1. Nerve cells transmit signals via changes in their membrane potential. At rest, the inside of the cell membrane is negatively charged due to high potassium and low sodium concentrations inside the cell. 2. When stimulated, the membrane becomes permeable to sodium, causing sodium to rush inside and depolarize the membrane. 3. The rapid sodium influx reverses the membrane potential briefly before sodium channels close and potassium channels open, allowing potassium to leave and repolarize the membrane.

1. Nerve Impulses (pg 6)

2. Nerve Impulses
• Nerve cells are able to respond to a stimulus
(excitability) and transmit an impulse
(conductivity)

3. 1. Resting Membrane
• K+ is concentrated inside the cell

4. Resting Membrane
• K+ is concentrated inside the cell
• Na+ is concentrated outside the cell

5. Resting Membrane
• K+ is concentrated inside the cell
• Na+ is concentrated outside the cell
• Membrane impermeable to passive diffusion
of Na+ and K+

6. Resting Membrane
• K+ is concentrated inside the cell
• Na+ is concentrated outside the cell
• Membrane impermeable to passive diffusion
of Na+ and K+
• The inside of the cell contains more negatively
charged ions than the outside

7. Resting Membrane
• K+ is concentrated inside the cell
• Na+ is concentrated outside the cell
• Membrane impermeable to passive diffusion
of Na+ and K+
• The inside of the cell contains more negatively
charged ions than the outside
• The inside of the cell membrane is 70
millivolts more negative than the outside

8. Resting Membrane
• K+ is concentrated inside the cell
• Na+ is concentrated outside the cell
• Membrane impermeable to passive diffusion
of Na+ and K+
• The inside of the cell contains more negatively
charged ions than the outside
• The inside of the cell membrane is 70
millivolts more negative than the outside
• Resting membrane potential = -70 mV

9. 2. Depolarizing membrane
• A stimulus arrives, making the membrane
permeable to Na+

10. Depolarizing membrane
• A stimulus arrives, making the membrane
permeable to Na+
• Na+ rapidly enters the cell, driven by the
concentration gradient and the electrical
(charge) gradient

11. Depolarizing membrane
• A stimulus arrives, making the membrane
permeable to Na+
• Na+ rapidly enters the cell, driven by the
concentration gradient and the electrical
(charge) gradient
• The inside of the membrane becomes more
positive (less polarized)

12. 3. Reverse Polarization
• So much Na+ enters the cell that the polarity
is reversed (positive on the inside, negative on
the outside)

13. Reverse Polarization
• So much Na+ enters the cell that the polarity
is reversed (positive on the inside, negative on
the outside)
• This only lasts for an instant

14. 4. Repolarization
• Na+ channels close (no Na+ can enter or leave
the cell)

15. Repolarization
• Na+ channels close (no Na+ can enter or leave
the cell)
• K+ channels open. K+ rapidly leaves the cell,
driven by the concentration gradient.

16. Repolarization
• Na+ channels close (no Na+ can enter or leave
the cell)
• K+ channels open. K+ rapidly leaves the cell,
driven by the concentration gradient.
• As K+ leaves, the inside of the cell becomes
negative and the outside becomes positive
and the membrane is repolarized

17. Step E: Moving Ions
• The cell pumps Na+ out and K+ in to restore
the original condition
Na+ Na+ Na+ Na+ Na+ Na+ Na+
K+ K+ K+ K+ K+ K+ K+
Negative charge
K+ K+ K+ K+ K+ K+ K+
Na+ Na+ Na+ Na+ Na+ Na+ Na+