Autonomic Cholinergic Physiology Flashcards
What is the major neurotransmitter in the ANS?
Acetylcholine
What are the 2 major sites in which acetylcholine acts in autonomic transmission?
Communication between all Preganglionic and postganglionic autonomic neurons, communication between all postganglionic parasympathetic neurons and their target organs
What is the postganglionic neurotransmitter that stimulates the target organ in the SNS?
Norepinephrine
What type of stimulation slows the heart?
Vagal stimulation
What is the transferable chemical mediator released by stimulation of the vagus nerve?
Acetylcholine
Is ANS effects on target organs electrical or chemical?
Chemical
What muscle in the eyes causes accommodation?
Ciliary muscle
In general what are the effector functions of the PNS?
Smooth muscle contraction, glandular secretion, cardiac inhibition
What are coupled to second messenger systems which in turn trigger the target cell response?
Muscarinic Ach receptors
What type of receptors are metabotropic, trigger intracellular biochemical cascades, are relatively slow sustained processes, recruit multiple effectors, undergo amplification of signal?
Muscarinic ACh receptors
How many ACh muscarinic receptor subtypes are there?
5
What is the second messenger in muscarinic receptors (M3,M1,M5)?
IP3 (phospholipase C system)
The binding of ACh to a muscarinic ACh receptor stimulates what type of G protein? (M3,M1,M5)
Gq
What is the end product of the phospholipase C system, that triggers the opening of the ER lumen causing a large increase in intracellular Ca+?
IP3 (M3,M1,M5)
The Gq protein stimulates what system to produce the second messenger IP3?
Phospholipase C system
What type of ACh muscarinic receptors cause smooth muscle contraction and stimulation of secretion?
M3 (also M1,M5)
The binding of ACh to a muscarinic ACh receptor stimulates what type of G protein? (M2,M4)
Gi
Gi inhibits what from converting ATP to cAMP?
Adenylate Cyclase system
What is the second messenger in muscarinic ACh receptors M2,M4 that is used to create PKA?
cAMP (adenylate cyclase system)
A reduction in PKA has what effect on the heart?
Reduced contraction
What stimulates cardiac muscle?
Increased adenylate cyclase
What inhibits cardiac muscle?
Decreased adenylate cyclase
What stimulates smooth muscle?
Increased phospholipase C
What inhibits smooth muscle?
Increased adenylate cyclase
What stimulates glands?
Increased phospholipase C
What mediate the effects of vagal stimulation and lead to bradycardia?
M2 - muscarinic receptor
In M2 muscarinic receptor vagal stimulation bradycardia can be induced in the SA node by what vagus nerve?
Right vagus
In M2 muscarinic receptor vagal stimulation bradycardia can be induced in the AV conductive tissue by what vagus nerve?
Left vagus
The binding of ACh to a M2 muscarinic ACh receptor causes what 2 effects?
Activation of K+ channels
Inhibition of adenylate cyclase
Why aren’t muscarinic receptors ideal for ganglionic transmission?
Too slow
What type of receptor is used for all Preganglionic neuronal-ganglionic terminals?
Nicotinic acetylcholine receptors
What properties of nicotinic ACh receptors make them ideal for Preganglionic neuronal cleft signaling?
Fast response - rapid onset, rapid offset
ACh held tightly within the cleft
Receptor protein functions as an ion channel activation leads to Na+ influx ( and some Ca+ influx) leads to depolarization of post synaptic neuron and activation of postganglionic neuron describes what?
Ionotropic receptor (nicotinic receptor)
What mediates transmission at both sympathetic and parasympathetic autonomic ganglia?
Acetylcholine acting at nicotinic ACh receptors
Ionotropic receptors (ion channels), fast transmission ( order of milliseconds) and no 2nd messenger coupling is characteristic of what?
Nicotinic ACh receptors
What are 2 nicotinic antagonists that block transmission?
Curare, hexamethonium
Nicotinic receptor transmission is potentiated with what substance?
Acetylcholinesterases
Different subtypes of nicotinic receptors exist do to different combinations of what in the pentameric ionotropic receptors?
Alpha, beta, gamma, delta, epsilon subunits
What receptor subtype is found at the skeletal NMJ, causes depolarization and contraction, and has agonist of ACh and nicotine
Nm
What receptor subtype is found in autonomic ganglia and the adrenal medulla cause depolarization and firing of post synaptic neurons and have agonists of ACh and nicotine?
Nn
What subtype of nicotinic receptor is found in the brain and spinal cord, has pre-Junctional control of transmitter release, and has agonists of ACh and nicotine?
Ncns
What are 2 examples of cholinesterases?
Acetylcholinesterases
Butyrylcholinesterase
What has a high affinity for ACh, found at cholinergic synapses and neuroeffector junctions in pre and post synaptic membranes, important for termination of action of ACh released from neurons, choline re uptake important for recycling and synthesis of new transmitter describes what?
AChE
Prefers butyrylcholine, also termed pseudocholinesterase or non-specific cholinesterase, present in plasma, function unclear, not important for termination of neuronally released ACh but important for termination of action of some cholinergic drugs describes what?
BChE
AChE degrades ACh into what 2 constituents?
Choline and acetic acid
What 2 constituents joined by choline acetyltransferase are needed to synthesize ACh?
Choline and acetyl-CoA
