M&R S3 - The Resting Membrane Potential

Question 1

Can a membrane potential be found in all types of cells?

Answer 1

Yup

Question 2

What is the resting membrane potential?

Answer 2

The potential inside the cell relative to the outside

Question 3

Describe the range of resting membrane potentials seen in animal cells

Answer 3

Animal cells have membrane potentials from -20mV to -90mV

Nerve cells = -50 to -75mV

Smooth muscle cells = -50mV

Cardiac and skeletal muscle = -80 to -90mV

Question 4

How can membrane potential be measured?

Answer 4

A micro-electrode:

Fine glass pipette

Penetrates into the cell

Filled with conducting solution (KCL)

Tip diameter is 1um

Another electrode is placed in the surrounding fluid and a voltmeter used to identify difference in potential across the membrane

Question 5

How is the membrane potential created and controlled?

Answer 5

Selective permeability of membrane to ions through utilisation of transport and channel proteins

These proteins can be gated to allow control of the ion levels intracellularly

See Session 2 for more detail

Question 6

What is the intra and extra-cellular concentration of: Na+ K+ Cl- Other Anions

Answer 6

Na+:

Intra- 10mM

Extra - 145mM

K+:

Intra - 160mM

Extra- 4.5mM

Cl-:

Intra - 3mM

Extra - 114mM

A- (Other Anions):

Intra - 167mM

Extra - 40mM

Question 7

How is the resting membrane potential created?

Answer 7

At rest the membrane has open K+ channels,

K+ diffuses out As Anions cannot follow, the cell becomes negatively charged

The movement of K+ ions out of the cell is opposed by the electrical gradient (they are moving up the gradient).

When electrical and chemical gradients exert the same force on K+ ions the resting potential has been reached

Question 8

Define ‘Equilibrium potential’ in terms of ions

Answer 8

The membrane potential at which there is no net movement of that ion across the membrane

Concentration gradient = Electrical gradient

Question 9

What is the Nernst equation?

Hint: Assume 37 degrees celsius

Answer 9

Ions in = concentration of ions inside the cell

Ions out = Concentration of ions outside the cell

Question 10

Give a brief description of membrane depolarisation

Provide an example of how this might come about

Answer 10

Membrane potential decreases in size towards 0

May only be by a few millivolts, not necessarily an action potential

Cell interior becomes less negative

This could come about by the opening of Na+ or Ca2+ channels

Question 11

Give a brief description of membrane hyperpolarisation

Provide an example of how this may come about

Answer 11

Membrane potential increases in size

Potential falls below resting

Cell interior becomes more negative

This could come about by the opening of K+ or Cl- channels

Question 12

Which type of channel dominates the resting permeability of a cell?

Why is the resting potential not equal to the equilibrium potential for this ion?

Answer 12

K+ channels are predominantly open at rest

Resting potential is higher than equilibrium potential -70mV vs -95mV)

Tjis is because other types of channel are also open

Question 13

What effect will changing the equilibrium potential of K+ ions have on a cells resting potential?

Why?

Answer 13

Will change the resting potential in the same direction as the change in equilibrium potential for K+

Resting potential is predominantely influenced by K+ permeability/equilibrium potential

Question 14

Explain what is calculated by the Goldman-Hodgkin-Katz equation

Write out the equation, explain the meaning of any symbols present

Answer 14

The GHK equation provides a good approximation of membrane potential as determined by Na+, K+ and Cl- ions

Vm = Membrane potential

P_Na P_K P_Cl = Relative permeabilities of the ions

[ion] = concentration of the ion

R = Gas constant

T = Temperature (celsius)

F = Faraday’s number

Question 15

What are the two types of channel gating?

Give a brief description of each type

Answer 15

Ligand Gating:

Channel is opened or closed by binding of a chemical ligand which may be an intra or extra cellular messenger

Voltage Gating:

The channel opens or closes in response to changes in the membrane potential

Question 16

Where types of cells are synaptic connections found between?

What are the two types of synaptic transmission?

Answer 16

Synaptic transmission occurs between nerve, muscle, sensory cells and glands

Fast and slow synaptic transmission

Question 17

What is the distinction between fast and slow synaptic transmission?

Answer 17

Fast:

The receptor proteins is also an ion channel, the binding of neurotransmitter causes the channel to open

Slow:

The receptor protein and ion channel are separate proteins.

Question 18

What is are the patterns of slow synaptic transmission?

Provide a brief explanation of each

Answer 18

Direct G-protein gating:

Receptor is directly linked to the ion channel by G protein

This process is localised and quite rapid

Gating via intracellular messenger:

G-protein linked receptor activates an enzyme, iniatiating a signalling cascade resulting in the opening of the ion channel

This activation occurs throughout the cell

Question 19

Describe the action of Excitatory synapses

Hint: Channels, Potential change

Answer 19

Excitatory transmitters open ligand gated channels, this causes membrane depolarisation

Transmitters include Acetylcholine, Glutamate

Graded with the amount of transmitter

Can be permeable to Na+, Ca2+ or cations in general

Results in an Excitatory Post Synaptic Potential (EPSP)

Has a longer time course than an action potential

Question 20

Describe the action of inhibitory synapses

Hint: Channels, Potential change

Answer 20

Inhibitory transmitters open ligand gated channels, this causes membrane hyperpolarisation

Transmitters include Glycine, GABA

Graded with the amount of transmitter

Permeable to K+ or Cl-

Results in an Inhibitory Post Synaptic Potential (IPSP)

Has a longer time course than an action potential