nerve
accounts for 90% of
all preganglionic
parasympathetic
fibers in the body
 Parasympathetic
fibers from the Vagus
nerve supply almost
every thoracic and
abdominal organ
C.N. III
C.N. VII
C.N. IX
C.N. X
THE PARASYMPATHETIC SYSTEM
• Sacral Outflow
– Axons run from the spinal
cord with the ventral rami of
S2-S4
– Fibers branch into pelvic
splanchnic nerves
– Most fibers go on to synapse
in intramural ganglia near the
effector organ
– Pelvic splanchnics innervate
the distal large intestine,
urinary bladder, ureters and
reproductive organs
ANS RECEPTORS
• Cholinergic Receptors
– Activated by acetylcholine (Ach)
– Two types:
• Muscarinic
– Found on all effector cells stimulated by postganglionic
cholinergic fibers (all parasympathetic target organs
and some sympathetic)
• Nicotinic
– Found on motor end plates of skeletal muscle
– Found on all postganglionic neurons (sympathetic and
parasympathetic)
– Found on the hormone producing cells of the adrenal
medulla
ANS RECEPTORS
ANS RECEPTORS
• Adrenergic Receptors
– Activated by epinephrine and norepinephrine
– Two types:
• Alpha ()
– Epinephrine has a greater effect on these than
norepinephrine
– Found on all sympathetic target organs except the heart
– Usually stimulatory when NE or Epinephrine binds to them
• Beta ()
– Found in the heart, adipose tissue and most sympathetic
organs
– Usually inhibitory when either hormone binds to them
(except in the heart)
– Cause dilation of blood vessels
ANS RECEPTORS
VISCERAL REFLEXES
• Visceral Reflex Arcs