1) An impulse travels along a neuron when the inside becomes more positively charged than the outside due to the flow of sodium ions into the cell during depolarization. 2) The sodium-potassium pump normally keeps the inside negatively charged by pumping out 3 sodium ions and pumping in 2 potassium ions for each pump cycle. 3) When the membrane potential reaches threshold, voltage-gated sodium channels open, sodium rushes in, and the inside becomes positively charged, allowing the impulse to move along. Then, voltage-gated potassium channels open and potassium exits, repolarizing the cell back to its resting potential.

1. Movement
of
A
Nerve
Impulse

2. General Blurbs
 An impulse is an electrical signal.
 An impulse that is not carrying a signal is:
“POLARIZED”
 The inside of a neuron is NEGATIVELY charged.
 The inside of a neuron is 70 milliVolts more
negative than the outside
 The difference is referred to as the: RESTING
MEMBRANE POTENTIAL.
 The RESTING MEMBRANE POTENTIAL is –70mV.
 For a nerve impulse to MOVE, the inside must
become more positiviely charged than the
outside.

3. Nerve Impulse

4. How do you get the inside more negatively
charged?
SODIUM/POTASSIUM PUMP
Nerve cell protein channels that:
Uses a molecule of ATP to:
 Moves 3 Na+ ions out of the cell and simultaneously moves 2
K+ ions into the cell. Produces an environment where there is
more SODIUM outside of the cell and more POTASSIUM in the
cell. Occurs when there is no impulse to keep the voltage at
-70mV.
 The difference in charges across the pump produces a
negative charge inside the nerve cell.
A. This is the RESTING MEMBRANE POTENTIAL = -70mV

5. Getting the Nerve Impulse to Move
Voltage Gate Channels
 An impulse is caused by the movement of ions across the cell
membrane.
 At – 70mV the protein channels close.
 At the leading edge of an impulse, neuron depolarizes
slightly(-50mV). This is the THRESHOLD POTENTIAL.
This triggers the opening of the Voltage gate and
B. SODIUM IONS flow into the cell…causes the inside to
have a TEMPORARY positive charge.
 THIS IS THE ACTION POTENTIAL (DEPOLARIZATION)…+30
to 35 mV.
C. Then the Voltage-gated POTASSIUM channels open
and potassium exits the cell.
 This REPOLARIZES the cell to the RESTING POTENTIAL…and
the impulse moves on.

6. Why does the action potential move in
only one direction?

10. Synapse
 JUNCTION BETWEEN A NEURON AND ANOTHER
CELL(MUSCLE OR GLAND) OR NEURON.
 Axon of neuron and dendrite of another do not actually
touch:
 Small gap between them: Synaptic cleft.
 Synapses use NEUROTRANSMITTERS to pass the
impulse to the next cell.
 Neurotransmitters are chemical.
 Most common: Acetylcholine(Ach) (endorphins and
enkephalins)
 When action potential reaches the TERMINAL END of an
axon, the neurotransmitter is released into the synaptic
cleft and binds to receptors on dendrites.
 When receptors bind to neurotransmitter, the process
begins on the next neuron.

11. Refractory Period
 The very short period of time where a
portion of a membrane cannot initiate
another action potential.
 Ensures the impulse is one directional.
 Nerve is “reset.”