DONE Action Potential Flashcards
What is an increase in conductance?
An increase in the number of open channels for a particular ion
Absolute refractory period
during depolarisationMost sodium channels inactivated = can’t fire A.P. as clan only open again from closed state (go from inactive to closed during HYPERPOLARISATION)
Relative refractory period
Hyperpolarization = sodium channels recovering from inactivation, voltage gated potassium channels close
Sodium channel subunit
1 alpha subunit to form functional sodium channel
Potassium channel subunit
4 x alpha subunit to form 1 functional potassium channel
What is lidocaine?
Local anaesthetic = is membrane permeable in its unprotonated form
Blocks sodium channels = no A.P.
What is the length constant?
Distance it takes for the potential to fall to 37% of its original value
Longer length = faster conduction velocity
What is capacitance?
Ability to store charge = property of lipid bilayer
High capacitance = voltage changes more slowly in response to current injection
Membrane resistance
Lower resistance = more ion channels open = more loss of local current across membrane
High resistance = change in voltage spreads further along axon
How does a myelin sheath improve conduction?
Large increase in membrane resistance
Decrease membrane capacitance
Which both increase length constant
Acetylcholine esterase
Breaks down ACh
How is transmitter released?
Calcium enters through calcium channels Binds to synaptotagmin Vesicle brought close to membrane Snare complex makes fusion pore Transmitter released through pore
What does d-tubocurarine do?
Competitive block of nAChR = paralysis
What does succinylcholine do?
Depolarising block = adjacent sodium channels inactivated = no depolarisation
Myasthenia gravies
Autoimmune disease of nAChR by antibodies
Loss of functional nAChR = end-plate potentials fail to reach threshold = muscle weakness + fatigue
