M&R Session 3 (Lecture 3.1) Flashcards Preview

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How can a membrane potential be measured?

1) Microelectrode (fine glass pipette) which penetrates the cell membrane.
2) Filled with conducting solution (KCl)
3) Measures membrane potential


How are membrane potentials expressed?

In millivolts relative to the extracellular solution


Why are membrane potentials set up?

The membrane is selectively permeable to different ions.


How is the permeability of ions changed in membranes?

Opening or closing of ion channels, gated channels and concentration gradient


How is the resting membrane potential set up?

Open K+ channels dominate the membrane ionic permeability at rest.
K+ effulx occurs due to chemical gradient so membrane becomes more negative.
No channels open for anions (A-) e.g. proteins.
Electrical gradient of K+ wants it to flow back into cell but when chem=elec, no net flow.


State the electrical gradient equation.



State the chemical gradient equation.

RT ln [K+o]/[K+i]


What is the Nernst equation for potassium?

At equilibrium, the electrical and chemical gradient for K+ balance, so that there is no net driving force on K+ across the membrane.

V=RT/ZF ln [K+o]/[K+i]


What is Ek equation.

Ek=61/z log [K+o]/[K+i] at 37 degrees C


What would the membrane potential be if the cell was selectively permeable for potassium only?

At Ek i.e. -94.6mV


Give examples where changing the membrane potential is necessary?V

1) Action potential in nerve and muscle cells
2) Muscle contraction
3) Secretion of hormones and NTs
4) Transduction of sensory info and electrical activity
5) Postsynaptic actions of fast synaptic transmitters


What is depolarisation?

Decrease in size of the membrane potential from its normal value e.g. -70 to -50 mV


What is hyperpolarisation?

An increase in the size of the membrane potential from its normal value e.g. -70 to -90 mV


What does increasing the membrane permeability of one ion do?

Causes the membrane potential to move towards the equilibrium potential for that ion


What does the GHK equation stand for and what does it allow?

1) Stands for Goldman-Hodgkin-Katz

2) Includes permeabilities of Na+, Cl- and K+ for a real cell which has imperfect selectivity for ions (i.e. >1).


Give an example of a less selective channel and describe its actions.

1) nAChR

2) Have an intrinsic ion channel
3) Opened by Ach
4) Lets Na+ and K+ through but not A-
5) Moves membrane potential towards 0 mV (betweem Ena and Ek)


Describe the three types of channels.

1) Ligand gated (opens/closes to ligand binding or channels open/close to secondary intracellular messengers)

2) Voltage gated (opens/closes in response to a voltage change in the membrane)

3) Mechanical gated (opens/closes in response to membrane deformation e.g. mechanoreceptors in carotid sinus)


Describe fast synaptic transmission.

Receptor protein is also an ion channel e.g. nAChR


What is an EPSP?

Excitatory post-synaptic potential.

Channels open causing the post synaptic membrane to depolarise e.g. Na or Ca influx.

1) Longer than AP (20ms compared to 1ms)
2) Graded with amount of transmitter
3) Transmitters include: ACh and Glutamate


What is an IPSP?

Inhibitory post0synaptic potential

Inhibitory transmitters open ligand-gated channels that cause hyperpolarisation e.g. K+ or Cl-

E.g. Glycine or GABA


Describe slow synaptic transmission.

Receptor and channel are separate proteins.

1) Direct G - protein gating (localised and quite rapid)
2) Gating via an intracellular messenger (throughout cell, amplification by cascade)


What two other factors can affect membrane potential?

1) Changes in ion concentration (most important is [K+], can be altered e.g. hyperkalaemia.

2) Electrogenic pumps e.g. Na+ pump, contributes few mV directly to the membrane potential making it more negative.