Physiology 2130 Lecture Notes - Lecture 29: Autonomic Nervous System, Muscarinic Acetylcholine Receptor, Otto Loewi
1 May 2018
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Department
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Professor
Lecture 029: Autonomic Nervous System II
Otto Loewi: wanted to uncover if the transmission of signals is chemical in nature or electrical
● Stimulated vagus nerve
○ See that the heart rate slows
● Remove a fluid sample (with the transmitter) from the slowed heart
● Add fluid to recipient heart
○ See that the heart rate slows
● Thus: transmission must be chemical in nature
Receptor Agonist Antagonist Action Mechanism
●Nicotinic Skeletal
Muscle (NM)
●ACh
●Nicotine
●d-Tubocurarine
(South America
Indian poison)
●α-Bungarotoxin
(Snake poison)
●Ligand
Gated
●Opens Na+/K+ Channels
●Fast EPSP
●Nicotinic ANS
Ganglion (NN)
●ACh
●Nicotine
●Hexamethonium ●Ligand
Gated
●Opens Na+/K+ Channels
●Fast EPSP
●Muscarinic ANS
Ganglia,
Parasympathetic
Organs (5 subtypes)
●ACh
●Muscarine
(toadstool
pois on)
●Atropine ●G-protein
coupled
●Modify K+, Ca2+ Channel
conductances
●Slow effects (EPSP)
○Because it’s a GPCR
●Adrenergic Alpha (4
subtypes)
●NorE > Epi ●Phentolamine ●G-protein
coupled
●Slow EPSP
●Slow IPSP
●Adrenergic Beta (3
subtypes)
●NorE < Epi ●Propranolol ●G-protein
coupled
●Slow EPSP
●Slow IPSP
Points to remember
● Nicotinic receptor at ANS ganglion has a different structure to that at the NMJ
●Both the nicotinic receptor at ANS ganglion and at the NMJ is ionotropic with fast
EPSP
● Muscarinic receptor (GPCR, slow EPSP) also occur at the ANS ganglia
● At the ANS ganglia, ACh acts on TWO different postsynaptic receptor types
○ Nicotinic
○ Muscarinic
●Metabotropic receptors (acting through G-proteins) have different subtypes
○ Muscarinic (5)
○ Adrenergic Alpha (4)
○ Adrenergic Beta (3)
●Co-transmission
○ More than one receptor types fires
○ Can have very fast electrical changes or very slow electrical changes
○ Has the possibility of different things occuring at the same ganglia
■ Leads to different types of potentiation
○ANS Ganglia
find more resources at oneclass.com
find more resources at oneclass.com
■Nicotinic receptors
● Fast EPSP (10-550 ms)
● Initiates action potential
■Muscarinic receptors
● Slow EPSP (100 ms)
● Increase excitability
■Peptidergic receptors
● Very slow EPSP (minutes)
● Increase excitability
● Similar to long term potentiation
● Modify ion channels
○Increase sensitivity to
neurotransmitters
○Insert more ion channels into the membrane
○Alter gene expression to produce more ion channels
○Enteric Nervous System (plexuses in the gut)
■ Most postganglionic axon have varicosities (bulbous enlargement)
● Contains vesicles with neurotransmitters
■Adrenergic varicosities
● DECREASE/inhibit activity (hyperpolarizes)
● In postganglionic sympathetic nerves
● Release NorE to act on adrenergic receptors in smooth muscle,
blood flow, glands
■Cholinergic varicosities
● INCREASE/excite activity (in smooth muscle, blood flow, glands)
● In postganglionic parasympathetic nerves
■ATP Purinergic receptors
● ATP is the excitatory transmitter
● Fast excitatory synaptic effects
● In nerve gut plexus, ATP is co-sorted and co-released with
neurotransmitters
■ Varicosities also release peptides
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Otto loewi: wanted to uncover if the transmission of signals is chemical in nature or electrical. Remove a fluid sample (with the transmitter) from the slowed heart. Thus: transmission must be chemical in nature. Nicotinic receptor at ans ganglion has a different structure to that at the nmj. Both the nicotinic receptor at ans ganglion and at the nmj is ionotropic with fast. Muscarinic receptor (gpcr, slow epsp) also occur at the ans ganglia. At the ans ganglia, ach acts on two different postsynaptic receptor types. Metabotropic receptors (acting through g-proteins) have different subtypes. Can have very fast electrical changes or very slow electrical changes. Has the possibility of different things occuring at the same ganglia. Insert more ion channels into the membrane. Alter gene expression to produce more ion channels. Enteric nervous system (plexuses in the gut) Most postganglionic axon have varicosities (bulbous enlargement) Release nore to act on adrenergic receptors in smooth muscle, blood flow, glands.
