1. ANATOMY
Unit 2 Notes:
Nerve
Impulses

2. (1) What is a Nerve Impulse?
• Chain reaction of chemical events, allowing
your neurons to send “messages”.
• Synonymous Terms:
– Neuron Message
– Nervous System Response
– Depolarization & Repolarization

4. (2) The Basic Steps
1. Neurotransmitter binds to neuron.
2. Depolarization.
3. Repolarization.
4. Repeat #2 and 3 until reaching axon terminal.
5. Release of another neurotransmitter from axon
terminal.
6. Regain resting potential.

5. Neurotransmitter
Binds
Depolarization & Repolarization
Down The Axon
Release a neurotransmitter
+
Stimulate next move

6. (3) Resting Potential
• “Resting Potential”:
The natural state of a neuron when it’s not
doing anything.
• At Rest There is…
– Potassium (K+) on the inside of axon.
– Sodium (Na+) on the outside of axon.
– More cations on the outside than inside.
*This means that the outside is naturally more
positive than the inside (making the axon polar).

8. (4) Depolarization
• De = without
Polar = uneven charge
• Depolarization:
To remove the imbalance of charge.
• What Happens?
– Sodium pumps open.
– Sodium ions fly thru channels into axon.
– Temporarily increases positive charge inside
axon, removing polarization.

10. (5) Repolarization
• Re = repeat
Polar = uneven charge
• Repolarization:
To regain the charge imbalance.
• What Happens?
– Potassium pumps open.
– Potassium ions fly thru channels out of axon.
– Temporarily increases positive charge back on
the outside of the axon, regaining polarization.

12. (6) Reaching the Terminals
• A neurotransmitter will be released.
• This neurotransmitter will:
– Bind to another neuron or organ.
– Make something else happen (muscle
contraction or another nerve impulse).

14. (7) Regaining Resting Potential
• Even though the axon is polarized at the
end, the ions are on the wrong sides of the
axon.
• Must actively transport ions:
– Sodium must go back out.
– Potassium must go back in.
• Requires ATP.

16. …Let’s Review All That Again…

17. (8) Myelin Sheath
• Where Is It?
– Covers the outside of the axon.
– Wraps around Na/K pumps.
• What Is Its Purpose?
– Block some of the Na/K pumps.
– Increases the speed of nerve impulse.
• How Does It Work?
– Just like main-roads versus the freeway.
– Main Roads = Axon without myelin sheath.
– Freeway = Axon with myelin sheath.