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					NERVOUS TISSUE
Nervous system; nervous tissue + connective tissue
 connective tissue;
     CNS; in meninges, choroid plexus,
          around the blood vessels
     PNS; connective tissue sheath;
                endoneurium; nerve fiber
                perineurium; bundle
                epineurium; nerve
          capsule of the ganglion
Nervous system;
 CNS; brain and spinal cord; white and gray matter
  PNS; nerve fibers and ganglia
Fig. 5-1. General functional organization of the central
          and peripheral nervous system
Fig. 5-2. Meningeal connective tissue
Fig. 5-3. Structure of peripheral nerve
Nervous tissue;
     cells
     intercellular substance(tissue fluid)



Cells; nerve cells(neuron), neuroglial cells
I. NEURON
reception, processing and transmission of stmuli
excitability(irritability) and conductivity
cell body(nucleus and perikaryon)
      and cell processes(axon and dendrite)
Fig. 5-4. General structure of neuron
1. Cell body
3-120 μm in diameter
triangle, round or ovoid in shape


A. Nucleus
central located large nucleus
euchromatin
    ***** vesicular N
large and prominent nucleolus; ribosomal RNA synthesis
    ***** owl’s eye
B. Perikaryon
       nissle body, Golgi complex, mitochondria,
       cytoskeleton, cytoplasmic inclusions

Nissle substance(nissle body)
   basophilic granular area; rER, polyribosme
   no nissle body in axon hillock and axoplasm
   degeneration; chromatolysis or nissle reaction
Golgi complex; perinuclear halo
Mitochondria; 0.1-0.8 μm, filamentous type, rich in axon terminal
Lysosome; hydrolytic enzyme
   primary lysosome, secondary lysosome,
   multivesicular body, lipofuscin pigment
Cytoskeleton; neurotubule, neurofilament, microfilament
  Neurotubule(microtubule); 24nm in diameter
       material transportation especially in axoplasm
       microtubule associated proteins(MAPs)
                MAP-1
                MAP-2; not in axon
                tau MAP(MAP-3); only in axon
       kinesin; microtubule-activated ATPase; anterograde transport
       dynein; retrograde transport
       colchicine, vinblastin
  neurofilament; 10nm in diameter
       neurofibrils; 2 μm in diameter
       marker substance for neuron
  microfilament
       actin filament; attached to plasmalemma by fodrin
Cell inclusions
  lipofuscin granule; brownish-yellow
         undigested materials by lysosome
  melanin granule; in catecholaminergic neuron from Dopa
  lipid droplet
  glycogen granule; mainly in embryo
Fig. 5-5. Ultrastructure of neuron
Fig. 5-6. Motor neuron of spinal cord.
Pararosaniline-toluidine blue(PT) stain
Fig. 5-7. Motor neurons of spinal cord
          Toluidine blue stain
Fig. 5-8. Neuronal cell body
2. Processes
    ****neuropils; aggregated neuronal cell processes

A. Dendrite
    one or more per cell


B. Axon
    axoplasm, axolemma
    axon hilock
    initial segment
    myelinated and unmyelinated axon
    terminal arborization
    end bulb or boutons
 Table 1. Differences between the axon and the dendrite

     Characteristics                           Axon                    Dendrite
          Quality                One or no axon                 One or more
          Length                 Short(200μm) to long(1m)       Shorter than 700μm
          Diameter               Somewhat uniform diameter      Become thinner
          Branch       Angle     Right angle                    Acute angle
          ing          Point     Distal to cell body            Proximal to cell body

Morpho Nissle body               Non in axon hillock and        In main trunk or
logical                          axoplasm                       proximal dendrite
        Golgi body               Existence                      No existence
          Dendritic spine        No existence                   Existence
          Myeline                Myelinated or unmyelinated     Unmyelinated
                       Golgi     Only with rapid Golgi method   With any Golgi methods
          Staining     Reduced   More argyrophilic              Less argyrophilic
                       silver
Bioche    MAPs                   tau-MAP                        MAP-2
mical
Functio   Functional             Efferent                       Afferent
nal
Fig. 5-9. Neuronal cell processes
D. Synapse

