NEUROTRANSMITTER CHEMISTRY OF THE AUTONOMIC NERVOUS SYSTEM Flashcards
What is the traditional classification of autonomic nerves based on?
It is based on the primary transmitter molecules—acetylcholine or norepinephrine—released from their terminals and varicosities.
What are cholinergic fibers?
Cholinergic fibers are peripheral ANS fibers that synthesize and release acetylcholine.
Which fibers are considered cholinergic?
All preganglionic efferent autonomic fibers and somatic motor fibers to skeletal muscle are cholinergic.
What type of fibers release norepinephrine?
Most postganglionic sympathetic fibers release norepinephrine; they are noradrenergic fibers.
What is the role of acetylcholinesterase (AChE)?
AChE efficiently splits acetylcholine into choline and acetate, terminating the action of the transmitter.
How is acetylcholine synthesized?
Acetylcholine is synthesized in the cytoplasm from acetyl-CoA and choline through the action of choline acetyltransferase (ChAT).
What is the function of vesicular monoamine transporter (VMAT)?
VMAT is responsible for transporting catecholamines into storage vesicles.
What is the rate-limiting step in catecholamine synthesis?
The conversion of tyrosine to dopa by tyrosine hydroxylase is the rate-limiting step.
What happens to norepinephrine after its release?
Norepinephrine can be metabolized by several enzymes, and its metabolic products are excreted in urine.
What are the two processes that terminate noradrenergic transmission?
Termination occurs through simple diffusion away from the receptor site and reuptake into the nerve terminal by NET.
What do the vesicles of cholinergic and adrenergic nerves contain?
The vesicles contain other substances in addition to the primary transmitter, sometimes in the same vesicles and sometimes in a separate vesicle population.
What roles do cotransmitters play in cholinergic and adrenergic nerves?
Cotransmitters provide a faster or slower action to supplement or modulate the effects of the primary transmitter and participate in feedback inhibition of the same and nearby nerve terminals.
What influences the growth of neurons and transmitter expression?
Neurotrophic factors released from target tissues influence growth and synapse formation by neurons.
How can the transmitters released from specific neurons change?
Transmitters can change in response to environmental factors such as the light-dark cycle.
