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Lab Exercise 13

Lab Exercise 13. Histology of Nervous Tissue. Portland Community College BI 231. Major divisions of the nervous system. Central nervous system (CNS)- brain and spinal cord

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Lab Exercise 13

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  1. Lab Exercise 13 Histology of Nervous Tissue Portland Community College BI 231

  2. Major divisions of the nervous system • Central nervous system (CNS)- brain and spinal cord • Peripheral nervous system (PNS)- comprises all nerves that connect the brain and spinal cord to muscles, glands and receptors.

  3. Nerves • Cranial nerves are those that are connected to the brain • Spinal nerves are connected to the spinal cord. • Both contain sensory information from receptors and send motor signals.

  4. Motor (Efferent) NeuronsEfferent = Away from CNS • These are neurons that carry information from CNS to the body • Groups of axons running together are the Nerves when they are outside the CNS and Tracts inside the brain and spinal cord • The cell bodies are clustered in groups in the CNS and are called nuclei • Brain gray matter is made up of millions of nuclei. • It is gray because there is no myelin around the cell bodies • These axons exit the spinal cord on the ventral side

  5. Motor (efferent) division of PNS • Somatic nervous system- contains efferent neurons extending from the CNS to skeletal muscle. • Autonomic nervous system- contains efferent neurons from CNS to smooth muscle, cardiac muscle and glands

  6. Sensory (Afferent) NeuronsAfferent = Toward the CNS • These carry sensory information from the body to the CNS (brain and spinal cord) • Their axons run in the same group as the motor neurons (nerves=groups of axons) • Their cell bodies are clustered outside of the spinal cord and are called ganglia • These axons enter the spinal cord on the dorsal side

  7. Sensory (afferent) division • Afferent neurons that receive stimuli from somatic sensory receptors that detect general sensations • Receive stimuli from visceral sensory receptors • Special sensory receptors that detect special sensations (smell, taste, vision, hearing, equilibrium)

  8. Organization of nervous system

  9. Neuron

  10. Myelin • Some axons are surrounded by a myelin sheath • Multilayered lipid and protein covering formed by Schwann cells around axons • Oligodendrocytes in the CNS • The covering is the plasma membrane of the Schwann Cell • The Schwann Cell can cover more than one axon • Insulates axon

  11. Nodes of Ranvier • Areas between Schwann Cells that do not contain Myelin • Involved in saltatory conduction

  12. Dendrite Neuron Cell Body Nucleus Axon Hillock Axon

  13. Schwann Cell Axon Node of Ranvier Myelin Sheath Telodendria Axon Terminal (Synaptic end bulbs)

  14. Classification • Sensory (afferent) neurons conduct nerve impulses from sensory receptors • Motor ( efferent) neurons conduct nerve impulses from the CNS • Interneurons form links between sensory and motor

  15. Multipolar Neuron • Most common type of neuron • Interneurons and motor neurons Cell Body Axon Dendrites (trigger zone)

  16. Anaxonic Neurons • A small number of multipolar neurons contain only dendrites or • Cannot distinguish dendrites from axons • Functions are poorly understood.

  17. Bipolar Neuron • Location: special senses (smell, vision, hearing) Dendrite (trigger zone) Axon Cell Body

  18. Unipolar Neuron • All are sensory afferent • Cell bodies are located in the dorsal root ganglia Dendrite (trigger zone) Axon Cell Body

  19. Association or Interneurons • Neurons between the afferent and efferent neurons. • Are only in the CNS

  20. Axon Myelin Sheath Neuron Node of Ranvier Perineurium Fascicle Epineurium

  21. Glial Cells • Associated with neurons • Provide Supportive scaffolding • Segregate and insulate neurons • Outnumber neurons by 10 to 1

  22. Star Shaped Many functions Regulates levels of O2 , & CO2 Exchanges between capillaries and neurons (blood-brain barrier) Nutrient transfer Supporting Cells in the CNS Astrocytes

  23. Supporting Cells in the CNSMicroglia • Protect CNS from disease-causing organisms • Monitor the health of neurons • Act as phagocytes eating microorganisms and debris

  24. Ependymal cells • These cells are modified epithelial cells that line the ventricles of the brain and central canal of spinal cord. • Facilitate circulation of CSF

  25. Supporting Cells in the CNS Oligodendrocytes • Produce the myelin sheath which provides the electrical insulation for some neurons in the CNS

  26. Supporting Cells in the PNS Schwann Cells • Form the myelin sheath around axons in the PNS

  27. Satellite cells • Surround neuron cell bodies in peripheral ganglia and regulate levels of oxygen, carbon dioxide and nutrients.

  28. The synapse • Axons generate action potentials which are transmitted across synapses • Formed by presynaptic membrane and postsynaptic membrane on an effector cell • The synaptic cleft is a narrow space that separates these

  29. The End The End

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