Propagation of Ap
10/22/2012
Communication Along and Between Neurons (Ch.6)
• Receptors receive stimuli, and convert them to nerve impulses
• Alternating graded and all-or-none signals on the membrane of a single neuron
• Graded potentials decay with distance
(electrotonic conduction); longdistance transmission depend on transforming signals to APs
• Typically, alternating electric (within neuron) and chemical signals
(between neurons)
• Postsynaptic potential affected by number and frequency of APs
Passive spread of electric signal
Sub-threshold current flowing along the membrane decays with distance:
• Resistance of cytoplasm
• Leakage of charge across the membrane
Passive spread of electric signal
Electrotonic conduction depends only on the physical properties of a cell Signal decay with distance depends on membrane and longitudinal resistance to current flow:
• Resistance of cytoplasm (Rl)
• Leakage of charge across the membrane (Rm)
Vm and the time it takes to stabilize (charge has to accumulate) depend on the membrane capacitance
1
10/22/2012
Passive spread of electric signal
Passive electrotonic conduction:
• The change in Vm decays exponentially with distance
• The rate of the decay depends on Rl and Rm- the spread of a current along the membrane is enhanced with low Rl and high Rm
Passive spread of electric signal
The signal decay can be expressed by:
Vx = Vo· e-x/λ
Vλ = 0.37Vo
The length constant (λ), depends on of Rl and Rm, is defined as the distance at which the steady-state potential shows 63% drop in amplitude
Passive spread of electric signal
Vx = Vo· e-x/λ
(λ of neurons is 1-2mm)
Assuming λ=1mm, what would be the magnitude of the spinal depolarization if it was to travel a distance of 1m to the axon terminal by electrotonic conduction and induce a 10mV change in Vm?
0.01 = Vo · e-1000/1 = Vo · e-1000
Vo = 0.01 · e1000 ~ 10430V
2
10/22/2012
Propagation of AP
Electrotonic
Communication Along and Between Neurons (Ch.6)
• Receptors receive stimuli, and convert them to nerve impulses
• Alternating graded and all-or-none signals on the membrane of a single neuron
• Graded potentials decay with distance
(electrotonic conduction); longdistance transmission depend on transforming signals to APs
• Typically, alternating electric (within neuron) and chemical signals
(between neurons)
• Postsynaptic potential affected by number and frequency of APs
Passive spread of electric signal
Sub-threshold current flowing along the membrane decays with distance:
• Resistance of cytoplasm
• Leakage of charge across the membrane
Passive spread of electric signal
Electrotonic conduction depends only on the physical properties of a cell Signal decay with distance depends on membrane and longitudinal resistance to current flow:
• Resistance of cytoplasm (Rl)
• Leakage of charge across the membrane (Rm)
Vm and the time it takes to stabilize (charge has to accumulate) depend on the membrane capacitance
1
10/22/2012
Passive spread of electric signal
Passive electrotonic conduction:
• The change in Vm decays exponentially with distance
• The rate of the decay depends on Rl and Rm- the spread of a current along the membrane is enhanced with low Rl and high Rm
Passive spread of electric signal
The signal decay can be expressed by:
Vx = Vo· e-x/λ
Vλ = 0.37Vo
The length constant (λ), depends on of Rl and Rm, is defined as the distance at which the steady-state potential shows 63% drop in amplitude
Passive spread of electric signal
Vx = Vo· e-x/λ
(λ of neurons is 1-2mm)
Assuming λ=1mm, what would be the magnitude of the spinal depolarization if it was to travel a distance of 1m to the axon terminal by electrotonic conduction and induce a 10mV change in Vm?
0.01 = Vo · e-1000/1 = Vo · e-1000
Vo = 0.01 · e1000 ~ 10430V
2
10/22/2012
Propagation of AP
Electrotonic