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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??? - PowerPoint PPT Presentation
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Neurological DisordersLesson 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
• Chemically via synapses• Electrically via axons
Chemical Signal
Electrical Signal
Electrical Signal
Electrical Signal
Chemical Signal
Electrical 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.
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
Voltage-gated potassium (K+)
channel
Na+/K+ Pump
Allow Na+ to flow through.
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
Na+/K+ Pump
Open when the membrane potential
is at -50 mV
Open when the membrane potential
is at +40 mV
Keep this in mind for later…
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
Na+
K+
K+K+
Na+
Na+Na+
Na+
More Na+ outside
More K+ inside
More negatively charged proteins
At rest
- -
- -
The Axon’s Membrane Potential
Na+
K+
K+K+
Na+
Na+Na+
Na++ + + +
- - - -
- 70mV
At rest
The Axon’s Membrane Potential
At rest
The Action Potential
Na+
K+
K+K+
Na+
Na+
Na+
Na+
+ +
Does anyone remember the voltage at which the voltage-gated Na+ channels open?-50 mV - Threshold
After stimulation
Na+ Na+
Na+Na+
Na+
The Action PotentialAfter stimulation
- 50 mV
- 70 mV
0 mV
Depolarization
The Action Potential
K+
K+K+
Na+ Na+
Na+Na+
Na+
Does anyone remember the voltage at which the voltage-gated K+ channels open?
After depolarization
Does anyone remember the voltage at which the voltage-gated K+ channels open?+ 40 mV
K+
K+
K+
The Action Potential
- 50 mV
- 70 mV
0 mV
Depolarization Hyperpolarization
40 mV
After depolarization
The Action Potential
How does the axon return to its resting membrane potential with Na+ outside and K+ inside?
Na+ Na+
Na+Na+
K+
K+
K+
Na+
After hyperpolarization
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.
Na+ Na+ Na+
Na+Na+
K+ K+
K+
The Action Potential
- 50 mV
- 70 mV
0 mV
Depolarization Hyperpolarization
40 mV
After hyperpolarization
Modeling the Action Potentialalong the length of the axon
Outside
Inside
Blue toothpick = Na+ ion channel
Black-eye pea = Na+ ion
Red toothpick = K+ ion channel
Black toothpick = Na+/K+ Pump
Lima bean = K+ ion
The Action Potential along the Axon
How does Novocain work?
• Novocain inhibits the voltage-gated Na+ channels.
PAIN
• What happens if the voltage-gated Na+ channels can’t open?– The axon can’t send Action Potentials.– Meaning you can’t feel pain!
No Signal
1.
2.
3.
4.
5.
Homework: The Stages of the Action Potential
Write a summary of what is happening at each stage of the action potential.
1. The membrane is at rest. More Na+ is outside the cell.
2. The voltage-gated Na+ channelopens. Na+ enters the axon.Depolarization.
3. The voltage-gated Na+ channelcloses and the voltage-gated K+ channel opens.
4. K+ ions leave the axon.Hyperpolarization.
5. The Na+/K+ pump restores the resting membrane potential by pumping Na+ out and K+ in.
The Stages of the Action Potential
