1.3 Signal Propagation, Transmission and Integration Flashcards
Lecture 3
After injecting current into cells what happens to the associated membrane potential
the potential changed show transient, non-linear rising phases as well as a plateau
plotting the plateau membrane potential (Vm) against the injected current gives a β¦
linear relationship and obeys Ohmβs law
V = IRin
What is Rin
neurons input resistance and depends on Rm normalised for SA
What does Rm depend on
distribution of ion channels
Equation for Rin
Rm/4(pi)(a^2)
What does injecting current in to a cell do
induces a voltage change in time which is caused by an outward current across the membrane (Im)
equation for Im
Im = Ii + Ic
what is Ii
current across Rin
what Ic
current discharging the membrane capacity Cm
what is the equation to the rate of change of the membrane potential
π«π½π(π) = π°ππΉππ (π β (π^(β(π/ π)))
what gives the palteau value
ImRin
what affects the rate of change
exponent -π/ π
what does it mean if π‘ = π
63% of max voltage reached
what is π
π = π πππΆπ
how to find the total current flow
sum of fast transient Ic discharging/charging Cm and slowly building up Ii through Rin
why is there a leakage current
originally we assumed isotropic potential distribution but the membrane is not
a perfect insulator so there will be a leaky current whenever voltage change occurs
how does local voltage changes propagate along different parts of the cell
it depends on the ration between the membrane resistance (rm) and the longitudinal resistance along the axon (ra)
what is ra
result of the fact that ion-based current in the axon is less efficient as electrons flow in a copper cable
how can passive properties of an axon be modelled
by assuming distinct compartments connected by the axonal resistance
what is the voltage change spreads along the axon
Ξπ(π₯) = Ξπo.π^(β π₯/ π)
π = β(ππ/ππ)
what does lambda mean
indicates the distance from the initial voltage change at which the membrane potential drops to 37%
efficiency of electronic conduction influencesβ¦
spatial summation in triggering synaptic potentials as well as the propagation of AP
What is a factor in the propagation of AP
electronic conduction
- once the membrane at any point on the axon reaches threshold depolarisation an AP is generated in that region
- local depolarisation spreads passively causing successive adjacent regions to reach the threshold and generate an AP
What happens when AP propagrates from right to left?
causes a difference in membrane potential in 2 adjacent regions of the axon and the difference creastes a local circuit causing the depolarisation to spread passively