6. Synaptic Transmission

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Questions and Answers

What is the primary function of GABAergic synapses as described in the content?

To enhance excitatory synaptic transmissions.

To generate action potentials without excitatory inputs.

To increase the frequency of neuronal firing.

To prevent excitation via excitatory synapses. (correct)

Which factor is most effective for GABAergic synapse inhibition of excitatory inputs?

Inhibitory synapses that exclusively target dendritic spines.

Inhibitory synapses that are far from the soma.

Inhibitory synapses that are located distal on dendrites.

Inhibitory synapses that are close to the excitatory inputs. (correct)

What role do dendrites play in synaptic transmission?

They are responsible for generating intrinsic action potentials.

They solely transmit excitatory signals to the soma.

They integrate synaptic inputs from various sources. (correct)

They only amplify local action potentials.

Which of the following is a method used for the localization of neurotransmitters?

Immunocytochemistry. (C) Signup and view all the answers

What characterizes distal synapses on dendrites compared to proximal ones?

They are generally weaker than proximal synapses. (B) Signup and view all the answers

What occurs during hyperpolarization of a neuron?

An efflux of K+ ions out of the cell (D) Signup and view all the answers

What defines the absolute refractory period in a neuron?

The neuron cannot fire at all (C) Signup and view all the answers

In chemical synapses, what is the role of synaptic vesicles?

They store neurotransmitters for release (B) Signup and view all the answers

Which structures are involved in forming a chemical synapse?

Presynaptic membrane, synaptic cleft, and postsynaptic membrane (B) Signup and view all the answers

What is a characteristic feature of electrical synapses?

They allow for bidirectional ion flow between cells (A) Signup and view all the answers

What is typically true about the direction of information flow at a synapse?

It flows from presynaptic neurons to target cells only (C) Signup and view all the answers

Which of the following is an example of where electrical synapses can be found?

Myocardium (D) Signup and view all the answers

Which type of synapse involves an axon connecting to a dendritic spine?

Axospinous (B) Signup and view all the answers

What characterizes Gray's type I membrane differentiation?

Thicker postsynaptic membrane (A) Signup and view all the answers

Which neurotransmitter is considered an amine?

Acetylcholine (B) Signup and view all the answers

What is the role of SNARE complexes during vesicle cycling?

Facilitating fusion of vesicles with cell membrane (A) Signup and view all the answers

During which stage of vesicle cycling does synaptotagmin play a crucial role?

Vesicle priming (B) Signup and view all the answers

What primarily distinguishes the classical model of vesicle cycling from the modern theory?

Mobility of vesicles (D) Signup and view all the answers

Which neurotransmitter group includes short amino acid chains?

Peptides (D) Signup and view all the answers

Where does the synthesis of peptide neurotransmitters primarily occur?

rER and Golgi apparatus (C) Signup and view all the answers

Which of the following is generally associated with Gray's type II synapse?

Symmetrical membrane differentiation (B) Signup and view all the answers

What primarily determines the postsynaptic response in terms of synaptic transmission?

Number and sensitivity of postsynaptic receptors (D) Signup and view all the answers

What does the term mEPSC refer to in synaptic transmission?

Miniature excitatory postsynaptic currents (B) Signup and view all the answers

How does an increase in presynaptic calcium concentration impact neurotransmitter release?

It increases the probability of release. (B) Signup and view all the answers

What is the reversal potential for an excitatory postsynaptic potential (EPSP)?

More positive than the action potential threshold (C) Signup and view all the answers

In terms of synaptic inhibition, what happens when the reversal potential is more negative than the action potential threshold?

It generates an inhibitory postsynaptic potential. (B) Signup and view all the answers

What does temporal summation of EPSPs involve?

Inputs that occur in succession at the same synapse (C) Signup and view all the answers

Which of the following best describes spatial summation of EPSPs?

Simultaneous EPSPs from different synapses (B) Signup and view all the answers

What effect does the presence of a short delay between two stimuli have on PSP summation?

It limits the potential for summation. (A) Signup and view all the answers

What is meant by the term 'quanta' in synaptic transmission?

The minimal unit of neurotransmitter released (B) Signup and view all the answers

Why might observing quantal increases in postsynaptic current (PSC) amplitude be challenging in practice?

Variability in receptor distribution prevents clear detection. (A) Signup and view all the answers

What characterizes the 'kiss and run' exocytosis method?

Partial release of neurotransmitter while the vesicle remains available for release (D) Signup and view all the answers

Which proteins are responsible for mediating the disassembly of the SNARE complex?

NSF and SNAP (D) Signup and view all the answers

How do ionotropic receptors facilitate neurotransmission?

By binding neurotransmitters that open the channel directly (C) Signup and view all the answers

What is the primary role of neurotransmitter transporter proteins in synaptic function?

To locate neurotransmitters in cytosol and reload them into vesicles (A) Signup and view all the answers

What does the variable 'Pr' in the equation for response represent?

The probability of vesicle release influenced by calcium levels (C) Signup and view all the answers

What is the total expected response at a synapse if the number of vesicles (N) is 3, the probability of release (Pr) is 0.5, and the quantal amplitude (Q) is 2?

