89. nerve tissue microscopic structure – practice 2013
TRANSCRIPT
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89. Nerve tissue
Microscopic structure – practice 2013
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Nerve tissue - morphology
cells : 1.neurons and 2.glial cells• extracellular material is extremely reduced replaced by
glial branched process• neuropil – high amount of synapses, dendrite´s
arborisation, non-myelinated axons• extensive vasculature with variable amount of
connective tissue both in CNS and PNS• blood-brain barrier in CNS
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Tissue microscopic structure: cells with processes – integrated communicating network
neuron theory – contact junctions among neurons
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N3 – cerebellum,HE
• NEURON is structural and functional unit of nerve tissue
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Nerve tissue microstructure (example 2 – brain )
Neuron
Glial c.
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Perikaryon (soma, cell body)receptor region, integration, trophic centre
• nucleus • large, lightly basophilic, with dispersed chromatin, prominent
nucleolus• RER
• abundant → substance of Nissl - tigroid• Golgi apparatus
• only in perikaryon!• cytoskeleton (neurofilaments)• mitochondria • inclusions
• lipofuscin, melanin
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Cytoskeleton
• Microtubules– axonal transport (anterograde, retrograde, microtubule-
associated motor proteins used ATP – dynein, kinesin) – shape regulation
• Neurofilaments (intermediate filaments in neurons)– resistance against deformations– regulatory process
• Microfilaments (aktin)
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Dendritesreceptor region
principal recieving site• arborisation (branching) increases receptive area of the cell (100 000 contacts and more)• dendritic spines (site of synapse - postsynaptic membrane,
actin microfilaments• neurofilaments (NF-L, NF-M, NF-H), other cytoskeleton units,
proteosynthetic apparatus except GA• always non- myelinated
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Axonconductive region
• transmit stimuli in the form of action potential to other neuron or effector cell
• 1 neuron has 1 axon• metabolically dependent on perikaryon• Golgi type I neurons – motor neurons of CNS with long
axon (up to 1 meter) terminate on skeletal muscle• Golgi type II neurons – short axons• axon hillock, initial segment – site of action potential
generation• axonal transport transport vesicles, mitochondria ,
proteins…by anterograde x growth factor, viruses..by retrograde
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Synapse effector region, unidirectional transmission of nerve impulse
presynaptic (axonal) terminal + postsynaptic (dendritic, somatic, axonal) membranesite of chemical message transmission in response to action potentialpresynaptic : synaptic vesicles with neurotransmitters, microtubules+kinesin,
mitochondriasynaptic cleft 40nmpostsynaptic membrane of effector cell: 1. nerve cell2. muscle cell3. secretory cell
axodendritic,axosomatic,axoaxonal, „en passant“
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Neurogliasupporting sell population for neurons
• provide neurons with structural support and maintain local condition for neuronal function
• forming 50% volume of CNS• 10 x more abundant than neurons
• histological staining• impregnation by Ag, Au salts, histochemical technics
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Glia - types
– in CNS 1. macroglia– astrocytes– oligodendrocytes– ependymal cells2. Microglia
- in PNS- Schwann cells- Satelite cells
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Neurons and neuroglia are cells with processes
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B45 Brain/CerebrumLFB, luxol fast blue, myelin staining
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B44 Brain/ Cerebrum (HE)
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Neuron, neuroglia, blood vessel
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N3 - cerebellum HE
• Purkyňova buňka• Granulární neuron
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B46 Small brain, cerebellum HE
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Spinal cord / cross section - B48
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B48 Spinal cord HE
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Ependym
• epitheloid arrangement of ependymal cells
• neural tube neuropithelium
remnant
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B49 Autonomic ganglion
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B50 Peripheral nerve
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Peripheral nerve
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Myelinated nerve fibres
Eg 13 - Myelinizovaný axon
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Myelinated nerve fibres
• in PNS: axons are invaginated into cytoplasm of enveloping Schwann cell (sheath is formed by layers of modified cell membranes) x in CNS: cell process of oligondrocytes form sheath
• nodes of Ranvier and internode, 1-2 mm
• Schmidt-Lanterman´s incisures
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Nerve fibres
• axons provided by special connective tissue capsules of ectodermal origin
• axons:– unmyelinated– myelinated
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Astrocytes (protoplasmic, fibrous)
• the largest of neuroglia• astrocytic end feet- connection to vessels
and neurons providing movement of wastes and metabolites to and from neuron
• regulate ionic concentration in intercellular space
• contribute to blood-brain barrier (together with tight junctions of endothelal
cells) mechanical support of neurons proliferation - glial scar glial fibrillary acidic protein
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Oligodendrocytes
• smaller, ↓intermediate fibres, darker nucleus
• formation of myelin sheath• myelinisation of several
axons
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Microglia
• the smallest, dark elongated nucleus
• they migrate to the sites of dead cells, proliferate, phagocytes (dead cells, cell debris…)
• mesoderm -derived
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Ependym
• epiteloid arrengement uspořádání– remnant of
neuroepithelium of neural tube* secretory elements
(cerebrospinal fluid)component of choroid plexus
of brain ventricles and central canal of spinal cord
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Unmyelinated nerve fibres
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N8 – Ganglion HE
Neuron
Satelite cells
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Arrangement of nerve tissue in the body, CNS and PNS
• CNS• clusters of neurons – cell
body: layers, columns (grey matter)
• bundles of axons: tracts, fasciculi, lemnisci (white matter)
• (grey and white matter differentiation: according to the content of myelin)
• PNS• clusters of neurons:
ganglia• bundles of axons: cranial spinal peripheral nerves