NERVOUS SYSTEM 2.11.16
Neuron Physiology
NEURONS


So, we know how neurons are structured (built)
but how do they actually work?
ACTION POTENTIALS
ACTION POTENTIAL

When a neuron is stimulated enough, it sends an
electrical impulse down through the axon to the
next neurons
ACTION POTENTIAL


Can only send one signal (the electrical impulse
transmits and a uniform strength and speed), so
how do we interpret different information from
the neurons?
They can very the frequency or number of pulses
ACTION POTENTIAL

Electricity
Human bodies are electrically neutral
 Equal amounts of positive and negative charges
occurring
 HOWEVER,



Certain areas are more positively or negatively charged
than others.
THEREFORE,
We have barriers to keep the positive and negative charges
apart (because they are attracted to each other)
 UNTIL, we are ready to use the energy their attraction
creates

ACTION POTENTIAL

Keep the charges separated to build potential
ACTION POTENTIAL

Example: Battery

Has a positive and a negative end, but cannot do
anything until connected to something that lets the
charges move toward each other
ACTION POTENTIAL
ACTION POTENTIAL

Voltage:
Measure of potential energy generated by separated
charges
 Normally measured in volts
 Measured in millivolts in people because such a small
amount


Call it membrane potential in people
ACTION POTENTIAL

The GREATER the distance between charges,
the HIGHER the voltage, and the LARGER the
potential
ACTION POTENTIAL

Current

The flow of electricity from one point to another

The amount of charge in a current is related to its
voltage and resistance

Resistance is whatever is getting in the way of the current
 Example: plastic, high resistance (an insulator from
electrical current)
 Example: metal, low resistance (a conductor for electrical
current)
ACTION POTENTIAL



What does all of this have to do with people?
Currents indicate the flow of negatively or
positively charged ions across the resistance of
your cells membranes
Remember: membranes separate the charges, so
they are what provide the potential to convert the
electricity into something useful
ACTION POTENTIAL

Resting membrane potential: there is a positive
charge outside the cell, and a negative charge
inside the cell
ACTION POTENTIAL



Sodium ions
provide the bulk of
the positive charge
outside the cell
Proteins and
phosphate ions
provide the
negative charge on
the inside
You still have some
negative and
positive ions on
both sides though
ACTION POTENTIAL

Remember: it is about the difference in charge
across the membrane

Is -70millivolts in people

Polarized
ACTION POTENTIAL

Sodium Potassium Pump
ACTION POTENTIAL

Sodium Potassium Pump






Protein
Straddles the membrane
For every 2 Potassium (K+) ions it pumps in, it
pumps 3 Sodium (Na+) ions out
This creates a difference between the concentration
of Na+ and K+
Because it pumps 3 positively charged ions out of the
cell while only bringing 2 inside
ELECTROCHEMICAL GRADIENT