Membrane Potential Flashcards
What is the main determinant of the membrane’s ionic permeability at rest?
Open K+ channels: selective permeability to K+
note: amount of K+ which moves to set up the voltage is very small
How can the membrane potential of cells be measured?
Microelectrode (fine glass pipette) filled with conducting solution (KCl) injected into cell and compared to electrode on surface of cell
Define equilibrium potential.
Membrane potential at which the chemical gradient balances the electrical gradient of an ion, meaning that there is no net movement of the ion across the membrane.
How does the resting potential of cells vary between types of tissue?
Cardiac muscle = ~ -80mV (resting potential close to Ek, but not exactly, therefore membrane not perfectly selective for K+)
Nerve cells = ~ -70mV (same as above)
Smooth muscle cells = ~ -50mV (increased contribution from other ion channels; lower selectivity for K+)
Skeletal muscle = ~ -90mV (close to Ek & Ecl; therefore more K+ & Cl- channels open)
What are some examples of functions of changes in membrane potential?
- triggering/control of muscle contraction
- action potentials (nerve & muscle cells)
- control of secretion of hormones and neurotransmitters
- transduction of sensory information into electrical activity by receptors
- post-synaptic actions of fast synaptic transmitters
Define depolarisation and hyperpolarisation.
DEPOLARISATION = decrease in size of the membrane potential from its normal value (LESS NEGATIVE)
HYPERPOLARISATION = increase in size of the membrane potential from its normal value (MORE NEGATIVE)
What is the difference between an EPSP & IPSP?
Excitatory post-synaptic potential (EPSP) = ligand-gated channels opened (Na+, Ca2+, cations) -> DEPOLARISATION
Longer time course than AP ensures all voltage-gated channels respond.
Graded with amount of transmitter (ACh, glutamate)
Inhibitory post-synaptic potential (IPSP) = ligand-gated channels opened (K+ & Cl-) -> HYPERPOLARISATION
Transmitters: glycine & GABA
