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Autonomic Nervous System
Organization of Nervous System:
Nervous system
Integration
Central nervous system
Peripheral nervous system
(CNS)
(PNS)
Motor
output
Brain
Spinal cord
Sensory
input
Motor division
Sensory division
(Efferent)
(Afferent)
“self governing”
Autonomic Nervous System
Somatic Nervous System
(Involuntary; smooth &
cardiac muscle)
(Voluntary; skeletal muscle)
Stability of internal environment depends
largely on this system
Marieb & Hoehn – Figure 14.2
Autonomic Nervous System
Ganglion:
A group of cell bodies located in the PNS
Comparison of Somatic vs. Autonomic:
Somatic NS
Cell body
location
CNS
NTs
Single neuron from CNS to effector organs
Effector
organs
Effect
+
ACh
Stimulatory
Heavily myelinated axon
Skeletal muscle
ACh = Acetylcholine
CNS
Two-neuron chain from CNS to effector organs
Sympathetic
Parasympathetic
Autonomic NS
ACh
NE
Ganglion
Postganglionic axon
(unmyelinated)
Preganglionic axon
(lightly myelinated)
+
CNS
ACh
Preganglionic axon
(lightly myelinated)
Ganglion
ACh
Postganglionic
axon
(unmyelinated)
Smooth muscle,
glands, cardiac
muscle
Stimulatory
or inhibitory
(depends
on NT and
NT receptor
Type)
NE = Norepinephrine
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Autonomic Nervous System
Organization of Nervous System:
Nervous system
Integration
Central nervous system
Peripheral nervous system
(CNS)
(PNS)
Motor
output
Brain
Spinal cord
Sensory
input
Motor division
Sensory division
(Efferent)
(Afferent)
Autonomic Nervous System
Somatic Nervous System
(Involuntary; smooth &
cardiac muscle)
(Voluntary; skeletal muscle)
Sympathetic division
Parasympathetic division
Autonomic Nervous System
Divisions of Autonomic Nervous System (ANS):
1) Sympathetic Division: (“fight or flight”)
• Readies body for stressful situations
• Heightens mental alertness
•  metabolic rate
•  heart rate / blood pressure
•  respiratory rate / bronchiole dilation
• Activates sweat glands
• Activates energy reserves
• Dampens non-essentials (e.g., digestion)
2) Parasympathetic Division:
(‘rest and digest”)
• Conserves energy at rest
•  metabolic rate
•  heart rate / blood pressure
•  digestive motility / blood flow
• Stimulates defecation / urination
•  digestive gland secretions
2
Autonomic Nervous System
Sympathetic division also called
the thoracolumbar division
Sympathetic Division Anatomy:
• Sympathetic pathways have short preganglionic
fibers and long postganglionic fibers
• Preganlionic fibers originate in spinal cord
between cord segments T1 – L2
• Autonomic ganglia located close to spinal
cord (arranged as sympathetic chain)
• 23 ganglia / chain
T1
(3 cervical, 11 thoracic,
4 lumbar, 4 sacral,
1 coccygeal)
L2
Sympathetic
chain
Marieb & Hoehn – Figure 14.5 / 14.6
Autonomic Nervous System
Pathways in sympathetic chain:
Sympathetic Division Anatomy:
1) Terminate directly in sympathetic chain
• Postganglionic axons exit out
gray ramus communicans
Spinal nerve
(unmyelinated
axons)
Lateral horn of
spinal cord
2) Ascend / descend several segments
before terminating
Gray ramus
communicans
Ventral root
Sympathetic chain
ganglion
(paravertebral ganglion)
White ramus
communicans
(myelinated axons)
Marieb & Hoehn – Figure 14.5
Rami communicantes only
associated with sympathetic division
• May ascend / descend to ganglia
located outside T1 – L2
Cervical ganglia: (fed via T1 – T6)
Serve head / thorax
Sacral ganglia: (fed via T10 – L2)
Serve genitalia / urinary bladder
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Autonomic Nervous System
