ND1: Resting potentials

Question 1

What is a membrane potential?

Answer 1

The potential difference between the inside and outside of a cell

Question 2

Conventionally, does the outside or the inside of a cell have a value of 0 mV?

Answer 2

Outside

Question 3

How is the membrane potential of a cell measured?

Answer 3

A microelectrode filled with a conducting solution (usually KCl) penetrates the cell membrane and a voltmeter measures the potential difference

Question 4

What is the unit of measurement of membrane potentials?

Answer 4

Millivolts (mV)

Question 5

What is the range of membrane potentials of animal cells at rest?

Answer 5

–20 to –90 mV

Question 6

What is the range of membrane potentials of cardiac and skeletal muscle cells at rest?

Answer 6

–80 to –90 mV

Question 7

What is the range of membrane potentials of nerve cells at rest?

Answer 7

–50 to –75 mV

Question 8

What are the five methods molecules can use to pass through the lipid bilayer of cells?

Answer 8

1. Diffusion through the cell membrane
2. Channels
3. Carriers/exchangers
4. Primary active transport
5. Secondary active transport

Question 9

What sets up the resting potential of the cell? How?

Answer 9

Na⁺/K⁺-ATPase

Actively transports 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, against their respective concentration gradients

Question 10

How much of the total energy consumption of a cell at rest is due to the Na⁺/K⁺-ATPase?

Answer 10

40%

Question 11

How is the equilibrium potential for an ion calculated? Use K⁺ as an example.

Answer 11

Nernst equation

Question 12

How does the resting membrane potential arise?

Answer 12

The membrane is more permeable to K⁺ at rest than it is to other ions

Question 13

What are ion channels?

Answer 13

• Proteins that enable ions to cross cell membranes
• They have an aqueous pore through which ions flow by diffusion

Question 14

What are the properties of an ion channel?

Answer 14

• Selectivity: for one (or a few) ion species
• Gating: the pore can open or close by a conformational change in the protein
• Rapid ion flow: always down the electrochemical gradient

Question 15

What is depolarisation?

Answer 15

A decrease in the size of the membrane potential from its normal value, i.e. the cell interior becomes less negative

Question 16

What is hyperpolarisation?

Answer 16

An increase in the size of the membrane potential from its normal value, i.e. the cell interior becomes more negative.

Question 17

How can the membrane potential for an ion be changed?

Answer 17

By changing the membrane permeability to a particular ion

Question 18

What are the three methods by which channel activity can be controlled?

Answer 18

1. Ligand gating
2. Voltage gating
3. Mechnaical gating

Question 19

How do ligand-gated ion channels work?

Answer 19

The channel opens or closes in response to the binding of a chemical ligand

e.g. channels at synapses that respond to extracellular transmitters (acetylcholine); channels that respond to intracellular messengers

Question 20

How do voltage-gated ion channels work?

Answer 20

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

e.g. channels involved in action potentials

Question 21

How do mechanical-gated ion channels work?

Answer 21

The channel opens or closes in response to membrane deformation

e.g. channels in mechanoreceptors (e.g. stretch receptors)

Question 22

Between which types of cell do synaptic connections occur?

Answer 22

• nerve cell – nerve cell
• nerve cell – muscle cell
• nerve cell – gland cell
• sensory cell – nerve cell

Question 23

What is the process of synaptic transmission?

Answer 23

1. Information is passed down the axon of the neuron as an action potential
2. Vesicles release their (neuro)transmitter at the presynaptic membrane in response to the action potential
3. (Neuro)transmitters carry the signal across the synaptic gap
4. (Neuro)transmitter binds to the receptor on the postsynaptic membrane and the receptor opens

Question 24

How do excitatory synapses work?

Answer 24

Excitatory transmitters (e.g. acetylcholine, glutamate) open ligand-gated ion channels and cause membrane depolarisation

This results in an excitatory postsynaptic potential (EPSP)

Question 25

How do inhibitory synapses work?

Answer 25

Inhibitory transmitters (e.g. glycine, γ-aminobutyric acid (GABA)) open ligand-gated ion channels that cause hyperpolarisation

This results in an inhibitory postsynaptic potential (IPSP)