Nervous Tissue

1. Nervous Tissue Graduate Microanatomy Spring 1999 Sandra H. Bolanos

3. Central Nervous System • Brain • Spinal Cord

4. Brain • Cranium (brain case) • Cortex Gray matter Nerve cell bodies • Interior Portion White matter Axons Ventricles CSF

5. Spinal Cord • Occupies two-thirds of the vertebral canal • Enveloped by meninges • Cervical and lumbar enlargements • Gray matter centrally located

6. Meninges • 3 layers of connective tissue membranes • Surround and protect brain and spinal cord Pia Mater Arachnoid Dura Mater

7. Peripheral Nervous System 31 pairs of spinal nerves 12 pairs of cranial nerves • Nerves that emerge from central nervous system:

8. Sympathetic Parasympathetic Autonomic Nervous System

9. Cellular Composition of CNS • Neurons and their processes • Support cells: Astrocytes Oligodendrocytes Ependymal cells Microglia

10. Astrocytes • In developing NS, form structural framework to guide migration of developing neurons • In developed NS, form • structural scaffolding for • more specialized neural • elements • Clear ECM of by-products • of neural activity and • contain glycogen reserves • Extend foot processes around • blood capillaries

11. Blood Brain Barrier • Capillaries of the CNS not fenestrated and have intercellular tight junctions between endothelial cells • Highly resistant to passage of ions or small molecules • Do not exhibit transendothelial transport in small vesicles • Astrocytes may influence capillaries to express these unique properties

12. Oligodendrocytes • Produce myelin within CNS • Each cell sends out several processes and myelinates several nearby axons

13. Ependymal Cells • Epithelial-like • Ciliated • Line cavities of brain ventricles and central canal of spinal cord forming sheets of cuboidal cells in contact with CSF

14. Microglia • Specialized macrophages • In areas of injury, proliferate and become actively phagocytic in clearing cellular debris and ingesting damaged myelin

15. Composition of PNS • Ganglia - a peripheral collection of nerve cell bodies together with efferent and afferent axons and support cells • Nerves - a collection of axons linked together by support tissue into an anatomically defined trunk

16. Ganglia • Sensory (spinal sensory ganglia) • Non-sensory (sympathetic or parasympathetic) • Dorsal root ganglia, cranial ganglia, autonomic ganglia • Neuron cell bodies, support cells, loose fibrocollagenous tissue

17. Nerves • Motor Innervate skeletal muscle (CNS) Innervate smooth muscle (PNS) • Sensory • Myelinated or Non-myelinated • Axons, Schwann cells, fibroblast cells, blood vessels

18. - 3 types of support tissue in a nerve trunk: • Endoneurium Surrounds individual axons, their associated Schwann cells, and capillary blood vessels • Perineurium Surrounds groups of axons and endoneurium to form fascicles • Epineurium binds individual nerve fascicles into a nerve trunk

19. Endoneurium Collagen fibers that are longitudinally oriented ECM rich in GAGs and sparse fibroblasts • Perineurium 7-8 concentric layers of epithelium-like flattened cells separated by layers of collagen and joined by junctional complexes Each layer of cells surrounded by an external lamina • Epineurium Outer sheath of loose fibrocollagenous tissue May also include adipose tissue and muscular artery that supplies the nerve trunk Epi Peri Fascicle Endo

20. Schwann Cells • PNS • Myelinate only one axon

21. Neurons • Gather information from sensory receptors • Process information and provide a memory • Generate appropriate signals to effector cells • Cell body, dendrites, axon, and synaptic bouton

22. Cell Body • Pale-staining • Conspicuous nucleolus • Little heterochromatin • Nissl bodies • Golgi complex • Mitochondria • Lysosomes • Neurofilaments • Microfilaments • Microtubules

23. Dendrites • Radiating processes of the cell body • Receive signals (synapses) from other neurons • Broader than axons • Extensive branching increases cell surface available for receiving signals from other neurons • Organelles similar to those of the perikaryon (no Golgi bodies) • As distance from cell body increases, smooth ER and NFs reduced but MTs and mitochondria still prominent

24. Axons • A single long process capable of generating a nerve impulse • More slender and usually longer than dendrites • Branch at right angles • Can be quite long (spinal motor neurons that supply foot muscles 40 inches in length) • Axon Hillock is conical extension of cell body from which axon arises • Axoplasm lacks Nissl bodies

25. Branches as it approaches its end forming small expansions • Terminal boutons contact other cells to form a synapse • At synapse, chemicals or electrical signals pass from one neuron to another cell known as the effector cell • Neurotransmitters act rapidly and locally to activate their target cells and neuromodulators that regulate these events

26. Neuron Shapes

27. Neuron Types

28. Myelin • Insulation minimizes leakage of current from membrane speeds up conduction along axons • Reduction of electrical capacitance wide axons lower capacitance than narrow ones increases diameter of axons increases speed of nerve conduction • Myelin-producing cells Oligodendrocytes (CNS) Schwann cells (PNS) • Nodes of Ranvier space between each unit of myelin increase efficiency of nerve conduction

29. Myelin

31. Synapses • Specialized region of contact where NT released from axon to stimulate another cell

33. Axonal Transport • Anterograde or retrograde • Fast or slow • Microtubules • Motor proteins • Ca2+ • ATP Minus end Plus end Kinesin Dynein