Transcript No Slide Title

Learning Objectives:
Describe the anatomical differences between
the sympathetic and parasympathetic nervous systems
Describe the differences in the neurotransmitters and their
receptors between the two systems
Describe how the sympathetic and parasympathetic systems
differ in their regulation of the major organ systems
Understand the nature of sympathetic and parasympathetic tone
Autonomic Nervous System
(Involuntary or Visceral Nervous System)
I.
II.
III.
IV.
Function --Overview
Anatomy
Neurotransmitters and receptors
Specific Organ Effects
I. Function-- Overview
Autonomic nervous system controls
involuntary functions:
•arterial pressure
•gastrointestinal motility
•gastrointestinal secretion
•urinary bladder emptying
•sweating
•body temperature
•pupilary dilation and constriction
Striking feature of the ANS is the rapidity and
intensity with which it can change visceral functions
(3-5 seconds)
nervous system
Peripheral
nervous system
Central
nervous system
Autonomic
nervous system
Somatic
nervous system
Parasympathetic
nervous system
Sympathetic
nervous system
Peripheral nervous system
Autonomic
nervous system
Somatic
nervous system
Innervates heart, blood vessels, visceral organs, glands,
and virtually all other organs with smooth muscle;
regulates function of these organs in a
manner beyond conscious (involuntary or automatic) control
Nerves innervating the skeletal muscles;
activity is under conscious (voluntary) control
Autonomic nervous system
Parasympathetic
nervous system
“rest and digest”
Sympathetic
nervous system
“Fight or flight”
ANATOMY
ANS is activated by centers located in spinal cord
brain stem and hypothalamus
ANS often operates by visceral reflexes:
subconscious sensory signals from visceral organs
can enter the spinal cord, brainstem or
hypothalamus and then return subconscious
reflex responses directly back to the visceral
organ to control its activities
ANATOMY
Autonomic nerves are composed of two neuron relays.
Preganglionic neurons have their cell bodies in the spinal cord
and their activity is controlled by higher brain centers
and spinal reflexes.
Postganglionic neurons send their axons directly to the
effector organ.
Spinal cord
ganglia
Preganglionic neuron
Postganglionic neuron
organ
Sympathetic Nervous System
1) preganglionic nerves leave spinal cord at the
thoracic and lumbar levels
2) preganglionic axons are short and myelinated
3) postganglionic axons are long and unmyelinated
4) ganglia are located near the spinal cord
Sympathetic nervous system.
Parasympathetic Nervous System
1) Nerves leave spinal cord at cranial and sacral levels
• cranial nerves innervate head, neck, thorax,
and abdomen
• sacral division forms the pelvic nerve and innervates the
remainder of the intestines, bladder and
reproductive organs
2) Preganglionic axons are myelinated and extremely long
3) Postganglionic axons are unmyelinated and short
4) Postsynaptic ganglia located near the effector organ
Parasympathetic nervous system
cranial
sacral
Next…………...
Neurotransmitters and receptors
ALL PREGANGLIONC AXONS USE ACETYLCHOLINE
AS THEIR NEUROTRANSMITTER
BUT…………….
Parasympathetic Postganglionic axons
release acetylcholine
Sympathetic Postganglionic axons
release norepinephrine
accept axons on sweat glands, piloerector muscles
of the hairs, and some blood vessels which release
acetylcholine
Adrenal medulla
Stimulation of sympathetic innervation of adrenal medulla
causes release of large quantities of epinephrine (80%)
and norepinephrine (20%)
Cholinergic receptors
Nicotinic
Muscarinic
Ganglionic Skeletal Neuronal
muscle
CNS
M1
M3 M5
M2
M4
Adrenergic receptors
a1
a1A a1B
a2
a1D
a2A a2B
b
a2C
b1
b2
b3
Receptors in the parasympathetic system
Nicotinic receptor
Muscarinic receptor
Neuroscience, Sinauer Asssoc., Inc
Adrenergic receptors in the sympathetic system
a1
a2
Neuroscience, Sinauer Asssoc., Inc
List of relevant receptors and their messengers
Cholinergic receptors:
nicotinic receptor--- ligand-gated ion channel
muscarinic receptor--- G-protein coupled receptor
Adrenergic receptors:
alpha (a1 and a2) receptors
a1: Gq increase in PI turnover
a2: Gi inhibition of adenylate cyclase
beta (b1 and b2) receptors
