Autonomic Nervous System Physiology Flashcards
Functions of ANS
- maintains homeostasis
- flight or flight system
- rest and digest
ANS is part of the _____ neurons
efferent
Effector muscles of ANS
smooth muscle, cardiac muscle, glands
3 division of ANS
- sympathetic
- parasympathetic
- enteric
How many cranial nerves
12 pairs
emerge from brain
How many spinal nerves
31 pairs
mixed nerves - afferent and efferent
Sectors of spinal cord
cervical
thoracic
lumbar
sacral
coccygeal
ANS organization
chain of two neurons that connect CNS and effector
linked by a synapse or ganglion (outside CNS)
excitatory and inhibitory
Preganglionic neuron
cell body in CNS and extends to ganglia
first neuron
lightly myelinated
Postganglionic neuron
cell body in ganglia and extends to target tissue
second neuron
unmyelinated
Neurotransmitters in ANS
Acetylcholine, epinephrine (E), norepinephrine (NE)
PSNS neuron length
preganglionic neuron is long
postganglionic neuron is short
ganglia is close to target organ
more isolated
SNS neuron length
preganglionic neuron is short
postganglionic neuron is long
ganglia is close to spinal cord
branching and mass discharge
SNS spinal cord sections
thoracic (T1-T12) and lumbar (L1-L2)
PSNS spinal cord sections
cranial (III, VII, IX, X - vagus nerve) and sacral (S2-S4)
What root do SNS autonomic neurons leave
ventral
Collateral ganglia
second set of ganglia in SNS
in front of vertebral column
lie close to viscera (internal organs like abdominal and pelvic)
Sympathetic chain/trunk
chain of ganglia running parallel to spinal cord on each side
3 collateral ganglia
celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion
3 pathways for SNS paraganglionic fiber
- synapse immediately with postganglionic neuron in sympathetic ganglion at same level
- travel up or down the chain and synapse in ganglia at other levels
- pass through chain without synapsing, continue to collateral ganglion as splanchnic nerve
Communicated rami
branches between spinal nerve and ganglia
White ramus communicans
branch that leads to ganglion from spinal nerve
myelinated preganglionic
Grey ramus communicans
branch that goes back into spinal nerve
unmyelinated postganglionic
SNS eyes
dilation of pupil
adjustment of far vision
SNS cardiovascular
increase heart rate
force of contraction
SNS blood vessels
constriction of smooth and cardiac
dilation of skeletal
SNS lungs
dilation of bronchioles
inhibition of mucus secretion
SNS digestive tract
decreased motility
inhibition of digestive secretions
SNS endocrine glands
stimulation of epinephrine and norepinephrine by adrenal medulla
SNS exocrine glands - sweat and salivary glands
stimulation of secretion
stimulation of small volume of thick saliva
SNS bladder
prevent voiding
SNS genitals
males - emission
female - uterus contraction
Adrenal Medulla
inner part of adrenal gland on top of kidneys
innervated by sympathetic preganglionic neurons
releases 80% epinephrine and 20% norepinephrine into blood
PSNS eyes
constriction of pupil
adjustment for near vision
PSNS cardiovascular
decrease heart rate
decrease contraction force
PSNS blood vessels
no innervation
dilation of penis and clitoris
PSNS lungs
constriction of bronchioles
stimulation of mucus secretion
PSNS digestive tract
increased motility
stimulation of digestive secretions
PSNS endocrine glands
no effect
PSNS exocrine glands - sweat and salivary
no effect
stimulation of large volumes of water enzyme rich saliva
PSNS bladder
void
PSNS genitals
erection
Dual autonomic innervation
most target tissues receive innervation from both SNS and PSNS
tone - background level of SNS and PSNS activity
when one system becomes active the other system turns down its activity
provides mroe control
Exceptions to dual innervation
adrenal medulla, most blood vessel, and sweat glands only receive SNS
Antagonistic effects of SNS and PSNS
opposite
SNS - GI tract down, heart rate up
PSNS - GI tract up, heart rate down
Cooperative effects of SNS and PSNS
working together
salivary glands - both systems stimulate but SNS small amount of thick saliva and PSNS large amount of thin saliva
male reproductive - PSNS erection and SNS emission
Cholinergic chemical transmitter
releases acetylcholine - ACh
Adrenergic chemical transmitter
releases norepinephrine - NE
Preganglionic neurons release _____
ACh in SNS and PSNS
Postganglionic neurons in PSNS release _____ to smooth cardiac gland muscles
ACh
Postganglionic neurons in SNS release _____ to smooth cardiac gland muscles
NE
Postganglionic neurons in SNS release ____ to sweat glands, blood vessels, skeletal muscle
ACh
Postganglionic neurons in SNS release ____ to smooth, cardiac gland muscles via bloodstream
E/NE
Cholinergic nerve terminal
preganglionic fibers in SNS and PSNS
acetyl-CoA and choline with enzyme choline acetyltransferase produces ACh
ACh is packages into vesicle at nerve terminal
increased Ca+ moves vesicle to membrane and releases ACh
enzyme acetylcholinesterase breaks down ACh into choline and acetate
choline is recycles back into terminal
Acetyltransferase
acetyl-CoA + choline = ACh
Acetylcholinesterase
ACh = choline + acetate
Varicosity
numerous swellings in postganglionic axon branches that release neurotransmitters along length of axon
Events at adrenergic varicosity
tyrosine is taken up into varicosity
tyrosine –> dopa –> dopamine–> NE
NE is taken back up and not broken down
2 types of cholinergic receptors
nicotinic and muscarinic
Nicotinic receptors
NM - somatic nervous system, skeletal muscle, bind ACh for muscle contraction
NN - autonomic nervous system, cell bodies of postganglionic neurons in SNS and PSNS, bind ACh from preganglionic endings
Ionotropic receptor - ligand-gated ion receptor
5 subunits and ACh binds to 2 alpha subunits to open pore
Muscarinic receptors
5 subtypes (M1-M5)
effector cell membranes or target tissues
Metabotropic receptor - G-protein signal transduction mechanism
7 transmembrane domains chained together
Adrenergic receptors
bind NE or E
2 types: alpha (2 subtypes) and beta (3 subtypes)
effector cell membranes or target tissues
Metabotropic receptor - G-protein signal transduction mechanism
7 transmembrane domains chained together
ACh
released from PSNS postganglionic neurons
released from SNS innervating sweat glands, blood vessels, skeletal muscles
bind to muscarinic receptors found on target tissue
NE
released from SNS postganglionic neurons
released from adrenal medulla
bind to adrenergic receptors found in target tissue
Convergence
numerous preganglionic neurons synapse with single postganglionic neuron
Divergence
small number of preganglionic neurons form synapses with large number of postganglionic neurons
PSNS divergence
1 preganglionic neuron to 1-3 postganglionic neuron
more specific and localized response
SNS divergence
1 preganglionic neuron to 1-20 postganglionic neuron
more diffuse response
ANS reflexes - spinal cord
sacral region - urination, defecation, erection
ANS reflexes - brainstem / medulla oblongata
blood pressure regulation, salivation, swallowing, vomiting, respiration
ANS reflexes - hypothalamus
regulates temperature, sending messages down spinal cord