Passive And Action Potentials Flashcards
Conductance equation
I = gV
Derived from ohms law V = IR
What does conductance show
- how many channels are open
- how many channels there are
- how much current the channel can pass
What does a change in current cause
Change in membrane potential (voltage)
How can a stimulus be applied (current)
- result of another neuron (at synapse)
- spontaneous (pacemaker cells)
- introduced to the system using electrophysiology techniques
What is cable theory, what does it predict
Propagation can be predicted
- models axons and dendrites as cylinders with RC circuits
What does a depolarizing current graph look like
Rectangle upwards
How does membrane potential change with increasing distance from current electrode- EPSP
Decrease in amplitude with distance- not regenerated and ions diffuse
How does membrane potential change with increasing distance from current electrode- AP
AP are regenerative. Threshold reached, all or none signal
How is a passive response formed
Stimulus opens ion channels and ions diffuse to spread potential (no voltage gated channels)
Passive properties in neurons
- membrane capacitance
- membrane resistance
— both affected by myelin - internal resistance ( intracellular longitudinal resistance along axons and dendrites)
What do the passive properties in neurons determine
Determine how far a passive potential generated at a dendrite will travel and whether the passive potential will result in an AP at axon hillock
How are passive potentials propagated
Diffusion (no ion channels)
Why does passive potential lag
Membrane capacitance and time it takes for ions to rearrange
What determines voltage response
Membrane resistance and membrane capacitance (shape and magnitude)
Voltage response wave looks like
Rounded squares
How fast can current and voltage change
Current instantaneous
Voltage lags- ions rearrange and membrane capacitance
When threshold is reached. What channels open
Nav
Outward current is ___ charge efflux
Inward current is ____ charge influx
Positive
Current is the flow of positive charge
What does a higher membrane capacitance do to ion rearrangement
Charges take longer to rearrange
What initiates passive potentials
Ion channels (nAC)
What is the length constant (upside down y)
Distance at which the potential is 1/e of its original value
(voltage change falls exponentially with distance from stimulation site)
Be able to compare passive and action potentials
Pg 8
What kind of responses can dendrites produce
Passive potentials (that are summed)
Dendritic Spikes- active potential
What percent of voltage is length constant from initial amplitude
37%
What is the length constant equation
Y - sqrt Rm/Ra (axial = internal)
What does an amplitude vs distance graph of passive potential look like
Middle has highest amplitude and is starting point of potential (current injection). Drops off exponentially on both sides as distance increases looks like a ^
How does increasing neuron diameter impact Rm, Ra, length constant y
Rm decreases- more plasma membrane, more leak channels
Ra decreases- larger diameter allows faster propagation inside neuron
Ra reduced by a greater factor than Rm- pir^2 bigger impact than 2pi*r (change r)
Y increases
What is conduction dependent on
Length and diameter (geometric factors)
- inversely proportional to length
- directly proportional to CSA
Explain steps of AP curve and what ions contribute
Pg 13
How to measure Vm
Internal electrode and extra cellular reference electrode
How to measure electrical signals in neurons
Electrophysiology techniques
What is important for unidirectional AP conductance? What is the term called
Neuronal backpropagation
1. Na channel inactivation
2. Increased Pk - slow K channel activation
- refractory period link
