Bioelectricity Flashcards
The net force propelling Na+ into the cell is very strong at rest: Why does only little Na+ enter the cell?
the membrane has a very low permeability to this ion at
rest. The small amount of Na+ that does enter is balanced by the action of the Na+-K+ pump, which transports Na+ out of the cell as fast as it leaks in, thereby maintaining the
concentration gradient that is typical of neurons.
Why can’t we use Nernst for membrane resting potential?
1- It deals with one ion only and cannot deal with the separate contributions of other ions;
2- The contribution of a particular ion to the resting potential will depend on the permeability of the
membrane to that ion. This factor is missing from the Nernst equation.
Important consequence of capacitance of the membrane
The capacitance of the membrane has the effect of reducing the rate at which the membrane potential changes in response to
a current pulse.
The membrane time constant corresponds to
to the time it takes Vm to build up to about 63% (strictly, 1-1/e) of its final value in response to a rectangular step of current. Typical range: 1 to 20 ms, depending on the neurone.
Importance of time constant
Because it can substantially change the time course of synaptic signals, thereby influencing the integrative
properties of the neuron.
Synaptic potentials are caused by
brief synaptic currents triggered by the opening of ligand-gated channels.
The larger the time constant, the _____ the duration of the synaptic potential.
longer
Why does a voltage signal decreases in amplitude with distance from its site of initiation within a neurone?
More current flows across the membrane near the site of injection than at more distant regions because the axial resistance, ra, increases with distance from the site of injection, and current always tends to follow the path of least resistance.
Membrane resistance decreases as cylindrical process length increases because
more channels are available for current to leak through the membrane
If current is injected into the dendrite at one point, how will the membrane potential change with distance along the dendrite?
Because Vm = Im rm (Ohm’s Law), the change in membrane potential, ΔVm(x), produced by the current becomes smaller as one moves down the dendrite away from the injection point.
A capacitor consists of
two conducting plates separated by an insulating
layer. The fundamental property of a capacitor is its ability to store charges of opposite sign: positive charges on one plate, negative on the other
the resistance along the core of a cylinder _______ as the cross-sectional area ________
decreases, increases
How does λ influences signalling?
- high Rm: λ is large -> PSP can spread farther
- low Rm: λ is small -> substantial ionic leak
- Axons/dendrites with a small internal
diameter; λ is small; ions will not spread far - Axons/dendrites with a large internal
diameter; λ is large; PSP spreads further
Importance of lambda
λ gives a measure of the efficiency of the electrotonic conduction in a given neurone. This efficiency has two important effects on neuronal function:
1- It influences spatial summation
2- It plays a role in the propagation of the action potential
Spatial Summation
summation of two or more inputs from different
locations occurring at about the same time
