Autonomic nervous system Flashcards
advantage of neurons in maintaining homeostasis over hormones
more rapid and generally discrete delivery
homeostasis circuit for ANS?
sensory NS –> CNS –> ANS
is the ANS pervasive
yes
describe how the enteric NS interacts with smooth muscle cells
via its varicosities, and through interstitial cells.
somatic NS:
- function
- effectors
- extrinsic/intrinsic contraction
- overall complexity
- no. nt’s/receptors
- nature of synapse
muscle contraction skeletal muscle fibres extrinsic - requries innervation simple 1 nt (ACl) and 1 receptor (nicotinic) neuromuscular junction, discrete delivery
autonomic NS:
- function
- effectors
- extrinsic/intrinsic contraction
- overall complexity
- no. nt’s/receptors
- nature of synapse
survival smooth/cardiac muscle, glands intrinsic - however innervation can modulate complex more than one nt/receptor junction; indiscrete delivery
the parasympathetic and sympathetic ns are
functionally opposing (only like one exception)
describe similarities of preganglionic neuron in sympathetic and parasympathetic ns
cell body located in spinal cord, hence myelinated
describe similarities of communication between pre and post ganglionic neuron in sympathetic and parasympathetic ns
occurs in ganglia (but location of ganglia differs)
ALWAYS ACh acting on nicotinic receptors (like somatic NS)
describe similarities of postganglionic neuron in sympathetic and parasympathetic ns
cell body in ganglia, hence unmyelinated (as its outside the spinal cord)
describe similarities of postganglionic neuron branching in sympathetic and parasympathetic ns
axons branch, have varicosities which contain nts in vesicles
describe similarities of transmission in sympathetic and parasympathetic ns
via junctions
-much bigger than neuromuscular junction, hence nt affects multiple effector cells (ie. not discrete)
all receptors are metabotropic
sympathetic ns
- location of ganglia
- is surgical denervation possible
- relative length of preganglionic neuron
- location of preganglionic cell bodies
- locatio n of axon output
sympathetic chain ganglion for cardiovascular targets; hypogastric and mesenteric ganglion halfway towards target
surgical denervation possible - as its not attached to rogan
relatively short as synapse is in ganglion
efferents descend from midbrain/hindbrain, while cell bodies are found in the intermediolateral horn of the spinal cord
-axons come out via lumbar and thoracic segments of the spinal cord
parasympathetic ns
- location of ganglia
- is surgical denervation possible
- relative length of preganglionic neuron
- location of preganglionic cell bodies
- location of axon output
on wall of target organ, hence relatively long length of preganglionic neuron and difficult to surgically denervate.
preganglionic cell bodies found in brain and sacral region of spinal cord
for facial organs, axons go by the facial nerve, vagus (X) nerve for face-down, sacral nerve for pelvis.
nt’s in the
- sympathetic ns
- parasympathetic ns
sympathetic: noradrenaline and ATP; peptides
parasympathetic: nitric oxide and ACh; peptides
describe nitrix oxide synthesis
in cytoplasm of varicosity, low Ca And CaM levels which activates NO synthetase, which converts L-arginine to L-citrulline and nitric oxide.
effect of NO* on SMC
NO* is very lipid soluble, so passes PM into SMC
converts guanylyl cyclase to cGMP, which reduces SMC Ca2+ levels, leading to intense muscle contraction.
describe NO* removal
NO* is a free radical. hence it’s very reactive and only lasts for about 30 seconds.
describe ATP synthesis and storage in terms of neurotransmission
cotransmitter - made along with NA and sometimes ACh, so stored in their vesicles
describe the receptors ATP acts on
atP –> Purigenic
- junctional or extrajunctional
- excitatory or inhibitory, depending on where target organ si
describe ATP metabolism
purigenic receptors are plentiful so its removed quickly.
ACl synthesis?
cytoplasm of varicosity (enzymes located here)
ACh storage
vesicles
ACh action?
MUSCARINIC RECEPTORS
prejunctional
-on varicosity
-reduces transmitter released on each subsequent stimulus
postjunctional
-on target
-atleast 5 types, all blocked by atropine
ACh removal?
acetylcholinesterase forms acetate and choline; choline recycled
results in no ACh being found in the bloodstream.
noradrenaline synthesis
actually inside vesicles (has the enzymes)
noradrenaline storage
vesicles
noradrenaline action?
prejuctional receptors
-alpha
-varicosity
-reduces nt release on subsequent stimulus
postjunctional receptors
-found on smooth/cardiac msucle and glands
-alpha and beta
–>when NA binds to alpha, secondary messengers are produced which causes muscle contraction
–> when NA binds to beta receptors, secondary messengers are produced causing muscle relaxation
how is noradrenaline removed
enzymes
reuptake
2 differences between reuptake I and reuptake II
I:
prejunctional: actively transported into the varicosity
inhibited by cocaine
ii:
extrajunctional: actively transported into target
inhibited by steroids (including corticosteriods, which are produced by stress)
regarding noradrenaline, what drugs counteract hypotension
would increase muscle contraction
alpha agonists
beta antagonists
regarding noradrenaline, what drugs would counteract hypertension
would increase muscle relaxation
alpha antagonists
beta agonists
where is adrenal medulla located
next to each kidney
describe adrenal medulla innervation
by sympaethic preganglionic neuron
no post ganglionic neuron; if anything adrenal medulla = modified postganglionic neuron
describe how adrenal medulla works
sympathetic NS activated
preganglionic neuron releases ACh which binds to nicotinic receptor on adrenal medulla, causing creation of adrenaline, which is released into the nearby bloodstream
how does sensory info get to the brain?
sensory neurons come via the dorsal root to the dorsal horn (somas in dorsal root ganglion).
synapses with CNS neuron
decussation
then goes up the spinothalamic tract, where it reaches the thalamus
describe two exceptions to this
cardiovascular: synapses with the nucleus of the tractus solitarius (brainstem) where it can then interact with cardiovascular centres. then it goes down by sympathetic/parasympathetic pathway to the heart.
stomach: as above, but only has a sympathetic pathway
from the brain where does info go
thalamus –> hypothalamus –> rostral ventrolateral medulla (integrates info) –> caudal entrolateral medulla (distributes info to the body)
CNS neuron synapses with relevant preganglionic neuron
describe leptin
fat levels in white fat cells increases
white fat cells secrete leptin
binds to receptors on neurons that synapse with the arcuate nucleus neurons
sympathetic neurons synapse with brown fat cells, inducing thermogenesis and fat burning
describe how insulin relates to the Arc nucleus
neuron between the liver and arc
describe how the male sexual response defies the functional antagonism of the ans
both are operating in delicate balance
describe sympathetic regulation of male sexual response
leads to the stimulation of tubes, and the constriction of the penile artery by noradrenaline and ATP. leads to ejaculation
describe the parasympathetic regulation of the male sexual response
nitric oxide
causes the dilation of the penile artery leading to an erection (stiffy)
how does viagra
phosphodiesterases get rid of NO. viagra targets these enzymes to reduce affects of NO, hence to counter impotence
