Neuroscience Chapter on Synaptic Transmission

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What triggers the release of neurotransmitters from synaptic vesicles?

The breakdown of SNARE proteins

The binding of neurotransmitter to receptors

An increase in intracellular Ca2+ concentration (correct)

The closing of voltage-gated Na+ channels

What role does synaptotagmin play in neurotransmitter release?

It breaks down neurotransmitters in the synaptic cleft

It promotes the binding of neurotransmitters to receptors

It generates action potentials in the postsynaptic cell

It reacts with SNARE proteins to facilitate membrane fusion (correct)

What happens to neurotransmitters after they diffuse across the synaptic cleft?

They bind to specific receptors on the postsynaptic membrane (correct)

They are immediately destroyed by enzymes

They are reabsorbed by the presynaptic neuron without binding

They create action potentials in the presynaptic neuron

What effect does the binding of neurotransmitter to ion channels have in the postsynaptic cell?

It creates graded potentials that can be excitatory or inhibitory Signup and view all the answers

How is the frequency of impulses related to the quantity of neurotransmitter released?

Higher impulse frequency increases the number of vesicles that exocytose Signup and view all the answers

What is the primary role of the presynaptic neuron in a synaptic connection?

To conduct impulses toward the synapse Signup and view all the answers

Which of the following describes a chemical synapse?

It relies on the release, diffusion, and receptor binding of neurotransmitters. Signup and view all the answers

What separates the presynaptic neuron from the postsynaptic neuron in a chemical synapse?

A fluid-filled synaptic cleft Signup and view all the answers

What determines the unidirectional communication characteristic of chemical synapses?

The diffusion of neurotransmitters across the cleft Signup and view all the answers

Which type of synaptic connection is most common between an axon terminal and a dendrite?

Axdendritic Signup and view all the answers

What is meant by the term synaptic integration?

The interaction of neurons to process and transmit information Signup and view all the answers

Which type of neurotransmitter receptor is characterized by slower, longer-lasting effects?

Metabotropic receptors Signup and view all the answers

In terms of summation, what does spatial summation involve?

Signals coming from different presynaptic neurons simultaneously Signup and view all the answers

Which step is NOT involved in the transmission across chemical synapses?

Change of impulse from electrical to thermal Signup and view all the answers

What is the primary function of neurotransmitters in synaptic transmission?

To facilitate the transfer of information between neurons Signup and view all the answers

What is one of the primary methods by which neurotransmitter effects are terminated?

Reuptake by astrocytes or axon terminal Signup and view all the answers

What is the typical range of time for synaptic delay in chemical synapses?

0.3 to 5.0 ms Signup and view all the answers

Which characteristic best describes electrical synapses?

Joined by gap junctions Signup and view all the answers

Which of the following processes is NOT a mechanism for terminating neurotransmitter effects?

Binding to additional receptors Signup and view all the answers

In which type of synapse does communication generally occur more rapidly?

Electrical synapses Signup and view all the answers

Which of the following neurotransmitters is usually excitatory?

Glutamate Signup and view all the answers

What characterizes the direct action of neurotransmitters?

Promotes rapid responses by altering membrane potential Signup and view all the answers

What type of receptors are involved in immediate and brief actions?

Ligand-gated ion channels Signup and view all the answers

Which type of neurotransmitter action usually has broader and longer-lasting effects?

Indirect action Signup and view all the answers

What is a characteristic of neural integration?

Groups of neurons contribute to broader neural functions Signup and view all the answers

What type of processing involves a single pathway to a specific destination?

Serial processing Signup and view all the answers

What is one example of a spinal reflex?

Knee-jerk response Signup and view all the answers

What type of processing allows one stimulus to generate multiple responses?

Parallel processing Signup and view all the answers

What determines the strength of postsynaptic potentials?

The duration of neurotransmitter binding and the amount released Signup and view all the answers

Which of the following correctly describes an excitatory postsynaptic potential (EPSP)?

It can lead to an action potential if it reaches the threshold. Signup and view all the answers

What is the primary effect of presynaptic inhibition?

It decreases the amount of neurotransmitter released. Signup and view all the answers

What do temporal and spatial summation have in common?

Both refer to the addition of multiple EPSPs to reach a threshold. Signup and view all the answers

How does synaptic potentiation affect neurotransmitter release?

It enhances the ability of the presynaptic cell to release more neurotransmitter. Signup and view all the answers

What role do chemically gated channels play in EPSPs?

They facilitate simultaneous movement of sodium and potassium ions. Signup and view all the answers

Which type of summation occurs when multiple presynaptic neurons stimulate a postsynaptic neuron at the same time?

Spatial summation Signup and view all the answers

What is the effect of inhibitory postsynaptic potentials (IPSPs) on the postsynaptic neuron?

They make the postsynaptic membrane more permeable to potassium or chloride ions. Signup and view all the answers

Which characteristic is NOT a feature of neurotransmitters?

Most neurons release only one type of neurotransmitter. Signup and view all the answers

Which phenomenon describes the increase in neurotransmitter release due to higher calcium ion concentrations in the presynaptic neuron?

