General Organization - CNS and PNS - PNS subgroups The basic units- the cells - Neurons - Glial cells Neurophysiology - 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+ K+K+ 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+ K+K+ Potassium wants to go out Sodium 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+ K+K+ The resting membrane potential is Negative

This is the resting membrane potential But we can change it

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

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

Example A chemical stimulus How can we depolarize a cell?

Axon Cell 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 channels Stimulating 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

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

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