Saltatory conduction and the all-or-nothing principle Flashcards
What is different about myelinated axons?
because depolarisation of the axon membrane can only occure at the nodes of Ranvier where no myelin is present
sodium ions can pass through the protein channel in the membrane here
longer localised circuits therefore arise between adjacent nodes
How does the action potential jump?
its jumps from one node to another in a proces known a salatory conduction
much faster than a wave of depolarisation along the whole length of the axon membrane
every time channels open and ions move it takes time, so reducing the number of places where this happens speeds up the action potential transmission
How is saltatory conduiction more energy efficient?
repolarisation uses ATP in the sodium pump, so by reducing the amount of repolarisation needed, saltatory conduction makes the conduction impulses more efficient
How does axon diameter affect the speed at which an action potential travels?
the larger the axon diameter, the faster the impulse is transmitted
this is because there is less resistance to the flow of ions in the cytoplasm, compared with those in a smaller axon
How does temperature affect the speed at which an action potential travels?
the higher the temperature, the faster the nerve impulse
this is because the ions diuffuse faster at higher temperature
however, this only occurs up to 40ºC, as higher temperature cause the proteins, such as the sodum-potassium pump, to become denatured
Why are nerve impulses said to be all-or-nothing responses?
a certain level of stimulus - the trheshold value - always triggers a response
if this threshold is reached an action potential will always be created
no matter how large the stimulus is, the same sized action potential will always be triggered
fi the threshold is not reached, no action potential will be triggered
What does the size of a stimulus affect?
the number of action potentials that are generated in a given time
the larger the stimulus the more frequently the action potentials are generated