1. THE NEURAL MEMBRANE
AT REST

2. ELECTRICAL PROPERTIES
Simple reflex : information needs to be quickly transmitted to the CNS and back
Information is transmitted through action potentials (change in the electrical properties of the
membrane)
Cells able to generate an AP have excitable membrane
At rest, these cells have a inside negative electrical charge (resting membrane potential) that
become positive during the AP

3. CYTOSOLIC AND EXTRACELLULAR FLUID
Water is the key ingredient in intracellular and extracellular fluid
Key feature – uneven distribution of electrical charge (O has a net negative
charge)
Ions are atoms or molecules with a net electrical charge dissolved in the water
Salz for example is a crystal of Sodium (Na+) and Chloride (Cl-)
Monovalent Ion: Difference between protons and electrons =1,
Divalent Ion: Difference between protons and electrons =2,
cation (+), anion (-)
When the crystal breaks down spheres of
hydration -layer of water are attracted to the ion
The orientation of the water molecules is
determined by the valence of the ion

4. IONS INVOLVED IN CELLULAR PHYSIOLOGY
Sodium Calcium
+ 2+
Potassium Chloride
+
-

5. THE PHOSPHOLIPID MEMBRANE
Hydrophilic: Dissolve in water due to uneven electrical charge (e.g., salt,
proteins, carbohydrates)
Hydrophobic: Does not dissolve in water due to even electrical charge (e.g., oil,
lipids in general)
The Phospholipid Bilayer
Hydrophilic
Hydrophobic
Resting and Action potentials depend on special proteins that are inserted in the
membrane

6. THE PROTEIN
Proteins are molecules assembled by combination of different amino acids (20 types)
Central alpha
carbon
R group
Amino group Carboxyl group

7. THE PROTEIN STRUCTURE
Peptide bond
Primary
Tertiary
Secondary
Quaternary

8. CHANNEL PROTEINS
Ion Channels
They form a pore through the membrane that hydrophilic
is ion selective
They can be opened and closed (gated)
by changing in the local microenvironment
of the membrane
hydrophobic
Ion Pumps
Formed by membrane spanning proteins
Uses energy from ATP breakdown
Neuronal signaling

9. THE MOVEMENT OF IONS
Diffusion: movement of ion due to concentration levels
Dissolved ions tend to distribute evenly by following down concentration gradient
Concentration gradient = difference of concentration of an ion across the membrane
Electricity
Electrical current (I, measured in Amperes) represents ion movement.
It’s regulated by
1) electrical conductance (g, measured in Siemens) or electrical
resistance (R, measured in Ω): ability (or inability) of an electrical
charge to migrate from one point to another
2) electrical potential (V, measured in volts): difference in charge
between cathode and anode

10. THE MOVEMENT OF IONS
Electrical current flows across the membrane by
Ohm’s law relationship
I =gV or I =V/R
Membrane potential: Voltage across the
neuronal membrane.
The resting potential is typically -65 mV
…let’ see why…

11. EQUILIBRIUM POTENTIAL
Example 1
Equilibrium is reached when
diffusional and electrical
Example 2 forces are equal and opposite
(equilibrium potential, Eion)

12. MEMBRANE POTENTIAL
In the membrane ions have different concentration between inside and outside,
and this gradient is established by action of ionic pumps, that use energy in
order to move ions against concentration forces
Membrane permeability determines membrane resting and action potentials

13. MEMBRANE POTENTIAL
Membrane permeability determines membrane resting and action potentials
Membrane rest potential is determined by the higher number of K vs. Na channels
open (resting potential close to Ek potential)