ICPP S9 Electrical Excitabilty Flashcards
Give 3 properties of an action potential.
Threshold must be reached
All or nothing
Propagated along axon at the same amplitude.
What is the conductance of the membrane to an ion dependant on?
What does increasing conductance to an ion result in?
number of channels for that ion that are open.
Membrane potential moving closer to equilibrium potential of that ion.
From voltage clamping and then observing the ionic movements in an action potential what can be observed?
Why does the voltage clamp hold the voltage at 0mV?
- Na+ channels open rapidly then inactive rapidly.
- K+ open more slowly and then close slowly.
Intermediate voltage between Ek and Ena.
Describe channel activity during an axonal action potential.
V-G Na channels open. Na+ influx Depolarisation This creates positive feedback loop causing more V-G Na channels to open. V-G Na channels inactive V-G K channels open. Na+ influx stops K+ efflux occurs. Repolarisation and hyperpolarisation.
Describe the difference between the states of the channels during ARP and RRP.
What is the function of the hyperpolarisation period of an action potential?
ARP - all Na+ channels inactivated
RRP - Na+ channels recovering from inactivation.
Allows for recover of inactive Na+ channels.
What is the structure of the alpha sub unit of a Na+ ion channel?
6 features.
1 peptide 4 repeats Each repeat 6TMS Inactivation particle between III/IV. Voltage sensor in each 4th TM Intracellular N and C terminus. Pore region between 5/6th TM domain.
What is the structure of an K+ ion channel?
5 features
4 alpha subunits
6 TM domains per peptide.
Voltage sensor in 4th TM domain per alpha sub-unit.
Intracellular N and C terminus.
Pore region between 5/6th TM domain of repeat.
What is the order of priority of axons that local anaesthetics block?
Name a local anaesthetic.
small myelinated
Un-myelinated
Large-myelinated
Procaine
Describe briefly the 2 pathway that local anaesthetics can take in order to block a pore.
Hydrophobic pathway
- enter the cell membrane and then enter and block pore.
Hydrophilic pathway
- enter pore after entering cell and becoming charged.
What are the 2 main factors in conduction velocity of an axon?
Diameter
Myelination
Describe local current theory.
Current injection into axon.
Causes repulsion of like, +ve charges and attraction of negative charges causing +ve charged to spread passively down axon.
What is the length constant?
The distance an electric potential will travel along a neurone for its potential to fall to 37% of original value.
What is capacitance?
What is resistance dependant on?
The ability of the bilayer to store charge.
Ion channels open
What is the relationship between capacitance and voltage changes in an axon?
The greater the capacitance the slower the voltage change in responses to current injection.
What is the relationship between resistance and the distance a change in voltage will travel?
The greater the resistance the further the change in voltage can travel down an axon.
