Autonomic Nervous System Flashcards
How does two-neuron relay work in sympathetic and parasympathetic nervous systems?
efferent ANS fibers leaving the CNS are preganglionic, and release ACh in peripheral autonomic ganglia to excite postgaglionic neurons that innervate peripheral targets
What is the difference between parasympathetic and sympathetic motor nerve fiber neurotransmitter release?
sympathetic nerve fibers are adrenergic: release norepinephrine by exocytosis from their varicosities
parasympathetic nerve fibers are cholinergic: release acetylcholine by exocytosis of vesicles from their varicosities
What are varicosities?
swellings like bead on a string no postganglionic neurons that allow them to release neurotransmitters in a “sprinkling” fashion along their axons
Where are nicotinic ACh receptors found in the ANS?
cholinergic synapses on skeletal muscle end-plates (neuromuscular junction)
synapses on postganglionic neurons in autonomic ganglia
adrenal chromaffin cells
What are the characteristics of Nicotinic ACh receptors?
fast ligand-gated ion channels
depolarizing - initiate action potentials
nonselective ion channels
relay electrical excitation from one cell to the next
What is the role of nicotinic receptors in ganglion?
they relay preganglionic action potentials as postganglionic action potentials
What receptors are the principal receptors in the target organs of the sympathetic and parasympathetic nerves?
GCPRs
Which specific GCPRs are key for the autonomic nervous system?
Muscarinic ACh receptors
adrenergic receptors
additional receptors that respond to cotransmitters like NO, ATP, and peptides
What is the function of Muscarinic ACh receptors of target organs of the ANS?
mediate parasympathetic effects
What is the function of adrenergic receptors of target organs of the ANS?
mediate sympathetic effects
What is the basic function of the sympathetic nervous system?
fight or flight
What is the basic function of the parasympathetic nervous system?
rest and digest
What is the effect of postganglionic fibers that release neurotransmitters at GCPRs?
initiates biochemical signaling cascade in the target tissue rather than sending action potential
Where is norepinephrine released from?
released locally in tissues at most sympathetic postganglionic varicosities
from the adrenal medulla chromaffin cells into the bloodstream
Where is epinephrine released from?
adrenal medulla chromaffin cells into the bloodstream
What are the principal sympathetic neurotransmitters?
norepinephrine and epinephrine - but also can use ACh
What is the location of, specific G-protein subunit, and effect of NE/E binding to alpha-1 adrenergic receptors?
location: smooth muscle.
Binds to Ga(q)
Effect is smooth muscle contraction
What is the location of, specific G-protein subunit, and effect of NE/E binding to Beta-1 adrenergic receptors?
location: heart, juxtaglomerular cells
Binds to Ga(s)
Effect is promotion of contraction, increase HR
What is the location of, G-protein subunit, and effect of NE/E binding to Beta-2 adrenergic receptors?
location: smooth muscle
Binds to Ga(s)
Effect is smooth muscle relaxation
What is the effect of ACh binding to nicotinic receptors?
channels are opened and can depolarize the cell to 0mV
What is the function of muscarinic ACh receptor M2 binding with released ACh?
What GCPR subunit/pathway is it associated with?
Couples to Ga(i), GBy
Function: Slows heart rate through (1) activation of a K+ channel via Gβγ subunits, leading to hyperpolarization, and (2) through inhibiting adenylyl cyclase via Gi, turning off the formation of the cAMP second messenger and reducing PKA activity
What is the function of muscarinic ACh receptor M3 binding with released ACh?
What GCPR subunit/pathway is it associated with?
Couples to Ga(q).
Function: elevate intracellular Ca2+ via IP3 pathway.
This does:
1) smooth muscle contraction
2) stimulates glands to secrete
3) elevates nitric oxide (NO) production in endothelial cells, which leads to smooth muscle relaxation and therefore vasodilation
What does AChE enzyme do?
catalyzes the inactivation of ACh via hydrolysis back into choline and acetate in the extracellular space of the synaptic terminal - prevents accumulation of ACh in the blood and therefore excess parasympathetic action
What is the role of ATP in the ANS?
it activates purinergic receptor (ligand-activated non-selective cation channels) which initiates smooth muscle contraction in the arterioles and vas deferens
What is the importance of NO in sexual arousal and how do ED drugs work?
NO potentiates blood flow during sexual arousal via stimulation of cGMP. ED drugs prolong the life of cGMP by stopping it’s breakdown by a PDE.
How does nitroglycerine work?
improves coronary circulation by releasing nitric oxide, which diffuses into vessel smooth muscle to allow for vasodilation.
How does the body respond to increase in arterial blood pressure?
- afferent input: baroreceptors sense increased tension in the aortic arch and carotid sinus in increase their action potential firing rate.
- action potentials are sent down baroreceptor axons to the medulla of the brainstem.
- efferent outflow: parasympathetic NS is excited and sympathetic NS is inhibited, leading to decrease in blood pressure.
How does the body respond to increase in arterial blood pressure?
- afferent input: baroreceptors sense increased tension in the aortic arch and carotid sinus in increase their action potential firing rate.
- action potentials are sent down baroreceptor axons to the medulla of the brainstem.
- efferent outflow: parasympathetic NS is excited and sympathetic NS is inhibited, leading to decrease in blood pressure.
How do baroreceptors counter orthostatic hypotension?
firing rate falls with decreased tension in aorta, action potentials transmitted to the brainstem decrease, sympathetic nervous system is excited and parasympathetic is inhibited
What is the exception to the general rule of norepinephrine always being a sympathetic transmitter?
sweat glands
What is the exception to the general rule that sympathetic pathway is a two-neuron pathway?
adrenal gland
alpha-1 receptor pathway
norepinephrine binds to a1 -> activates G(q) -> PLC -> IP3 & DAG -> increase calcium, activation of PKC
alpha-2 receptor pathway
norepinephrine binds to a2 receptor -> activates G(i) -> inhibits adenylyl cyclase -> cAMP decreased
beta receptor pathway
norepinephrine binds to beat receptor -> activates G(s) -> stimulates adenylyl cyclase -> cAMP increases and PKAs are activated
Alpha 1 location and effect
contract ANS smooth muscle, glands
Alpha 2 location and effect
varied effect - presynaptic terminals of adrenergic nerves - inhibits NE release
Beta 1 location and effect
increases HR and contraction, heart muscle, kidney juxtaglomerular cells, fat cells
beta 2 location and effect
relaxation
smooth muscle, glands, enteric neurons
Beta 3 location and effect
relaxation, prevention of urination
bladder, fat cells
