Transcript The Action Potential

Neurological Disorders
Lesson 2.2 - Differentiated
How do our neurons signal
electrically?
Electrical
Signal
Do Now:
• Ethan needs to have a
cavity filled. Before his
doctor begins drilling, she
gives him Novocain to
prevent pain.
• How do you think Novocain
works???
– Novocain stops our neurons
from signaling electrically.
– But how do our neurons
signal electrically???
Neurons Send Signals
Electrical
Signal
Electrical
Signal
Chemical
Signal
• Chemically via synapses
• Electrically via axons
Electrical
Signal
Chemical
Signal
What is the Action Potential?
• The action potential is how neurons send signals
electrically down their axons.
• Neurons do this by using the potential energy
stored in their membrane potentials.
Electrical
Signal
First, what is electricity?
• The flow of charged particles – also known as ions.
• But, can ions just flow into the axon??
– No!
Na+
The Axon’s Ion Channels and Pumps
• The axon has ion channels and pumps that act as
doors through which ions enter and exit the axon.
• These channels and pumps allow ONLY specific
ions to flow or be pumped through them.
The Axon’s Ion Channels and Pumps
Voltage-gated
sodium (Na+)
channel
Allow Na+ to flow
through.
Voltage-gated
potassium (K+)
channel
Na+/K+
Pump
Allow K+ to flow
through.
Pump Na+ out of and
K+ into the axon.
But wait, what does “Voltage-gated” mean?
• “Voltage-gated” – means that the channel opens
at a specific voltage.
• This means that the voltage of the membrane is
like a key that opens the channel.
The Axon’s Ion Channels and Pumps
Voltage-gated
Na+ channel
Voltage-gated
K+ channel
Open when the
membrane potential
is at -50 mV
Open when the
membrane potential
is at +40 mV
Keep this in mind for later…
Na+/K+
Pump
The Axon’s Membrane Potential
• Refers to the potential energy stored at the
membrane.
• There is potential energy because there is a
charge difference between the inside and the
outside of the axon.
The Axon’s Membrane Potential
At rest
Na+
Na+
Na+
Na+
More Na+ outside
Na+
-
-
More K+ inside
K+
K+
-
K+
More negatively
charged proteins
The Axon’s Membrane Potential
At rest
Na+
Na+
Na+
Na+
Na+
++++
- - - K+
K+
- 70mV
K+
The Axon’s Membrane Potential
At rest
The Action Potential
After stimulation
Na+
Na+
Na+
Na+
Na+
Na+
+ +
Na+
K+
Na+
K+
Na+
K+
Na+
Does anyone remember the voltage at which
the voltage-gated Na+ channels open?
-50 mV - Threshold
The Action Potential
After stimulation
0 mV
Depolarization
- 50 mV
- 70 mV
The Action Potential
After depolarization
K+
K+
K+
Na+
Na+
K+
Na+
Na+
K+
K+
Na+
Does anyone remember the voltage at which the
voltage-gated K+ channels open?
+ 40 mV
The Action Potential
After depolarization
40 mV
0 mV
Depolarization
- 50 mV
- 70 mV
Hyperpolarization
The Action Potential
After hyperpolarization
Na+
K+
Na+
Na+
Na+
Na+
K+
Na+
Na+
K+
Na+
K+
Na+
Na+
K+
K+
How does the axon return to its resting membrane potential
with Na+ outside and K+ inside?
Na+/K+ Pump moves Na+ out and K+ into the axon.
The Action Potential
After hyperpolarization
40 mV
0 mV
Depolarization
- 50 mV
- 70 mV
Hyperpolarization
Modeling the Action Potential
along the length of the axon
Black-eye pea = Na+ ion
Outside
Inside
Blue toothpick =
Na+ ion channel
Lima bean = K+ ion
Red toothpick =
K+ ion channel
Black toothpick =
Na+/K+ Pump
The Action Potential along the Axon
How does Novocain work?
• Novocain inhibits the voltage-gated Na+ channels.
PAIN
No Signal
• What happens if the voltage-gated Na+ channels
can’t open?
– The axon can’t send Action Potentials.
– Meaning you can’t feel pain!
Homework: The Stages of the Action Potential
Write a summary of what is happening at each
stage of the action potential.
3.
2.
1.
4.
5.
The Stages of the Action Potential
3. The voltage-gated Na+ channel
closes and the voltage-gated K+
channel opens.
2. The voltage-gated Na+ channel
opens. Na+ enters the axon.
Depolarization.
1. The membrane is at rest.
More Na+ is outside the cell.
4. K+ ions leave the axon.
Hyperpolarization.
5. The Na+/K+ pump restores
the resting membrane
potential by pumping Na+ out
and K+ in.