L5 The action potential Flashcards
What does depolarisation mean?
The membrane potential becomes less negative (or even positive)
What does hyperpolarization mean?
The membrane potential becomes more negative
What is the driving force depending upon an ion?
the direction of the movement of ion (influx or efflux)
the charge the ion carries
Describe the stages of a neuronal action potential?
1- Na channel opening- the membrane potential is driven towards Ena influx
2-
What does absolute refractory period mean?
no stimulus, however strong, can elicit a second action potential-all Na+ channels inactivated
What does relative refractory period mean?
a stronger than normal stimulus may elicit a second action potential (mixed population of inactivated and closed channels, plus the membrane is hyperpolarised)
What are the three type of gated ion channels?
- membrane voltage gated ion channels VGICs
- chemical substances-ligand gated ion channels LGICs
- physical stimuli- mechanical, thermal
What is an action potential?
brief electrical signals in which the polarity of the nerve cell membrane is momentarily reversed
Describe how positive feedback in an action potential occurs with Na+ channels?
Self reinforcing-Activation of Na+ channels causes further activation of more Na+ channels causing further depolarisation
Give an example of negative feedback in a stage of an action potential?
the activation of k+ channel is self limiting. depolarisation leads to conductance of k+ channels leading to efflux of K+ ions causing repolarization
What are ways to increase passive current spread?
- increase axon diameter-increases current spread
- decrease the leak of current across the axon-through adding an insulating material-myelin-conduction by myelinated axons is much faster than in non myelinated axon of the same diameter