transmission of nerve impulse between two adjacent nerve cells
electrical synapse; by gap junction
   bidirectional transmission
   a few in mammals
chemical synapse; with neurotransmitter
   unidirectional transmission
   presynaptic portion, synaptic cleft(20-30nm), postsynaptic portion
presynaptic portion; mainly axon terminal(bouton terminaux)
   synaptic vesicle; neurotransmitter; acetylcholine, norepinephrine
   mitochondria
axodendritic, axosomatic, axoaxonic, dendrodendritic, somatodendritic,
   somatosomatic
secretion of neurotransmitter
  nerve impulse on presynaptic membrane
  → calcium channel open
  → Ca+ influx
  → Ca+ + calmodulin of vesicular membrane
  → activation of Ca+/calmodulin dependant protein kinase
  → phosphorylation of synapsin
  → fusion of vesicular membrane and axolemma
  → exocytosis
  → receptor for neurotransmitter of postsynaptic membrane
  → depolarization
Fig. 5-10. Axon terminal
Fig. 5-11. Adrenergic nerve ending
Fig. 5-12. Ultrastructure of synapse
Fig. 5-13. Amino acid sequence of some neuropeptides
Fig. 5-14. Types of synapse
Fig. 5-15. Sequence of events during synaptic communication
E. Neuromuscular junction(motor end plate)
F. Axoplasmic transport(Axoplasmic flow, Axonal transport)
anterograde transport(orthograde transport)
   fast transport; 20-400mm/day
         vesicle(neurotransmitter, enzyme),
         mitochondria(50-100mm/day)
   slow transport; 0.1-6mm/day
         cytoskeletal protein; tubulin, neurofilament protein, actin
         plasmalemma or cytoplasmic protein;
                 clathrin, spectrin, calmodulin
         slow component a(SCa); 0.1-1mm/day
                 tubulin, neurofilament protein
         slow component b(SCb); 2-6mm/day
                 clathrin, spectrin, calmodulin, actin
retrograde transport; 100-200mm/day
   old vesicle, mitochondria, NGF, HRP, toxins, virus
kinesin, dynein
3. Classification
A. by number of processes
uipolar neuron
      no found in mammals
      found in invertebrate animals
pseudounipolar neuron
      T-shape; fuse the peripheral(axon) and the central(dendrite) processes
      in spinal ganglia and cranial ganglia
bipolar neuron
      axon and dendrite
      spiral and vestibular ganglion in inner ear, retina, olfactory epithelium
multipolar neuron
      most neurons of the body

B. by length of axon
Golgi type I neuron; multipolar neuron has a long axon
      projection neuron
Golgi type II neuron; multipolar neuron has a short axon
      interneuron

C. by function
motor neuron
sensory neuron
interneuron
Fig. 5-16. 3 main types of neurons
Fig. 5-17. Types of neurons
II. Neuroglial cells
    10 times of neuron
    mitotic activity
1. Central neuroglia
  neuroectodermal origin;
   astrocyte
   oligodendrocyte
   ependymal cell
  mesodermal origin
   microglia
Fig. 5-18. Neuroglial cells in CNS
Fig. 5-19. Nueroglial distribution in brain
A. Astrocyte
two types
     protoplasmic astrocyte; in gray mater
          thick and short several branching processes
     fibrous astrocyte; in white mater
          a few long processes
ovoid nucleus; dotted heterochromatin(potato shape)
a few lysosome, mitochondria, Golgi body, glycogen
rare rER and ribosome
8-nm intermediate filament; glial fibrillary acidic protein(GFAP)
Internal glial limiting membrane;
     perivascular feet(vascular end feet), gap junction
external glial limiting membrane ;
     forms layer between pia mater and neural elements
blood brain barrier;
     mainly with occluding junction between adjacent endothelial cells
function;
   structural function
   control the chemical and ionic environment
   medium for neuronal movement
   proliferates to form cellular scar tissue
   astrocyte in vitro;
         GABA receptor, angiotensin II receptor,
         natriuretic peptide receptor, VIP receptor,
         TRH receptor, adrenaline receptor
         ability to respond to several stimuli
   release metabolic and neuroactive molecules;
         angiotensinogen family
         vasoactive endothelins
         enkephalin
         somatostatin
   release some cytokine;
         effects to the myeline turnover of oligodendrocytes
specialized astrocytes;
  Muller cells in retina
  pituicytes in neurohypophysis
staining methods for processes;
  silver nitrate
  gold chloride
  mercury chloride
Fig. 5-20. Protoplasmic astrocyte
Fig. 5-21. Fibrous astrocytes
Fig. 5-22. Blood-brain barrier and astrocytes
B. Oligodendrocytes
a few and non branching processes
myeline formation
round and dense nucleus; smaller than the nucleus of astrocyte
moderately developed rER, free ribosome, Golgi body,
       mitochondria, microtubule
del Rio Hortega's stain method
Fig. 5-23. Myelin sheath of CNS and oligodendrocyte
C. Microglia
mesodermal origin
small and elongated nucleus; dense chromatin
MPS cell, antigen presenting cell
release immunoregulatory cytokines

D. Ependymal cell
simple cuboidal or columnar epithelium
some cilia and well developed microvilli
no basement membrane, no occluding junction

special typed ependymal cells;
  tanycyte; has long basal process
  choroid epithelial cells
        basement membrane, basal infolding(mitochondria)
        occluding junction
        CSF formation
Fig. 5-24. Microglial cells in gray mater of brain
            H-E stain
Fig. 5-25. Spinal cord gray mater. H-E stain
Fig. 5-26. Central canal of spinal cord.
           Toluidine blue stain
Fig. 5-27. Ependymal cells
2. Peripheral neuroglia
A. Schwann cell
myeline formation
Ranvier node
internodal segment
heterochromatic elipsoidal nucleus
mitochondria, Golgi body, lysosome, free ribosome
mesaxon; inner and outer


