1. The Neuron Building Blocks of our Nervous System

2. What is a Neuron?  A specialized cell transmitting nerve impulses or a nerve cell  The primary cell of our nervous system  Approx. 100 billion in our bodies  Three primary functions:  Collect sensory information  Process information  Control responses

3.  You feel a spider drop onto your foot!  This message is sent to your brain where it is processed.  Your neurons communicate to your muscle cells with a reaction. Example of Neuron Functions

4. Types of Neurons: Based on Function  Sensory Neurons (also called afferent neurons) gather information from our sense organs (Ex: touch, taste, smell, sight, etc…)  Interneuron (also called association or relay neurons) found in brain and spinal cord; job is to connect neurons together to relay information through central nervous system  Motorneurons (also called efferent neurons) send information from the brain to the muscles to respond

5. Regardless of the specialty of the neuron, they have the same key features: All Neurons will look different dependent upon their function but…  Axon  Axon Terminal  Nucleus  Myelin Sheath  Cell Body (Soma)  Dendrites  Synapse

6. Dendrites  Comes from a Greek root meaning tree branches  Can you guess which part it is?  The branching structures of a neuron that receives messages  Extends from the cell body

7. Cell Body (Soma)  The main portion of the neuron  Contains the nucleus and other organelles common in cells

8. Axon  The long extension of the neuron that carries nerve impulses away from the cell body (soma)

9. Axon Terminal  The hair-like ends of the axon  Where the message leaves the neuron

10. Myelin Sheath  The fatty substance that surrounds and protects nerve fibers  Acts as insulation  Incredibly important  Multiple Sclerosis is a disease that damages the myelin and it can cause all of the following:  Vision problems  Fatigue  Numbness  Muscle tightness  Dizziness  Poor balance & coordination  Facial pain  Slurred speech  Difficulty with walking and fine motor skills  Mood swings  Memory loss

11. Nucleus  An organelle (structures found in cytoplasm within eukaryotic cells) in the cell body that contains the genetic material of the cell  What does this mean?  Note—There are several other types of organelles and even other types of cells in the nervous system but we only have time for an overview!

12. Label your diagram.

13.  Messages are sent both chemically (neurotransmitters) and electrically (charges—positive or negative)  We’ll talk more about this later!  Chemicals are collected by the dendrites.  When enough are collected, it is processed in the cell body.  Sends an electrical charge down the axon (which is able to send it effectively because it’s insulated by the myelin sheath).  When it reaches the axon terminal, it releases those chemicals to continue to send the message to the next neuron(s).  The nucleus stores the genetic information of that cell, so though it isn’t directly involved in the communication, it is vital to your central nervous system! How do these cells communicate?

14. The Synapse  The gap (sometimes called a cleft) between the axon terminal of one neuron and the dendrites of another  Where the neurons send chemical messages to each other

15. Action Potential  Neurons only communicate in one direction (Which direction is that, again?)  Think of it like a pager.  When a neuron is depolarized enough it reaches a threshold.  This creates an Action Potential—or electrical signal that travels down the axon to the terminal to release more neurotransmitters (chemical messengers) to continue the relay of information to the next neuron  Action Potential are “all or nothing” reactions.  Think of them like static electricity on carpet!

16. Action Potentials

17. Action Potential Speed  Action Potentials move at a constant speed  However, that speed depends upon the type of axon transmitting the message.  The wider the axon and the more myelin insulation the faster they are. (Think of it like bandwidth.)  What types of information would require these faster speeds?

20.  The action potential reaching the axon terminal triggers the release of neurotransmitters across the synapse.  Neurotransmitters—a chemical messenger capable of transmitting a neural message from one neuron, across the synaptic cleft to another neuron or muscle Neurotransmitters

22. Example Effect:

23. Let’s review how a neuron key structures work by creating a model. Make sure you review this information before next session so you are very familiar with it!

24. How fast can these neurons send messages? Let’s find out!

25.  Finally, how do we think neurons are distributed throughout our bodies? Evenly? Concentrated in certain areas?  What are we basing this guess on?  Let’s find out!  We are going to do a 2-Point Threshold Test on the following body parts:  Cheek  Back of upper arm  Back of calf  Finger tip  Before you conduct the experiment:  What do you predict will happen?  Record your results. What actually happened?  Think about how to interpret your results for when we debrief as a class! Neural Density?

26.  Which areas were the least sensitive?  Which areas are the most sensitive?  Knowing what you do about how our body communicates and processes information, what do you think these finding imply?  Why would does our body function this way?  A little food for thought… Results of Two-Point Threshold Test?