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Grade 9 BIOLOGYTHE NERVOUS SYSTEM
WHAT DOES YOUR NERVOUS SYSTEM DO?
Your ideas:
Hear what Tim and Moby have to say...
WHAT IS PART OF THE NERVOUS SYSTEM?
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…?
WHAT DO NEURONS LOOK LIKE?
Label a neuron!
MAJOR TYPES OF NEURONS
Differences:
Similarities:
Motor
Sensory
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?
Remember… what does the sodium/potassium pump do?
Review of the Na+ / K+ pump
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
Na+ K+K+
ACTION POTENTIAL 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
Review:
How do polar molecules get across membranes?
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+K+
STEPS IN AN ACTION POTENTIAL1. Resting potential
Na+ outside, K+ inside Channels closed
2. Stimulus / Threshold Some Na+ channels open Na+ comes in If threshold is passed
they all open
3. Depolarization Na+ channels open, Na+ comes in and the cell
becomes positive Chain reaction of Na+ channels opening down the axon
4. Repolarization Na+ channels close, K+ channels open K+ moves out and the cell becomes negative
First... Watch the tutorial animation!
STEPS IN AN ACTION POTENTIAL5. Undershoot
K+ leaves as K+ channelsslowly close
Cell is MORE negativethan usual
6. Return to Resting Potential Both Na+ and K+ channels
close Na+ / K+ pump returns
Na+ and K+ to the rightplaces
First... Watch the tutorial animation!
Why did Na+ rush INTO the cell?
Why did K+ rush OUT of the cell?
Resting state: voltage gated Na+
and K+ channels closed; restingpotential is maintained.
1
2
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A stimulus opens some Na+channels; if threshold is reached,action potential is triggered.
Additional Na+ channels open,K+ channels are closed; interior ofcell becomes more positive.
5 The K+ channels closerelatively slowly, causinga brief undershoot.
Na+ channels close andinactivate. K+ channelsopen, and K+ rushesout; interior of cell morenegative than outside.
Neuroninterior
Actionpotential
Thresholdpotential
Resting potential
1
2
3
4
5
Na+
Na+
Na+
Na+
1 Return to resting state.
1
Neuroninterior
K+
K+
Another look at an action potential!
COMPLETE AND KNOW THIS CHART…Steps in an Action Potential
RestingPotential
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?
COMPLETE AND KNOW THIS CHART…Steps in an Action Potential
RestingPotential
Depolariz-ation
Repolariz-ation
Under-shoot
Return to Resting
Potential
Where is Na+ ?
Outside
Where is K+ ?
Inside
Na+ channels?
Closed
K+ channels?
Closed
What charge is inside?
Negative
What charge is outside?
Positive
For example…This is Resting
Potential
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!
Multiple Sclerosis (MS) happens when you lose your myelin sheath
neurons can’t send messages fast enough!
WHAT IS A REFLEX? A Reaction Time 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)
THE KNEE-JERK REFLEX...
