Neuroscience

1. Neuronal
signaling
Domina Petric, MD

2. Electrical signaling
Fundamental neuronal
process that underlies
all aspects of brain
function.

3. Unique properties of neurons
Intrinsically neurons are poor
generators of electricity.
Electrical signals are based upon the
flow of the ions across the neuronal
plasma membrane.

4. Resting potential vs. action potential
• Resting potential of the neuron varies in different
neurons between minus 40 mV and minus 90 mV.
• All or none nature of neurons: only depolarisation above
treshold will generate action potentials or spikes.
• Stronger stimulus gives rise of more action potentials,
but the amplitude is always the same (depending on the
type of the neuron).
• Number of action potentials is proportional to the
strength of the stimulus.

5. Nernst equation
• Ex is equilibrium potential for any ion.
• R is gas constant.
• T is absolute temperature (degrees Kelvin).
• z is valence of the permeant ion (electrical charge).
• F is Faraday constant (amount of electrical charge in a mole of an
univalent ion).
• (X)0 is concentration of ion X outside of the cell.
• (X)i is concetration of ion X inside the cell.

6. Simplified Nernst equation
• Ex = 58/z multiplied with log (X)0 /(X)i
• The equilibrium potential for an ion is
proportional to the concentration gradient.
• Proportionality is influenced by the valence of the
permeon ion.

7. Goldman equation
• Em is equilibrium potential when multiple ions may permeate the
membrane.
• V (or Em) is voltage across the plasma membrane.
• P is permeability of the plasma membrane to each ion.
Simplified
58 log x

8. Potassium and sodium ions

9. Action potential
https://faculty.washington.edu/chudler/ap3.gif
Absolute refractory period is
innactivation of sodium channels.

10. Electrical current
Early current is carried by sodium.
Late current is carried by potassium.
Current is a function of conductance and
driving force.

11. Action potential

12. Important molecules
• Sodium-potassium pump (ATPase pump) is the
most important molecule in the nervous system.
• Other ATPase pump is calcium pump.
• Ion exchangers are Na+/Ca++ exchanger and
Na+/H+ exchanger.
• Co-transporters are Na+/K+/Cl- co-transporter,
K+/Cl- co-transporter and Na+/neurotransmiter co-
transporter (GABA, dopamine).

13. Passive conduction decays over
distance
https://www.andrews.edu

14. Axon diameter
• Small diameter axons impose greater resistance to the
axial diffusion of ions (axial conduction of charge).
• Larger diameter axons are for less resistance and
facilitate the rapid conduction of passive current.
• Small diameter axons will have a slower propagation
rate of action potential conduction compared to larger
diameter axons.
• Myelin facilitates action potential propagation.

15. Regeneration of the action potential
in the node of Ranvier
http://antranik.org

16. Myelin
Increase of the propagation of action potentials:
efficiency and conduction velocity.
Advantage of economy: fewer ion channels need
to be produced by the cell body and inserted into
a much more reduced surface area of axonal
plasma membrane.

17. Literature
• https://www.coursera.org/learn/medical
-neuroscience/lecture: Leonard E.
White, PhD, Duke University
• https://faculty.washington.edu
• http://antranik.org
• https://www.andrews.edu