SYNAPSES

A junction where information is transmitted from one neuron to the next.

Synapse

The narrow gap that separates the presynaptic neuron from the postsynaptic cell.

Synaptic cleft

Distance of the synaptic clef

40 nm wide

process by which neurotransmitters are taken back into the synaptic vesicles

Reuptake

The membrane of the presynaptic terminal

Presynaptic membrane

It contains large numbers of -- -gated calcium channels.

voltage

1. Opening Calcium Channels

2. The closing of Chloride channels and Potassium Channels

3. Increase the excitatory receptors or decrease the inhabitants receptors

3 Way of repolarizing

1. Opening of chloride channels

2. Opening of Potassium Channels

3. Increase of Inhibitory receptors

3 Ways of inhibition

Acetylcholine

Norepinephrine

Glutamate

Excitatory

Decreasing the voltage to a less negative value makes the membrane of the neuron --,

more excitable

whereas increasing this voltage to a more negative value makes the neuron --

less excitable (hyperpolarized).

three ions across the neuronal somal membrane that are most important for neuronal function are --, --, --

sodium ions, potassium ions, and chloride ions.

Resting neuron, with a normal intraneuronal potential of

-65 millivolts

three states of a neuron possible

1. Resting

2. Inhibited

3. Excited

When a presynaptic terminal has secreted an excitatory transmitter into the cleft between the terminal and the neuronal somal membrane, that transmitter acts on the membrane excitatory receptor to increase --

the membrane's permeability to Na+

a postsynaptic potential that depolarizes the neuronal membrane, making the cell more likely to fire an action potential

excitatory postsynaptic potential

EPSP threshold

20

To fire an action potential, it must reach threshold, usually around -- mV

-45

The sum of multiple synapses firing at different locations at one time to create a net effect.

spatial summation

One or more presynaptic neurons transmit impulses in rapid-fire order

temporal summation

Not all summations lead to action potentials.

subthreshold stimulation of a neuron that increases responsiveness to further stimulation

Facilitation

does chemical synapse use neurotransmitter

Yes

does electrical synapse use neurotransmitter

No

Ligand-gated Na⁺ channels are in the --

postsynaptic membrane

Vast majority of synapses in humans are

chemical synapses

means the channel only opens when a neurotransmitter (the ligand) binds to it.

Ligand-gated

uses no neurotransmitters at all. Instead, ions pass directly from one cell to another via gap junctions.

Electrical synapses

So -- is what directly controls exocytosis.

calcium

Found on the postsynaptic membrane.

They open when a neurotransmitter (ligand) binds.

Ionotropic receptors (ligand-gated ion channels)

are found on the presynaptic axon and are essential for the action potential to travel down.

Voltage-gated sodium channels

Sodium that enters the postsynaptic cell does not travel back to the presynaptic neuron. It stays in the postsynaptic cell and changes its potential.

Ionotropic receptors produce -- responses than metabotropic receptors.

faster

the amount of neurotransmitter released is directly -- to how much calcium enters.

proportional