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Histology of Nervous Tissue

Histology of Nervous Tissue. Cells of nervous tissue. Neurons and supporting cells. Neurons Functional units of the nervous system - relay sensory (afferent) stimuli from the internal and external environments - process, store and integrate information

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Histology of Nervous Tissue

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  1. HistologyofNervous Tissue

  2. Cells of nervous tissue Neurons and supporting cells • Neurons • Functional units of the nervous system • - relay sensory (afferent) stimuli from the internal and external environments • - process, store and integrate information • - transmit information to other neurons, muscles and glands • Composed of a cell body, dendrites, axon and its terminal • arborization and synapses • Form complex and highly integrated circuits

  3. Astrocyte Supportive cells Highly outnumber neurons CNS: Astrocytes Structural support Metabolic support Homeostasis Oligodendrocytes Insulation (myelin sheath) Microglia Phagocytosis Immunomodulation Ependymal cells PNS: Schwann cells Myelin Oligodendrocyte Microglia

  4. Functional compartments of the neuron Cell body Dendrites Axon Synapses

  5. Functional compartments of the neuron Cell body Dendrites Axon Synapses

  6. Functional compartments of the neuron Cell body Dendrites Axon Synapses

  7. Functional compartments of the neuron Cell body Dendrites Axon Synapses

  8. Cell body (Soma, Perikaryon) Nucleus

  9. Neuronal Cytoskeleton Neuro- filaments Neurofilaments (8-10 nm) Microtubules (20-25 nm) • Gives shape and support for the cell • (Neurofilaments) • Facilitates intracellular transport • (Microtubules) SER Microtubules Cross section Microtubules Neurofilaments Longitudinal section

  10. Nissl bodies RER + polysomes Nissl RER Polysomes

  11. Dendrites Form majority of receptive field Usually multiple and branched at acute angles May possess spines Transmit toward cell body (receptor potentials, graded) Organelles (similar to cell body)

  12. Dendritic spines

  13. Dendrites Form majority of receptive field Usually multiple and branched at acute angles May possess spines Transmit toward cell body (receptor potentials, graded) Organelles (similar to cell body)

  14. Axon Usually singular Smaller caliber and often longer than dendrites Right angle branching Organelles Lacks Nissl High cytoskeleton content Originates at the axon hillock Transmits action potentials away from cell body Neurons Muscles and glands Terminal arborization Terminal buton Pre-synaptic element Initial segment of the axon

  15. Comparison of axon and dendrite

  16. Chemical synapses

  17. Chemical synapses

  18. Classified according to post-synaptic structure Dendrite (Axodendritic) Cell body (Axosomatic) Axon (Axoaxonic) Muscle cell (neuromuscular junction)

  19. Chemical synapses Pre-synaptic terminal (buton) Neurotransmitter (synaptic) vesicles Mitochondria Synaptic cleft Post-synaptic cell with postsynaptic density Terminal buton Synaptic vesicles Active zone on presynaptic membrane Transmitter release Synaptic cleft Post synaptic density Postsynaptic density Dendritic spine

  20. Classification of neurons By shape and function Multipolar Most numerous and heterogeneous group Efferent or association Pseudounipolar Sensory (afferent) Bipolar Sensory, organs of special sense Developmental stage for all neurons

  21. Motor (efferent) Association Types of neurons Sensory (afferent) Pseudounipolar Multipolar Bipolar Pseudounipolar

  22. Segregation of axons and cell bodies in the nervous system In both CNS and PNS cell bodies are found in clusters and neuron processes travel in bundles. Such groupings are based on common function and/or common connections. CNS Gray matter - composed primarily of neuron cell bodies and supporting cells Cortex - neuronal cell bodies arranged in layers covering the outer layers of the brain, e.g., the cerebrum and cerebellum Nucleus - group of neuron cell bodies in the interior of the CNS White matter - regions of CNS rich in myelinated axons Appears white in fresh tissue due to presence of lipid-rich myelin Composed of tracts - bundles of axons that course together G G W W W G G W

  23. Segregation of axons and cell bodies in the nervous system PNS Ganglia (singular = ganglion) - groups of cell bodies with a similar function Nerves (both cranial and spinal nerves) - bundles of axons coursing together Nerve Ganglion

  24. (Multipolar) (Pseudounipolar) (Multipolar) Reflex arc

  25. Supporting Cells • CNS • Astrocytes • Oligodendrocytes • Ependymal cells • Microglia • PNS • Schwann cells Neuroglial cells (neural ectoderm)

  26. Astrocytes • Stellate morphology • Fibrous • Protoplasmic • Functions • Physical support • Nutritional support • Ion homeostasis • Transmitter uptake • Scar formation • Immune function Cell of origin for some brain tumors (astrocytomas)

  27. Fibrous Cap Perivascular end foot Cap Protoplasmic

  28. Oligodendrocytes • Interfascicular and satellite • Interfascicular oligodendrocytes form the myelin sheath in the CNS Interfascicular Satellite

  29. Ependymal cells Line the ventricles and central canal of brain and spinal cord Cilia Microglial cells "Brain macrophages“ Derived from mesoderm

  30. Schwann cells Satellite Schwann cells Surround cell bodies Ensheathing Schwann cells Surround axons

  31. Myelinsheath • Segmental, multilamellar, lipid-rich wrapping of axons formed by the plasma membranes of: - Oligodendrocytes in CNS (interfascicular) - Schwann cells in PNS • Functions to increase speed of conduction (saltatory conduction) by insulating the axon

  32. Internode Myelin sheath Node of Ranvier Internode: Single myelin segment Node of Ranvier: Specialized region of the axon between internodes, rich in sodium channels; site where depolarization occurs

  33. Myelin Myelin Axon Axon Cross section of a myelinated axon

  34. Myelinsheath CNS PNS • Oligodendrocytes in CNS Multiple internodes per cell Multiple axons per cell • Schwann cells in PNS One internode per cell One axon per cell Schwann cells Oligodendrocyte

  35. Myelination in the PNS – Schwann cells

  36. Unmyelinated axons Schwann cell nucleus

  37. Myelination in the CNS - Oligodendrocytes

  38. Connective tissues in the peripheral and central nervous systems

  39. Peripheral nervous system Endoneurium Perineurium Epineurium Ep P En

  40. Central nervous system Meninges (meningitis) Dura mater Arachnoid membrane Pia mater

  41. Dura mater Arachnoid membrane Pia mater Brain Dura mater Arachnoid membrane Pia mater Brain Blood vessel

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