Neurophys 1 Ex1

Front 1

A. Goldman-Hodgkin-Katz equation for the resting membrane potential- relates

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the membrane potential of a neuron to the permeability of several ions in the membrane, allows you to calculate the membrane potential under different conditions if you know the permeability of those ions and the concentration of those ions

Front 2

The fact that sodium channels have a refractory period
during which they cannot be activated gives some

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directionality to the propagation of the action potential,
from soma to terminal, or more properly, from stimulus
initiation point outward

Front 3

PK : PNa : PCl at action potential

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Act.Pot.: 1 : 20 : .45

Front 4

c. Resting membrane potential is largely determined by

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potassium as the K permeability is higher than the Na permeability at rest

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c. Membrane potential has two components, the electrical and chemical gradient, cells are generally more negative on the inside than on the outside so the electrical gradient drives K

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inside the cell

Front 6

d. The concentration of K is higher on the inside than on the outside so the chemical gradient drives K

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outside the cell

Front 7

b. Na is high outside the cell, low inside the cell, this time both the chemical and electrical gradients want to

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to pull Na inside the cell

Front 8

c. So if you allow the membrane potential to reach ENa and open Na channels, the concentration gradient will

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push Na into the cell and the now positive membrane potential will push positive ions out of the cell

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d. The fact that normal resting membrane potential is –60mV which is closer to the equilibrium potential of K tells us that the permeability of K at rest

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is higher

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driving force

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This is the membrane potential minus the equilibrium potential of K, this is a voltage gradient that will make the K ions move creating a current, Ik. c. V= (Emp- Ek) so Ik = (gk) (Emp-Ek)
e. Basically, the force which is going to push an ion either into or out of a cell is going to create a current

Front 11

a. The idea of driving force due to the difference between the membrane potential and the equilibrium potential for a given ion applies to

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both currents through voltage-gated channels and to currents which flow through ligand-gated channels

Front 12

Driving force is a

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potential energy gradient

Front 13

In most neurons, ECl = -75 mV, so hyperpolarization results
from

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GABA(a) receptors opening Cl- channels

Front 14

In dorsal root ganglion cells, ECl = -43 mV, depolarization
below threshold, “clamps” the membrane and prevents

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further depolarization above threshold

Front 15

In some neurons, Cl- is passively distributed; in these cases,
ECl = EMP. This causes

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no voltage change, but reduces
membrane resistance, resisting change by other synaptic
inputs (a more passive “clamp”).

Front 16

F. Length constant- graded synaptic potentials decrement with

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distance as they spread along the membrane

Front 17

a. Membrane length constant is defined as

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that length along the membrane at which the voltage signal is reduced to 37% of its original amplitude

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Active properties- the action potential properties

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i. All or none- propagate without decrement from axon hillock down to axon
ii. Codes information by frequency and pattern (amplitude does not change

Front 19

b. Passive properties- involved with graded phenomena properties

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i. Synaptic potentials- release of a neuro transmitter to the dendrite of another neuron
ii. Not all or none
iii. Decrements in amplitude with distance
iv. Information is coded by the amplitude and duration of signals
v. Can summate in two ways
1. temporal summation, according to the membrane time constant
2. spatial summation, according to the membrane length constant

Front 20

Time constant- introducing the idea of capacitance here, increasing C introduces a lag time which slows

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the rate at which the membrane potential can change so time constant is directly related to capacitance.

Front 21

The membrane time constant, τ, is the
amount of time it takes for the membrane to

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reach 63% of its final steady-state value

Front 22

temporal summation graph at the end of lec

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a. Tau= the time that it takes the membrane to charge up to 63% of the final value is the membrane time constant. (characteristic of the post synaptic neuron)
b. We are comparing two different cells, one with a tau of 1msec and another cell with a tau of 10msec
c. In the first graph we get four EPSPs when a neurotransmitter is released, however we get no AP because of the short tau, however when the tau is longer, temporal summation can occur and as a result our four EPSPs lead to an action potential

Front 23

spatial summation graph at the end of lec

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a. This is dependent on the length constant
b. We have two postsynaptic neurons here with different length constants, cell b is 1mm and cell c is. 1mm. a smaller constant signifies more degradation
c. In cell b the amplitude of the synaptic potential that reaches the trigger zone is much greater than the amplitude of the synaptic potential that reaches the trigger zone in cell c
d. Due to the larger decrement in the synaptic potential of cell c, it may not be able to trigger an action potential

Front 24

Membrane Length Constant affects the decrement with distance
as graded synaptic potentials spread over the surface of the
neuronal membrane (and thus affects

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Spatial Summation