The Nervous System

1. The Nervous System Chapter 11

2. Functions of the Nervous system I • Sensory (input): • Light • Sound • Touch • Temperature • Taste • Smell • Internal Chemical • Pressure • Stretch External Chemical

3. Functions of the Nervous system II • Integration: • Integration means making sense of sensory input. Analyzing stimuli based on experience, learning, emotion & instinct and reacting in a useful way (you hope). • Motor (output): • The response to the sesnsory input and subsequent integration. Sending signals to the muscles and other organs of the body instructing them how to respond to the stimuli.

4. The Basic Scheme

5. Organization of the Nervous system

6. The CNS compared with thePNS

7. the Central Nervous System Astrocytes Microglia Oligodendrocytes Ependymal Cells the Peripheral Nervous System Schwann Cells (a.k.a. Neurolemmocytes) Satellite Cells Support Cells of the Nervous system

8. Astrocytes & microglia Astrocytes & microglial cells protect the neurons of the CNS.

9. Astrocytes & microglia • Functions of astrocytes: • Connect neurons to capillaries. This makes up the “blood-brain barrier”. • Maintain the the electrochemical environment • Capture and recycle neurotransmitters • Absorb and return K+ and other ions. • Connected to one another and capable of communicating via gap junctions. Function of microglial cells: • Dendritic macrophages that phagocytize microbes and necrotic (dead) tissue.

10. Ependymal Cells & oligodendrocytes

11. Ependymal Cells & oligodendrocytes • Functions: • Ependymal Cells - Line the ventricles of the brain an central cnal of the spinal cord. They aid in the circulation of cerebrospinal fluid (CSF). • Oligodendrocytes - These cells have processes that wrap around the axons of neurons. This creates an insulation coating called a myelin sheath.

12. Schwann Cells & satellite cells • These are the suport cells in the peripheral nervous system. • Schwann cells provide the myelin sheath for peripheral axons. • Satellite cells serve a slightly similar function to astrocytes, supporting the cell bodies of peripheral neurons.

13. Neurons - the “action cells”

14. Characteristics of neurons • Long-lived • Generally last a life time with 90% are formed by the time you are 6 years old. The rest are produced when as you go through puberty. • Amitotic • Until recently it was thought that neurons didn’t regenerate at all! Some may but generally what you have at adulthood is all you get. • High metabolic rate • This means high oxygen demand and lots of mitochondria. Neurons also require glucose.

15. Myelin Myelin is a lipid-rich component of the cell membranes of Schwann cells and oligodendrocytes. It acts kind of like the insulation on an electrical wire.

16. The cycle of an Action Potential

17. Anatomy of an Action Potential

18. A Basic Neural Circuit

19. Type of neurons

20. Three structural classes of neurons • Multipolar • Most numerous • Many dendrites • Motor and association neurons • Unipolar • Second most numerous • Rounded body with one process • Somatic & general sensory neurons • Bipolar • Least common, found in special sensory organs

21. Comparison of neuron types

22. Functional categories of neurons