lecture 6 Flashcards
(29 cards)
what would happen if a dendrite didn’t have voltage dependant channels?
passive conduction of electrical signal:
still important for AP conduction and synaptic inputs summation
affect both active and passive conduction of signals
2 aspects of voltage spread
- space dependant properties
- time dependant properties
how does current flow over resistors
finds the path of least resistance
equation for tau
Tau = Rm*Cm
what is isopotential
the same voltage at all places
what has to happen before current can flow
you have to charge the capacitor
how does steady state voltage change as a function of distancwe
Lambda = SQRT (rm/(ri+ro)) Vx= Vo^e^-x/y
compare current flowing through small and large radius
large radius- large lambda, low resistance, fast
small radius- small lambda, high resitance, slow
lambda relationship in a circle
lambda ~ SQRT radius
what does capacitance do to the voltage
creates time dependance to the voltage change induced by a current
what does the addition of current do to the membrane capacitor
with more current you can charge the membrane more quickly
equation for time dependant properties
Vt= V (1-e^-t/T)
what is the relationship between length constant and conducting potential
if you have a large length constant, you will have a fast conducting potential
fat axons have fast conduction
skinny axons have slow conduction
what is the rate of charge
rate of charge is proportional to Rm*Cm (length constant)
what happens once an action potential has been generated
it needs to conduct down an axon or dendrite to some place in order to transfer a signal
what kind of flow does action potential conduction require
both active and passive current flow
how does myelin affect conduction speed
prevents the current from leaving
conducts non decrement-ally so it can drive a specific piece of membrane to threshold very quickly
jumps from one place to the next so generation of AP is quick but only in small parts
more energy efficient- less ions to move back and forth
nodes of ranvier
Na channels are concentrated here
saltatory conduction
the propagation of action potentials along myelinated axons from one node of Ranvier to the next node
“to hop”
myelin affects on time constant
high resistance means big R - slow charging in between membrane and slow transmission b/w nodes SHOULD be large time constant but no myelination at nodes so C is small (membrane area)
TLDR: small area of membrane can charge very fast so high time constant
comparing myelination to non myelination
a 500um diameter squid axon has a conduction velocity of 25m/s
a 5um diameter axon would have a conduction velocity of 25m/s
SAVE A LOT OF SPACE IN THE BRAIN
why isn’t there myelin on the dendrites
need to make a lot of synapses
what occurs in MS
multiple sclerosis - autoimmune disease that attacks and kills myelin, body replenishes myelin but constant killing and regeneration will cause scarring
what happens with demyleniation
synaptic response gets spread out in time and if you lose enough you can’t make any action potentials
- desynchronization
- no action potential at all (decreased conduction velocity so you don’t have enough V to reach threshold further down)
