8. Inhibition & Synaptic Plasticity

What is synaptic inhibition?

A process that reduces the likelihood that a postsynaptic neuron will fire an action potential

What is postsynaptic inhibition?

Inhibition that occurs when an inhibitory neurotransmitter produces a hyperpolarizing graded potential in the postsynaptic cell

How does postsynaptic inhibition affect membrane potential?

It hyperpolarizes the postsynaptic membrane making threshold harder to reach

Which ions are typically involved in postsynaptic inhibition?

Chloride ions entering the cell or potassium ions leaving the cell

What is presynaptic inhibition?

Inhibition that reduces neurotransmitter release from a presynaptic neuron

How does presynaptic inhibition occur?

An inhibitory neuron synapses on a presynaptic axon terminal or collateral

What effect does presynaptic inhibition have on neurotransmitter release?

It decreases or prevents neurotransmitter release at the synapse

What is selective presynaptic inhibition?

Inhibition that affects neurotransmitter release at only one specific axon terminal

What is global presynaptic inhibition?

Inhibition that prevents action potential generation and affects all targets of a presynaptic neuron

How does global presynaptic inhibition prevent signaling?

By preventing the action potential from reaching the axon terminals

What is synaptic plasticity?

The ability of synapses to strengthen or weaken over time

Why is synaptic plasticity important?

It underlies learning memory and adaptation of the nervous system

What is synaptic facilitation?

An increase in synaptic strength or responsiveness

What is synaptic depression?

A decrease in synaptic strength or responsiveness

What is long-term potentiation?

A sustained increase in synaptic strength following repeated stimulation

What structural changes can occur during long-term potentiation?

Increased neurotransmitter release increased receptor number or new synapse formation

Which receptor is associated with long-term potentiation?

The NMDA receptor

What is unique about the NMDA receptor?

It requires both ligand binding and postsynaptic depolarization to activate

How does synaptic inhibition interact with summation?

Inhibitory inputs can reduce or cancel excitatory summation

Can inhibition prevent an action potential even if excitatory inputs are present?

Yes if the net graded potential does not reach threshold

What does modulation of synaptic activity mean?

Altering synaptic strength by changing neurotransmitter release or receptor responsiveness