Pharmacology: Action Potentials Flashcards
depolarisation
membrane becomes more positive
hyperpolarisation
membrane becomes less positive
direction of change in potentials depends on
direction of ion movement and the charge carried
what drives the passive movement of ions through ion channels
electrochemical gradient
why do Na+ ions move inward
the concentration and electrical gradients draw Na+ inwards
what is the Na+ driving force
when ENa+ becomes mores -ve than Vm inward Na+ movement can occur
why do K+ ions flow outward
the outward conc. gradient is stronger than the inward electrical gradient
what is the K+ driving force
when EK+ becomes mores +ve than Vm outward K+ movement can occur
when Na+ channels open where in the membrane potential driven towards
ENa+ - more positive
depolarisation
when K+ channels open where in the membrane potential driven towards
EK+ - more negative
hyperpolarisation
what type of gated channels are responsible for action potentials
voltage-gated ion channels (VGICs)
what are action potentials
brief electrical signals where the polarity of the membrane is momentarily reversed allowing signalling over long distances
when is an AP generated
when a threshold is reached
when are Na+ channels activated by membrane depolarisation and when are K+ channels
- Na+, rapidly
- K+, with a slight delay
the activation of Na+ channels is what type of feedback and what does this mean
- +ve feedback
- activation of Na+ channels causes the activation of more Na+ channels
the activation of K+ channels is what type of feedback and what does this mean
- -ve feedback
- K+ channel activation turns of the stimulus for opening and therefore stops the opening of more K+ channels
what happens to Na+ channels during maintain depolarisation
enter a non-conducting, inactivated state
what is needed for an Na+ channel to enter the closed state
repolarisation
absolute refractory and why
no stimulus can elicit a second AP, all Na+ channels in inactivated state
relative refractory and why
a strong stimulus can elicit a second AP, mixed closed and inactivated Na+ channels
draw an action potential and label each stage
** notes
why do passive signals diminish
nerve cell membranes are ‘leaky’ and therefore passive signals don’t get very far do to current loss across the membrane and a decrease in potential
action potentials have a _ amplitude
constant
what happens when an axon is less ‘leaky’
local spread and conduction velocity
the local current spread is greater therfore there is an increase in AP conduction velocity
how is passive spread decreased
- axon diameter is increased, increases current spread
- insulting material decreases leak of current
what are insulated axons called
myelinated axons
in what type of axons do currents spread faster
myelinated compared to non-myelinated
name the insulating material in the
- PNS
- CNS
- myelin
- oligodendrocytes
describe what happens to the AP in terms of nodes of Raniver
the AP jumps from one to the next, this increases conduction velocity
where are nodes of Raniver
between myelin sheaths
what clusters at nodes of Raniver
Na+ channels - increasing the conduction velocity at each one