6 (D) Signup and view all the answers

What typically happens to vesicles in the clathrin-mediated endocytosis process?

They are internalized and recycled after neurotransmitter release (A) Signup and view all the answers

What is the expected outcome when there is variability in measured quanta at the same synapse?

It suggests changes in the postsynaptic receptor population (A) Signup and view all the answers

How is degradation of neurotransmitters achieved after their release?

Through enzymatic processes in the cytosol or synaptic cleft (B) Signup and view all the answers

Which statement about vesicle release probability is true?

It varies by synapse type, with values ranging from approximately 0.1 to 0.9 (D) Signup and view all the answers

Study Notes

Neuroscience Lecture Notes

Course: XY3291 - Neuroscience
Lecturer: Constantin-Iulian Chiță
Date: January 20th, 2025

Synaptic Transmission

The transmission of information across a synapse is crucial to the nervous system's function.
It generally occurs in one direction: neuron to target cell.

Action Potential

This is a temporary change in the neuronal membrane potential, facilitating electrical impulse transmission and neurotransmitter release.
Resting state potential: approximately -70 mV.
This negative potential arises from unequal ion distribution across the membrane.
Ion movement is enabled by active (Na+/K+ pumps) and passive (Na+ and K+ channels) transport.
Active transport requires energy (ATP).
Passive transport does not require energy and relies on ionic channels.

Action Potential Stages

Depolarization: Increased Na+ permeability causes Na+ ions to flow in, changing the membrane potential to positive values. This occurs after the threshold potential.
Repolarization: K+ ions flow out of the neuron, restoring the negative membrane potential to resting values.
Hyperpolarization: Further outflow of K+ causes the membrane potential to briefly become more negative than the resting state, before returning to the resting potential.
Refractory Period: A brief time interval where the neuron is unable to fire again, either absolutely or relatively.

Types of Synapses

Electrical Synapses: Faster transmission involving gap junctions, which allow direct ion flow between cells. These are bidirectional.
Chemical Synapses: Slower, more common, involving neurotransmitter release. This is directional from pre to post-synaptic neuron.
Presynaptic membrane: Terminal regions of axons (terminal buttons).
Synaptic cleft: Space between pre and post synaptic membranes.
Postsynaptic membrane: Can be on dendrites, soma (cell body), or axons.

Chemical Synaptic Transmission

Neurotransmitter Synthesis and Storage: Neurotransmitters (amino acids, amines, peptides) are stored in synaptic vesicles.
Vesicle Cycling: There are several stages: release, docking, priming, fusion, recovery and recycling. Different stages can be considered in separate pools.
Neurotransmitter Recepters: Ionotropic (directly gate ion channels) and metabotropic (indirectly gate ion channels).
Neurotransmitter Recovery and Degradation: Neurotransmitters are removed from the synaptic cleft via reuptake or degradation, to terminate the signal.

Neurotransmitter System

Research Methods: Studying neurotransmitters involves techniques like immunocytochemistry and in situ hybridization to understand where they are located and how they function.
Dale's Principle: A neuron generally releases only one type of neurotransmitter across all its synapses.
Categories: Neurotransmitters can be categorized as small molecules (amino acids, amines, purines) and peptides.

Principles of Synaptic Integration

Quanta: Assume each vesicle contains a fixed amount of neurotransmitter (e.g., ach, glutamate). Each vesicle's release is a "quantum."
Quantal Release: The postsynaptic response is calculated as a function of the number of vesicles released ([N] * Probability of release[P] * Quantal amplitude[Q]).
mEPSCs: Mini synaptic potentials may have their release triggered without an action potential.
Spatial Integration: Summation of EPSPs or IPSPs from different synapses.
Temporal Integration: Summation of EPSPs or IPSPs from the same synapse over time, if occurring closely.
Inhibition: Involves inhibitory inputs opposing excitatory input.
"Veto principle": GABAergic synapses preventing or limiting the effect of excitatory synapses.

Intrinsic Activity and Modulation

Pacemakers: Generate action potentials without external input; often discussed in relation to oscillations.
Ion Channels: Control membrane potential and contribute to activity, e.g., K+, and T-type Ca²⁺ channels.
Modulation: Synaptic potentials can be modulated by metabotropic signaling.

Dendritic Properties

Dendrites are crucial for integrating synaptic inputs.
Distal synapses (further from the soma/cell body) produce weaker signals than proximal synapses.
Dendrites can generate large signals in the local area.

Specific Neurotransmitters

Detailed information about neurotransmitters (e.g., acetylcholine, glutamate, GABA, glycine, dopamine, norepinephrine, epinephrine, serotonin, histamine, ATP) including their roles, precursors, removal mechanisms, and receptors.

Unconventional Neurotransmitters

Discussion on endocannabinoids and nitric oxide, including their functions, precursors, and removal mechanisms.

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Description

Explore the critical concepts of synaptic transmission and action potentials in the nervous system. This quiz covers the basics of neuronal communication, including ion movement and membrane potential changes. Test your understanding of nerve functions and electrical impulses.