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
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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?
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