1. Grade 9 BIOLOGY THE NERVOUS SYSTEM

2. What does your Nervous System do?
Your ideas:
Hear what Tim and Moby have to say...

3. What is part of the Nervous System?

4. ORGANIZATION OF THE NERVOUS SYSTEM
How many neuron connections do you have?
How is the nervous system divided up?
What are major parts of the nervous system…?

5. WHAT DO NEURONS LOOK LIKE?
Label a neuron!

6. MAJOR TYPES OF NEURONS
Differences:
Similarities:
Motor
Sensory

9. HOW DO NEURONS SEND A SIGNAL?
ELECTROCHEMICAL CHANGE that moves in one direction along
a neuron
involves changes in voltage
(charge) as well as in the
concentrations of ions
What charge does a cell have at rest?
Slightly negative
WHY?

10. Remember… what does the sodium/potassium pump do?
Review of the Na+ / K+ pump

11. The inside of the cell is negative because:
Na+ K+
The inside of the cell is negative because:
More positive ions are pumped out of the cell than into the cell (3 Na+ out / 2 K+ in)
Negatively charged proteins already in the cell
Some K+ ions leave through potassium channels

12. How do polar molecules get across membranes?
ACTION POTENTIAL
Review:
How do polar molecules get across membranes?
Change in the relative charges inside and outside the cell because of changes in ion concentration
In the cell membrane there are two types of gated ion channels (they open and close):
Na+ channels
K+ channels
There are also Na+/K+ pumps

13. How does it work? Questions:
Where is there more Na+? Inside or outside the cell?
Where is there more K+? Inside or outside the cell?
What do we need to do to make the inside of the cell change from negative to positive?
Na+ K+

14. Steps in An Action Potential
Resting potential
Na+ outside, K+ inside
Channels closed
Stimulus / Threshold
Some Na+ channels open
Na+ comes in
If threshold is passed
they all open
Depolarization
Na+ channels open, Na+ comes in and the cell becomes positive
Chain reaction of Na+ channels opening down the axon
Repolarization
Na+ channels close, K+ channels open
K+ moves out and the cell becomes negative
First... Watch the tutorial animation!

15. Steps in An Action Potential
Undershoot
K+ leaves as K+ channels
slowly close
Cell is MORE negative
than usual
Return to Resting
Potential
Both Na+ and K+ channels
close
Na+ / K+ pump returns
Na+ and K+ to the right
places
First... Watch the tutorial animation!
Why did Na+ rush INTO the cell?
Why did K+ rush OUT of the cell?

16. Another look at an action potential!
Resting state: voltage gated Na+ and K+ channels closed; resting potential is maintained. 1 2 3 4
A stimulus opens some Na+ channels; if threshold is reached, action potential is triggered.
Additional Na+ channels open,
K+ channels are closed; interior of cell becomes more positive. 5
The K+ channels close relatively slowly, causing a brief undershoot.
Na+ channels close and inactivate. K+ channels open, and K+ rushes out; interior of cell more negative than outside.
Neuron interior
Action potential
Threshold potential
Resting potential
Na+
Return to resting state. K+
Another look at an action potential!

17. Complete and know this chart…
Steps in an Action Potential
Resting
Potential
Depolariz-ation
Repolariz-ation
Under-shoot
Return to Resting Potential
Where is Na+ ?
Where is K+ ?
Na+ channels?
K+ channels?
What charge is inside?
What charge is outside?

18. Complete and know this chart…
Steps in an Action Potential
Resting
Potential
Depolariz-ation
Repolariz-ation
Under-shoot
Return to Resting Potential
Where is Na+ ?
Outside
Where is K+ ?
Inside
Na+ channels?
Closed
K+ channels?
What charge is inside?
Negative
What charge is outside?
Positive
For example…
This is Resting Potential

19. What does the Myelin Sheath Do?
Watch here!
With the myelin sheath you...
Only trade ions in the Nodes of Ranvier instead of all along the axon
= faster signal along the axon!
Multiple Sclerosis (MS) happens when you lose your myelin sheath
 neurons can’t send messages fast enough!

20. What is a REFLEX? A Reaction Time is... A Reflex is...
How fast you can react to something
Uses your brain! (catching a ball, saving a goal)
A Reflex is...
An automatic reaction that does NOT use your brain
Message goes to the spinal cord and back only
(moving your hand
away from something hot)

21. The Knee-Jerk Reflex...