Regulatory systems Nervous system Endocrine system Immune system Neurotransmitters Hormones Cytokines

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1 321. Nerve tissue Function: it 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 )

2 Regulatory systems Nervous system Endocrine system Immune system Neurotransmitters Hormones Cytokines

3 Mechanisms of signalling Endocrinne signalling hormones through vascular system Paracrine signalling short distance diffusion (local mediators cytokines) Autocrine signalling regulation (target and producer are identical) Synaptic signalling neurons neurotransmitters

4 Nerve tissue - overview Neurons are excitable cells that use the combination of electrical (membrane depolarisation) and chemical (synapse) signalling They respond to physical or chemical irritation Signal is transmitted to other neuron, muscle cell or gland Neurons form integrated communicating network composed from the cells with processes Transfer of excitation from receptor to efector = reflex

5 Tissue microscopic structure: cells with processes integrated communicating network neuroglia gap-junction neurons synapse Neuron theory contact junctions among neurons Beta III tubulin glial fibrilar acidic protein

6 Nerve tissue - morphology Neuron- Glia- receive stimuli and conduct nerve impulse via their processes supportive cells Body (soma, perikaryon) Phagocytosis Separating neurons Forming myelin Nutrition Axon Dendrites Neuron : Glia = (1:10)

7 Neuron - classification Size of perikaryon μm Classification: Projection Golgi type I (long axon - up to 1m) Motor neurons Sensory neurons Interneurons Golgi type II short axon

8 Classification of neurons According to number of processes: Multipolar Bipolar Pseudo-unipolar According to the morphology Granular, pyramidal, stelate, basket, horizontal, Martinotti, etc. According to the anatomical division: CNS (central nerve system) PNS (peripheral nerve system) Somatic Autonomous

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11 Perikaryon (soma, cell body) 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

12 Dendrites 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, NFM, NF-H), other cytoskeleton units, proteosynthetic apparatus except for GA always non-myelinated receptor region

13 Axon (conductive region) transmits stimuli in the form of action potential to other neuron or effector cell 1 neuron has 1 axon metabolically dependent on perikaryon axonal transport transport vesicles, mitochondria, proteins by anterograde x growth factor, viruses..by retrograde Axoplasma mitochondria, microtubules, MAP1 axon hillock perikaryon but structure similar to axon, initial segment site of action potential generation - iont channels threshold action potential

14 Action potential conduction From signalling to effector cell one direction only anterograde from initial segment to synapse Refractory period prevents the retrograde propagation of the depolarization wave. Synapse impuls is tranfered from presynaptic membrane to postsynaptic one (effector cell)

15 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 (actin filaments) Regulation of molecules transportation to plasma membrane Anchorage, regulation of movement

16 Axonal transport There is no proteosynthesis within axon transport is needed from perikaryon to the periphery using microtubules for enzymes, polypeptides, structural proteins (neurotransmitters except for peptides are produced within axon terminals) Anterograde transport to terminals fast up to 40 cm/day Retrograde transport back to body degradation Slow anterograde transport - diffusion

17 2 multipolar neurons connected synaptically biomedicalengineering.yolasite.com

18 Synapse effector region, unidirectional transmission of nerve impulse Axodendritic Bouton terminaux Bouton en passage Axosomatic Axoaxonal Excitatory (acetylcholine, glutamate) Inhibitory (GABA) presynaptic (axonal) terminal - bouton terminaux presynaptic cytoplasm : synaptic vesicles with neurotransmitters, microtubules+kinesin, mitochondria synaptic cleft 20 nm postsynaptic membrane of effector cell (dendritic, somatic, axonal)

19 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-γ-aminobutyric acid, glycine) Synapses thus can excite or inhibit impulse transmission.

20 Synaptic signalling

21 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

22 Glia - types in CNS 1. Macroglia Astrocytes Protoplasmatic fibrillar Oligodendrocytes Ependymal cells 2. Microglia - in PNS - Schwann cells - Satelite cells

23 Astrocytes (protoplasmic, fibrillar) 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

24 Astrocytes Radial glia, Müller cells, Bergmann glia, pituicytes A. protoplasmatic surround neurons and vessels in grey matter of the brain and spinal cord B. fibrillar smooth processes - GFAPwhite matter

25 Oligodendrocytes smaller, intermediate fibres, darker nucleus formation of myelin sheath Within white matter but also in grey matter myelinisation of several axons

26 Ependym epiteloid arrangement remnant of neuroepithelium of neural tube * secretory elements (cerebrospinal fluid) component of choroid plexus of brain ventricles and central canal of spinal cord Tanycytes (3rd ventricle)

27 Microglia the smallest, dark elongated nucleus they migrate to the sites of dead cells, proliferate, phagocytes (dead cells, cell debris ) mesoderm -derived

28 central and peripheral NS grey and white matter (2 types of nerve tissue) grey matter perikarya, dendrites, axons, neuroglia white matter myelinated axons + neuroglia

29 Nerve fibres axons are provided by special coat (cover) Axons form tracts in CNS (oligodendrocytes) or nerves in PNS (Schwann cells) Axons: unmyelinated myelinated

30 Unmyelinated nerve fibres CNS axons are located free among processes of neurons and glial cells PNS axons are located in simple clefts within Schwann cells

31 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 clefts

32 Myelin Origin membrane of oligodendrocyte or Schwann cell fusion 70% -lipids = phospholipids, glycolipids (cerebrosides, sfingomyelin), cholesterol Proteins connect membranes forming compact myelin Main (thicker) and intermediate (thiner) lines which are separated by electrolucid layers

33 Peripheral nerve

34 Peripheral Nerve System Nerves Axons forming bundle Connective tissue: Epineurium Perineurium Endoneurium Ganglia Accumulation of nervous cells (multipolar or pseudounipolar) Satelite cells Ovoid shape, capsule from connective tissue

35 Nerve tissue Regeneration: neurons in vivo in general do not divide in general (no neurogenesis except for specific region -hippocampus, first neuron of the olphactory tract) Stem cells are present in brain subependymal layer- they are not able to replace dying neurons in vitro / in experiments can neurons differentiate into neurons Axons in periphery may regenerate, if perikaryon is preserved Glial scar proliferation of glia (astrocytes) reparation of CNS

36 Differentiation of nerve tissue Nerve cells: Neuroblasts Nucleus, transient dendrite a-, bi-,multipolar Glial cells Migrate in the mantle and marginal layers