Resting And Changing Membrane Potential

Question 1

What is the range in resting potential of animal cells, cardiac and skeletal muscles and nerve resting potentials

Answer 1

1. Animal cell resting potential ranges between -20mV to -90mV
2. Cardiac and Skeletal muscle cells had the largest resting potential range of between -80mV to -90mV
3. Nerve cells have resting potential that ranges between -50mV to -75mV

Question 2

What is the membrane potential for cardiac myocytes, neurones, skeletal muscle myocytes and cardiac muscle myocytes?

Answer 2

Cardiac myocytes: -80mV

Neurones: -70mV

Skeletal muscle myocytes: -90mV

Smooth muscle myocytes: -50mV

Question 3

What are the properties of a channel?

Answer 3

1. Selectivity
2. Gating
3. Rapid ion flow: always down the electrochemical gradient

Question 4

What are gated channels?

Answer 4

Channels that can open and close

Question 5

What are the different types of gating?

Answer 5

1. Ligand gating:
   - Channels open or close in response to a ligand binding
   - e.g. channels at synapses that respond to Extracellular transmitters.
   - Channels that respond to intracellular messengers
2. Voltage gating
   - Channels open or close in response to a membrane potential
   E.g. channels involving action potentials
3. Mechanical gating
   - Channels opens or close in response to membrane deformation
   E.g. channels in mechanoreceptors e.g. carotid sinus stretch receptors, hair cells

Question 6

What is fast synaptic transmission?

Answer 6

• In fast transmission, the receptor protein is also the ion channel
• Transmitter binding causes the channel to open

E.g. Excitatory post synaptic potentials (EPSP) and Inhibitory post-synaptic potential (IPSP).

Question 7

What is slow synaptic transmission?

Answer 7

The receptor and channel are separate proteins:

1. Direct G-protein gating
   - Localised
   - Quite rapid
2. Gating via an intracellular messenger
   - Thoughout cell
   - Amplification by cascade

Question 8

What are other factors that can influence membrane potential?

Answer 8

1. Change in ion concentration
   - Most important is extracellular K+ concentration (~4.5 mM normally)
   - Sometimes altered in clinical situations
   - Can alter membrane excitability e.g. in heart.
2. Electrogenic pumps
   - NA/K - ATPase

Pg 32-33