Pathways in sympathetic chain:
Sympathetic Division Anatomy:
3) Exit sympathetic chain before terminating
in collateral (prevertebral) ganglia
Cervical
ganglia
Collateral
ganglion
T1
Celiac
ganglion
L2
Adrenal medulla
Celiac ganglion:
Serves upper abdominal cavity
Sacral
ganglia
Spanchnic
nerves
• Form splanchnic nerves (fed via T5 – L2)
Mesenteric
ganglia
• Pass-through point for splanchnic
nerve feeding adrenal medulla
Mesenteric ganglia:
Serve lower abdominal cavity
Marieb & Hoehn – Figure 14.5 / 14.6
Autonomic Nervous System
Paraympathetic division also called
the craniosacral division
Parasympathetic Division Anatomy:
• Sympathetic pathways have long preganlionic
fibers and short postganlionic fibers
• Terminal ganglia located near effector tissue
• Preganglionic fibers originate in brain stem
and S2 – S4:
Vagus
nerve
• Occulomotor Nerve (III)
• Ciliary ganglia: Pupillary sphincters / ciliary
muscles
• Facial Nerve (IIV)
• Pterygopalatine ganglia: Nasal / lacrimal
glands
• Submandibular ganglia: Salivary glands
• Glossopharyngeal Nerve (IX)
S2
• Otic ganglia: Salivary gland
S4
Splanchnic
nerves
90% of
PNS fibers
• Vagus Nerve (X)
• Intramural ganglia: Visceral organs
• Sacral Segments (S2 – S4):
Marieb & Hoehn – Figure 14.4
• Intramural ganglia: Large intestine / bladder /
genitalia
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Autonomic Nervous System
ANS Physiology:
Fiber Types:
• Cholinergic Fibers: Synthesize / secrete acetylcholine (NT)
• All preganglionic fibers (sympathetic and parasympathetic divisions)
• Postganglionic fibers of parasympathetic division
• Adrenergic Fibers: Synthesize / secrete norepinephrine (NT)
• Postganglionic fibers of sympathetic division (sans sweat glands / piloerector muscles)
Synthesis of Neurotransmitters:
• NTs synthesized / stored in varicosities of nerve fibers
Autonomic Nervous System
• Postganglionic neuron forms diffuse, branching
networks at synapse
ANS Physiology:
• NTs released from varicosities (“beads”)
Neuroeffector Junction of ANS:
• Innervation by multiple ANS fibers may occur
• Postsynaptic receptors spread across target
Varicosities
Smooth muscle
cells
Autonomic
nerve fiber
Remember:
Precision strike
vs.
Saturation bombing
Synaptic
vesicles
Marieb & Hoehn – Figure 9.27
Neuromuscular junction
5
Autonomic Nervous System
ANS Physiology:
Fiber Types:
• Cholinergic Fibers: Synthesize / secrete acetylcholine (NT)
• All preganglionic fibers (sympathetic and parasympathetic divisions)
• Postganglionic fibers of parasympathetic division
• Adrenergic Fibers: Synthesize / secrete norepinephrine (NT)
• Postganglionic fibers of sympathetic division (sans sweat glands / piloerector muscles)
Synthesis of Neurotransmitters:
• NTs synthesized / stored in varicosities of nerve fibers
Acetyl-CoA + Choline
Tyrosine
hydroxylation
choline
acetyltransferase
Removal:
1) Reuptake (~ 80%)
2) Diffusion (~ 20%)
3) Destruction (> 1%)
Dopa
monoamine
oxidase
decarboxylation
Acetylcholine
Dopamine
• Catalyzed by acetylcholinesterase
• Choline recycled…
hydroxylation
Norepinephrine
Autonomic Nervous System
Nature of receptor
dictates effects of NTs
ANS Physiology:
Receptor Types:
A) Adrenoreceptors (bind E / NE):
G protein-linked
receptor systems
• Located on target tissues of sympathetic nervous system
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Autonomic Nervous System
ANS Physiology:
Receptor
G – protein Receptor Systems:
Effector
G protein
• Receptors interact with G-proteins to trigger cellular event
Cellular
response
A. Receptors:
