Autonomic Nervous System Flashcards
(39 cards)
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
