Neurological Disorders Lesson 2.2 - Differentiated

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