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Flashcards in Session 3 Deck (22):

How is the membrane potential measured?

Using a voltmeter with an extracellular electrode and fine glass pipette microelectrode that impales the cell, around which the membrane reforms. A KCl/other conducting solution is used


Which animal cells generally have the largest (most negative) resting potentials?

Cardiac and skeletal muscle cells, ~-80 to -90mV


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

All negative; ~ -20 to -90mV range


Which ion channels dominate the membrane ionic permeability in most cells at rest?

Voltage in sensitive K+ channels


How does the resting membrane potential arise?

Membrane is selectively permeable to K+ (voltage in sensitive); there is an outward concentration gradient, but an inward electrical gradient; the equilibrium potential of K+ is about -95mv, but the membrane potential is closer to -70mV as the membrane is not perfectly selective (leak)


How do smooth muscle cells achieve a lower resting potential of around -50mV?

The membrane has a lower selectivity for K+; there is increased contribution from other channels


How do skeletal muscle cells achieve a more negative resting potential of around -90mV?

Cl- channels are open


What is the equilibrium potential?

The charge at which the electrical and concentration gradients of an ion balance so that there is no net driving force on K+ across the membrane


How can the equilibrium potential be calculated?

By using the Nernst equation


What is ‘depolarisation’?

A decrease in the size of the membrane potential from its normal value; cell interior becomes less negative – not necessarily positive, just closer to 0


What is ‘hyperpolarisation’?

An increase in the size of the membrane potential from its normal value; the cell interior becomes more negative


How are changes in the membrane potential brought about?

Changing the activity of ion channels


What is the Goldman-Hodgin-Katz equation?

Theoretical equation that takes into account permeabilities of important ions when calculating a theoretical membrane potential; it also depends on the number of channels open


Which ions do nicotinic acetylcholine receptors allow through their intrinsic channel?

Na+ and K+ (and Ca2+; they are anionic)


What are three mechanisms of gating of channel?

Ligand gating, voltage gating, mechanical gating


What is mechanical gating?

Channels open in response to membrane deformation; e.g. channels in mechanoreceptors, carotid sinus


What is the difference between fast and slow synaptic transmission?

Fast: receptor protein is also an ion channel (conformational change)
Slow: receptor and ion channel are separate proteins


What is the difference between excitatory synapses and inhibitory synapses?

Excitatory open channels causing membrane depolarisation (Na+/Ca2+), inhibitory open channels that cause hyperpolarisation (K+/Cl-)


Which transmitters cause ‘EPSP’s?
What are ‘EPSP’s?

Excitatory postsynaptic potential; longer time course than AP, graded with amount of transmitter; Ach, glutamate


Which transmitters cause ‘IPSP’s?
What are ‘IPSP’s?

Inhibitory post-synaptic potential; longer course than AP; transmitters include glycine and GABA


What are two mechanisms of slow synaptic transmission?

Direct G-protein gating, gating via intracellular messenger (cascade)


What are electrogenic pumps?

Carrier proteins, that can slightly alter the membrane potential; example is Na+ pump