Download The Autonomic Nervous System

The Autonomic Nervous System
Basic
Setup of the Nervous
System
Nervous Tissue
Peripheral Nervous
System
Spinal and Cranial
Nerves
Central Nervous
System: Integration
and Command
Brain
Spinal Cord
Sensory
Sensory
Skin, skeletal
muscle and joints
Motor
Visceral
Visceral Organs
Somatic:
Control of skeletal
muscles
Autonomic:
Regulates smooth
muscle, cardiac
muscle and glands
Sympathetic:
Fight or Flight
Parasympathetic
Rest and Digest
Basic
Setup of the Nervous
System
Nervous Tissue
Peripheral Nervous
System
Spinal and Cranial
Nerves
Sensory
Sensory
Skin, skeletal
muscle and joints
Motor
Visceral
Visceral Organs
Somatic:
Control of skeletal
muscles
Autonomic:
Regulates smooth
muscle, cardiac
muscle and glands
Sympathetic:
Fight or Flight
Parasympathetic
Rest and Digest
What does the ANS do?
• Certain fairly slow, bodily functions are so
routine, we can have them operate without
conscious control
• Occasionally, things
happen that require
instantaneous diversion
of energy
• Stop doing the routine and
shift resources into escape.
Hurry Up and Wait Things
How does the ANS
work?
• The ANS consists of
motor neurons that:
– Innervate smooth
and cardiac muscle
and glands
– Operate via
subconscious control
– Have viscera as
most of their
effectors
Motor
Somatic:
Control of skeletal
muscles
Autonomic:
Regulates smooth
muscle, cardiac
muscle and glands
Comparison of Somatic
and Autonomic Systems
ANS Versus Somatic
Nervous System (SNS)
• The ANS differs from the SNS in the
following three areas
– Effectors
• Who
– Efferent pathways
• How are the
neurons arranged
– Target organ responses
• What: excitatory or inhibitory
Effectors
SNS
ANS
Skeletal muscles
Cardiac muscle
Smooth muscle
Glands
Efferent Pathways
SNS
ANS
• Heavily myelinated
axons of the somatic
motor neurons extend
from the CNS to the
effector
• Axons of the ANS are a
two-neuron chain
– The preganglionic (first)
neuron has a lightly
myelinated axon
– The ganglionic (second)
neuron extends to an
effector organ
Target Organ Response
SNS
• All somatic motor
neurons release
Acetylcholine (ACh),
which has an
excitatory effect
ANS
• Preganglionic fibers
release ACh
• Postganglionic fibers
release norepinephrine
or ACh and the effect is
either stimulatory or
inhibitory
• ANS effect on the
target organ is
dependent upon the
neurotransmitter
released and the
receptor type of the
effector
Review: Somatic vs. Autonomic
efferent neurons
Somatic
Autonomic
Voluntary
Effectors: Skeletal M.
Involuntary
Effectors: Cardiac M.
Smooth M
Glands
Neurons extend from
CNS to effectors
without synapsing.
Two neurons to get from
CNS to effectors; therefore
one synapse.
"Two neuron chain"
Comparison of Somatic and
Autonomic Systems
Comparison of Somatic and
Autonomic Systems
Things this figure points
out:
1. Myelination
2. One- vs. two-neuron
chain
3. Length of pre- and
post-ganglionic
neurons
4. Effector organs
5. Neurotransmitters
Adrenal Glands
Divisions of the ANS
• The two divisions of the ANS are the sympathetic
and parasympathetic
• Basically, the sympathetic mobilizes the body
during extreme situations.
• Basically, the parasympathetic performs
maintenance activities and conserves body energy
• The two divisions counterbalance each other’s
activity (for the most part).
Parasympathetic: Rest and Digest
Sympathetic: Fight or Flight
Role of the
Parasympathetic
Division
• Concerned with keeping body
energy use low
• Involves the D activities – digestion, defecation,
and diuresis
• Its activity is illustrated in a person who relaxes
after a meal (Thanksgiving)
Role of the
Parasympathetic
Division
– Blood pressure is low
– Heart rate is low
– Respiratory rates are low
– Gastrointestinal tract activity is high
– The skin is warm because the blood is in the
skin
– The pupils are constricted
Role of the
Sympathetic
Division
• The sympathetic division
is the “fight-or-flight” system (Big Dog)
• Involves E activities – exercise, excitement,
emergency, and embarrassment
Role of the
Sympathetic Division
• Promotes adjustments during exercise –
– blood flow to organs is reduced,
– flow to muscles is increased
• Its activity is illustrated by a person who is
threatened
– Heart rate increases
– Breathing is rapid and deep
– The skin is cold and sweaty: the blood is in the
muscles, not in the skin.
– The pupils dilate: “to better see you with”
Anatomy of ANS: Sympathetic vs.
Parasympathetic
• There are two main
differences in the
anatomy of the
sympathetic and
parasympathetic
systems.
– Where the ganglia (or
second synapses) are.
