The electric field inside the cell membrane
A typical cell membrane has a thickness of 7.0 nm.
What is the strength of the electric field inside the cell membrane?
∆V 70x10 V3
E = = −9
∆d 7.0x10 m
E = 1.0 x 10 V/m
Uninsulated axon signal propagation
A wave of potential travels down the axon.
Sodium channels open → potassium channels open → membrane recovery
Analyzing the axon, Part I: Resistance
What is the resistance along the length of a typical axon of length 1.0 mm and radius 5.0
μm? Ignore the resistance of the membrane, and assume that the resistivity of the fluid
inside the axon is 2.0 Ωm.
R = A
2.0Ωm (1x10 m)
R = −6 2
R = 25 MΩ
Analyzing the axon, Part II: Capacitance
What is the capacitance of a typical axon of length 1.0 mm and radius 5.0 μm? The
dielectric constant of the cell membrane is 9.0, and the thickness is a typical 7.0 nm.
( ) −3
9 (ε0)(2π7x10 m)
C = 7x10 m3 C = 360 pf
Analyzing the axon, Part III: Signal speed
For the typical axon of the previous two slides, how fast will an action potential
propagate from one end to the other?
L L .001m