Session 3 Flashcards
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
