Grade 12 BIOLOGY THE NERVOUS SYSTEM Part 1 – Sending a signal

What does your Nervous System do? Your ideas: If we have time, you can 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…? The Nervous System Central Nervous System Peripheral Nervous System Autonomic Nervous System Skeletal muscles / Exterior senses Sympathetic Nervous System Parasympathetic Nervous System Emergencies / “Flight or fight” Non- Emergencies Somatic Nervous System Brain Spinal cord

WHAT DO NEURONS LOOK LIKE? Try the label a neuron activity!

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: 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

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

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+

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!

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?

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!

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?

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

What does the Myelin Sheath Do? 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!

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)

The Knee-Jerk Reflex...