ANS Flashcards
Where are the SNS nerves located?
T1-L2
Preganglia near the spinal cord
What do the post ganglia nerves do in the SNS?
Secrete nor-epi—> adrenergic fibers
- dopamine enters synaptic vessel
- dopamine beta hydroxylase converts dopamine to norepinephrine
- an action potential releases norepinephrine from the synaptic vessel
How is a norepinephrine signal terminated?
- re-uptake
- dilution by diffusion
- metabolism: monoamine oxidase (MAO) and catecholamines-o-methyl transerase (COMT)
How does SNS stimulation work on a cellular level?
- works on G coupled protein mechanism (not ion gated channel)
- activates adenolate-cyclase—> ∆es ATP into cAMP
- PDE3 stops mechanics of cAMP
What is the Alpha 1- post synaptic reaction?
** flight or flight
- activation increases intracellular Ca++
—> smooth muscle contraction and peripheral vasoconstriction
- bronchoconstriction: not what we want (ß-2= bronchodilation)
- inhibits insulin secretion
- stimulates glucogenolyis and gluconeogenesis
- mydriasis
- GI relaxation
What does Alpha 2 stimulation do?
- negative feedback loops*
- presynaptic in PNS
- decreased Ca entry into cell
- limits release of norepinephrine —> says “we’ve had enough”
- Post synaptic in CNS: (precedex)
- sedation
- decreased sympathetic outflow
- hypotension
- platelet aggregation
What happens with ß-1 stimulation at the postsynaptic receptor?
(ß-blockers block this)
- primarily the HEART
- increases HR, conduction velocity, and myocardial contractility
What happens we ß-2 stimulation occurs at the postsynaptic receptor?
(Balances alpha)
- stimulation leads to smooth muscle relaxation
- peripheral vasodilation
- decreases BP
- Bronchodilation.
- increases insulin secretion
- increases glycogenolysis and gluconeogenesis
- decreases GI motility
What is true regarding PNS?
- cranio-sacral nerve origin: CN III, V, VII, X and sacral nerves 2,3,4
- preganglia:near origins of innervation
- post-ganglia secrete ACH—> cholinergic fibers
What does acetylcholine (Ach) do?
- activates both arms of ANS
- choline + acetylcholine CoA—> acetylcholine
- Ca mediated action potential
- deactivated by AchE
What are the cholinergic receptors?
Nicotinic
Muscarinic
What happens to the heart with SNS and PNS stimulation?
SNS stim:
- increases HR and conduction velocity
- increases automaticity and contractility
PNS stim:
- decreases HR, conduction velocity and slightly decreases contractility
What happens to bronchial smooth muscle with SNS and PNS stimulation?
SNS stim:
- relaxation
PNS stim:
- contraction
What happens to the GI tract with SNS and PNS stimulation?
SNS stim: - decreased motility and secretion - sphincter contraction PNS stim: - increased motility and secretion - sphincter relaxation
What happens to the gallbladder and urinary bladder with SNS and PNS stimulation?
SNS stim:
- relaxation of gall bladder and smooth muscle of bladder
- urinary sphincter contracts
PNS stim:
- contraction of gall bladder and smooth muscle of bladder
- urinary sphincter relaxation
What is down regulation?
Extended exposure to agonists decreases the number of receptors, BUT not their response
- results in tachyphylaxis (rapidly decreased response to successive doses of a drug, rendering it less effective)
What is up regulation?
Chronic depletion of catecholamines or use or antagonists increases the number of receptors, BUT not their sensitivity
- may account for withdrawal syndrome with ß-blockers
There are 3 types of receptor desensitization: receptor uncoupling, sequestration, and down regulation. What is occurring in each?
RECEPTOR UNCOUPLING:
- inability of receptor to bind G protein —> alters function of receptor
- occurs rapidly (seconds to minutes)
SEQUESTRATION
- movement of receptors from cell surface to intracellular compartments
- occurs more slowly (minutes- hours)
- still reversible
DOWN-REGULATION:
- movement of receptors from cell surface to intracellular compartments, BUT then destroyed.
- prolonged process (hours-days)
What is pheochromocytoma?
Uncontrolled release of catecholamines d/t adrenal gland tumor
—> constant CNS stimulation
What are catecholamines?
(Catechole structure and amine/protein)
- both neurotransmitters and hormones
- act on adrenergic receptors
- dopamine, epinephrine, norepinephrine, isoproterenol, dobutamine
What are sympathomimetics?
- compounds that resemble catecholamines
- missing certain structures
- any drug that acts at SNS is considered a sympathomimetic
- some act on SNS, but don’t resemble catecholamines
What is an indirect sympathomimetic?
Ephedrine
- synthetic non-catecholamine
- releases endogenous norepinephrine from post ganglionic sympathetic nerve endings
What is a direct- acting sympathomimetic?
(Phenylephrine)
- catecholamines and synthetic catecholamines
- activate adrenergic receptors directly
_________________ is a pure alpha agonist, while _________________ is a pure ß-agonist.
- phenylephrine
- isoproterenol
What are the main things that cause autonomic dysfunction?
Aging: - orthostasis—> compensatory vasoconstriction fails - temperature instability - decreased stress response - decrease pre-junctions terminals Diabetes: - diarrhea - impotence - gastroporesis - hemodynamic instability —> hypotension
What does the adrenal medulla do?
Release epinephrine (80%) and norepinephrine in response to Ach trigger at cholinergic fibers d/t Ca++ influx
