88. nerve tissue enables the body to respond to changes in its external and internal stimuli = ...
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Synaptic signalisationTRANSCRIPT
88. Nerve tissue
enables the body to respond to changes in its external and internal stimuli
= > Nervous system regulates the function of internal organs (+ endocrine and immune system )
Regulatory systems
Nervous system Endocrine system Immune system
CytokinesHormonesNeurotransmitters
Synaptic signalisation
Nerve tissue - overview• neurons are excitable cells that use the combination of electrical
(membrane depolarisation) and chemical (synapse) signalling • integrated communicating network composed from the cells with
processes• anatomically: central and peripheral nervous system (CNS and
PNS)• embryonic origin: neuroectoderm (microglia – mesenchyme!)• regeneration: neurons in vivo in general do not divide in general x
glial scar• in vitro / in experiments can neurons differentiate into neurons
Neurons (nerve cells) a neuroglia (supporting cell population)
Beta III tubulin and glial fibrilar acidic protein
central and peripheral NSgrey and white matter (2 types of nerve tissue)
white matter– myelinated axons + neuroglia
grey matter– perikarya, dendrites, axons, neuroglia
Tissue microscopic structure: cells with processes – integrated communicating network
neuron theory – contact junctions among neurons
neurons - synapse
neuroglia - gap-junction
N3 - Mozeček HE
• NEURON is structural and functional unit of nerve tissue
Neurons and neuroglia are cells with processes
2 multipolar neurons connected synaptically
biomedicalengineering.yolasite.com
Nerve tissue - morphology
cells : 1.neurons and 2.glial cells• extracellular material is extremely reduced replaced by
glial branched process• neurons receive stimuli and conduct nerve impulse via
their processes • action potential transmission to the next cell through
synapses (= intercellular contacts)• extensive vasculature with variable amount of connective
tissue both in CNS and PNS• blood-brain barrier in CNS
Perikaryon (soma, cell body)receptor region, integration, trophic centre
• nucleus • large, lightly basophilic, with dispersed chromatin, prominent
nucleolus• RER
• abundant → substance of Nissl - basophilic• Golgi apparatus
• only in perikaryon!• cytoskeleton (neurofilaments)• mitochondria • inclusions
• lipofuscin, melanin
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)
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
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
Synapse effector region, unidirectional transmission of nerve impulse
presynaptic (axonal) terminal postsynaptic membrane (dendritic, somatic, axonal) synaptic cleft 20 nmpresynaptic cytoplasm : synaptic vesicles with neurotransmitters, microtubules+kinesin,
mitochondriapostsynaptic membrane of effector cell: 1. nerve cell2. muscle cell3. secretory cell
axodendritic,axosomatic,axoaxonal, „en passant“
synaptic cleft
Synaptic transmission
• action potential opens calcium channels in presynaptic membrane
→ Ca2 influx triggers exocytosis of synaptic vesicles into synaptic cleft
→ reaction with receptors of postsynaptic membrane promotes depolarisation (excitatory s., neurotransmitters: acetylcholine, glutamine,serotonine) or hyperpolarisation (inhibitory s., neurotransmitters: GABA--aminobutyric acid, glycine)
Synapses thus can excite or inhibit impulse transmission.
Neuroglia“connective tissue“ of CNS
• 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
Glia - types
– in CNS 1. macroglia– astrocytes– oligodendrocytes– ependymal cells2. Microglia
- in PNS- Schwann cells- Satelite cells
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
Oligodendrocytes
• smaller, ↓intermediate fibres, darker nucleus
• formation of myelin sheath• myelinisation of several
axons
Microglia
• the smallest, dark elongated nucleus
• they migrate to the sites of dead cells, proliferate, phagocytes (dead cells, cell debris…)
• mesoderm -derived
Ependym
• epiteloid arrengement– remnant of
neuroepithelium of neural tube* secretory elements
(cerebrospinal fluid)component of choroid plexus
of brain ventricles and central canal of spinal cord
Nerve fibres
• axons provided by special connective tissue capsules of ectodermal origin
• axons:– unmyelinated– myelinated
Peripheral nerve
Unmyelinated nerve fibres
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
Myelinated nerve fibres
Eg 13 - Myelinizovaný axon
N8 – Ganglion HE
Neuron
Satelite cells
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- fatty)
• PNS• clusters of neurons:
ganglia• bundles of axons: cranial spinal peripheral nerves
Neuron, neuroglia, blood vessel
Nerve tissue microstructure (example 2 – brain )
Neuron
Glial c.