Synaptic Transmission

neurons are separate cells that do not touch

neuron doctrine

how does a signal cross from one neuron to the next?

synapse

what is the sender of a signal?

presynaptic neruon

what is the reciever of a signal?

post synaptic neuron

What is the gap between neurons called?

synaptic cleft

Does a signal need to cross the synaptic cleft?

Yes

From where does a signal usually occur to and from?

presynaptic terminal to post synaptic dendrite

Can a synapse connect to another part of the neuron?

Yes, cell body, axon, or even muscle cell

Does information travel in one direction in the synapse? from where to where?

yes, pre to post

What the the three step neuron communication conversion?

electrical to chemical to electrical

action potential travels down the axon to the terminal

first - electrical

signal is converted into chemical messenger (neurotransmitter)

second - chemical

neurotransmitters cause new electrical change in postsynaptic neuron

third - electrical

Where are the electrical signals turned into chemical signals?

synaptic terminal

What else is the synaptic terminal referred to?

axon terminal, bouton

What are the tiny sacs in the presynaptic terminal?

vesicles

What are the vesicles in the presynaptic terminal filled with?

neurotransmitters

What do the vesicles wait for, and why?

action potential, to release their contents

What needs to occur for neurotransmitters to need to be released?

action potential

Where are neurotransmitters released to?

synaptic cleft

What does channel depolarization trigger? (remember this is unit 9)

voltage-gated calcium channels

What is Calciums ionic distribution at rest?

high outside, low inside

What happens to calcium ions when the action potential is depolarizing

Calcium rushes in to the cell

What drives calcium to rush into the terminal?

concentration gradient

What ion is the signal that tells the vesicles to release their neurotransmitters?

calcium

What does calcium cause the vesicles to do?

move to fuse with the presynaptic membrane

What does fusing with the presynaptic membrane allow for?

vesicle opens up and releases neurotransmitters

What are vesicles made out of?

membrane

What causes vesicles to fuse with the synaptic membrane?

SNARE complex

What is a SNARE complex composed of?

group of proteins

Where are SNARE proteins located in the neuron?

vesicles, cell membrane

What do SNARE proteins allow for?

cell membrane and vesicles to bind together

Through what process do neurotransmitters release?

exocytosis

Once released, where do neurotransmitters diffuse?

the synaptic cleft

is the synaptic cleft small or large? How quick do neurotransmitters cross?

extremely small, very quickly

Does the presynaptic terminal run out of vesicles?

no, vesicles are recycled

Vesicles are ______, and refilled with _______ which allows for the terminal to keep _____ without running out.

recycled, neurotransmitters, signaling

Why must neurotransmitters be cleared from the synaptic cleft?

stop the signal and prevent continuous stimulation

What are the four mechanisms of neurotransmitter signal termination?

Reuptake, glial uptake, enzymatic degradation, and diffusion.

The active transport of neurotransmitters back into the presynaptic neuron that released them.

reuptake

What proteins enable neurotransmitter reuptake?

Transporter proteins

What can happen to neurotransmitters after reuptake?

repackaged and reused

The absorption of neurotransmitters from the synaptic cleft by nearby glial cells.

glial uptake

Which glial cells are especially involved in neurotransmitter uptake?

Astrocytes

The breakdown of neurotransmitters by enzymes in the synaptic cleft.

enzymatic degradation

What breaks neurotransmitters into smaller pieces? And what does it cause?

enzymes, can no longer bind to postsynaptic receptors

Neurotransmitters spread away from the synaptic cleft, decreasing their concentration near receptors.

signal termination: diffusion

Is diffusion an active or passive signal termination mechanism?

Passive

Why must a synapse reset after each signal?

To allow discrete, precisely timed signals rather than continuous stimulation.

What are the two major types of synapses?

Chemical and electrical synapses.

Which type of synapse is more common in the nervous system?

chemical synapses

How do electrical synapses transmit signals?

direct ion flow between connected cells

What structures physically connect neurons at electrical synapses?

Gap junction channels.

What do gap junctions connect?

The cytoplasm of adjacent cells

What can pass through gap junctions?

ions and other small molecules

are electrical synapses fast or slow

fast

Are electrical synapses usually unidirectional or bidirectional?

bidirectional

How do electrical synapses synchronize neuronal activity?

groups of neurons become active at nearly the same time

How do electrical synapses compare with chemical synapses in plasticity?

less plasticity

Why isn't synchronizing all neurons always desirable?

blocks information processing and causes neurological disorders like epileptic seizures