Action potentials & synapses

Question 1

What are synapses?

Answer 1

Communication between neurons, where one cell sends a signal (chemical or electrical) to another cell. The cells are not touching.

Question 2

What is a graded potential?

Answer 2

The signals generated from synapses that travel down dendrites, cell body and to the axon hillock. The axon hillock is where it is decided whether if an action potential will fire.

Question 3

What is an action potential?

Answer 3

The signal travelling down the axon. Then, from the axon terminals of this cell, you have a synapse.

Question 4

What types of synapses can there be?

Answer 4

Electrical (via ions) or chemical synapses

Question 5

What are electrical synapses? What are their characteristics?

Answer 5

Often called gap junctions. When electrical information it is much faster.
Neurons have to be very close together
Much less common in brain than chemical synapses

Question 6

What happens in an electrical synapse?

Answer 6

When an electrical stimulation or action potential is sent down the first neuron, ions flow through gap junction channel, directly crossing into the second.

Question 7

What are chemical synapses?

Answer 7

Nuanced signals (not all or none)
Slower than electrical synapses
Much more common in the brain

Question 8

What happens in the first stage of chemical synaptic communication?

Answer 8

Presynaptic neuron
When nerve impulse comes down to neuron
1) Nerve impulse arrives at axon terminal
2) Positively charged action potential opens these little gates in the cell (voltage gated) by increasing voltage in cell
3) Voltage gated calcium channels open, Ca2+ floods into cell
4) Elevated level of Ca2+ within cell activates synaptic vesicles, release neurtransmitters
5) Neurotransmitters diffuse from the presynaptic terminal across synaptic cleft, free to bind to receptors on the postsynaptic neuron
6) When bound, opens up a channel that allows specific ions to flow through and into the cell, changing the postsynaptic membrane potential
7) Excitation or inhibition of a cell known as a postsynaptic potential (graded potential)

Question 9

What’s the purpose of synaptic vesicles?

Answer 9

Hold all chemical signals (neurotransmitters) that are going to be released into the synaptic cleft. Activation leads to release of neurotransmitters into the synaptic cleft.

Question 10

What do voltage gated Ca2+ channels do?

Answer 10

They open up when voltage is increased in cell to let calcium in

Question 11

What happens after elevated level of Ca2+ within cell activates synaptic vesicles?

Answer 11

Neurotransmitters are released into the synaptic cleft, and free to bind with receptors on the postsynaptic neuron

Question 12

What happens when action potential travels down to the terminal button?

Answer 12

When the membrane of the terminal button is depolarised by an arriving action potential, the voltage-dependent calcium channels are opened.

Question 13

What is excitation and inhibition?

Answer 13

An increase or decrease in charge of postsynaptic neuron; a postsynaptic potential

Positively charged ion - excitation, increases charge of cell; e.g. sodium
Negatively charged ion - inhibition, decreases charge of cell; e.g. chloride

Question 14

What happens after neurotransmitter binds?

Answer 14

Neurotransmitter reuptake

Neurotransmitters are generally actively returned to the presynaptic cell; sometimes broken down or repackaged

Question 15

Where do the Ca2+ enter?

Answer 15

The terminal button; the channels are on the presynaptic terminal

Question 16

What are the types of synapses?

Answer 16

Axodendritic, axosomatic, and axoaxonic synapses

Question 17

What do axodendritic synapses occur on?

Answer 17

Axodendritic synapses can occur on the smooth surface of a dendrite, or on dendritic spines.

Question 18

What do axosomatic synapses occur on?

Answer 18

Axosomatic synapses occur on the somatic membrane.

Question 19

What do axoaxonic synapses occur on?

Answer 19

Axoaxonic synapses consist of synapses between two terminal buttons (less common)

Question 20

What is a decrease in voltage postsynaptically known as?

Answer 20

IPSPs (Inhibitory Post-Synaptic Potentials) - cell is less likely to fire

Question 21

What is a increase in voltage postsynaptically known as?

Answer 21

EPSPs (Excitory Post-Synaptic Potentials) - cell is more likely to fire

Question 22

Where do graded potentials go?

Answer 22

EPSPs and IPSPs move across the cell membrane from the dendrites down towards axon hillock
Charge of cell is changed moving down towards hillock
Information is summed there (so IPSPs and EPSPs can cancel out)

Question 23

When will an action potential fire?

Answer 23

It will fire once a threshold is reached. It depends on the summing in the axon hillock.

Question 24

What is an action potential?

Answer 24

A nerve impulse. It is a rapid, electrical signal that travels down a single cell. It is all about the movement of ions.

Question 25

What is the cell membrane?

Answer 25

It is a phospholipid bilayer maintaining the negative charge within the cell.

Question 26

What is the cell membrane made of?

Answer 26

Phospholipids. Phospholipids on each side - phosphate attached to lipids - forming a bilayer

Question 27

What does the cell membrane do in terms of ions?

Answer 27

It prevents the movement of ions so that they can only move through dedicated channels

Question 28

Outside the cell there is a lot of ____, whereas inside the cell there is a lot of _____.

Answer 28

Sodium (Na+); Potassium (K+)

Question 29

The cell membrane is ____ charged

Answer 29

Negatively

Question 30

Where is the action potential generated?

Answer 30

Axon hillock

Question 31

What is the threshold membrane potential?

Answer 31

-55mV. It is the threshold which if reached, an action potential will be fired.

Question 32

What happens when the threshold membrane potential is reached?

Answer 32

The voltage gated sodium channels in the membrane open and Na+ rushes in, propelled by electrostatic pressure and forces of diffusion. It rapidly depolarises the cell membrane and causes Na+ gates to open. The repolarisation is the action potential.