Autonomic Nervous System Flashcards
Drugs that target the ANS mimic or block the actions of what class of molecules?
neurotransmitters
Which part of the nervous system do most drugs influence (regardless of whether that system is targeted or not)?
ANS
How many steps if the process of signaling the effector organs through the ANS?
2 steps (pre and post ganglionic)
What are the two major divisions of the ANS and where are they located? Where do they originate from?
Sympathetic (thoracolumbar) and parasympathetic (craniosacral). Originate in nuclei in the CNS
Where do the sympathetic preganglionic fibers terminate and where do the post ganglionic fibers run to?
terminate in ganglia of the paravertebral chains and run to tissues
Where do the parasympathetic preganglionic fibers terminate and where do the post ganglionic fibers run to?
terminate in walls of innervated organs and run to more specific location within the organ
What neurotransmitter is used by the somatic nervous system and to which receptor does it bind?
Acetylcholine binds to Nm-type nicotinic receptor (Nm=nicotinic muscle)
Which neurotransmitter is released by both the sympathetic and parasympathetic preganglionic neurotransmitters and to what receptor does it bind?
acetylcholine binds to Nn-type nicotinic receptor on postganglionic neurons (nicotinic neuronal)
What neurotransmitter is used by postganglionic parasympathetic neuron and to which receptor does it bind?
Acetylcholine binds to a muscarinic receptor (G-protein linked)
What neurotransmitter is used by postganglionic sympathetic neuron and to which receptor does it bind?
Norepinephrine binds to adrenergic receptor of type a or b (G protein linked)
Name 3 exceptions where sympathetic post ganglionic fibers do not release norepinephrine.
- Sweat glands-ACH
- Renal Vascular Smooth Muscle-Dopamine
- Chromaffin cells are specialized post-ganglionic neurons that release epi and NE from the adrenal medulla
Which division of the ANS tends to have a more widespread output and which tends to be more discrete?
Sympathetic-more widespread (pre:post is 1:20)
Parasympathetic-more discrete (Pre:post is 1:1)
Where is the enteric nervous system located?
in the walls of the GI system
Where does the enteric nervous system get input from?
preganglionic parasympathetic fibers, postganglionic sympathetic fibers, and sensory input from the wall of the gut
What does the enteric nervous system control?
smooth muscle of the gut, and secretory cells (motility and secretion)
Explain the synthesis of Ach.
From acetyl coA and choline by choline acetyltransferase, then packaged into vesicles for storage
Explain the degradation of Ach.
acetylcholinesterase-mediated cleavage of ACH into acetate and choline which are then recycled
Why are drugs that block the synthesis, storage and release of ACH not particularly useful?
effects are not selective
What is the mechanism of action of Botulinum toxin A
blocks local Ach release to inhibit muscle contraction
Explain the synthesis of NE.
- tyrosine hydroxylated to DOPA
- DOPA decarboxylated to dopamine
- within vesicles dopamine is hydroxylated to NE
Explain the termination of NE signaling.
within the cleft diffusion and reuptake; outside the cleft NE is metabolized and excreted
What are drugs that block NE synthesis, storage and release used to treat?
hypertension
To which G protein are M2 and M4 receptors coupled and what is it’s effect intracellularly?
they are coupled to Gi and inhibit adenylate cyclase (decreases cAMP) and activate K+ channels causing hyperpolarization
To which G protein are M1, M3 and M5 receptors coupled and what is it’s effect intracellularly?
they are coupled to Gq which activates phospholipase C causing increase in DAG and IP3 leading to increased Ca2+ levels
Where are alpha 1 and 2 adrenergic receptors located?
vascular smooth muscle, presynaptic nerve terminals, and platelets in the brain
Where are beta adrenergic receptors located?
on most types of smooth muscle, cardiac muscle, some presynaptic nerve terminals and the brain
What is the main effect of alpha 1 adrenergic receptor activation?
increase in PLC leading to increase in IP3 and DAG leading to smooth muscle contraction
What is the main effect of alpha 2 adrenergic receptor activation?
inhibition of Adenylate Cyclase leading to decrease in cAMP, and activation of K+ channel (hyperpolarization); inhibition of NT release
What is the main effect of beta 1 adrenergic receptor activation?
Increase in adenylate cyclase causing increase in cAMP leading to increase in force and rate of contraction of heart
What is the main effect of beta 2 adrenergic receptor activation?
Increase in adenylate cyclase causing Increase in cAMP leading to smooth muscle relaxation
What is the main effect of beta 3 adrenergic receptor activation?
Increase in adenylate cyclase causing Increase in cAMP leading to lipolysis
What are presynaptic receptors that respond to the transmitter substances released called?
autoreceptors
Are autoreceptors usually inhibitory or excitatory?
inhibitory
Name 5 major targets for drugs to modulate the ANS.
transmitter synthesis, storage, release and termination and NT receptors.
How to nicotinic neuronal and nicotinic muscular receptors differ from each other?
subunit composition, each is made up of 5 subunits but the subunits differ
Action and receptor for sympathetic nervous system on SA node?
accelerates; Beta 1 and 2 receptors
Action and receptor for parasympathetic nervous system on SA node?
decelerates; M2 receptor
Action and receptor for sympathetic nervous system on Bronchiolar Smooth muscle?
relaxes; Beta 2 receptor
Action and receptor for parasympathetic nervous system on bronchiolar smooth muscle?
contracts; M3 receptor
Action and receptor for sympathetic nervous system on Bladder wall?
relaxes; Beta 2
Action and receptor for parasympathetic nervous system on Bladder wall?
contracts; M3