b1 b2: Gs stimulation of adenylate cyclase
Adrenergic receptors:
alpha (a1 and a2) receptors
a1: Gq
increase in PI turnover
a2: Gi
inhibition of adenylate cyclase
beta (b1 and b2) receptors
b1 b2: Gs
stimulation of adenylate cyclase
NE and Epi have same potency at a1 receptors
b receptors are much more sensitive to catecholamines
than a1 receptors
NE and Epi are equipotent at b1 receptors
b2 receptors are preferentially activated by Epi
a1 receptors:
vascular smooth muscle, on GI and bladder sphincters, and radial
muscle of the eye
cause excitation (contraction)
Gq
IP3
a2 receptors
presynaptic nerve terminals, platelets, fat cells, walls of GI tract
cause inhibition (relation, dilitation)
inhibition of adenlyate cyclase and decrease in cAMP
b1 receptors
SA node, AV node, ventricular muscle of heart
produce excitation (increaes heart rate, contactility, increased conduction
velocity
stimulation of adenylate cyclase and increase in cAMP
b2 receptors
vascular smooth muscle of skeletal muscle, bronchioles, walls fo Gi tract and
bladder
produce relaxation (dilation of vascular smooth muscle and bronchioles,
relaxation of bladder wall)
stimulation of adenylate cyclase and increase in cAMP
Comparison of the Components of the
Peripheral Nervous System
Parasympathetic Nervous System
Preganglionic
Neuron
Synaptic connection
Neuron length
Neurotransmitter
Ganglion near organ
Long
Acetylcholine
Postganglionic
Neuron
At organ
Short
Acetylcholine
Sympathetic Nervous System
Preganglionic
Neuron
Postganglionic
Neuron
Synaptic connection
Ganglion near spinal cord
At organ
Neuron length
Short
Acetylcholine
Long
Norepinephrine
Neurotransmitter
Somatic Motor Nervous System
Synaptic connection
Neuron length
Neurotransmitter
At skeletal muscle
Long
Acetylcholine
Organs are usually innervated by both systems
in opposing roles
Sympathetic Nervous System
Receptors at Target Organs
Organ
Action
Receptor
Heart
heart rate
contactility
AV node conduction
Vascular smooth
muscle
constrict blood vessels
dilates blood vessels
in skeletal muscles
Gastrointestinal
Tract
motility
constricts sphincters
a2, b2
Bronchioles
dilates bronchiolar
b2
pupil
dilation
a1
b1
a1
smooth muscle
Bladder
relaxes bladder wall
constricts sphincter
b2
a
Sympathetic Nervous Con’t
organ
sweat glands
goose bumps
action
sweating
contracts
receptor
muscarinic
a
kidney
renin secretion
b1
Male genitalia
ejaculation
a
fat cells
lipolysis
b1
Parasympathetic Action
Organ
Heart
Action
heart rate
contractility
AV node conduction
Receptor
M
Gastrointestinal
Tract
motility
relaxes sphincters
Bronchioles
constricts
M
Male sex organs
erection
M
Bladder
Pupil
contracts wall
relaxes sphincter
constriction
M
M
M
Ganglionic blockers
These drugs block both divisions of the autonomic nervous system
equally.
However, the end-organ response may show a predominant adrenergic
or cholinergic. Therefore interruption of ganglionic transmission has
the effect of selectively eliminating the dominant component.
Sympathetic and Parasympathetic
“tone”
Continual basal activity of the sympathetic
and parasympathetic systems allows either branch
of the ANS to increase or decrease its activity
of a stimulated organ
Sympathetic tone caused by basal secretion
from adrenal medulla
Denervation supersensitivity
Guyton and Hall fig 60-4
“Alarm” or “Stress” Response
Large portions of the sympathetic nervous system discharge
simultaneously-----this increases the body’s ability to perform
vigorous muscle activity
Increased arterial pressure
Increased blood flow to the skeletal muscles with concurrent decrease
blood flow to GI tract, kidneys
Increased metabolism
Increased blood glucose concentration
Increased glycoglysis in liver and muscle
Increased muscle strength
Increased mental activity
Increased rate of blood coagulation
Autonomic Reflexes
cardiovascular reflexes
gastrointestinal reflexes
bladder emptying
sweating
blood glucose concentration
sexual reflexes
Enteric Nervous System
Gastrointestinal tract nervous system
Myenteric plexus (auberbach’s)
meissner’s plexus (submucosal)
Sympathetic and Parasympathetic systems
interact with the Enteric System
Acetylcholine most often excites and
Norepinephrine inhibits