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Nervous tissue 1


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Nervous tissue 1

  1. 1. Nervous tissue
  2. 2. Morphology examples
  3. 3.  Conducts electrical impulses (signals) to the CNS & transmits impulses from the CNS to various structures of the body  Conveys information from one area to another Neural tissue
  4. 4. Morphogenesis of the neural tissue includes:  Proliferation;  Determination & differentiation;  Address migration of cells;  Address growth of processes of neurons;  Formation of intercellular junctions - synapses;  Apoptosis.
  5. 5. Neurulation
  6. 6. Cells in the neural tube
  7. 7. Ependymal (inner) layer Cambial cells Ependymal cells Mantle layer Neuroblasts Glioblasts Neurons Astrocytes Oligodendrogliocytes Marginal layer White matter of CNS organs
  8. 8. Gray matter (cell bodies) White matter (myelinated axons)
  9. 9. Neural tube • CNS (brain &spinal cord) Retina of the eye Olfactory organ Neural crest • Neural ganglia (spinal &cranial; autonomic) • Neurolemmocytes Adrenal medulla Diffuse endocrine cells Pigmental cells Cells of arachnoid & pia mater Placodes • Sensoepithelial cells of organ of Corti & equilibrium Receptor cells of taste organ Epithelium of lens
  10. 10.  Neurons Generate &Transmit nerve impulses  Neuroglia Support neural tissue Help supply nutrients to neurons Protect neurons Form barriers Neural tissue cells
  11. 11. Morphological classification of neurons - based on number of processes found on cell body  Unipolar  Bipolar  Multipolar  Pseudounipolar
  12. 12. Unipolar neurons  Have only one axon  Rare
  13. 13. Pseudounipolar neurons  Have a single process that extends from the cell body & subsequently branches into an axon & dendrite  Sensory neurons – located mainly in spinal & cranial ganglia
  14. 14. Bipolar neurons  2 processes. Have a single dendrite and an axon  Are present in some sense organs: retina, spiral ganglion.
  15. 15. Multipolar neurons  >2 processes. Have two or more dendrites and one axon  Most common type of neuron. >99% of neurons
  16. 16. Functional classification of neurons  motor neurons - efferent (conduct impulses from CNS to other neurons, muscles or glands);  sensory neurons - afferent (receive stimuli from the internal & external environment). Conduct nerve impulses to the CNS.  interneurons act as connectors of neurons in chain. They most commonly connect sensory & motor neurons.  secretory neurons - neurons of hypothalamus: supraoptic & paraventricular nuclei – neurons produce hormones: vasopressin & oxytocin); - all neurons produce neurotransmitters of synapses.
  17. 17. Nervous Tissue
  18. 18. Sensory – interneuron – motor neuron
  19. 19. Neurons  Functional unit of nervous system  Special neuronal characteristics Convey APs (excitable) Longevity Do not divide High metabolic rate
  20. 20. Neuron structure  Cell membrane with Na+-K+ pumps, that maintain the necessary ion gradients.  Nucleus with one prominent nucleolus (“owl-eye” nucleus)  Cytoplasm with various cytoplasmic organelles & inclusions, & cytoskeletal components
  21. 21. Neuron has  Cell body (perikaryon, soma)  Processes:  Only one axon  One & more dendrites
  22. 22. Nucleus with Nucleolus Parts of a Neuron Axons or Dendrites Cell body Neuroglial cells
  23. 23. Neuron structure Cell body (perikaryon or soma)  single nucleus with prominent nucleolus  Nissl bodies (chromatophilic substance) are stained basophilic  rough ER & free ribosomes (polysomes) for protein synthesis  Golgi complex  Mitochondria  Lysosomes
  24. 24. Microtubules (neurotubules) move material inside cell Neurofilaments (specific type of intermediate filaments) give cell shape and support Microfilaments (actin) associated with the cell membrane Neurofilaments & neurotubules form neurofibrils – is artefact. Neurofibrils appear at time of slide preparing & can be distinguish inside of neurons Lipofuscin pigment clumps (harmless aging) Lipid inclusions  Cell processes = dendrites & axon
  25. 25. Perikaryon or soma Cell body is location for most protein synthesis neurotransmitters & repair proteins
  26. 26. Dendrites  Conduct impulses towards the cell body  Typically short, highly branched  Surfaces specialized for contact with other neurons (spines) – increase the area useful for synapse formation  Have arborized terminals – permit a neuron to receive stimuli at the same time from many other neurons  Contains neurofibrils & Nissl bodies
  27. 27. Axon Conducts impulses away from cell body  Long, thin cylindrical process of cell  Arises at axon hillock – a region of the soma that lacks rER & ribosomes but contains many neurotubules & neurofilaments  May has collaterals (branching at right angles from the main trunk)  Axon terminals (many small branches from which impulses are passed to another neuron or other type of cell)  Swollen tips called synaptic
  28. 28. Transport  Dendritic – the movement of substances & organelles through the dindrites  Axonal - the movement of substances & organelles through the axon
