Synapses Flashcards

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.

Synapses Flashcards

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Questions and Answers

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

What occurs at an axodendritic synapse?

What is an axosomatic synapse?

What does it mean if a neuron is presynaptic?

What is the role of synaptic vesicles?

What is the synaptic cleft?

What happens during synaptic transmission's presynaptic events?

What initiates postsynaptic events in synaptic transmission?

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

What occurs during inhibitory postsynaptic potential (IPSP)?

Match the type of summation with its description:

What are common neurotransmitters?

What are the methods of inactivation of neurotransmitters?