Download Autonomic vs. Somatic Nervous System

Objectives
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Know ANS divisions and organization
z Functional
units
z Principal neurotransmitters
z Receptor types
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Identify sensory input to ANS
z Explain
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how it integrates function (BP)
List main physiological responses under ANS
control
z Distinguish
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SNS from PSNS mediated responses
Understand the consequences of ANS
dysregulation
Autonomic vs. Somatic Nervous
System
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AUTONOMIC
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Effectors: cardiac & smooth muscle, viscera & glands
Efferent: 2‐neuron chain
Neurotransmitter (NT) effects
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Stimulatory or inhibitory dependent on NT & receptor type
SOMATIC
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Effectors: skeletal muscles
Efferent: Heavily myelinated axons from CNS to
Efferent: Heavily
CNS to muscle
Neurotransmitter Effects: ƒ
Acetylcholine excitatory effect in nicotinic (N1) receptors
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Autonomic Nervous System
Efferent motor neurons: innervate viscera & involuntary
muscle
Afferent sensory neurons respond to:
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Stretch (heart, arteries)
Glucose PCO2, PO2 (blood)
Glucose,
Osmolarity & pH (blood & intestinal content)
Temperature (skin & internal organs)
SNS & PSNS
Functional unit
2 neuron pathway
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Sympathetic
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Preganglionic
neurons
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Ni ti i receptor
Nicotinic
t (N2)
Thoracolumbar spinal
cord: T1-L3
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Postganglionic:
Adrenergic neuron;
Adrenergic receptor
z α 1: vasculature
z α 2: presynaptic
z β 1: heart, adipose
z β 2 : bronchioles,
vasculature
z β 3: adiposethermogenic
Postganglionic
neurons
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Preganglionic:
Cholinergic neuron;
Paravertebral or
prevertebral ganglia
z Distant to target organ
Parasympathetic
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Preganglionic
neurons
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Brainstem: cranial nerve
nuclei
z III oculomotor
z VII facial
z IX glossopharyngeal
z X Vagus
Sacral spinal cord
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Preganglionic: Cholinergic
neuron; Nicotinic (N2) receptor
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Postganglionic: Cholinergic
neuron; Muscarinic receptor
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Nicotinic: ion
ion-gated
gated
G-protein coupled
Effect on cell
z Excitatory or inhibitory:
ecepto & o
organ
ga spec
specific
c
receptor
Postganglionic
neurons
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Parasympathetic ganglia
z Near or in wall of target
organ
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Neurotransmitters
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Principal: Acetylcholine & norepinephrine
N ttraditional
Non
diti
l
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ATP
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Colocalized with NE in SNS
Purinoceptors (i.e., smooth muscle cells)
Nitric oxide
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Pre & postganglionic neurons SNS & PSNS
Enteric nervous system
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2 networks of neurons
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Myenteric
y
z Motility
Submucous
z Secretions
3 types of neurons
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Motor
Sensory
z mechanical, thermal, osmotic &
chemical
Interneurons
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Enteric nervous system
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Part of the PNS
Operates largely independently of the CNS
Coordinates gastrointestinal function
Monitors the state of lumen and gut wall
Responds appropriately
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Activating intrinsic reflexes
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Mixing and propulsive & peristaltic movements
Change blood flow & secretions of water & electrolytes
Enteric nervous system
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Neurons & glia organized
into ganglia
Neurotransmitters:
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Acetylcholine
z ↑ motility
z ↑ intestinal secretions
z ↑ enteric hormone release
N
Norepinephrine
i
hi
z ↓ acetylcholine effects
Others: VIP, opioids, 5-HT,
Substance P, NO, etc.
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SNS: “fight or flight”
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Dilation of pupils
↑ HR,
HR contractility & BP
Blood flow
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↑ Bronchial dilation
↑ Respiratory rate
↑ Fuel mobilization
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Exercise
Excitement
Embarrassment
↓ non-essential organs
Glucose & FFA
PSNS: “rest-digest”
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Conserve & restore energy
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SLUDD responses:
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↓ HR, airway & pupil diameter
P d i l ffear
Paradoxical
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Digestion
Defecation
Diuresis
salivation, lacrimation,
urination, digestion &
defecation
3 “decreases”
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Normally PSNS tone > SNS
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No escape/“No win situation”
Massive PSNS activation
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Loss of urination & defecation
control
↓HR & BP
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SNS/PSNS
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Dual/antagonistic: GI, CV
Exclusive SNS
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Adrenal medulla
Sweat glands
Erector pili muscles
Kidneys: RAS →↑ MABP
Most blood vessels
Exclusive PSNS
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Erectile tissues
SNS/PSNS: Dual/antagonistic
modulation of CV function.
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Carotid sinus & aortic arch pressure
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↑ Pressure
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Afferent signals integrated in brainstem
↓ SNS activity & ↓ BP
↑ PSNS activity & ↓ HR
↓ Pressure
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↑ SNS activity
y & ↑ HR & BP
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SNS & PSNS: Dual/antagonistic
modulation of GI function
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PSNS favors digestive processes
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Increased gut motility, acid & enzyme secretions
Relaxation of sphincters
SNS inhibits digestive processes
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Contraction of sphincters
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Pyloric,
y
, ileo-cecal & internal anal
Inhibition of motor neurons throughout the gut
SNS: Exclusive modulation of
thermoregulation
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↑ Environmental temperature
z Sweat gland activation
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Skin vasodilation
z Warm blood to surface
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↓ Environmental temperature
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Skin vasoconstriction
z Blood retained in vital organs
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Shivering
Piloerection
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ANS during fever
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Increased body
temperature 1-4°C
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Upregulation of
thermostatic set point
Body “feels cold”
Autonomics kick in
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Skin vasoconstriction
z Blood retained in vital organs
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Shivering
Piloerection
No sweating
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SNS/PSNS: Cooperative
control of sexual function
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Erection
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PSNS: Vasodilation of penile
blood vessels
z ACh & NO
SNS: ↓ tone during erection
Emission (ejaculation)
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SNS: smooth muscle
contraction distal epididymis
z Emission
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Autonomic nervous system
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ANS divisions and organization
z Functional
units
z Principal neurotransmitters
z Receptor types
Sensory input to ANS & role in control of BP
z Main physiological responses under SNS &
PSNS controll
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z Coordinated/antagonistic/exclusive
z ANS
dysfunction?
z Examples? Manifestations?
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