Cellular Neurophysiology Midterm 1

NSCI 20111

Hippocampal place cells

spike when in specific location, recalled in dreams in correct sequence

Ohms Law

V = IR

Current

I; dQ/dt

Capacitance

Ability of a capacitor to store Q, measured in F. V = Q/C. C ~ A/D

Capacitor

Two conducting plates separated by a dielectric

Specific capacitance

per-unit measure of capacitance

Membrane capacitance

Cm = Cspecific * Area

Electrochemical equilibrium

When the electromagnetic and diffusion vector driving forces sum to zero

Equilibrium potential

Calculated with Nernst equation. Voltage at which electrochemical equilibrium is achieved

Nernst equation

Eion = RT/zF ln (Oion)/Iion; Eion = 58/zlog10(Oion/Iion)

GHK equation

58log( (Pk(Ok) + Pna(Ona) + Pcl(Icl)) / (Pk(Ik) + Pna(Ina) + Pcl(Ocl)) ) — note that Cl is reversed because it is negative

Primary active transport

Uses energy from ATP, pushes 3 Na out and brings 2 K in.S

Secondary Active Transport

Uses energy from concentration gradients; 3 Na ions enter, but also bring 1 K

Primary Active Transport sequence

1. Na Binding

2. Phosphorylation from ATP

3. Conformational change inverts transporter, releasing Na and bringing in K

4. Dephosphorylation inverts again, releases K

5. GOTO 1

Membrane time constant

Defines rate of voltage change; time it takes for V = 0.63Vmax. 𝜏 = RC

Membrane length constant

A measure of how far current travels along the membrane before it decays; λ is the length at which Vm = 0.37Vmax; λ = sqrt(Rm/Ra)

Membrane resistance

How much current can flow out through the membrane. Negatively correlated with λ. Higher Rm = more ion channels

Axial resistance

Resistance to flow within the axon, negatively correlated with λ. Larger diameter = lower Ra

Threshold

Voltage at which a passive potential activates voltage gated ion channels, starting an action potential

Node of ranvier

Gaps in the myelination of a neuron, where an AP takes place

Oligodendrocytes

Glial cells which produce myelin

Myelin

Insulates membrane of an axon, increasing the size of the dielectric (D), decreasing capacitance. Increases membrane resistance. Results in an increased passive and active propagation of charge.

Saltatory conduction

AP propagation with myelination

Voltage clamp method

1. measure membrane potential

2. Compare Vm to desired command voltage

3. Inject or withdraw current based on difference

4. Measure compensatory current

Capacitive current

The current which flows onto the membrane after a change in voltage

Tetrodotoxin (TTX)

Pufferfish poison, blocks voltage gated Na channels

Tetraethylammonium (TEA)

Blocks voltage gated potassium channels

Ionic current

I[ion] = g[ion](Vm - E[na]) = conductance * net driving force