B. Satellite cell(capsular cell)

surround the pseudounipolar neurons in spinal and cranial ganglia
flattened cells have heterochromatic nucleus
in cytoplasm; a few Golgi body, lysosome, free ribosome
one of Schwann cell
III. Myeline sheath
sheath cell(neurilemma cell); oligodendrocyte and Schwann cell
inner and outer mesaxon
lipoprotein; OsO4, luxol fast blue
major dense line; fusion between two inner layers
    by myeline basic protein(MBP)
intraperiod line; fusion between adjacent two outer layers
    by proteolipid protein; in oligodendrocyte
   by protein zero(P0); in Schwann cell
myeline associated glycoprotein(MAG);
   induce the fusion of axon and the Schwann cell for myeline formation
Schmidt-Lantermann cleft
insulating area; saltatory conduction
conduction velocity;
   unmyelinated nerve; 0.6-2m/sec
   myelinated nerve; 1-100m/sec
Table 2. Classification of nerve fiber from its diameter and conduction velocity

Groups            Diameter     Velocity    Examples
                  (μm)         (m/sec)
Aα   Group I      12-20        70-120      α-motor nerve
                                           neuromuscular spindle
                                           Golgi tendon organ
Aβ   Group II     5-12         30-70       neuromuscular spindle
                                           encapsulated nerve endings

Aϒ                3-6          15-30       ϒ-motor nerve

Aδ   Group III    2-5          12-30       temperature and pain receptor
                                           (relatively thick diameter)

B                  <3          3-15        preganglionic fiber

                                           visceral afferent fiber

C    Group IV     0.1-1.5      0.5-2       temperature and pain receptor
                                           (relatively thin unmyelinated fiber)
                                           postganglionic fiber
Fig. 5-28. Cross section of peripheral nerve.
           Toluidine blue stain
Fig. 5-29. Longitudinal section of peripheral nerve
Fig. 5-30. Consequence of myelination
Fig. 5-31. Myelinated nerve fiber
Fig. 5-32. Myelinated peripheral nerve fiber
Fig. 5-33. Unmyelinated nerve fiber
Fig. 5-34. Unmyelinated axon
Fig. 5-35. Connective tissue surround the nerve fibers
Fig. 5-36. Cross section of thick nerve. PT stain
Fig. 5-37. Cross section of small nerves. PT stain
IV. Degeneration and regeneration of
     nervous system
peripheral nerve injury; able to regeneration
central nerve injury; unable to regeneration
transneuronal degeneration
transsection of nerve axon;
  distal region; Wallerian degeneration
  proximal region; axon reaction
1. Wallerian degeneration

degenerative change(axonal degeneration)
    axon; swelling and fragmentation(after 3-5 days)
           → phagocytosis by Schwann cell and macrophage
    myeline sheath; wide the Schmidt-Lantermann cleft(after 1-2 days)
           → destruction and shrinking of myeline sheath
           → fragmentation
           → disappear of lamellar structure and convert to the lipid droplet
           → phagocytosis by Schwann cell and macrophage
Bunger's band;
    formed by proliferation of Schwann cells
    fill the injury region
    induce the axonal growth
axon sprouts; promotion by NGF(secreted by Schwann cell and macrophage)
***** neuroma
2. Axon reaction
Chromatolysis
  migration of the nucleus to the peripheral portion
  decrease in cytoplasmic basophilia;
       dissolution of Nissle substance
  increase in volume of perikaryon
Fig. 5-38. Main changes that take place in an injured nerve fiber
X. Research methods in neuroanatomy
1.   General staining methods
2.   Immunocytochemistry
3.   In situ hybridization
4.   Tract tracing method
      A. Using retrograde tracing method
        HRP, WGA(wheat-germ agglutinin)
      B. Using anterograde tracing method
        Marchi method
        Nauta method
        autoradiographic study
        using anterograde materials(eg, lectin)
   Table 3. General staining methods
Staining methods   Reagents                    Observable substance

H-E                Hematoxyline                nucleus of neuron and glial cells.
                                               cytoplasm of neurons, blood and
                   Eosine                      lymphatic vessels

Nissle             Basic aniline dye           neuronal cell body, especially Nissle
                                               substance, nucleus of neuroglial
                   (cresyl violet, methylene   cells, blood and lymphatic vessels,
                                               connective tissue
                   blue)
Myeline            OsO4, luxol fast blue,      myeline

                   Potassium dichromate,
                   hematoxyline
Reduced silver     Silver nitrate              neurofibrils


Golgi’s silver     Silver nitrate, mercury     neuronal cell body and
                                               processes(10% of neurons),
                   chloride                    neuroglial cells, some blood vessels

Ramon y Cajal      Gold chloride, mercury      astrocyte

                   chloride
Rio Hortega’s      Silver carbonate            neuroglial cells(according to
                                               modifications)

				
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