General Organization- CNS and PNS- PNS subgroups

The basic units- the cells- Neurons- Glial cellsNeurophysiology- Resting, graded and action potentials

Neural interactions

Fundamentals of the nervous system

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

-- - - - ---

+ +++ +++

inside

outside

• 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

Neurophysiology

-- - - - ---

+ +++ +++

inside

outside

Ohm’s law

--- - ----

+ ++

+ +++

inside

outside+++

-Current: ions

Resistance: membrane permeability

Voltage: potential across the membrane

--- - ----

+ ++

+ +++

inside

outside+++

-

Resistance: membrane permeability

How can ions move across the membrane?

2) Chemically (ligand) – gated channels

1) Leak channels

- Can be ion-specific or not (e.g. the Acetylcholine receptor at the neural-muscular junctions is permeable to all cations)

Ion channels

3) Voltage – gated channels

4) Mechanically – gated channels

- Ion selective- Gates can open (and close) at different speeds

- Found in sensory receptors

--- - ---

-

+ ++

+ +++

inside

outside +++

-

The driving force: the electrochemical gradient

Na+

K+

K+

Na+

The driving force: the electrochemical gradient

In a resting state, Potassium is the key player

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)

Na+

K+

K+

Na+

Potassium wants to go outSodium wants to go in

- The neuronal membrane is much less permeable to Na+ than to K+ . The result: Na+ stays out- How do we keep this gradient?

The sodium/potassium pump acts to reserve an electrical gradient

- Requires ATP

- Throwing 2 K+ in, while throwing 3 Na+ out

Na+

K+

K+

Na+

The resting membrane potential

is Negative

This is the resting membrane potential

But we can change it

The Membrane is Polarized

DepolarizationMaking the cell less polarized

HyperpolarizationMaking the cell more polarized

This is the resting membrane potential

How can we change it?

Stimulus

ExampleA chemical stimulus

How can we depolarize a cell?

AxonCell body

Dendrites

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

Think about a membrane with 50 channelsStimulating them with 4 ligand molecules or 40 will make a difference

The graded potential is increased with a stronger stimulus

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

Mem

bran

e po

tenti

al

- A Graded/local potentialA short-range change in a membrane potential upon a stimulus

- Graded potentials spread locally but die out

Mem

bran

e po

tenti

al

Who said you have to depolarize?A stimulus can lead to hyperpolarization

How would that occur?