autonomic nervous system physiology 2 Flashcards
what system conveys all outputs from central nervous system to rest of body? (except motor innervation of skeletal muscle)
The Autonomic nervous system
is the autonomic nervous system voluntary or involuntary?
IT is involuntary
What does the autonomic nervous system regulate?
regulates
all vascular and visceral smooth muscle
all exocrine and certain endocrine secretions
heartbeat
energy metabolism
blood vessels, heart, lungs, liver, bladder/genitalia etc/
the autonomic nervous system is part of what branch of the peripheral nervous system?
it is the involuntary branch of the efferent division of the peripheral nervous system
what are the two divisions of the autonomic nervous system?
parasympathetic and
sympathetic
most visceral organs are innvervated by what division of the ANS?
most visceral organs innervated by both divisions
what is the function of the parasympathetic nervous system?
- restorative/maintenance (housekeeping)
- rest and digest (parasympathetic dominant)
what is the role of the sympathetic nervous system?
- most activated in emergency, strenuous, or stressful sitation
- fight or flight
describe the nerve pathway organization of the ANS
parasympathetic - long preganglionic fiber - acts on a shorter fiber then closer to the target tissue - cell body is within the central nervous system
sympathetic - short pre-ganglionic fiber - long post ganglionic fiber
what two neurotransmitters are principally used by the ANS?
acetylcholine and noradrenaline
all preganglionic ANS nerves release what neurotransmitter?
acetylcholine
postganglionic parasympathetic nerves release what nuerotransmitter?
postganglionic sympathetic nerves release what nuerotransmitter?
parasympathetic = acetylcholine
sympathetic = noradrenaline
how does the brain influence the ANS?
“higher” centers in the brain can influence ANS - brain corticol pathways can modify autonomic function and vice versa
ex) panic attacks induce sympathetic activation and vagal stimulation suppresses cortical seizures
what other neurotransmitters are used within the enteric division of the ANS?
nitric oxide (vasodilator), ATP, Vasoactive intestinal peptide
arterioles and veins are innervated by what branch of the nervous system?
sympathetic branch
sweat glands are innervated by what branch of the nervous system?
mainly sympathetic innervation and post-ganglionic fiber release of acetylcholine, not noradrenaline
what branch of nervous system innervates the ciliary muscle of the eye (responsible for holding the lens of the eye) ?
innervated by parasypathetic nervous system only
- responsible contraction, near vision accomodation
what branch of nervous system innervates the bronchial smooth muscle?
innervated only by the parasympathetic nervous system (contraction)
with
indirect sympathetic influence - muscle tone highly sensitive to circulating adrenaline which produces relaxation
can both primary neurotransmitters cause relaxion/contraction? Or does one contract and the other relax?
both systems can cause relaxation or contraction of muscle - it’s all dependent on the tissue activated
describe the two types of neurotransmitter receptors?
1) ionotropic receptor - found on cell body within the ganglia N2 type
2) metabotropic receptor - G-protein coupled- targets the autonomic nervous system - respond to acetyl choline and noradrenaline - don’t contain the ion channel, they have a G protein receptor which mediates the effect
what receptor is present on all the postganglionic fibers and ANS cell bodies?
N2/ nicotinic receptor
what activates the nicotinic receptors?
the acetylcholine release from pre-ganglionic parasympathetic or sympathetic nerves
the tabacco derivative nicotine activates what receptors?
the nicotinic receptors
where are the N1 type receptors found?
at the skeletal neuromuscular junction
acetylcholine binding to ionotropic receptors prompts what response?
it binds and opens the Na+/K+ channel -
the N2 Ach receptor is ionotropic , so the response if depolarization of the post-synaptic cell
- rapid/fast response
The binding of acetylcholine to the muscarinic receptor prompts what response?
binding to muscarinic recpetor causes a G protein response - a vareity of pathways can be activated this way and produce either contraction or relaxation of muscle
where are muscarinic receptors found?
on smooth muscle, glands, cardiac muscle
what are the 5 types of muscarinic acetylcholine receptors?
they are all G-protein-coupled metabotropic receptors (slower acting- b/c don’t involve ion channel)
- odd numbered receptors (M1,3,5) coupled to Gq and stimulate inosital phosphate (release Ca2+ into cells)
- even numbered receptors (M2,4) couple to inhibit adenylyl cyclase (i.e. reduce cAMP)
where are M4, and M5 receptors found?
found in CNS - role is poorly understood
what is the response of the M1 muscarinic receptors?
excitatory
-stimulates gastric acid secretion
what is the response of the M3 muscarinic receptors?
