Nerve cells IV Flashcards
What is the refractory period?
Short period of decreased excitability after AP in which neuron can’t respond to given stimuli
What are the 2 types of refractory periods?
Absolute and relative
Describe an absolute RP
Immediately after AP, inactivation stage causes Na+ inactivation so no 2nd stimuli will produce AP
Describe a relative RP
After an absolute AP, AP is possible with strong stimuli (hyperpol), VG K+ channels still open so 2nd stronger stimuli needed to trigger AP
What are the consequences of a RP
Limits frequency of generating a neuron AP Accounts for unidirectional propagation of AP along an axon Long duration (produce more than one AP) Frequency coding (for stimulus intensity)
Describe frequency coding
Determines firing frequency of neuron, limited by absolute RP
RP encodes strength of stimuli
Short AP duration allow huge variation in firing frequency and so response to stimulus strength
Describe how the diameter of neurons influences propagation velocity
AP velocities vary in axons
Fast conduction - Motor neuron (eg 100m/s)
Slow conduction - Pain neuron (eg 0.5m/s)
What 2 conditions does propagation velocity depend on?
Axon diameter - Larger diameter, faster flow
Axon resistance - Higher resistance, faster flow
Describe myelinated neurons
To double speed of conduction, need 4x the axon diameter
Not feasible in mammals as they have too many neurons
Summarise nerve cells IV
AP display an all or nothing phenotype
RPs encode frequency at which neurons fire APs
Neurons encode strength of stimuli through the frequency at which AP are propagated along neurons
Saltatory conduction allows rapid action potential transmission via small diameter neurons.
AP flow through different neurons at different rates depending on two parameters of axon diameter and myelination
