The Action Potential Flashcards
What is the action potential?
Transientchangein themembrane potentialcapable of nondecremental self propagationalong an axon of the neurone which allows neurones tocommunicatewith other neurones.
List the properties of the action potential. (5)
- Robust
- Rapid
- Orthodromic
- All or nothing
- Frequently encoded
What is a compound action potential (CAP)?
A population response, sum of action potentials from all the axons simultaneously contributing to the signal.
What are graded potentials/postsynaptic potentials?
Small changein membranepotentialbelow threshold that occurs is a small region of the neuronal membrane.
What determines the magnitude of graded potentials?
Magnitudeof membrane potentialchangerelatedto thesizeof thestimulus
What are the features of a graded potential?
Can be Depolarising (EPSP)orhyperpolarising(IPSP), have a decremental response and are not self propagating.
What is summation?
-Process thatdetermines whetheranaction potential will begeneratedfrom the combinationof excitatory and/or inhibitorypostsynaptic potentials
What is spatial summation?
Cumulative change inpostsynaptic membrane potentialas a result ofmultiple, differentsimultaneous inputs
What is temporal summation?
cumulative change inpostsynaptic membrane potentialas a result ofsequential repeatedinputs
Who led key experiments to record the AP extracellularly?
Erlanger and Gasser, 1920’s
Who led key experiments to record the AP intracellularly?
Hodgkin and Huxley, 1939.
Electrode is inserted inside the axon and outside of the cell, to measure the differences in membrane potential, whilst also applying a stimulus to see how membrane potential changes.
Who invented the Voltage clamp technique?
Hodgkin and Katz, 1949
What is the purpose of the voltage clamp experiment?
To identify if Na+ is controlling the peak depolarisation in an action potential.
What were the findings of the voltage clamp experiment?
They used various concentrations of Na+ and stimulated an action potential in each, discovering that in lower concentrations the peak and the rate of rise of an action potential was lower.
What happens to voltage gated ion channels at rest?
Neither of the voltage gated ion channels are open.
When the action potential is rising what happens to the VG ion channels?
Na+ voltage gated ion channels open quickly, causing a sodium influx into the cell, they shut when reaching the peak of the action potential.
When the action potential is falling what happens to the VG ion channels?
K+ voltage gated ion channels open causing K+ to efflux out of the cell, they take time to close so they cause hyperpolarisation.
How is the refractory period generated?
Voltage Gated Na+ Channels have 2 gates, Inactivation gate and activation gate. After depolarisation the inactivation gate closes to prevent the stimulation of another action potential causing a refractory period.
How is the refractory period generated?
Voltage Gated Na+ Channels have 2 gates, Inactivation gate and activation gate. After depolarisation the inactivation gate closes to prevent the stimulation of another action potential causing a refractory period.
What occurs as a result of loss of function in voltage gated Na+ Channels?
- Don’t fireaction potentials
- Reduced transfer of information
- E.g.lossofsensations
What occurs as a result of gain of function in voltage gated Na+ Channels?
- Over fireaction potentials
- Excess transfer of information
- E.g.increased sensitivitytosensations
How is the strength of a stimulus shown through the action potential?
Firing rateof action potentialsencodes thestrength of thestimulus. An Increased stimulus=increased frequencyNOTamplitude
How does axon diameter affect conduction velocity?
Inc. diameter → Inc. velocity.
How does the presence of myelin affect conduction velocity?
Presence of Myelin increases velocity as well but it is dependant on the size of the axon as axons < 1 micrometre don’t benefit from myelination.