M3= excitatory response (glandular/smooth muscle)
- located in exocrine glands, GIT and airways
- G protein couples to Ca2+ second-messenger system (IP3)
ex) increase glandular secretions, increase GIT motility
what is the response of the M2 - muscarinic receptors?
M2= inhibitory response - found on the atria of the heart-
- receptor couples to increase K+ conductance
- receptor couples to increase K+ conductance and inhibit calcium channels (decrease heart contraction)
what is the response of increased K+ on heart muscle?
increase of K+ hyperpolarizes membranes and makes it less likely to hit the threshold potential
the sympathetic nervous system has what effect on the heart?
it speeds it up
what are the two types of neurotransmitter receptors of the parasympathetic division?
nicotinic receptor and muscarinic recpetor
what are the two main classes of adrenergic receptors?
- alpha 1,2, and beta 1,2
where are the adrenergic receptors found?
on effector organ synapses - post synaptically, after postganglionic sypathetic nerves
how do the alpha and beta adrenergic receptors differ?
they are all G protein coupled, but intracellular coupling differs!
different classes of adrenergic receptor have different sensitivity for NA vs. AD
noradrenaline is much more potent on alpha receptors
on beta 2 receptors adrenaline is more potent than noradrenaline
what is the response of alpha 1 adrenergic receptors
excitatory repsone
- located on most sympathetic target cells
- G protein couples to Ca2+ second messenger system
ex) increase contraction of arterioles - raised blood pressure
what is the response of alpha 2 receptors?
inhibitory resonse
- located in digestive system - reduce the motality of the GI tract
- G protein couples to inhibit cyclic AMP system
ex ) decreased smooth muscle contraction - reduced GIT motility
also found pre-synaptically on cholinergic terminals where they can inhibit Acetylcholine release - can block the firing of the parasympathetic firing
what is the response of beta1 andrenergic receptors?
excitatory response
- located in heart - increase rate and force of heart contraction - couples via G protein to cyclic AMP/PKA
what is the response of the beta 2 andrenergic receptor ?
inhibitory
- smooth muscle of some vessels and organs
- found in the lungs and respond most to circulating adrenaline
- produces relaxation of smooth muscle
- vasodilation in skeletal muscle beds ( increase blood flow)
- R couples to cyclic AMP/PKA, nitric oxide release, reduces intracellular calcium
how are nuerotransmitters degraded post synapse?
noradrenaline is mainly taken up by the cells then metabolised/recycled
acetylcholine is broken down by the acetylcholinesterase at the synapse
drugs that act on the nerve terminal prevent what?
they effect neurotransmitter release
drugs that act on the post-synaptic membrane effect what?
the neurotransmitter-receptor interaction
describe the use of pilocarpine?
pilocarpine = muscarinic agonist
used as treatment of glaucoma - two effects
1) ciliary muscle contracts reducing tension on suspensory ligaments- lens can bulge out lowering intraocular pressur e
2) constriction of pupil may also reduce acqueous humour drainage blocked by iris
describe the use of atropine
it is a muscarinic antagonist (all muscarinic acetylcholine recpetors)- blocks the parasympathetic action
- inhibits secretions (salivary, bronchial, and sweat)
- bronchial muscle relaxation
- tachycardia (increase to 80/90 beats/min)
*used to reduce salivary and bronchial secretion during surgery - bradycardia, GIT hypermotility - use it for slow heart rate and over activiyt of the gut*
describe the use of salbutamol
adrenergic agonist -
activates beta 2 adrenergic receptors
- dilates bronchioles, treatment of asthma
- lack of effect at beta 1 means no side effects on the herat
describe the use of phenylephrine
it is an alpha1 agonist used as a nasal decongestion
describe the use of atenolol
adrenergic antagonist
blocks beta 1 andrenergic receptors - and lowers blood pressure - treatment of hypertension
describe the use of prazosin
adrenergic antagonist - blocks alpha 1, used for hypertension
what is diabetic autonomic neuropathy?
quite common disorder
- primary disorder of ANS
- neuropathy leads to dysfunction of cardiovascular, GI, urinary and reproductive systems
compare and contrast the nicotinic and muscarinic symptoms (site of receptor and respond to ACh from….)
nicotinic = site of receptor = all autonomic ganglia , motor end plates of skeletal muscle fibers, some CNS cell bodies and dendrites, respond to ACh fro parasympathetic and sympathetic nerve fibers, motor neurons, some CNS presynaptic terminals
muscarinic = site of receptor = effector cells (cardiac muscle, smooth muscle/glands), some CNS cell bodies and dendrites. respond to ACh from parasypathetic postganglionic fibers, some CNS presynaptic terminals
