Transcript N1 - Kůra mozku HE

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
Neurotransmitters
Hormones
Cytokines
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 NS
grey and white matter (2 types of nerve tissue)
grey matter– perikarya, dendrites, axons, neuroglia
white matter– myelinated axons + neuroglia
Tissue microscopic structure: cells with
processes – integrated communicating network
neuroglia gap-junction
neurons synapse
neuron theory – contact junctions among neurons
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, microtubuleassociated motor proteins used ATP – dynein, kinesin)
– shape regulation
• neurofilaments (intermediate filaments in neurons)
– resistance against deformations
– regulatory process
• microfilaments (aktin)
Dendrites
receptor 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
Axon
conductive 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 nm
presynaptic cytoplasm : synaptic vesicles with
neurotransmitters, microtubules+kinesin, mitochondria
postsynaptic membrane of effector cell:
1. nerve cell
2. muscle cell
3. secretory cell
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-g-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 cells
2. 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
Satelite cells
Neuron
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 )
Glial c.
Neuron