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.