  29. 29. Axonal Transport  Axonal transport system moves substances slow axonal flow  movement in one direction only -- away from cell body  movement at 1-5 mm per day fast axonal flow  transports in either direction  at 100-500 mm per day  moves organelles & materials along surface of microtubules  for use or for recycling in cell body •Anterograde transport – carries material away from the soma •Retrograde transport – carries material toward the soma for reutilization, recycling, or degradation
  30. 30. Neuroglia Macroglia  Astrocytes  Oligodendrocytes  Ependymal cells Microglia  Neuroglia of CNS: astrocytes, oligodendrocytes, ependymal cells, microglia Neuroglia of PNS: neurolemmocytes (Schwann cell), satellite cells
  31. 31. Neuron and Neuroglia
  32. 32. CNS Neuroglia  Astrocytes  protoplasmic (CNS gray matter)  fibrous (CNS white matter) Function: 1. scavenge ion & debris (wastes) from neuron metabolism & supply energy for metabolism. 2. Provide structural support for nervous tissue 3. Form a protective barrier between pia mater & the nervous tissue of the brain & spinal cord 4. Form scar tissue after injury to the CNS
  33. 33. Neuroglia of CNS  Astrocytes  Promote tight junctions to form blood-brain barrier 1. Endothelium of the capillary (between endothelial cells there are tight junctions) 2. basement membrane of endothelium 3. perivascular membrane – is formed by foot processes of astrocytes
  34. 34. Blood-brain barrier 1 – endothelium; 2- basement membrane; 3 – astrocyte’s body, 4 – foot processes of astrocyte; 5 – neuron, 6 – neuron’s processes; 7- oligodendroglial cell
  35. 35. Neuroglia of CNS  Ependymal Cells  Line ventricles of the brain, spinal cord central canal, choroid plexus  Secrete & move liquor  Form blood-liquor barrier: 1. Endothelium of capillary 2. Basement membrane of endothelium 3. Loose connective tissue 4. Basement membrane of ependymal cells 5. Ependymal cells
  36. 36. Oligodendrocytes  Produce the myelin sheath which provides the electrical insulation for certain neurons in the CNS Neuroglia of CNS
  37. 37. Neuroglia of CNS  Microglia Specialized macrophages Ag-presentation Has mesenchymal origin
  38. 38. Supporting cells in the PNS  Satellite cells  Schwann cells / neurolemmocytes
  39. 39. Neuroglia of PNS  Schwann cells or neurolemmocytes  Wrap around portion of only one axon to form myelin sheath  Satellite cells are flattened cells  Surround neuron cell bodies in ganglia, provide support and nutrients
  40. 40. Satellite Cells
  41. 41. The End
  42. 42. Nerve fibers  Myelinated fibers  Unmyelinated fibers
  43. 43. Unmyelinated Myelinated Localization Mostly in the autonomic NS In the CNS and PNS Speed of the conduction of the nerve impulse low (0,5-2 m/s) High (5-120 m/s) Nerve fiber of the cable type (cytoplasm of the Schwann cell can contains 10-20 axons of different neurons) Nerve fiber contains only 1 axon. But in tne CNS 1 oligodendrocyte can takes part in the process of myelinization until 40-50 nerve fibers. Structural components 1.axon (many axons) 2.cytoplasm of the Schwann cell + mesaxon (mesaxons) 3.basement membrane 1.axon 2.myelin sheath with Schmidt- Lanterman clefts and node of Ranvier. 3.cytoplasm and nucleus of the Schwann cell. 4.basement membrane. Conduction of the nerve impulse is continuous. Conduction of the nerve impulse is salutatory (from the node to node of Ranvier – nerve impulse jumps)
  44. 44. Myelinated and Unmyelinated Axons
  45. 45. Unmyelinated nerve fibers
  46. 46.  Axons surrounded by a lipid & protein covering (myelin sheath) produced by Schwann cells.  Myelin sheath is composed of multiple layers of Schwann cell membrane wrapped concentrically around the axon.  The myelin sheath is segmented because it is formed by numerous Schwann cells.  The junctions where two adjacent Schwann cells meet is devoid of myelin.  gaps called nodes of Ranvier  Areas of incomplete fusion of the Schwann cell membrane occur, & small amounts of Schwann cell cytoplasm are trapped between the membranes – Schmidt-Lanterman clefts (defects in the myelin formation) Myelinated nerve fiber
  47. 47. Schmidt- Lanterman clefts
  48. 48. Myelin sheath
  49. 49. Myelination in the CNS Myelin sheaths are formed by oligodendrocytes
  50. 50. Myelination in the PNS Myelin sheaths are formed by Schwann cell
  51. 51. Myelin Sheath  Whitish, fatty (protein-lipid), segmented sheath around most long axons  It functions in: Protection of the axon Electrically insulating fibers from one another Increasing the speed of nerve impulse transmission
  52. 52. Myelin Sheaths
  53. 53. Nodes of Ranvier  Gaps in the myelin sheath between adjacent Schwann cells  They are the sites where collaterals can arise
  54. 54. Nodes of Ranvier
  55. 55. Conduction of nerve impulse A – in the unmyelinated nerve fiber (continuous) B – in the myelinated nerve fiber (salutatory)
  56. 56. Nerve endings Functionally they can be divided into 3 groups:  synapses – provide the connection between neurons;  efferent (motor) endings – transmit signals from the NS to the working organs (muscles, glands); are present on the axons.  receptor (sensitive) endings – receive the irritation from the external environment and from the internal organs; are present on the dendrites.
