Action Potentials

Question 1

Define action potential:

Answer 1

• Fundamental unit of information in the nervous system

- short lasting event in which the electrical membrane potential of cell readily rise and falls

Question 2

What cells do action potentials occur in?

Answer 2

• Neurons
• Muscle cells
• Cardiac cells
• Endocrine cells

Question 3

Define action potential:

Answer 3

The difference in electric charge across a cell membrane

Question 4

What resting potential do electrically excitable cells tend to be?

Answer 4

-40 to -90 mV

Question 5

What do we call cells at their resting potential?

Answer 5

polarised

Question 6

What do we call cells which are more positive than their resting potential?

Answer 6

Depolarisation

Question 7

What do we call cells which are more negative than their resting potential?

Answer 7

Hyperpolarisation

Question 8

How does a potential difference across a cell membrane arise relating to k+ ion?

Answer 8

From an in balance of k+ ions inside the cells than the outside

Question 9

Finish the sentence:

Excitable cells must have a ….

Answer 9

negative (hyperpolarised) resting potenial

Question 10

What do impermeable membranes mean relating to chemical gradient?

Answer 10

Cannot exist

Question 11

What is an electrochemical equilibrium?

Answer 11

When the ions are balanced

Question 12

What is an opposing electrical gradient?

Answer 12

Chemical gradient increasing whilst electrical gradient is decreasing

Question 13

What can stop all k+ ions reaching a chemical equilibrium?

Answer 13

an opposing electrical gradient

Question 14

What is another name for opposing electrical gradient?

Answer 14

-Reversal potential

or

-Nernst potential

Question 15

What is a reversal potential?

Answer 15

Membrane potential where the chemical and electrical gradients of an ion across a biological membrane are in equilibrium

Question 16

What is the net flow of ions across a membrane at reversal potential?

Answer 16

No net flow

Question 17

What does the Nernst equation show?

Answer 17

Equilibrium potential of an ion dependent on intra and extra cellular concentrations

Question 18

What is the Nernst equation?

Answer 18

Ex = RT/zF ln [X]out/[X]in

Question 19

What does R mean in the Nernst equation?

Answer 19

The universal gas constant

Question 20

What does Ex mean in the Nernst equation?

Answer 20

The equilibrium potential

Question 21

What does T mean in the Nernst equation?

Answer 21

The temperature in Kelvin

Question 22

What does z mean in the Nernst equation?

Answer 22

The valence of the ion

Question 23

What does F mean in the Nernst equation?

Answer 23

The Farady constant

Question 24

What does [X]out mean in the Nernst equation?

Answer 24

Concentration of ion outside cell

Question 25

What does [X]in mean in the Nernst equation?

Answer 25

Concentration of ion inside cell

Question 26

What is the universal gas constant equal to?

Answer 26

8.3145 JK-1mol-1

Question 27

What is the temperature in Kelvin equal to at 37C?

Answer 27

310.15K

Question 28

What is the faraday constant equal to?

Answer 28

96485 C mol-1

Question 29

During depolarisation of membrane potential what opens?

Answer 29

Voltage-gated Na+ channels open

Question 30

What does voltage-gated Na+ channel-mediated depolarisation trigger?

Answer 30

A chain reaction

Question 31

When is a chain reaction triggered?

Answer 31

At an action potential threshold

Question 32

Describe an action potential:

Answer 32

- Na+ flow into cell due to depolarisation opening voltage-gated Na+ channels - Result in a region of positive charge across the membrane - Local depolarisation causes Na+ channels nearby to open - More Na+ ion can flow into cell - Voltage-gated K+ channels also activated by depolarisation (much more slowly) - K+ leave the cell - Na+ channel inactivates - More voltage-gated K+ channels open causing hyperpolarisation - Resting membrane potential re-established

Question 33

Finish the sentence: | Voltage-gated Na+ channels rapidly...

Answer 33

inactivate after activation

Question 34

Finish the sentence: | Due to depolarisation voltage-gated K+ channels activate more...

Answer 34

Slowly than voltage-gated Na+ channels

Question 35

Is electrical resistance within an axon higher or lower in thinner axons?

Answer 35

Higher

Question 36

What is meant bu a higher electrical resistance in thinner axons?

Answer 36

Slower conduction of signal

Question 37

What do myelin sheath do?

Answer 37

Insulate the axon from negative external charge

Question 38

What are the effects on electrical transmission due to myelin sheath?

Answer 38

Faster transmission

Question 39

Can myelinated axon store some of the charge?

Answer 39

Yes

Question 40

What acts as signal boosters to prevent storage of charge?

Answer 40

Nodes of Ranvier

Question 41

What are at Nodes of Ranvier?

Answer 41

Highly density of volt-gated Na+/K+ channels

Question 42

How does a Nodes of Ranvier work?

Answer 42

When a propagating action potential reaches the Node a new action potential is initiated

Question 43

What is the action at the Nodes of Ranvier called?

Answer 43

Saltatory conduction

Question 44

What makes up myelin sheath in PNS?

Answer 44

Schwann cells

Question 45

What makes up myelin sheath in CNS?

Answer 45

Oligodendrocytes

Question 46

What initiates an action potential?

Answer 46

- Anything which causes a depolarisation beyond action potential threshold - Under physiological conditions normally generated by ion channels

Question 47

What are different types o d ion channels which can generate an action potential?

Answer 47

- Voltage-activated - Extracellular-activated (Ligand/light/heat/cold -activated) - Intercellular-activated - Stretch-activated

Question 48

Describe the role of action potential in synaptic transmission:

Answer 48

- Action potential reaches presynaptic neurones - Ca2+ enter voltage-gated Ca2+ channels - Causing Na+ neurotransmitters to be released across the synapse - Na+ reaches postsynaptic neuron and initiated a new action potential

Question 49

Is the size of action potential does change what does?

Answer 49

The number of frequency

Question 50

Why is it important to calculate the equilibrium potential?

Answer 50

If we know what ion channel is permeable to, we can predict what opening that channel will do to the membrane potential