A quick guide to the action potential

1. The Action Potential
Tai Kao-Sowa
Stanford University

2. Resting Potential
- Negative 70 mV
- Inside: Potassium (K+),
anions
- Outside: Sodium (Na+)
- Na+ > K+
Na+ Na+ Na+ Na+ Na+
K+
K+ K+
K+
Proteins(-)-
+
Na+

3. Resting Potential
- Voltage gated ion channels
- Ligand gated ion channels
(neurotransmitter)
- Mechanical gated ion
channels (stretching)
Na+ Na+ Na+ Na+ Na+
K+
K+ K+
K+
Proteins(-)-
+
Na+

4. Stimulus
- Neurotransmitters open
channels, change membrane
potential
- Negative 55 mV threshold
- Otherwise graded potential
- Threshold triggers m-gate
Na+ Na+ Na+ Na+ Na+
K+
K+ K+
K+
Proteins(-)-+ (e- or Na+ enters)
Na+

5. Depolarization
- Sodium enters cell until ~+40
mV
- h-gate closes entry
- Na+ moves down inside axon,
triggers next action potential
Na+ Na+
Na+
Na+
Na+
K+
K+ K+
K+
Proteins(-)
-
+
Na+

6. Repolarization
- N-gate lets potassium out of
axon (-)
- Overshoot until inside is -75
mV
Na+
Na+
Na+
Na+
K+K+
K+
K+
Proteins(-)-+
Na+
Na+

7. Refractory Period
- Absolute
- Na+ ion channels (m gate) will not
reopen
- 1-2 ms
- Relative
- Hyperpolarized membrane
- 3-4 ms total
- Sodium Potassium Pump (2 K+, 3
Na+)
Na+ Na+ Na+
K+
K+ K+
K+
Proteins(-)-
+
Na+
Na+
Na+

8. Saltatory Conduction
Nodes of Ranvier
200 m/s vs 2 m/s
Na+ travels farther down,
conserves energy

9. Synapse
Electrical vs Chemical
Different neurotransmitters
interact with different ligand-
gated ion channels
Net sum of many synapses =
binary output

10. - Side effects of inhibitory
action by electrode limited
(probably)
- Excitatory action can cause
noise, limit selectivity
- Different effect if electrode is
close to body or axon of
neuron
Electrode
-https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1300089/pdf/9929489.pdf
-https://microprobes.com/files/pdf/publications/gen-knowledge/cogan_2008_neural_stimulation.pdf