24 Questions
What is the main function of the parasympathetic division of the ANS?
Performs maintenance activities and conserves body energy
Where is Acetyl-CoA synthesized in neurons?
Mitochondria
What is the rate-limiting step in Acetylcholine (ACh) synthesis?
Action of choline transporter in ACh synthesis
Which enzymes catalyze the synthesis of Acetylcholine (ACh)?
Choline acetyltransferase (ChAT)
What is the function of Cholinergic neurons?
Contain small membrane-bound vesicles with ACh
How is choline transported into neuron terminals?
By a Na+-dependent membrane choline cotransporter
What triggers the release of vesicles at the terminal?
Extracellular Ca2+ influx
Which proteins interact with Ca2+ ions to destabilize storage vesicles?
Vesicular associated membrane proteins (VAMPs) and synaptosome associated protein (SNAP)
Which substances can unpredictably prolong muscle paralysis when used as adjuncts to general anesthesia?
Streptomycin and neomycin
How do botulinum toxin and β-bungarotoxin affect the release of ACh from vesicles?
By enzymatic removal of amino acids from fusion proteins
What effect does Latrotoxin, found in black widow spider venom, have on synaptic vesicles?
Causes all stored ACh to empty into the synaptic gap
Which agents inhibit Ca2+ entry during the release process of vesicles?
Mg2+ and various aminoglycoside antibiotics
What is the main function of the Sympathetic division of the ANS?
Mobilizing the body during extreme situations
Which enzyme catalyzes the synthesis of Acetylcholine (ACh) from acetyl-CoA and choline?
Choline acetyltransferase (ChAT)
What is a direct inhibitor of the enzyme Choline acetyltransferase (ChAT)?
Naphthoquinones
Which group of drugs can block the carrier that transports choline into neuron terminals?
Hemicholiniums
Where is Acetyl-CoA synthesized in neurons before being used in Acetylcholine (ACh) synthesis?
Mitochondria
What is the role of the antiporter that transports synthesized ACh into vesicles?
Removing protons
What is required for the release of Acetylcholine (ACh) from the vesicles into the synaptic cleft?
Increased Ca2+ concentration
Which proteins interact with Ca2+ ions to destabilize the storage vesicles during the release process?
SNAP and VAMPs
How do Mg2+ ions and aminoglycoside antibiotics affect the release of Acetylcholine (ACh) from vesicles?
Prolong the release
What is the mechanism through which Botulinum toxin and β-bungarotoxin block the release of Acetylcholine (ACh) from vesicles?
Enzymatic removal of amino acids from fusion proteins
What effect does Latrotoxin from black widow spider venom have on the synaptic vesicles?
Causes emptying of all ACh stored in the vesicles
What is the impact of agents like streptomycin and neomycin on muscle paralysis when used during general anesthesia?
Prolong muscle paralysis unpredictably
Study Notes
Autonomic Nervous System (ANS)
- The ANS has two divisions: Sympathetic and Parasympathetic
- The Sympathetic division mobilizes the body during extreme situations
- The Parasympathetic division performs maintenance activities and conserves body energy
- The two divisions counterbalance each other's activity
Cholinergic Transmission Synthesis
- Cholinergic neurons contain large numbers of small membrane-bound vesicles concentrated near the synaptic portion of the cell membrane
- ACh is synthesized in the cytoplasm from acetyl-CoA and choline by the catalytic action of Choline acetyltransferase (ChAT)
- α-ketoacids and naphthoquinones are direct inhibitors of the enzyme ChAT
- Acetyl-CoA is synthesized in mitochondria, which are present in large numbers in the nerve ending
Choline Transport
- Choline is transported from the extracellular fluid into the neuron terminal by a Na+-dependent membrane choline cotransporter (Carrier A)
- This carrier can be blocked by hemicholiniums
- The action of the choline transporter is the rate-limiting step in ACh synthesis
ACh Transport and Release
- Synthesized ACh is transported from the cytoplasm into the vesicles by an antiporter that removes protons (carrier B)
- This transporter can be blocked by vesamicol
- Release of ACh is dependent on extracellular Ca2+ and occurs when an action potential reaches the terminal and triggers sufficient influx of Ca2+ ions
- The increased Ca2+ concentration "destabilizes" the storage vesicles by interacting with special proteins: VAMPs and SNAP
Inhibitors of ACh Release
- Mg2+ and various aminoglycoside antibiotics (e.g. streptomycin and neomycin) can inhibit Ca2+ entry and unpredictably prolong muscle paralysis
- Botulinum toxin and β-bungarotoxin block the ACh vesicle release process through the enzymatic removal of two amino acids from one or more of the fusion proteins
- Latrotoxin, the toxin in black widow spider venom, causes all the ACh stored in synaptic vesicles to empty into the synaptic gap, resulting in muscular spasm
Test your knowledge on the two divisions of the autonomic nervous system - Sympathetic and Parasympathetic, as well as cholinergic transmission. Learn how these divisions function, their roles in the body, and the process of cholinergic transmission in neurons.
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