1. Nerve Impulse Conduction
Neuron Function
Nerve Impulse Conduction

2. Cell Membrane Potential
A resting neuron’s cell membrane is polarized
Polarized = electrically charged
Charge inside the cell is different than the charge outside the cell
Potential difference is the measure of the difference in the electrical charge

3. Question to think about:
What does depolarized mean?

4. Resting Membrane Potential
Normal distribution of ions across the resting membrane results the outside of the membrane being more positively charged :
K+ is high inside
Na+ is high outside
Cl- is high outside

5. Resting Membrane Potential
Ions concentrations are maintained by active transport
Channel proteins pump ions across the cell membrane

6. Action Potential: aka Nerve Impulse
Normal resting membrane has a potential difference of -70 mV
When a significant stimulus is applied the membrane potential will change the potential difference to +30 mV
Threshold stimulus is the amount of a stimulus needed to begin the change along the cell membrane

7. Action Potential
Depolarization occurs when the Na+ channels open and Na+ moves into the cell.
The result is a more positive ion concentration on the inside
Thus the membrane surface is more negatively charged compared to the inside of the axon.

8. Repolarization Behind the action potential the K+ channels will open
The exit of K+ causes the membrane to once again become more positively charged

9. Re-setting the membrane
If another action potential is to be conducted ……the Na+ must be pumped back across the membrane….( must re-set the “game board” to play again)

10. Polarized once again
Because 3 Na+ will be pumped out for every 2 K+ that are pumped in……the result is a more positive charge on the outside of the axon

11. Takes only about 1/1000 of a second
The Entire Process…….
Takes only about 1/1000 of a second

12. All-or-None Response
If a neuron responds to a stimulus it responds completely…..there is no partial nerve impulse
All impulses carried on an axon will be the same strength
If the intensity of the stimulus increases, it causes more impulses per second…….but does not increase the strength of the individual impulse

13. Refractory Period
Time following a nerve impulse when another impulse can not occur regardless of the strength of the stimulus
Time when the membrane is being repolarized and is returning to the original conditions of the resting membrane

15. Speed of the impulse Affected by:
Myelin – myelin speeds up the conduction….. Saltatory conduction caused by myelin – impulse “jumps” from node to node
Axon Diameter – larger diameter = faster
Speed of the impulse

16. Neuron to Neuron
Chemicals called neurotransmitters convey the impulse from the presynaptic neuron across the synaptic cleft to the postsynaptic neuron.
Same thing occurs
when impulse is being
conveyed to an effector
(muscle, gland, etc….)

17. Neuron to Neuron Release of neurotransmitters is by exocytosis
Action potential causes Calcium to enter the synaptic knob.
Calcium is entering the synaptic knob triggers the release of the neurotransmitter

18. Neurotransmitters Over 30 different neurotransmitters
Cell membranes contain receptors which specifically match with each individual neurotransmitter
See pages for tables with info on neurotransmitters