Synaptic potentiation Signup and view all the answers

Study Notes

Nervous system introduction

The nervous system allows information to flow from neuron to neuron
Neurons are connected by synapses

Synapses

Synapses are junctions for information transfer
They connect one neuron to another neuron, or to an effector cell.
Synapses can be chemical or electrical

Types of Synapses

Chemical Synapses:
- Most common type of synapse.
- Specialized for releasing and receiving chemical neurotransmitters.
- Two parts:
  - Axon terminal of the presynaptic neuron: Contains synaptic vesicles filled with neurotransmitter.
  - Receptor region on the postsynaptic neuron's membrane: Receives neurotransmitters.
  - Separated by a fluid-filled synaptic cleft.
- Transmission mechanism:
  - Action potential arrives at the axon terminal
  - Voltage-gated Ca2+ channels open, and Ca2+ enters the axon terminal
  - Ca2+ entry causes synaptic vesicles to release neurotransmitters by exocytosis
  - Neurotransmitters diffuse across the synaptic cleft, and bind to specific receptors on the postsynaptic membrane
  - Binding of neurotransmitters open ion channels, resulting in graded potentials
  - Neurotransmitter effects are terminated by reuptake, enzymatic degradation, or diffusion
Electrical Synapses:
- Less common than chemical synapses
- Neurons are electrically coupled by gap junctions.
- Communication is very rapid, unidirectional or bidirectional.
- Found in regions responsible for eye movements, hippocampus, and areas involved in emotions and memory
- Often abundant in embryonic tissue

Synaptic connections

Axodendritic: Between axon terminals of one neuron and dendrites of others
Axosomatic: Between axon terminals of one neuron and soma (cell body) of others
Axoaxonal: Between axon terminals of one neuron to another.
Dendrodendritic: Between dendrite to dendrite
Somatodendritic: Between dendrite to soma

Postsynaptic potentials

Neurotransmitter receptors cause graded potentials.
Strength varies by:
- Amount of neurotransmitter released
- Time neurotransmitter stays in cleft
Two types based on effect of chemical synapse:
- EPSP (Excitatory postsynaptic potential)
- IPSP (Inhibitory postsynaptic potential)

Excitatory Synapses and EPSPs

Neurotransmitter binding opens chemically gated channels.
Allows flow of Na+ and K+ in opposite directions simultaneously.
Na+ influx is greater than K+ efflux resulting in graded potential depolarisation called Excitatory postsynaptic potential (EPSP).
Triggers action potential if threshold is reached

Inhibitory Synapses and IPSPs

Neurotransmitter binding opens channels (e.g., K+ or Cl- channels).
If K+ channels open, K+ moves out of the cell.
If Cl- channels open, Cl- moves into the cell.
Reduces the ability to produce an action potential.

Summation of Synaptic Events

Single EPSP cannot trigger an action potential, but EPSPs can summate to influence the postsynaptic neuron.
IPSPs can summate similarly.
Two types of summation:
- Temporal summation: Rapid firing of presynaptic neurons causing EPSPs close in time.
- Spatial summation: Simultaneous firing of multiple presynaptic neurons causes EPSPs that occur simultaneously at various locations on the postsynaptic neuron

Synaptic Potential

Repeated use increases the ability of a presynaptic cell to excite postsynaptic neuron
Ca2+ concentration increases in presynaptic terminal, causing release of more neurotransmitter
Leads to more EPSPs

Neurotransmitters

Most neurons make multiple neurotransmitters.
Released at different stimulation frequencies
Produce different effects depending on receptors.
Classified by: -Chemical structure
- Function

Neurotransmitter Receptors

Channel-linked receptors (ionotropic):
- Ligand-gated ion channels.
- Action is immediate and brief.
- Excitatory receptors, e.g., for Na+, contribute to depolarization.
- Inhibitory receptors, e.g., for Cl-, cause hyperpolarization.
G protein-linked receptors (metabotropic):
- Responses are indirect, complex, slow, often prolonged.
- Involve transmembrane protein complexes.
- Use second messenger systems.
- Cause widespread metabolic changes.
- Example: Muscarinic ACh receptors

Neural Integration

Neurons function as groups to contribute to broader neural functions.
There are billions of neurons in the CNS requiring smooth operation

Patterns of Neural Processing

Serial processing:
- Input travels along one pathway to a specific destination.
- All-or-none manner to produce specific response (Reflex)
Parallel processing:
- Input travels along several pathways.
- Different parts of circuitry deal with information simultaneously.
- Important for higher-level mental functioning. (eg. Sensing smell)

Review Questions

What are the different types of postsynaptic potentials?
How does summation occur?
How is long-term memory formed?
What are 2 types of neurotransmitter receptors?
What is the difference between serial and parallel processing?

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz explores the mechanisms of neurotransmitter release, including the roles of synaptotagmin and other components of synaptic transmission. Test your knowledge on the processes that govern communication in the nervous system and the characteristics of chemical synapses. Perfect for students of neuroscience and biology courses.