Resting Cell Membrane -- Session 3

Question 1

What is a membrane potential?

Answer 1

An electrical potential difference across a cell membrane

Question 2

What is used to measure membrane potential?

Give the characteristics for the unique component of the measuring device/

Answer 2

Microelectrode with a micropipette

• • one electrode measures the extracellular fluid & a micropipette measures voltage inside the cell membrane
• • teh micropipette has a diameter of >1micrometres and is filled with a conducting solution (KCl/solution which is a s similar as possible to intracellular fluid to prevent excess disruption)

Question 3

How is a membrane potential expressed?

Answer 3

A value which is relative to the outside of the cell

Question 4

What is the range for membrane potential for animal cells?

Answer 4

-20mV to -90mV

Question 5

What is the membrane potential range for cardiac muscle?

Answer 5

-80mV to -90mV

Question 6

What is the membrane potential range for nerve cells?

Answer 6

-50mV to -75mV

Question 7

Why do membrane potentials occur?

Answer 7

The membrane is selectively permeable to different ions due to transmembranous channel proteins.

Question 8

What are the charactersitics of ion channels?

Answer 8

1. Are specific to one/ a few ion species
2. Gating – teh channel can be opened or closde by a conformational change in the protein molecule
3. Ion flow always occurs down the electrochemical gradient

Question 9

What is specific about potassium channels?

What movement of K+ ions occur at rest?

Answer 9

They are voltage insenstive and tend to open at resting potential

• • Increased K+ inside cell so ions move out down chemical gradient
• • Negative charge on the inside of the cell so ions are attracted bck into the cell down an electrical gradient

Question 10

How is a membrane potential generated?

Answer 10

K+ channels are open so K+ can diffuse out down a conc. gradient
Anions cannot follow (cant diffuse through the membrane) so negative anions build up in cell.
Negative charge is present on inside in comparison to the outside.
Membrane potential opposes K+ outward diffusion so equilibrium arises.

Question 11

What is an equilibrium potential?

Answer 11

The membrane potential where the electrical and diffusion forces balance each oter so there is no further net movement of an ion

Question 12

What equation crayon use to calculate the potassium equilibrium potential?

Answer 12

Nernst equation

Question 13

What are the two terms which can be used to describe changes of the membrane potential from its resting level and describe them.

Answer 13

HYPERPOLARISATION – an increase in the membrane potential so the inside becomes less negative
DEPOLARISATION – a decrease in the membrane potential so the inside becomes more negative

Question 14

What will cause depolarisation of cells?

Answer 14

Opening Ca2+ or Na+ channels

Question 15

What will causes hyperpolarisation of cells?

Answer 15

Opening K+ or Cl- channels

Question 16

How can you determine how important each ion is to determining the membrane potential?

Answer 16

It depends upon how easily the ion can diffuse through the membrane relative to other ions
— depends on: the number of channels and how easily they let the ion through

Question 17

How is ion channel opening determined?

Answer 17

Gating mechanisms which open and close the cells

Question 18

What are the two main forms of hating mechanisms?

Answer 18

Ligand gating – channel is opened/closed by binding of a chemical ligand (can be extracellular transmitter or and intracellularly messenger)
Voltage gating – channel opens or closes in response to changes in membrane potential

Question 19

What is a specific characteristic of a receptor in a fast synaptic transmission?

Answer 19

The receptor is also a ligand gated ion channel

Question 20

What type of channels do depolarising transmitters open?

Answer 20

Channels with positive reversal potentials

– channels for Na+, Ca2+ or cations

Question 21

What type of potential change do depolarising transmitters cause?

Answer 21

Excitatory postsynaptic potential

– causes excitation of cells

Question 22

What type of channels do hyper polarising transmitters open?

Answer 22

Negative reversal potentials

– channels for K+ or Cl-

Question 23

What type of change in potential do hyperpolarising transmitters cause?

Answer 23

Inhibitory postsynaptic potential

– lead to inhibition

Question 24

What happens in slow synaptic transmission?

Answer 24

The receptor is not an ion channel
It signals to the channel in one of two ways:
1. Within the membrane
2. By an intracellularly messenger
--- both involve GTP-binding protein

Question 25

What are the characteristics of channels signalling within the membrane?

Answer 25

Is localised

Very rapid

Question 26

What are the benefits of signalling the ion channel by an intracellularly messenger?

Answer 26

It occurs throughout the cell

Is amplified by a cascade

Question 27

What is responsible for the distribution of ions between the intra and extra cellular fluid?

Answer 27

The selective permeability of the membrane

Question 28

Why is the value calculated for a resting membrane potential not often the value measured?

Answer 28

The membrane is not permeable to one ion only. Other ions ar Beale to diffuse in and out which has an effect on the actual resting potential value.

Question 29

What contribution does Na+-K+-ATPase make to the maintainance of the resting membrane potential?

Answer 29

It generates the potential by removing Na+ bringing K+ into the membrane.
It helps to maintain the ion gradient.