Isnt It Ionic

1
Isnt It Ionic?
K
Cl-
Ca
Na

• Electrical Activity in Neurons is IONIC
• An ION is an atom having fewer/more electrons
  than protons
• Thus, ions have electrical charge (/-)
• However, regardless of their charge, they are
  also subject to entropy, like any other atom
• That is, they will move from areas of high
  concentration to areas of low concentration (but,
  this requires that they be in a solution, for
  example, water).

2
Isnt It Ionic?

• Semi-Permeable Membrane
• Electrical Gradients
• Concentration Gradients
• The Nernst and Goldman Equations!

3
Voltage - A Charge Difference

• Like pressure in household plumbing
• Drives current flow
• Some handy voltages to know
• wall outlet, 110 volts
• Pentium chip, 4 volts
• AAA battery, 1.5 volts
• resting neuron, 0.070 volts

Wow!
4
Neurons can run at low voltages (-70 mV)
because action potentials are regenerative
The drawback is that regenerating electrical
signals takes time
5
Meet The Potentials
Voltages
Resting, Synaptic, Action
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Meet The Potentials - Resting
The Resting Potential is a K equilibrium potent
ial
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Meet The Potentials - Resting
The Sodium/Potassium PUMP
Acts to maintain proper concentrations of sodium
and potassium necessary after a neuron has
fired ACTION POTENTIALS
8
Meet The Potentials - Synaptic
These are brief positive (YES!) or negative (NO!)
changes in membrane voltage They summate
This is much the same way that sensory receptors
work. Substitute a stimulus for the
transmitter and you have a generator potential
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-70 mV
-60 mV
-70 mV
Resting, Synaptic, Action
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-70 mV
-60 mV
-50 mV
Resting, Synaptic, Action
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-70 mV
-60 mV
-50 mV
Resting, Synaptic, Action
12
Meet The Potentials - Action!
30 mV
-50 mV
-70 mV
0 1 2 3 4 msec
13
30 mV
-70 mV
OUT
IN
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30 mV
The Action Potential
-70 mV
0 1 2 3 4 msec
1. Rising Phase Na Entry 2. Falling Phase K
Exit 3. The Na/K pump restores ion
concentrations
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The Action Potential
A Chain Reaction Down The Axon
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The Action Potential
A Chain Reaction Down The Axon
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The Action Potential
A Chain Reaction Down The Axon
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Action Potentials in an Unmyelinated Axon
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Action Potentials in an Myelinated Axon
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Release the Hounds! . . .uh, I mean
neurotransmitter
21
Calcium is Required for Neurotransmitter Release
. . .zzzzzzz
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-70 mV
-60 mV
-50 mV
Resting, Synaptic, Action