– Where they exit the
spinal cord
Location of Ganglia
• Parasympathetic
Ganglia (synapses)
are on the target
organ
• Sympathetic Ganglia
(synapses) are near
the spinal cord
Anatomy of ANS
Parasympathetic
exits either in:
a. cranial
nerves
b. sacrally
Sympathetic
exits from
T1- L2
Parasympathetic Division Outflow
Cranial Cranial
Outflow Nerve
Occulomotor
(III)
Facial (VII)
Glossophary
ngeal (IX)
Vagus (X)
Sacral
S2-S4
Outflow
Ganglion
Ciliary
Effector
Organ(s)
Constricts iris
Pterygopalatin Salivary, nasal,
Submandibular and lacrimal
glands
Otic
Parotid salivary
glands
Located within
the walls of
target organs
Located within
the walls of the
target organs
Heart, lungs,
and most
visceral organs
Large intestine,
urinary bladder,
ureters, and
reproductive
organs
Sympathetic Outflow
Sympathetic Chain
Ganglia
Cardiac and
Pulmonary
Plexuses
Splanchnic
Nerves
Pre Post
Ganglionic
Sympathetic
Outflow
• Arises from spinal
cord segments T1
through L2
• Sympathetic neurons produce the
lateral horns of the spinal cord
• Postganglionic fibers innervate the
numerous organs of the body
Sympathetic Chain
• Sympathetic
neurons go up and
down the
sympathetic chain,
in order to provide
reduncancy.
Visceral Reflexes
• Some people consider the
autonomic nervous system to be a
purely motor system, despite the
presence of the sensory neurons.
• Clearly, because
there are autonomic
reflexes, there
has to be a
sensory
component
Sweating
Visceral Reflexes
Referred Pain
• Pain stimuli
arising from the
viscera are
carried in
sympatheric
nerves.
• Often visceral
pain is perceived
as somatic in
origin
Referred Pain
• This may be
due to the
fact that
visceral pain
afferents
“piggyback”
on somatic
pain fibers
Interactions of the Autonomic
Divisions
• The parasympathetic and
sympathetic nervous systems
interact in three ways;
– Antagonism
– Tone
– Cooperatively
You don’t want a picture 
Antagonism between the
Autonomic Divisions
• Most visceral
organs are
innervated by both
sympathetic and
parasympathetic
fibers
• This results in
dynamic
antagonisms that
precisely control
visceral activity
Antagonism between the
Autonomic Divisions
• Heart:
– Sympathetic increases rate & force
– Parasympathetic decreases rate & force
• Lungs
– Sympathetic dilates air passages
– Parasynpathetic constricts air passages
• Digestive System
– Sympathetic decreases activity
– Parasympathetic increases activity
• Urinary System
– Sympathetic inhibits urination
– Parasympathetic promotes urination
ANS Tone
• Tone can be considered to be a
system acting on it own.
– Increased tone means increased
activity
– Decreased tone means decrease activity.
• It’s a bit like a gas pedal, you control “activity” by
how much you press.
– Pedal to the metal equals a lot of sympathetic activity.
– Foot off the gas means less sympathetic activity.
• Both sympathetic tone and parasympathetic
tone exist.
Sympathetic Tone
• The sympathetic division controls blood
pressure and keeps the blood vessels in a
continual state of partial constriction
• This sympathetic tone (vasomotor tone):
– Constricts blood vessels and causes blood
pressure to rise as needed
– Prompts vessels to dilate if blood pressure is
to be decreased
Sympathetic Tone
Increased Tone =
Vasoconstriction
“Tone up the muscle”=
constriction
Decreased Tone =
Vasodilation
Parasympathetic
Tone
• Parasympathetic tone:
– Slows the heart
– Dictates normal activity
levels of the digestive and
urinary systems
• The sympathetic division
can override these effects
during times of stress
Parasympathetic Tone
Increase Tone =
Decrease HR
Decreased Tone =
Increase HR
Cooperation between
the Autonomic
Divisions
• ANS cooperation is best seen in control of
the external genitalia
• Parasympathetic fibers cause vasodilation
and are responsible for erection of the
penis and clitoris
• Sympathetic fibers cause
ejaculation of semen in males
and reflex peristalsis in females
Neurotransmitters and
Receptors
• Acetylcholine (ACh) and norepinephrine
(NE) are the two major neurotransmitters
of the ANS
• Cholinergic fibers – ACh-releasing fibers
• Adrenergic fibers – NE-releasing fibers
Neurotransmitters and
Receptors
• Cholinergic fibers –
– All preganglionic axons
– All parasympathetic postganglionic axons
– May bind to two different receptors
• Nicotinic
• Muscarinic
• Adrenergic fibers –
– Sympathetic postganglionic axons
Neurotransmitter Comparison of
Somatic and Autonomic Systems
• Cholinergic fibers
• All preganglionic
axons
• All
parasympathetic
postganglionic
axons
• May bind to two
different
receptors
– Nicotinic
– Muscarinic
nAChR
NE
mAChR
• Adrenergic fibers –
– Sympathetic postganglionic axons
Neurotransmitter Comparison of
Somatic and Autonomic Systems
nAChR
NE
mAChR
The cell bodies of postganglionic autonomic fibers are located in:
ANS Neurotransmitters
• Neurotransmitter effects can have different
effects on different targets.
