1. Nervous System Cells

2. The Nervous System The Nervous system is responsible for communication Composed of the: Brain Spinal Cord Nerves

3. Organization of the Nervous System Central Nervous System (CNS) Brain Spinal Cord Peripheral Nervous System (PNS) Cranial Nerves Spinal Nerves

4. Afferent and Efferent Divisions Afferent Division – consists of all of the incoming sensory pathways Efferent Division – Consists of all of the outgoing motor pathways

5. Somatic and Autonomic Divisions Somatic Nervous System (SNS) Somatic Motor Division – carries information to the somatic effectors (skeletal muscles) Somatic Sensory Division – carries feedback information to somatic integration centers in the CNS

6. Autonomic Nervous System (ANS) Efferent division of the ANS carries info to the autonomic or visceral effectors (smooth and cardiac muscle) Sympathetic division – “fight-or-flight” response Parasympathetic division – “rest-and-repair” division Visceral Sensory division carries feedback info to autonomic integrating centers of the CNS

8. Cells of the Nervous System Neurons – excitable cells that conduct the impulses that make possible all nervous system functions Glia – (glial cells) support the function of neurons in various ways

9. Glia (Neuroglia) 900 billion in the human nervous system Retain their capacity for division (makes them susceptible to cancer)

10. Astrocytes Found only in the CNS Largest and most numerous Feed the neurons “Blood-brain barrier”

11. Microglia Small, stationary cells found in the CNS In inflamed tissue they enlarge and move about in order to carry out phagocytosis of microorganisms and cellular debris

12. Ependymal Cells Resemble epithelial cells Form thin sheets that line the fluid cavities of the brain Some secrete the fluid Cilia to circulate fluid

13. Oligodendrocytes Cell with few branches Help hold nerve fibers together Produce the fatty myelin sheath around nerve fibers in the CNS

14. Schwann Cells Found only in the PNS Functional equivalent of oligodendrocytes Wrap around nerve fiber

15. Nodes of Ranvier Short space in the myelin sheath between adjacent Schwann cells

16. Multiple Sclerosis

17. Neurons The human brain contains about 100 billion neurons All neruons consist of a cell body and at least two processes–an axon and a dendrite

19. Structural Classification of Neurons Multipolar – have only one axon but several dendrites Bipolar – have only one axon and only one highly branched dendrite Unipolar – have only a single process extending from the cell body

20. Structural Classification

21. Functional Classification Neurons can be classified according to the direction in which they conduct impulses Afferent neurons – transmit to the spinal cord or brain Efferent neurons – transmit away from the brain or spinal cord Interneurons – conduct impulses toward motor neurons (entirely within the CNS)

22. Reflex Arc

23. Nerves and Tracts Nerves are bundles of peripheral nerve fibers held together by several layers of connective tissue Endoneurium – surrounds each nerve fiber Perineurium – surrounds each fascicle Epineurium – surround the nerve In the CNS bundles of nerve fibers are called tracts

24. Nerve Structure