1. Animal Cell
Cell Membrane

2. Cell Membrane of a Neuron

3. Ion Channels Voltage-Gated Ion Channels
Cell membrane proteins that pass ions in and out of the cell
Voltage-Gated Ion Channels
gates are regulated by membrane voltage
Chemical-Gated Ion Channels (Receptors)
gates are regulated by
neurotransmitters
Ionotropic
fast
Metabotropic (G-protein coupled)
requires second messenger cascade
slow

4. Electrochemical Gradient
Inside the Cell
More K+
Less Na+
Outside the Cell
More Na+
Less K+
Ion Flow Mantra: Na+ In, K+ out

5. Depolarization/Hyperpolarization

6. Action Potential Phases2
Rapid 3 1
Threshold 4
Phase Ion responsible Ion Channel Responsible
1. Threshold Na+ Chemical-gated Na+ channel
2. Rapid Depolarization Na+ Voltage-gated Na+ channel
3. Repolarization K+ Voltage -gated K+ channel
4. After Hyperpolarization K+ Na+/K+ pumps

7. Na+/K+ Pumps After the Action Potential,
Na+/K+ pumps move Na+ ions back out of the cell and move K+ ions back into the cell
The movement is against the concentration gradient of each ion so it requires energy (ATP)
The pumps move 3 Na+ ions for every 2 K+ ions

8. Unmyelinated Propagation

9. Myelinated Propagation

10. Synaptic Action Voltage-gated Ca2+ channels Synaptic Potentials: EPSP
IPSP

11. Synaptic Potentials Excitatory Postsynaptic Potential (EPSP)
triggered by excitatory neurotransmitters
open ligand-gated Na+ channels
allows Na+ to flow inside the cell
causing a slight depolarization of the postsynaptic cell
moves the postsynaptic cell closer to firing an action potential
Inhibitory Postsynaptic Potential (IPSP)
triggered by inhibitory neurotransmitters
open ligand-gated K+ channels or Cl- channels
allows K+ to flow out of the cell or Cl- to flow inside the cell
causing a slight hyperpolarization of the postsynaptic cell
moves the postsynaptic cell further from firing an action potential

12. The Battle to -55mV
IPSP
EPSP