From Neuron to Brain: From Neuron to Brain: Pedagogic ApproachPedagogic Approach
KAMALES BHAUMIK
Movement of charged ions across the cell membrane
aq
V∈
=
aVq
CceCapaci =∈=tan
∈==− 1
221 2
2
aq
CVEenergySelf
480 ≈∈=∈ lipidwater
Intracellular
fluidExtracellular
Fluid
Voltmeter
Inside of the cell is negative with respect to outside.
Most of the cells have a resting membrane potential in the range of -30mV to -80mV
Resting Membrane Potential
Nernst Potential
Nernst Potential
Chemical Potential = Partial Molar Gibbs Free Energy
Chemical Potential CRTcc ln0 += µµ
Electrochemical Potential zFVCRT ++= ln0µµV∆
1V 2V
1C 2C
11ln zFVCRT +
22ln zFVCRT +=
Nernst Potential
2
112 ln
CC
zFRT
VVV =−=∆
mVzFRT
25=
( )2
1log303.225CC
V Na ×=∆
mVCC
2
1log60≈
NernstPlanck
Nernst-Planck Equation
FVzCRT iiii ++= ln0µµ12 −−= TLmolFluxJ i
dxd
CuJ iiii
µ−=
xV
FzCuxC
RTuJ iiii
ii ∂∂−
∂∂−=
lationsEinsteinRTuD ii Re'=
FICK’s Law
OHM’s Law
Integration of Nernst Planck Equation
CONSTANT FIELD MODEL
Goldmann Hodgkin Katz (GHK) Model
122
211
lnClClKKNaNa
ClClKKNaNa
CPCPCPCPCPCP
FRT
V++++=
Excitation of cells at resting membrane potential
Passive Response
Excitable Cells
Action Potential
All or None response
Currents Flowing in and out of the membrane During Action Potential
Capacitative current
dtdV
Cm
Resting membrane potential = K-Nernst potential
Peak of action potential = Na-Nernst Potential
Nonlinearity in the current flow
Necessity of a voltage clamp machine
Separation of ionic currents
TTX (Tetrodotoxin) Na-Channel Blocker
TEA (Tetra-ethyl-ammonium) K-channel blocker
Na and K channel conductance depends on membrane voltage
Chloride and non-specific ions follow Ohm’s law
Equivalent Circuit
Propagation of Axon Potential
mIxV
factor=
∂∂
2
21
2
2
22
2 1ty
vxy
∂∂=
∂∂
∑+∂∂==
∂∂
iimm I
tV
CItV
vfactor 2
2
2
11
Rods and cones
Bipolar Cells
Ganglion Cells
Rods and Cones
Bipolar cells
Ganglion Cells
Receptive field of Ganglion cell
+ve -ve-ve
+ve contribution-ve -ve
Distance
Intensity of
signal
-2 -1 0 1 2
A Gaussian function, whose mean value is kept at zero, is given by:
)2
exp(2
1),(
2
2
2 σπσσ x
xg −=
where σ is called the standard deviation
Small σ
Large σ
+ve contribution-ve -ve
22
2
21
2
2
2
2
121 2
121
),( σσ
σπσπσσ
xx
eeDOG−−
−=
Thank you