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 systemEndocrine systemImmune 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 NS grey 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 b iomedicalengineering.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)

Dendrites receptor region principal recieving site arborisation (branching) increases receptive area of the cell ( 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 axodendritic,axosomatic,axoaxonal, „en passant“ synaptic cleft

Synaptic transmission action potential opens calcium channels in presynaptic membrane → Ca 2 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 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 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.