Synapses Flashcards

Questions and Answers

Which of the following are types of synapses? (Select all that apply)

Axosomatic (correct)

Axodendritic (correct)

Axoneural

Axoaxonic (correct)

What occurs at an axodendritic synapse?

The axon terminates on the dendrite of another neuron.

What is an axosomatic synapse?

A synapse between the axon terminal of one neuron and the cell body of a second neuron.

What does it mean if a neuron is presynaptic?

It is the neuron before the synapse. Signup and view all the answers

What is the role of synaptic vesicles?

They contain chemicals/neurotransmitters in the axon terminal of the presynaptic neuron. Signup and view all the answers

What is the synaptic cleft?

It is the space between the presynaptic and postsynaptic neurons. Signup and view all the answers

What happens during synaptic transmission's presynaptic events?

An action potential invades the axon terminal, Ca++ channels open, and neurotransmitter is released. Signup and view all the answers

What initiates postsynaptic events in synaptic transmission?

Neurotransmitters bind to receptors on the postsynaptic neuron. Signup and view all the answers

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

Movement of membrane potential towards 0mV Signup and view all the answers

What occurs during inhibitory postsynaptic potential (IPSP)?

The membrane potential moves away from 0mV. Signup and view all the answers

Match the type of summation with its description:

Temporal summation = Summation of events that happen at different times to produce an AP Spatial summation = Summation of events that occur at different locations to produce an AP Grand synaptic potential = Electrical sum of all EPSPs and IPSPs at any point in time Signup and view all the answers

What are common neurotransmitters?

Acetylcholine, biogenic amines, amino acids, peptides. Signup and view all the answers

What are the methods of inactivation of neurotransmitters?

Re-uptake, uptake by glial cells, enzyme degradation, and diffusion away from the synapse. Signup and view all the answers

Study Notes

Types of Synapses

Three main types: axodendritic, axosomatic, axoaxonic.
Axodendritic: axon connects with the dendrite of another neuron.
Axosomatic: synapse between axon terminal of one neuron and the soma of another neuron.
Axoaxonic: axon of one neuron synapses with the axon of another neuron.

Presynaptic and Postsynaptic Neurons

Presynaptic neuron: neuron located before the synapse.
Postsynaptic neuron: neuron located after the synapse.

Synaptic Vesicles

Contain neurotransmitters (NT) within the axon terminal of the presynaptic neuron.
Each neuron secretes only one type of neurotransmitter.

Synaptic Cleft

The gap that separates presynaptic and postsynaptic neurons.
Typically 30-50 nanometers wide with a floating membrane.

Postsynaptic Membrane

Composed of a phospholipid bilayer containing proteins and receptors for neurotransmitters.

Synaptic Transmission - Presynaptic Events

Action potential (AP) reaches the axon terminal.
Voltage-gated Ca++ channels open, increasing cytoplasmic Ca++ concentration.
Ca++ causes synaptic vesicles to move and fuse with the terminal membrane.
Neurotransmitters are released into the synaptic cleft via exocytosis.

Synaptic Transmission - Postsynaptic Events

Neurotransmitters bind to receptors on the postsynaptic neuron.
Chemically gated ion channels open, altering the membrane potential (MP), either depolarizing or hyperpolarizing based on neurotransmitter type.

Postsynaptic Potentials

Two types of potentials:
- Excitatory Post Synaptic Potential (EPSP): MP moves towards 0mV.
- Inhibitory Post Synaptic Potential (IPSP): MP moves away from 0mV.

Ionic Mechanisms of EPSP

Monovalent cation channels open upon NT binding, allowing Na+ influx and K+ efflux, driving MP closer to 0mV.
Calcium channels also open, causing further depolarization.

Ionic Mechanisms of IPSP

Cl- channels open, allowing negative charge influx, driving MP away from 0mV.
K+ channels open, causing K+ to exit the cell, enhancing negativity.

Summation in Postsynaptic Neurons

Postsynaptic neurons require MP to exceed threshold for AP generation.
Temporal summation: accumulation of events over time.
Spatial summation: accumulation of events over different locations.

Grand Synaptic Potential

The combined electrical effect of all EPSPs and IPSPs.
If the grand potential exceeds threshold, voltage-gated Na+ channels open, initiating an action potential.

Common Neurotransmitters

Include Acetylcholine (ACh), biogenic amines, amino acids, and peptides.
Some can have both excitatory and inhibitory effects (e.g., dopamine via D1 and D2 receptors).

Inactivation of Neurotransmitters

Mechanisms include:
- Reuptake by presynaptic neurons (e.g., serotonin, norepinephrine).
- Uptake by glial cells (e.g., astrocytes handle glutamate).
- Enzymatic degradation in the synaptic cleft (e.g., acetylcholinesterase hydrolyzes ACh).
- Diffusion away from the synapse, potentially entering the bloodstream (e.g., norepinephrine).

Description

This quiz focuses on the different types of synapses, specifically axodendritic, axosomatic, and axoaxonic. Each card provides definitions and key characteristics to help you understand these essential neural connections. Perfect for students studying neuroscience or related fields.