1. Neurophysiology Opposite electrical charges attract each other- +
inside
outside
Neurophysiology
Opposite electrical charges attract each other
In case negative and positive charges are separated from each other, their coming together liberates energy
Thus, separated opposing electrical charges carry a potential energy

2. Neurophysiology Voltage (V)
measure of differences in electrical potential energy generated by separated charges
Current (I)
the flow of electrical charge between two points
Resistance (R)
hindrance to charge flow - +
inside
outside

3. Ohm’s law

4. Voltage: potential across the membrane- +
inside
outside
Current: ions
Voltage: potential across the membrane
Resistance: membrane permeability

5. How can ions move across the membrane?- +
inside
outside
Resistance: membrane permeability
How can ions move across the membrane?

6. Ion channels 1) Leak channels 2) Chemically (ligand) – gated channels
- Can be ion-specific or not (e.g. the Acetylcholine receptor at the neural-muscular junctions is permeable to all cations)

7. 3) Voltage – gated channels
- Ion selective
- Gates can open (and close) at different speeds
4) Mechanically – gated channels
- Found in sensory receptors

8. the electrochemical gradient
The driving force:
the electrochemical gradient
outside + + + + + + + + + + - - - - - - - - -
inside

9. In a resting state, Potassium is the key player
The driving force:
the electrochemical gradient K+
Na+ K+
Na+
In a resting state, Potassium is the key player

10. Potassium wants to go out (chemical force), but also wants to go in (electric force)
Potassium will diffuse via leak channels until equilibrium is reached (higher concentrations INSIDE)

11. Potassium wants to go out
Sodium wants to go in K+
Na+ K+
Na+
- The neuronal membrane is much less permeable to Na+ than to K+ . The result: Na+ stays out
- How do we maintain this gradient?

12. The sodium/potassium pump acts to reserve an electrical gradient
- Requires ATP
- Throwing 2 K+ in, while throwing 3 Na+ out

13. The resting membrane potential is NegativeK+
Na+ K+
Na+

14. This is the resting membrane potential
But we can change it

15. The Membrane is Polarized
Depolarization
Making the cell less polarized
Hyperpolarization
Making the cell more polarized

16. This is the resting membrane potential
How can we change it?
Stimulus

17. How can we depolarize a cell?
Example
A chemical stimulus

18. Cell body
Axon
Dendrites

19. Sodium channels opening leads to depolarization
-70 mV
- Generation of a graded potential (aka local)
A short-range change in a membrane potential upon a stimulus

20. The graded potential is increased with a stronger stimulus
Think about a membrane with 50 channels
Stimulating them with 4 ligand molecules or 40 will make a difference

21. A graded potential can spread locally
Cations will move towards a negative charge
The site next to the original depolarization event will also depolarize, creating another graded potential

22. Graded potentials spread locally but die out
Membrane potential
- A Graded/local potentialA short-range change in a membrane potential upon a stimulus
Graded potentials spread locally but die out

23. How would that occur? Who said you have to depolarize?
A stimulus can lead to hyperpolarization
Membrane potential
How would that occur?

24. Graded potentials
- Proportional to the stimulus size
- Act locally, starting from the stimulus site
- Attenuate with distance
- Spread in both directions
- Take place in many types of cells

25. Action potentials do/are NOT
- Proportional to the stimulus size
- Act locally
- Attenuate with distance
- Spread in both directions
- Take place in many types of cells