S4 - Resting Membrane Potential And Changing Membrane Potential

Question 1

What is the membrane potential?

Answer 1

The electrical potential difference across a membrane

Question 2

How do you measure the resting potential?

Answer 2

Using a voltmeter an electrodes.

Connected to a microelectrode which penetrates the cell membrane.

Question 3

What is the range of resting potentials in human cells?

Answer 3

-20mV to -90 mV

Question 4

What is the range of resting potential in cardiac and skeletal muscle cells?

What is the range of resting potential in nerve cells?

Answer 4

• 80mV to -90mV

- 50mV to -75mV

Question 5

What is selective permeability?

Answer 5

Cell membranes are more permeable to certain types of ions

E.g. in nerve cells, the membrane is more permeable to K+ than Na+

Question 6

Which way do the electrical and chemical gradients for K+ go?

Answer 6

Chemical gradient = in to out

Electrical gradient = out to in

Question 7

Why is equilibrium potential not always reached for a certain ion?

Answer 7

Due to leakage of other ions through the membrane

Question 8

What is the equilibrium potential?

Answer 8

At equilibrium, the electrical and chemical gradients are balanced so there’s not net movement across the membrane

Question 9

What do you use the Nernst equation for?

Answer 9

To calculate the membrane potential of an ion in equilibrium (based of the extra- and intra-cellular concentrations)

Question 10

What is the resting membrane potential of smooth muscle cells?

Answer 10

-50mV

Question 11

What is depolarisation?

Answer 11

Inside cell becomes less negative (decrease in membrane potential size)

Question 12

What is hyperpolarisation?

Answer 12

Inside cell becomes more negative (increase in membrane potential size)

Question 13

How does a change in membrane potential arise?

Answer 13

A change in the membrane’s selectivity for particular ions - membrane potential shifted towards the equilibrium potential for that ion

Question 14

What are inhibitory synapses?

Answer 14

Transmitters that open ligand-gated channels and cause hyperpolarisation (permeable to K+ or Cl-)

Question 15

Receptors and channels are two separate proteins, what two ways does synaptic transmission occur??

Answer 15

1. Direct G-protein gating (localised, rapid)

2. Gating via an intracellular messenger (throughout the cell, amplification occurs)

Question 16

What 2 factors affect membrane potential?

Answer 16

1. Changes in ion concentration (most important is K+, can be altered in clinical situations
   e. g. more action potential in the heart)
2. Electrogenic pumps (e.g. the Na+ - K+ - ATPase pump)