1. The Neuron

2. Basic Constitution
The major features: soma (the cell body), dendrites (the receiving end) and axon (the outgoing end)

4. Neurons differ in size, shape and physiological properties
Bipolar neuron
e.g., retina, olfactory bulb
Unipolar neuron
Invertebrates
Multipolar neuron
pyramidal cell

5. Neuronal State: Membrane Potential
Membrane potential: the difference between electric potentials within the cell body and its surrounding.

6. Speciality of Membrane
Permeability of the membrane
Ions types: Potassium, Sodium, Calcium and Chloride
Ion channel types:
Leakage channel: always open
Voltage-gated channel: sensitive to the size of membrane potential
Neurotransmitter -gated channel: sensitive to the binding of
neurotransmitters
Ion bump : generating concentration difference for ions within and
outside the cell
And others

7. Resting potential Ion pump generates concentration difference of ions;
Under natural force, ions diffuse from high to low concentrations
Positive charged ions (cations) leak through leakage channels,
but the membrane is not permeable to the anions binding to cations;
A electrical potential is generated.
A balance is reached when the electrical force matches diffusion force

8. Neuronal Interaction Chemical synapses and neurotransmitters
Synapses: the contact sites between neurons
Pre- and post- synaptic neurons
Action potential triggers the release of
neurotransmitter
Neurotransmitters drift across the synaptic cleft
Neurotransmitter-gated channels open, generating electrical current (or postsynaptic potential (PSP))
Dependent on the sign of PSP, synapses are
clarified as excitatory and inhibitory ones.

9. Action potential: Membrane potential increases due to external input.
When its value is larger than a threshold,
voltage-gated channels are open, ions influx and efflux the cell.
Voltage-gated channels are closed very quick, leading to
an electrical pulse.

10. Summary of Neural Signaling Mechanism
Resting potential
-Special permeability of the membrane for ions
-Ion bump account for the concentration gradient of ions
-Leakage channel only for cations
-A balance between electric and diffusion force
Basic synaptic mechanism
-Action potential triggers the release of neurotransmitter at
the axon terminal of pre-synaptic neuron
-Neurotransmitter drift across the synaptic cleft
-Neurotransmitter opens the neurotransmitter-gated channels, generating
PSP at the post-synaptic neuron
The mechanism for generating action potential?
-The increase of membrane potential triggers the opening of
voltage-gated channels

11. The Profile of Action Potential
Rising phase (Depolarization):
A sharp increase of the membrane potential to a positive value
Falling phase (de-polarization):
Followed the rising phase quickly, a sharp decrease in the
membrane potential, which even overshoot the resting potential
Returning phase:
The membrane potential gradually returns to the resting value

12. The minimal mechanism Rising phase (depolarization):
The membrane voltage change triggers the opening of voltage-gated sodium channels
The influx of sodium depolarizes the neuron
(up to V=+35mV)
Falling phase (de-polarization):
The sodium channels become inactive at around 1ms after their opening
Meanwhile, the potassium channels open—the efflux of potassium ions overshoots the resting potential (down to V=-80mV).
Returning phase
The hyper-polarization causes the close of potassium and sodium channels
Ion bump may be called to retain the concentration gradients of
potassium and sodium ions

13. The status of channels Inactive of Na+ channel; Opening K+ channel
The opening of
Na+ channel
Closing of Na+ &
K+ channels
The opening of
leakage channel

14. Review Questions:
Name 3 types of neurons.
What is a membrane potential?
What ion channels/pumps are responsible for keeping the resting membrane potential?
What ion channels/pumps are responsible for generating the action potential?
By which ways are the neurons repolarized?
What is meant by the absolute refractory period?

15. Name 1,2,3,4,5,6 and 7
What is “A” & “B” ?