• 7 trans-membrane segments (each segment = similar –helix sequences)
• Interact with various G-proteins depending
on sequence of 3rd intracellular loop
Wolfe – Figure 4.3
Autonomic Nervous System
ANS Physiology:
Receptor
G – protein Receptor Systems:
Effector
G protein
• Receptors interact with G-proteins to trigger cellular event
Cellular
response
B. G proteins:
• Composed of three unique sub-units (, , )
• No intrinsic enzymatic activity; activates enzymes
G protein Activation:
1) Ligand binds to receptor
2) Receptor / G protein interact
• GDP (-subunit) replaced
by GTP; dissociation occurs
3) -subunit activates effector
Hydrolysis of GTP to GDP causes –subunit to
dissociate from effector and rejoin other subunits
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Autonomic Nervous System
ANS Physiology:
Receptor
G – protein Receptor Systems:
Effector
G protein
• Receptors interact with G-proteins to trigger cellular event
Cellular
response
C. Effectors:
A) Adenylate cyclase (2nd messenger – cAMP)
Activated by
GS proteins
Inhibited by
GI proteins
Lodish – Figure 20.20
Autonomic Nervous System
ANS Physiology:
G – protein Receptor Systems:
Receptor
Effector
G protein
• Receptors interact with G-proteins to trigger cellular event
Cellular
response
C. Effectors:
A) Adenylate cyclase (2nd messenger – cAMP)
• Synthesizes cAMP from ATP
Methylxanthines
(e.g., caffeine)
Inactivates cAMP
8
Autonomic Nervous System
ANS Physiology:
Receptor
G – protein Receptor Systems:
Effector
G protein
• Receptors interact with G-proteins to trigger cellular event
Cellular
response
C. Effectors:
A) Adenylate cyclase
B) Phospholipase C
(2nd messenger – cAMP)
Diacylglycerol
(DAG)
(2nd messengers – IP3 / DAG)
• IP3 activates release of Ca++ (ER)
• DAG activates protein kinase
Inositol triphosphate
(IP3)
Phosphoinositol
(PIP)
Wolfe – Figure 6.6 / 6.9
Autonomic Nervous System
Nature of receptor
dictates effects of NTs
ANS Physiology:
Receptor Types:
A) Adrenoreceptors (bind E / NE):
G protein-linked
receptor systems
• Located on target tissues of sympathetic NS
• Divided into two types:  and β receptors
(most common)
1 receptors
Effect:
Location:
(+) Excitatory (+)
2 receptors
Effect:
(constricts blood vessels)
Membrane of adrenergic
axon terminals
Gastrointestinal tract / bladder
Gastrointestinal tract
(constricts sphincters)
(inhibits GI function)
Vascular smooth muscle - skin
Location:
(-) Inhibitory (-)
(inhibits NE release)
Phenylephrine
(1 agonist)
Mechanism
of Action:
Iris of eye
Pancreas
(dilates pupil of eye)
(inhibits insulin secretion)
G protein coupled to
phosphorylase C
Mechanism
of Action:
GI protein coupled to
adenylate cyclase
9
Nature of receptor
dictates effects of NTs
Autonomic Nervous System
ANS Physiology:
Receptor Types:
A) Adrenoreceptors (bind E / NE):
G protein-linked
receptor systems
• Located on target tissues of sympathetic NS
• Divided into two types:  and β receptors
1 receptors
2 receptors
(+) Excitatory (+)
Effect:
Location:
Effect:
Predominately in the heart
(-) Inhibitory (-)
Vascular smooth muscle - skeletal
(dilates vessels)
muscle
Location:
(increases contraction rate / strength)
Kidney
Lungs
(triggers renin (hormone) release)
(dilates bronchioles)
Propanolol
Albuterol
(β-blocker)
(2 agonist)
Mechanism
of Action:
GS protein coupled to
adenylate cyclase
Gastrointestinal tract
(relaxes GI tract)
Mechanism
of Action:
GS protein coupled to
adenylate cyclase
Nature of receptor
dictates effects of NTs
Autonomic Nervous System
ANS Physiology:
Receptor Types:
A) Adrenoreceptors
Activated by
