Revision 3: The Resting Cell Membrane

Question 1

define the resting membrane potential, give values for different cells, and describe how it is measured

Answer 1

the potential of a quiescent cell not undergoing an action potential or other events relative to the potential of the extracellular solution

Animal cells range from -20<->-90mV, SMCs: -50mV, Nerve cells: -50<->-90mV, Cardiac and skeletal muscle cells: -80<->-90mV

It is measured by using a very fine mircopipette (microelectrode) that will penetrate the PM of a cell, with a diameter of <1micrometre filled with conducting solution (KCl)

Question 2

How is the resting membrane potential set up?

Answer 2

The PM is selectively permeable (allows certain molecule through) to different ions due to channel proteins

Open K⁺ channels dominate the membrane ionic permeability at rest, and when the electrical and chemical gradients for K⁺ are equal and opposite there will be no net movement

Question 3

The equilibrium potential definition and calculation

Answer 3

Def.: membrane potential at which there is no net movement of the ion across the membrane (ie. the electrical and chemical gradients are equal and opposite)

Calculation: Nernst equation: requires conc. of the ion in and outside of the cell, the membrane potential, the valency of the ion (eg, for Ca²⁺ the valency would be +2)

In the equation (don’t need to know it): R is the gas constant, T is the temperature in kelvin, Z is the valency, F is faraday’s number

Question 4

Define de- and hyperpolarisation and explains mechanisms that may lead to these

Answer 4

Depolarisation: decrease in the size of the cell potential, or the cell becomes less -ve

Eg. from opening Ca²⁺ or Na⁺ channels

Hyperpolarisation: increase in the size of the cell potential, or the cell becomes more -ve, so that the potential is less -ve than the resting potential

Eg. from opening K⁺ or Cl^- channels

Question 5

how do changes in ion channel activity lead to changes in membrane potential?

Answer 5

cells normally have channels open for >1 type of ion, contribution of each ion to the membrane potential depends on how permeable the membrane is for that ion, therefore changes in the cell’s permeability to even a signel ion can change the membrane potential

Question 6

roles of ion channel activity in signalling

Answer 6

Synaptic transmission, can occur between nerve/muscle/sensory cells or glands

Types: Fast (receptor=ion channel): Excitatory: leads to depolarisation, can be permeable to Na+/Ca2+/cations in general, leads to EPSPs (excitatory post synaptic potentials), longer time course than APs, graded with the amount of NT eg ACh, glutamate

• >Inhibitory: leads to hyperpolarisation, permeable to K+/Cl-, leads to IPSPs, NTs include Glycine, Gamma-aminobutyric acid (GABA)
• Slow (receptor is not the ion channel), linked by: G proteins: localised, quite quick
• > Intracellular messengers: throughout cell, leads to amplification of signal by cascade