C13 properties of nerves and impulses Flashcards
all or nothing rule
if the intensity of a stimulus is below a certain threshold value, no action potential is generated
but if the intensity of the stimulus exceeds the threshold value an action potential is initiated
the action potential that is initiated is always the same size +40mv
and it remains the same size as it is propagated along the axon
no energy is lost during transmission
Notes on all or nothing rule
an increase in the intensity of the stimulus does not give a greater action potential instead of the frequency of action potential increases
a nervous impulse is either initiated or not and it is always the same size
this is the all or nothing
what does the all or nothing rule allow the action potential to do
it allows it to act as a filter
preventing minor stimuli from setting up nervous impulses so the brain is not overloaded with information
study point
a stronger stimulus produces a greater frequency of action potential as the intensity of stimulation increases but the stimulation increases but the size of the impulses is always the same
what are the 3 factors that impact the speed of conduction of the nerve impulse
temperature
the diameter of the axon
myelination
how does increased temperature impact the speed of conduction of the nerve impulse
ions move faster at higher temperatures than at lower temperatures as they have more kinetic energy
so birds and mammals the two warm-blooded taxa
transmit nervous impulse more quickly and have faster responses than all other groups of animals
How does the diameter of the axon impact the speed of conduction of the nerve impulse
the greater the diameter of the axon
the greater its volume in relation to the area of the membrane
more sodium ions can flow through the axon so impulses travel faster
How does the amount of myelination impact the speed of conduction of the nerve impulses
speeds up the rate of transmission by insulating the axon
sodium ions flow through the axon
but a myelinated nerve fibre only deploarises where the resistance is low
the voltage-gated ion channels at the nodes of Ranvier
open allowing sodium ions in
the consequence is that the action potential appears to jump from node to node this is known as saltatory conduction
define saltatory conductions
transmission of a nervous impulse along a myelinated axon in which the action potential jumps from one node of Ranvier to the adjacent node
study point
myelinated axons use less ATP to transmit impulses than non-myelinated axons of equal diameter because active transport of sodium ions occurs only at nodes rather than along the whole length of the axon.
