Neurotransmitter Release Mechanism

Questions and Answers

What role does soluble α-SNAP play in synaptic transmission?

Binding to the SNARE complex to promote NSF binding (correct)

Promoting the degradation of synaptobrevin

Facilitating the uptake of calcium ions into the presynaptic terminal

Inhibiting the release of neurotransmitters

How does botulinum toxin affect synaptic transmission?

It activates postsynaptic receptors

It enhances the release of neurotransmitters

It blocks vesicle exocytosis (correct)

It increases calcium ion influx into the presynaptic terminal

What happens to the intracellular calcium concentration [$Ca^{2+}$]i after fusion completion?

It fluctuates randomly without any specific direction

It increases rapidly to promote further vesicle fusion

It rapidly decreases as Ca2+ is extruded and taken up by mitochondria (correct)

It remains constant to maintain synaptic activity

Which protein is responsible for the recycling endocytosis of synaptobrevin?

synaptobrevin itself Signup and view all the answers

In the context of Lambert-Eaton myasthenic syndrome, what does a positive antibody study for voltage-gated calcium channels indicate?

An autoimmune response targeting calcium channels leading to muscle weakness Signup and view all the answers

What is the main function of the N-ethylmaleimide–sensitive factor (NSF) in the SNARE complex?

To provide energy for SNARE complex disassembly Signup and view all the answers

Which of the following statements best describes the process of synaptic transmission?

Neurotransmitters are released into the synaptic cleft and bind to postsynaptic receptors. Signup and view all the answers

What initiates the process of vesicle fusion at the presynaptic terminal?

Opening of voltage-gated calcium channels leading to calcium influx Signup and view all the answers

Which component of the SNARE complex is located in the presynaptic membrane?

syntaxin Signup and view all the answers

Study Notes

SNARE Protein Functionality

Composed of v-SNAREs (from vesicle membranes) and t-SNAREs (from target membranes).
Key v-SNARE includes Synaptobrevin.
Key t-SNAREs include Syntaxin-1 and SNAP-25.

Synaptotagmin

Functions as a calcium sensor during exocytosis.
Binds Ca2+, promoting neurotransmitter release.

Docking and Priming Stages

After docking near the presynaptic membrane, Sec-1/Munc18, Munc13, and RIM facilitate SNARE complex assembly.
Priming stage 1 involves coiling of SNARE helices, forming a stable trans-SNARE complex.
Priming stage 2 sees complexin insertion into the trans-SNARE complex, preventing premature fusion.

Calcium Influx and Fusion

Voltage-gated Ca2+ channels allow calcium influx aligning with presynaptic active zones.
Ca2+-bound synaptotagmin binds acidic phospholipids, displacing complexin and initiating fusion-pore opening.

Synaptic Transmission Sequence

Membrane fusion occurs when the fusion pore opens, leading to neurotransmitter release.
Following fusion completion, intracellular calcium levels decline rapidly through PMCA and mitochondrial uptake.

SNARE Protein Recycling

Soluble α-SNAP binds to the SNARE complex and recruits NSF ATPase, leading to protein recycling.
Synaptobrevin undergoes recycling endocytosis, while syntaxin and SNAP-25 remain for subsequent vesicle fusion.

Botulinum Toxin Effects

Botulinum toxin prevents vesicle exocytosis by occupying binding sites on SNARE proteins, inhibiting neurotransmitter release.
True statements regarding its mechanism do not include preventing action potentials or calcium channel opening.

Gap Junctions in Electrical Synapses

Comprised of two connexons, permitting communication between adjoining neurons.

Key Neurotransmitter in Neuromuscular Junctions

Acetylcholine is the primary neurotransmitter involved.

Saxitoxin Poisoning Case

Symptoms include vomiting, diarrhea, and facial numbness after consuming potentially contaminated mussels, indicating possible saxitoxin exposure.

Lambert-Eaton Myasthenic Syndrome (LEMS)

Positive antibody studies for voltage-gated calcium channels suggest LEMS in a patient with small cell carcinoma and muscle weakness.

Description

Explore the intricate process of neurotransmitter release involving SNARE proteins and calcium signaling. This quiz covers key components like v-SNAREs, t-SNAREs, and the role of synaptotagmin in exocytosis. Test your knowledge on the sequence of events leading to synaptic transmission.