Quiz 8- ANS Flashcards
ANS is not ____ but ____
automatic
involuntary
Autonomic Nervous System
control at an unconscious level
reflexes are fast and specific
innervation of smooth muscle, not striated
cell bodies originate in the brainstem or cord
ANS control points
hypothalamus- water balance, temp control, hunger
pons- respiration and cardiovascular control
medulla- respiration and cardiovascular control
Divisions are distinguished by…
structural anatomy, neurotransmitters, and functionality
- parasympathetic
-sympathetic
-enteric
Division characteristics
all divisions control internal homeostasis by reflexes
almost all are negative feedback loops
limiting changes in physiological factors
all respond to external/internal stimuli
tracts are components of…
cranial and spinal cord nerves
SNS
solely excitatory
conscious
3 cells: motor cortex Betz cells- spinal cord interneurons- a-motor neurons
a-motor neurons are myelinated and use ACh as NT
ANS
excitatory or inhibitory
2 cells: cells arise within cord and project out to syapses on neurons either near cord or further away
ganglia= 2nd cell body outside of cord
pre- and post-ganglionic cells
post ganglionic cells innervate targets
Types of branches
sympathetic- built into cord
parasympathetic- built into brain stem and cord
characterization of branches
anatomical origin of pre-ganglionic cell body
anatomical location of synapses between pre- and post-ganglionic cell
NTs used at synapses
length of pre- and post-ganglionic cell axon
Origin of first cell consequences
varied influence from regions of cord and brain
ganglia position consequences
no real functional impact, anatomically important
axonal length consequences
no real functional impact, unless a slight change in speed of response
different NT consequence
enormous clinical impact
Signal of ANS
pre ganglionic neuron -(ACh/NT)- post ganglionic neuron-(NT)- target operator/effector
Signal termination
pre-ganglionic to ganglionic neuron
ganglia to target
pre ganglionic to ganglionic neuron termination
Acetylcholinerastes degradation of ACh
targets of nerve gases and insect sprays
ganglia to target termination
active reuptake, enzyme degradation
monoamine oxidase
Parasympathetic properties
energy conservation
bradycardia
hypotension
increase digestion and absorption
SLUD
SLUD
Salivation
Lacrimation
Urination
Defecation
sympathetic properties
flee or flight against danger
tachycardia
hypertension
salivation (shared)
perspiration
ANS is structured as a classic reflex arc…
response can occur without cortical influence
fast and innate
Sympathetic Branch
1st cell body is found in spinal cord lateral horn
pre-ganglionic cells project via spinal nerve ventral roots to sympathetic chain ganglia along either side of cord
some pre-ganglionic fibers innervate ganglia near target tissues
- splanchnic nerve and adrenal medulla
Sympathetic ganglia
chain ganglia
collateral ganglia
adrenal medulla
chain ganglia
directly adjacent, both sides of cord, majority of fibers
targets: organs and glands of head heart and lungs
collateral ganglia
ganglia are in abdominal cavity
targets: GI tract, pancreas, liver, renal, colon
adrenal medulla
modified chain ganglia
1st neuron passes through chain ganglia w/o synapsing
synpases directly on post ganglionic cells w/ adrenal medulla
significance of adrenal medulla
meant to affect a large number of cells at the same time
Chromaffin cells
(adrenal medulla)
stained with chromium dye
post ganglionic neurons w/o axons
Parasympathetic branch
neurons arise either in the brain stem via cranial nerves III,VII,IX,X or from regions S2-S4 of the cord
pre ganglionic axonal fibers are long and terminate on post ganglionic cells near targets
Tissue innervation
usually both branches innervate the same target tissue with almost always an opposite effect
maximizes fine level of control
(sometimes they compete with one another)
in what case does only one branch innervate a target tissue
sweat and adrenal
Neurochemistry
in cases where both branches innervate the same tissue NT released must be different
Parasympathetic NT release
ACh
Sympathetic NT release
norepinephrine
epinephrine
Cholinergic pathways
ACh synapses are cholinergic
two subclasses: muscarinic or nicotinic- can be agonistic or antagonistic
agonistic
chemicals that bind to a receptor and activate a biochemical process
antagonistic
chemicals that bind to the same receptor and inhibit a biochemical process
Nicotinic Receptors structure
assembly of 5 subunits
ligand-gated ion channel
found predominantly within CNS
Nicotinic Receptor significance
all versions of the receptor bind ACh with different affinities
differential tissue expression
all have different agonists and antagonists
Muscarinic receptors
muscarine= mushroom chemical
receptors= GPCRs, different structure than nicotinic, different agonist and antagonist
expressed in NMJs, ganglia, CNS
Adrenergic Receptors
differential binding of epinephrine VS norepinephrine
common clinically used agonists: phenylephrine, midodrine
theraputic uses: treatment of anaphalactic shock etc.
Adrenergic subtypes
a-adrenergic
B-adrenergic
types of a-adrenergic
a1- smooth muscle contraction
a2- inhibition of secretion
types of B-adrenergic
B1- increased heart rate, heart contractility
B2- smooth muscle relaxation
B3- lipolysis (fat)
norepinephrine stimulates
all a-adrenergic and B1
epinephrine stimulates
a-adrenergic and B-adrenergic
ANS reflexes
rapid focused pathways to detect perturbation in physiological pathways and drive them back toward normality
ANS reflexes examples
baroreceptors
pupil dilation
visual accommodation
micturition
heart rate
blood vessel diameter
Baroreceptor reflex
Aortic arch sinus- narrowing of blood vessel wall
when sitting blood pools and rapid standing changes gravity
drop in BP sensed by baroreceptors
adrenergic influences drive blood vessel contraction+ increase heart contraction, drive BP to normal
Pupil dilation
balance between contraction of dilator and sphincter
low light- pupil dilation via adrenic inputs
bright light- pupil constriction via muscarinic inputs
lense accommodation
change in lense shape to focus objects as they near the eyes
far vision- pupil dilation
reflex is affected by age
micturition reflex
as bladder fills, contraction of detrussor muscle, 2 sphincters (one involuntary, one voluntary)
after empty: inhibition of detrussor muscle and contraction of internal sphincter
above 500 mL=impossible to ignore- micturition
Why is micturition an unusual ANS reflex?
conscious control of external sphincter
Fight or Flight
response to physical, emotional, chemical and other types of potentially damaging stimuli
whole body response meant to minimize stress-mediated damage
response via sympathetic inputs
Parasympathetic tone
bradycardia
hypotension
increased GI activity
pupil constriction
constriction of lung branches
hypoglycemia
increased urine production
not organized for mass discharge
hypoglycemia
increased insulin release
Body functional Balance
dual innervation= generally antagonistic
pathophysiology
ANS deficit
baroreflex failure
hypoventilation
Holmes Adie Syndrome
Orthostatic hypertension
baroreflex failure
severe hypertension and tachycardia in response to exercise
hypoventilation
sleep buildup of CO2
Holmes Adie syndrome
one eye doesn’t respond to light properly
orthostatic hypertension
hypertension on quickly standing up
