Lecture 3- Electrophysiology of the cell membrane

Question 1

Do non-excitable cells have a resting membrane potential?

Answer 1

Yes all cells do whether they are excitable or not

Question 2

What is a chemical gradient?

Answer 2

The energy provided by the difference in concentration across the plasma membrane

Question 3

What is an electrical gradient?

Answer 3

The energy associated with moving charged molecules (e.g. ions) across a cell membrane. This is when a membrane potential exists.

Question 4

What is an electrochemical gradient?

Answer 4

It is the measure of the driving force on a charged solute (ion). It takes into account both the concentration gradient and the electrical gradient (charge difference) across a membrane.

Question 5

What does the Nernst equation calculate?

Answer 5

The diffusion potential for an ion. In other words, if diffusion can occur freely what will the membrane potential be when the electrical and chemical gradients are at equilibrium.

Question 6

What does it mean when the electrochemical gradient is equal to O?

Answer 6

It is calculated by adding up the chemical potential and the electrical potential. Therefore when the answer is O these have cancelled each other out. At equilibrium there will be no net movement of ions and no driving force for ion movement.

Question 7

At equilibrium is there zero movement of ions?

Answer 7

No, movement is constantly occurring it is just that there is no net movement/ driving force. Individual movements will still be occurring.

Question 8

Do the self test questions from lecture 3 on how to apply the Nernst equation….

Answer 8

Find the answers (written out in folder or in lecture slides)

Question 9

Resting membrane potential is largely due to…..

There is small influence from…

Answer 9

potassium as permeability for this across the self membrane is significantly greater. However, this is modulated by a small current of Na+ which is let in/ out by leaky channels. This is what keeps the resting membrane potential from just being that ideal for potassium (-97= calculated in a Nernst equation) and more similar to -70mv.

Question 10

What is the purpose of Na+, K+ ATpase across the membrane?

Answer 10

They maintain the concentration gradient for K+ and Na + across the cell membrane by actively using ATP to pump the ions against their concentration gradient in a ratio of 3 Na+ out and 2 K+ in. Otherwise Na+ would constantly come in and K+ out until the concentrations were altered permanently.

Question 11

What does altering the cell membrane by the closing/ opening of channels do? What is the term given for this?

Answer 11

It alters the ratio of ion concentration outside and inside the cell. This alters the membrane potential of the cell. This is described as being a small local change in ion conductance and therefore a local potential.

Question 12

What is Depolarisation?

Answer 12

A move of the cell’s membrane potential towards zero (becoming more positive)

Question 13

What is an overshoot?

Answer 13

Membrane potential continues to become positive but has gone beyond O

Question 14

What is repolarization?

Answer 14

When the membrane potential is becoming more negative but is still above the normal resting membrane potential

Question 15

What is hyperpolarization?

Answer 15

The Membrane potential becomes more negative than the resting membrane potential.

Question 16

How might we measure a membrane potential?

Answer 16

One electrode sits inside the cell and one outside. We can then measure the difference in charge. We can also inject a charge this way and see what happens.

Question 17

What is the normal distribution of ions like in and out a typical cell?

Answer 17

K+ is high inside and low outside

Na+ is low inside and higher outside

Question 18

Is a cell typically more negative inside than outside?

Answer 18

Yes, that is what a RMP of -70mv would suggest

Question 19

Describe local potentials? How do these differ from action potentials?

Answer 19

Local potentials are graded in size and only effect one small area of the cell membrane (not the whole cell). They decrease amplitude over distance (because fade with time) and they can summate with time (temporal) or with space (spatial). If this occurs and threshold is met then an all or nothing action potential results.

Question 20

Describe how diameter of an axon reflects resistance and potential decay…

Answer 20

Small diameter= more resistance and therefore more rapid decay
Large diameter= less resistance and therefore less rapid decay (response is over longer period)

Question 21

Where is the threshold for action potential generation likely to be in relation to resting membrane potential?

Answer 21

10 mv over the RMP (like -60mv)

Question 22

Will an action potential/ spike always overshoot?

Answer 22

Yes

Question 23

Why are action potentials described as being regenerative?

Answer 23

because they can be propagated (move along axon) without a decrease in amplitude.