Wave propagation Flashcards
Explain how waves of depolarisation occur
During an action potential, some of the sodium ions that enter the neurone diffuse sideways. This causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part causing depolarisation. This continues down the axon. This sideways diffusion is called local currents.
How does conduction along a myelinated neurone differ from a non-myelinated neurone?
In a myelinated neurone myelination provides electrical insulation so depolarisation only happens at the nodes of Ranvier. The action potential jumps between nodes of Ranvier -this is called saltatory conduction. In a non-myelinated neurone depolarisation occurs along the whole length of the axon. Therefore, conduction is faster in a myelinated neurone.
Describe how speed of conductance can be increased.
A larger diameter of axon increases the speed of conductance, due to less ion leakage due to a smaller SA:V ratio. A higher temperature increase the speed of conductance as the ions have more kinetic energy and respiration can occur faster. Myelination increases the speed of conductance.
What is the all-or-nothing principle?
Over a certain threshold the action potential is the same change in voltage, no matter how big the stimulus.
What happens when there is a bigger stimulus?
An action potential will fire more frequently.
What is the refractory period?
The ion channels are recovering, sodium ion channels are closed and cannot be made to reopen. Potassium ion channels are slow to close and potassium ions flood out, causing hyperpolarisation.
What is the purpose of the refractory period?
Ensures action potentials are discrete and do not overlap, and that they are unidirectional. Also there is a limit to the frequency of impulses.