• Different effects are due to different receptors
(α1, α2 ,β1, β2)
– NTs can be excitatory or inhibitory depending upon
the receptor type. In adrenergic receptors, α1 is
stimulatory and α2 is inhibitory
– Different organs carry different receptors. For
example, there are α NE receptors in blood vessels
and β NE receptors in cardiac muscle.
• This allows pharmaceutical targeting.
Noradrenergic Receptors
Two main types ( and ) and subdivisions:
Adrenergic Receptor Types
• Alpha 1:
• In walls of blood
vessels leading to
places other than
skeletal muscles,
brain & lungs.
• Not on heart (cardiac
muscle)
• Alpha 2:
• On membranes of
platelets.
• Beta 1:
• On heart (cardiac
muscle) & kidneys
• Beta 2:
• On coronary
arteries, bronchioles
& on smooth muscle
walls of digestive &
urinary systems
Allows stimulation of some
things (bronchodilation)
without affecting heart
rate.
Adrenergic Receptor Effects
• Alpha 1:
• Excites (constricts)
smooth muscles in
certain blood vessels
& in spincters
directing blood to
skeletal muscles
• Dilates pupils.
• Alpha 2:
• Promotes blood
clotting
• Beta 1:
• Cardiac Muscle
Increases heart rate
& strength
• Beta 2:
• Depresses (dilates)
smooth muscle in
bronchioles &
coronary arteries
increasing blood flow
to heart and air flow
to lungs.
 and  ADRENERGIC RECEPTORS
1 – stimulation
2 – inhibition
1 – stimulation
2 – inhibition
NE Pharmaceuticals
• 1 stimulants would constrict blood
vessels and dilate the eyes.
• 2 stimulants promote blood clotting
• 1 stimulants increase HR and beat
strength.
• 2 stimulants dilate bronchials and
coronary vessels. More air, more blood.
– You are inhibiting sympathetic tone, thus
causing dilation.
Cholinergic Receptors
• The two types
of receptors
that bind ACh
are nicotinic
and muscarinic
• These are
named after
drugs that bind
to them and
mimic ACh
effects
Cholinergic Receptors
Nicotinic Receptors
• Nicotinic receptors are found on:
– Motor end plates (somatic targets)
– All ganglionic neurons of both sympathetic
and parasympathetic divisions
– The hormone-producing cells of the adrenal
medulla
• The effect of ACh binding to nicotinic
receptors is always stimulatory
Comparison of Somatic and
Autonomic Systems
nAChR
NE
mAChR
Muscarinic Receptors
• Muscarinic receptors occur on all effector cells
stimulated by postganglionic cholinergic fibers
• The effect of ACh binding:
–
–
–
–
–
Can be either inhibitory or excitatory
Depends on the receptor type of the target organ
Slows heart rate and strength of muscle contractions
Increases digestive activity
Constriction of the iris
Effects of Drugs
• Atropine – blocks parasympathetic effects
– Bella donna (and antidote to nerve gas)
• Neostigmine – inhibits acetylcholinesterase and
is used to treat myasthenia gravis
• Tricyclic antidepressants – prolong the activity of
NE on postsynaptic membranes
• Over-the-counter drugs for colds, allergies, and
nasal congestion – stimulate -adrenergic
receptors
• Beta-blockers – attach mainly to 1 adrenergic
receptors and reduce heart rate and prevent
arrhythmias
Cholinergic blockers
• Muscarinic blockers block parasympathetic
effects on target organs.
– Atropine used topically during eye exams to dilate
pupils
– May be used to reduce salivation and respiratory
secretions.
Drugs that Influence the ANS
Drugs that Influence the ANS
Localized Versus Diffuse Effects
• The parasympathetic division exerts shortlived, highly localized control
• The sympathetic division exerts longlasting, diffuse effects
Effects of Sympathetic
Activation
• Sympathetic activation is long-lasting
because NE:
– Is inactivated more slowly than ACh
– Is an indirectly acting neurotransmitter, using
a second-messenger system
– Epinephrine is released into the blood and
remains there until destroyed by the liver
Levels of ANS Control
• The hypothalamus is the main
integration center of ANS activity
• Subconscious cerebral input via limbic
lobe connections influences hypothalamic
function
• Other controls come from the cerebral
cortex, the reticular formation, and the
spinal cord
Levels of ANS Control
Hypothalamic Control
• Centers of the hypothalamus
control:
– Heart activity and blood pressure
– Body temperature, water balance,
and endocrine activity
– Emotional stages (rage, pleasure)
and biological drives (hunger,
thirst, sex)
– Reactions to fear and the “fight-orflight” system