  57. 57. Electrical In mammals are rarely present. They are as nexus – provide the passive transport of the electric current through the cleft from the cell to other in the both directions and without delay. Chemical Mostly distributed. The conduction of the nerve impulse is determined by the special substance - neurotransmitters. The conduction of the nerve impulse is only in the one direction and with delay. The are divided into: Axodendritic, occurs between axons and dendrites Axosomatic, occurs between axons and the cell body Axoaxonic, occurs between axons and axons Dendrodendritic, occurs between dendrites and dendrites. Synapses are divided into:
  58. 58. Synapses  Presynaptic neuron  Postsynaptic neuron
  59. 59. Synapses  Axodendritic synapses  Axosomatic synapses  Axoaxonic synapses  Dendrodendritic synapses
  60. 60. Synapse structure  Presynaptic element Axon terminal Synaptic vesicles Neurotransmitters Mitochondria  Synaptic cleft  Postsynaptic elements NT receptors May generate AP
  61. 61. Synaptic Transmission  An AP reaches the axon terminal of the presynaptic cell and causes V-gated Ca2+ channels to open.  Ca2+ rushes in, binds to regulatory proteins & initiates NT exocytosis.  NTs diffuse across the synaptic cleft and then bind to receptors on the postsynaptic membrane and initiate some sort of response on the postsynaptic cell.
  62. 62. Efferent nerve endings Motor Are present in the striated and smooth muscles. By structure they are like synapses, but there are some features: nearly to the muscle fiber the axon loses the myelin sheath and gives some small branches. They are covered by the Schwann cells and basement membrane. The transmission of the excitation is provided by the neurotransmitter - acetylcholine. Secretory Are present in the glands Can make next influences: - hydrokinetic (mobilization of the water); - proteokinetic (secretion of the proteins); - synthetic (to increase the synthesis); - trophic (to maintain the normal structure and function).
  63. 63.  Motor unit  One neuron  Muscle cells stimulated by that neuron • Neuromuscular junctions – association site of nerve and muscle
  64. 64. Receptor nerve endings  exteroreceptors (receive the signals from the external environment). They are: visual, auditory, olfactory, taste, tactile receptors.  interoreceptors. They are divided into visceroreceptors – receive signals from the inner organs; and proprioreceptors – receptors of the locomotor system.
  65. 65. Physiological classification of the receptor nerve endings  mechanoreceptors (pressure, vibration)  chemoreceptors (taste, smell)  thermoreceptors (cold, warm)  pain receptors
  66. 66. Morphological classification Receptor nerve endings Free(simple) They are consists of terminal branches of the dendrites of the sensory neuron. They provide the perception of the pain, cold, warm, tactile signals. They are present inside of the epithelium and in the loose connective tissue, which is located beneath. It is consists of only of the dendrite. Restricted (compound) Encapsulated They are surrounded by the connective tissue capsule. Structure: branches of the dendrite surrounding Schwann cells connective tissue capsule. Examples: Vater-Pacini corpuscles Meissner’s tactile corpuscles Ruffini’s curpuscles Bulb of Krause Neuromuscular spindles Tendon organ of Golgi Unencapsulated They are consist of the branches of the dendrites that are surrounded by the Schwann cells. They are present in the dermis of the skin and in the lamina propria of the tunica mucosa.
  67. 67. Free nerve endings (pain, temperature, light touch) Merkel endings (touch) Pacinian corpuscle (vibration, deep pressure) Krause’s end bulb (touch) Meissner’s corpuscle (touch) Ruffini’s corpuscle (stretch) (Fibroblasts, collagen, fluid) (Collagen fibers) Receptor nerve endings
  68. 68. Free nerve endings
  69. 69. Meissner corpuscle
  70. 70. Vater-Pacini corpuscle
  71. 71. Pacinian corpuscle
  72. 72. Neuromuscular spindle
  73. 73. Vater-Pacini corpuscles – are present on the connective tissue of the skin and inner organs. They are responsible for the sensation of the pressure and vibration. Meissner’s tactile corpuscles - are located in the papillary layer of the dermis in skin, mostly: tips of fingers, lips, nipple and area which is around. Ruffini’s curpuscles – are located in the connective tissue of the skin and in the capsules of the articulations. Take in pressure. Bulb of Krause – is present in the papillary layer of the dermis, lamina propria of the tunica mucosa in the oral cavity. It is mechanoreceptor. Neuromuscular spindle – receptors of the sprain of the muscle fibers. It has motor and sensory innervations. Tendon organ of Golgi – receptor of the sprain. It is located in the places where the skeletal muscle fibers join to the tendon.
  74. 74. Good bye! ☻