Lecture 5: Resting and action potentials

Question 1

Give an example of juxtacrine signalling.

Answer 1

Notch signalling pathway: important in neural development

Question 2

What is the ligand involved in juxtacrine signalling?

Answer 2

The signalling molecule is attached to the surface of one cell

Question 3

Why is juxtacrine signalling called direct signalling?

Answer 3

Attached ligand interacts with receptor molecule on immediate neighbour cell

Question 4

Give an example of autocrine signalling.

Answer 4

T cells produce IL-2 which binds to its own receptors, activating the cell

Question 5

What is autocrine signalling

Answer 5

The signal travels out of the cell and binds to the outer membrane of the same cell

Question 6

Give examples of hormones involved in paracrine signalling.

Answer 6

Histamine, prostaglandins

Question 7

What is paracrine signalling?

Answer 7

A signal molecule leaves one cell and interacts with a receptor molecule on the immediate neighbour cell

Question 8

Give examples of neurotransmitters involved in neural signalling.

Answer 8

Acetylcholine, noradrenaline

Question 9

List the 5 types of chemical communication from fastest to slowest.

Answer 9

Juxtacrine
Neural
Autocrine
Paracrine
Endocrine

Question 10

What is the charge of a cell inside, relative to outside?

Answer 10

Negative due to high concentration of amino acids inside the cell

Question 11

Where is a higher concentration of negative chloride ions found?

Answer 11

Outside the cell

Question 12

What is the cell membrane leaky to

Answer 12

Sodium and potassium ions

Question 13

How is the balance of ions kept in place with a leaky membrane?

Answer 13

Sodium-potassium pump

Question 14

What does the sodium-potassium pump do?

Answer 14

Uses ATP to push 3 sodium ions out for every 2 potassium ions (against their chemical gradients)

Question 15

What is GABA?

Answer 15

A neurotransmitter

Question 16

What does GABA do?

Answer 16

Open ligand-gated chloride channels, changing post-synaptic membrane potential

Question 17

What does the potential to do work come from?

Answer 17

Separation of charged particles

Question 18

What is the typical resting potential of a cell?

Answer 18

-70mV

Question 19

What is the difference between ligand-gated channel and a signal-gated channel?

Answer 19

Ligand channels opens/closes in response to extracellular signal. signal gated channel opens/closes in response to intracellular molecule

Question 20

When is a leak channel open?

Answer 20

Always

Question 21

When does a voltage gated channel open?

Answer 21

In response to change in the membrane potential

Question 22

How do voltage gated channels change in response to voltage?

Answer 22

Charged region of the protein can change shape if the voltage across them changes

Question 23

What covers the channel of a voltage channel when it is inactivated?

Answer 23

A ball-and chain region

Question 24

What do ribbon models show?

Answer 24

The proteins backbone (without considering R groups_

Question 25

What is a space filling model?

Answer 25

Shows the actual space taken up by all the atoms in the protein

Question 26

What is the first stage of an action potential that takes the cell out of the resting state?

Answer 26

Depolarization

Question 27

What happens after a cell is depolarised?

Answer 27

Rising phase of the action potential followed by the falling phase of the action potential

Question 28

What occurs after the initial falling phase of the action potential, before the cell returns to resting state?

Answer 28

Undershoot

Question 29

Why does the cell react differently to membrane potentials that are of the same magnitude but occur during different parts of the action potential cycle?

Answer 29

Two types of voltage gated ion channels allow their ions through at different rates

Question 30

How do ions move when the voltage gated ion channels are open?

Answer 30

Down their electro-chemical gradient

Question 31

Sodium and potassium channels are affected at the same time, so why are ions allowed through at different rates?

Answer 31

Sodium channels are very efficient, so permeability increases sharply, whereas potassium is slower

Question 32

What happens during depolarising phase?

Answer 32

Sodium channels open, sodium moves into the cell

Question 33

What happens during repolarising?

Answer 33

Sodium channels are inactivated, potassium channels open

Question 34

What happens during hyperpolarisation?

Answer 34

Potassium channels remain open, sodium channels reset

Question 35

On what principle are action potentials initiated?

Answer 35

All-or-none principle

Question 36

What is the all-or-none principle?

Answer 36

Depolarisation reaches threshold or not, therefore there is an action potential or not

Question 37

When is threshold of an action potential reached?

Answer 37

When the opening of the voltage-gated Na+ channels stimulates other channels to open in a + feedback loop

Question 38

What is the name given when a new stimulus can have have no greater effect?

Answer 38

Absolute refractory period

Question 39

How long does the absolute refractory period last?

Answer 39

1-2ms

Question 40

What does the absolute refractory period determine?

Answer 40

Maximum action potential frequency

Question 41

What is the relative refractory period?

Answer 41

Na channels can be reopened but permemability of sodium ions needs to exceed permeability of potassium ions

Question 42

The relative refractory period has an _______ threshold

Answer 42

Increased

Question 43

How long does the relative refractory period last?

Answer 43

3-15ms