The nervous system is responsible for all behavior, thoughts, and actions in the body. It works with the endocrine system to maintain homeostasis. The nervous system has three main functions - sensory input, integration of information, and motor output responses. It is divided into the central nervous system (brain and spinal cord) and peripheral nervous system, with the peripheral system further divided into afferent and efferent divisions. Neurons are the basic structural and functional units of the nervous system and come in various types like multipolar neurons. The nervous system also contains supporting glial cells that help regulate the chemical environment for neurons.

1. The Nervous System

2. Facts: Responsible for all behavior Every thought, action, and behavior controlled here Works together with the endocrine system to achieve homeostasis Cells communicate by electrical signals

3. Three Main Functions: Sensory input Integration Motor output

4. Sensory Input Our bodies have millions of sensory receptors They detect changes Changes are called “stimulus” This is where all stimuli is collected Called the “afferent pathway”

5. Integration Your brain makes decisions about what to do with the stimulus It processes the info gathered It establishes a set point

6. Motor Output Causes a response to the stimulus Activates effector organs Sends signal down “efferent pathway”

7. Nervous System Divisions Central Nervous System (CNS) CNS includes brain & spinal cord Peripheral Nervous System (PNS)’ PNS broken down into afferent & efferent divisions Sensory division = Afferent division Motor division = efferent division Both CNS and PNS work together You can’t have one without the other

8. Nervous System Histology Nervous tissue is highly cellular Less than 20% of cns is extra-cellular space Cells densely packed together Tissue is made up of two principal types of cells (nerve cells and supporting cells)

9. Supporting Cells in CNS Glial cells (neuroglia) Glial cells have branching processes and central cell body, like neurons Smaller than neurons Outnumber neurons in CNS 9 to 1 They make up half the mass of the brain

10. Common Glial Cells in CNS Astrocytes Control chemical enironment around neurons “ mop up” leaked potassium ions & recycle them Recapture/recycle neurotransmitters Microglia Monitor health of neurons Protect against microorganisms Can turn into macrophages which destroy foreign intruders Fact: immune system cells are denied access to CNS Oligodendrocytes Make up myelin sheaths

11. Supporting Cells in PNS Satellite Cells Surround neuron cell bodies Play a role in controlling the chemical environment of the neurons Schwann Cells Surrounds & forms myelin sheaths around larger nerve fibers in PNS Functionally similar to oligodendrocytes

12. Neurons Structural units of the nervous system Highly specialized cells Have extreme longevity with good nutrition (100 years plus) Neurons are amitotic - no ability for mitosis. Cannot be replaced if destroyed Have a high metabolic rate - need high amounts of oxygen & glucose. Cannot survive more than a few minutes without oxygen

13. Neuron Anatomy The most common neuron is multipolar They are made up of four basic parts: Dendrites - receive signals from previous neurons Cell body - controls/sustains neuron Axon - allows nerve signals to travel along neuron Terminal bodies - release neurotransmitters at tips Myelin sheaths cover axon in many neurons. Protects, insulates, and speeds up conduction. Myelinated neurons include “nodes of Ranvier” Function … speeds up signal transmission Myelinated neurons faster conductors than unmyelinated

14. Multipolar Neuron

15. Drugs & Neurotransmitters Inside of hypothalamus is our “pleasure center” Motivates much of human behavior Responsible for anything that gives us pleasure/joy Our ability to feel good involves neurotransmitters Drug use re-programs how these neurotransmitters work

16. Speed (Methamphetamine) Artificially stimulates brain to provide pleasure flush When outside chemicals are introduced, brain produces less neurotransmitters “ why bother?!?!?”

17. Cocaine Comes in snorted form (white powder) Stimulates pleasure center then squeezes it dry Hooks to dopamine transporter protein So, it blocks reabsorption of dopamine … ..the neurotransmitter remains in synapse and stimulates receptor cells over and over again Increased heart rate, blood pressure, sexual appetite

18. As dopamine is blocked, it accumulates in synapse It’s washed away Brain dopamine supply becomes inadequate to maintain normal moods The sending cells cannot make dopamine fast enough to make up for the loss and pleasure circuits go dry Cannot experience pleasure without the drug Catch-22: cocaine needed to experience pleasure, but more use = more depletion of neurotransmitter supply Weight loss, trouble sleeping, mood swings, death Incredibly difficult to treat

19. Crack Cheaper than cocaine More potent Smokable form of cocaine Produces higher high and a deeper crash!! Intensely addictive

20. Heroin Is a depressant Far more expensive than cocaine Demands higher doses to achieve the same effect When addicted and going without, body goes into incapacitated nausea and convulsions With an overdose, lungs fill with fluid and user drowns.