1. Electrochemical Impulses
Homework: Polarization…Handout Questions #1-15

2. SBI 4U: Metablic Processes
Luigi Galvani
18th century
Found muscle of dead frog would twitch if electricity passed through it.
Lead to lots of research in the field of electrical conductivity of muscle tissue and the body
Section 1.3

3. SBI 4U: Metablic Processes
Emil Dubois-Reymond
1840
German physiologist
made instruments that could measure current in nerves and muscles.
Section 1.3

4. SBI 4U: Metablic Processes
Willem Einthoven
1906
Dutch physiologist
made first electrocardiogram (ECG) that measured electrical impulses in the heart
Nobel Prize, 1924
Section 1.3

5. SBI 4U: Metablic Processes
Hans Berger
1929
German physiologist
measured electrical changes associated with brain activity, the electroencephalaograph (EEG) was born.
Section 1.3

6. Julius Bernstein
1902
Suggested nerve impulses were an electrochemical message created by the movement of ions through the nerve cell membrane.

7. Cole and Curtis 1939 Provided evidence to back up Bernstein's theory.
Found rapid change in the potential (voltage) across a squid neuron when it was excited.

8. SBI 4U: Metablic Processes
Cole and Curtis found that the resting potential of the nerve was -70 mV.
A negative value means more negative ions are on the inside of the nerve cell than outside.
Section 1.3

9. SBI 4U: Metablic Processes
When the nerve became excited, the potential went up to +40 mV (more positive ions inside)
This was termed the action potential.
The action potential did not last long and the nerve cell went back to its resting potential.
Section 1.3

10. RESTING POTENTIAL
The nerve cell contains K+ ions and the surrounding fluid contains Na+ (salty banana). This difference is maintained by Na + /K + pumps.
Na + and K + can also diffuse through channels in the membrane, but the resting membrane is more permeable to K+ than Na+.

11. This means more K+ will diffuse out than Na+ will diffuse in.
Consequently the outside of the nerve cell is more positive than the inside.

12. SBI 4U: Metablic Processes
Resting potential is -70 mV because there are fewer positive ions inside the nerve cell than outside.
The resting membrane is said to be charged or polarized.
Section 1.3

13. ACTION POTENTIAL
When the nerve cell becomes excited, it becomes more permeable to sodium than potassium.
Scientists believe that sodium and potassium channels have “gates” that open and close opposite of one another. As one type of gate opens, the other closes.

14. Sodium rushes into the cell which causes a reversal of charge called a depolarization.

15. Once the voltage becomes positive, the sodium gates close.
That is why the max action potential under normal situations is only +40 mV.

16. The critical amount of electricity that is required for a nerve cell to fire is known as the threshold level.
Stimuli below this level do not initiate a response.

17. Sodium-potassium pumps actively restore the original resting potential by moving sodium out and potassium back in.
K+ gates reopen to allow some K+ to exit.
This is called repolarization.

18. The repolarization will fall below the resting membrane potential for a period of time.
This is called the refractory period. / (hyperpolarized)
Nerve cells cannot transport a second message until the resting potential is reset.

19. All-or-None
Any amount of stimulus above the threshold level gets the same response from the nerve cell.
Nerve firing is an all-or-none response. It fires maximally or not at all.

20. Propagation of the Signal
Depolarization moves along the axon of the nerve cell in a wave.
Depolarization in one area affects the ion gates of the next area and so on.

21. In myelinated neurons the depolarization jumps from node to node which increases the speed of the impulse.