nicotines
Activated by toxins
(bind E / NE):
from toadstools
atropine
(muscarinic antagonist)
B) Cholinoreceptors (bind ACh):
• Located on postganglionic neurons / target tissues of parasympathetic NS
• Divided into two types: nicotinic & muscarinic
Nicotinic
Effect:
Location:
(+) Excitatory (+)
Motor end plate – skeletal muscle
Muscarinic
Effect:
Location:
(+) Excitatory (+) & (-) Inhibitory (-)
Parasympathetic organs – sans heart
(contracts skeletal muscle)
All postganglionic neurons
(activate postgangionic neurons)
Mechanism
of Action:
(excites organ activity)
G protein coupled to
K+ channel…
Heart
(inhibits heart rate)
Chromaffin cells – adrenal medulla
Sweat glands – sympathetic NS
(triggers release of E / NE)
(activates sweat glands)
Ligand-gated ion channel
Mechanism
of Action:
G protein coupled to
phosphorylase C
(Majority of locations)
10
Autonomic Nervous System
ANS Physiology:
Parasympathetic
Muscarinic
receptors
Autonomic
ganglion
Visceral
dffector
cell
Cholinergic fibers
Nicotinic receptors
Visceral
effector
cell
Autonomic
ganglion
Sympathetic
Adrenergic fibers
Adrenergic
receptors
(α / β)
Autonomic Nervous System
ANS Physiology:
Costanzo – Figure 2.1
11
Autonomic Nervous System
ANS Physiology:
Control of Autonomic Functioning:
A) Brain stem / Spinal cord
•
•
•
•
Vasomotor center (cardiovascular)
Respiratory center
Micturition center (urination)
Swallowing / coughing / vomiting
B) Hypothalamus
• Main integration center
• Body temperature
• Water balance
• Food intake
• Links emotion with ANS
C) Cortical control
• Links emotional past with ANS
• Voluntary cortical ANS control possible
Costanzo – Figure 2.4
Autonomic Nervous System
Sympathetic = “fight or flight”
Parasympathetic = “rest and digest”
ANS Physiology:
Interactions of Autonomic Divisions:
A) Antagonistic Interactions:
• Pupil:
Systems do not ‘compete’ with each other;
coordinated by nervous system
• Parasympathetic = Constriction (circular fibers)
• Sympathetic = Dilation (meridional fibers)
• Heart (sinoatrial node):
• Parasympathetic = Decrease heart rate
• Sympathetic = Increase heart rate
B) Synergistic Interactions:
• External genitalia
• Parasympathetic = Vasodilation of blood vessels (erection of tissue)
• Sympathetic = Smooth muscle contraction (ejaculation / reflex contraction)
* Tone:
• Basal rate of activity present in a system
• Allows increase / decrease by single system
Blood vessels under sympathetic tone
Decrease output = vasodilation of vessel
Increase output = vasoconstriction of vessel
12
Autonomic Nervous System
Sympathetic = “fight or flight”
Parasympathetic = “rest and digest”
ANS Physiology:
Interactions of Autonomic Divisions:
Sympathetic
C) Coordinated Function within Organ:
Parasympathetic
• Bladder:
• Filling = Relaxed detrusor muscle; contracted internal sphincter
• Emptying = Contracted detrusor muscle; relaxed internal sphincter
Costanzo – Figure 2.4
Autonomic Nervous System
Adrenal Medulla:
• Large sympathetic ganglion
Cortex
Medulla
• Postganglionic cells = Chromaffin cells
• Releases catecholamines (epinephrine (80%) and norepinephrine (20%))
methylation
• Catecholamines transported via blood (= hormone)
• Delayed effect (3 – 5 sec.); prolonged effect (2 – 4 min. to clear from system)
• Stimulation of cardiovascular function / metabolic rate (helps deal with stress)
• Perceived purpose:
1) Safety factor (dual mechanism – backs up sympathetic nervous system)
2) Stimulate structures not directly innervated (e.g., every cell of body…)
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