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Nerve Tissue 1 Nerve tissue 1 1.Nerve tissue – characteristics, histogenesis and classification 2.Neurons – classes and structure: cell body (perikaryon) neuronal processes 3.Nerve fibers – types 4.Synapses 5.Neurotransmitters and receptors Nerve tissue . Textus nervosus: cells – nerve and glial cells extracellular matrix . main functions: sensing stimuli and creating, analyzing and integrating information regulates and controls body functions provides the unity with the environment . properties: irritability capacity to respond to a stimulus – generation of a nerve impulse conductivity capacity to transfer the response throughout the neuron by the plasma membrane Prof. Dr. Nikolai Lazarov 2 Classification of nervous system Prof. Dr. Nikolai Lazarov 3 Neurulation embryonic origin: neuroectoderm formation of neural tube (neurulation) begin of the process – E17 neural (primary embryonic) induction – signaling molecules (growth factors) from the underlying notochord: neural plate neural groove neural fold neural tube CNS neural crest ganglion ridge PNS transverse segmentation of neural tube and its closure – regulated by BMPs: cranial neuropore – Е25 caudal neuropore – Е27 Prof. Dr. Nikolai Lazarov 4 Histogenesis . undifferentiated neuroepithelial cells (stem cells) – pluripotential: . unipotent progenitor cells: neuroblasts (immature neurons) unipolar, bipolar and multipolar glioblasts (glial precursor cells) oligodendrocytes protoplasmic astrocytes fibrillar astrocytes ependymal cells . microglia mesenchymal origin? . histogenesis – zones: ependymal layer mantle layer marginal layer Prof. Dr. Nikolai Lazarov 5 Nerve cells . neuron – more than 10 billion in the human NS cell body (perikaryon) axon – Golgi type І and ІІ neurons dendrites Prof. Dr. Nikolai Lazarov 6 Cell body . perikaryon (Gr. peri, around + karyon, nucleus) a trophic, synthetic and receptive center of the neuron diameter – 20-40 µm (4-120 µm) . composition: shape – pyramidal, stellate, fusiform, flask-shaped etc. large, euchromatic nucleus with a prominent nucleolus organelles: Nissl bodies Golgi complex mitochondria microtubules neurofilaments lipofuscin and neuromelanin Prof. Dr. Nikolai Lazarov 7 Nerve processes . axon (Lat. axis, axle or pivot) length – 1 mm-100 cm diameter – 0.2-20 µm . structure: axon hillock initial segment collateral branches axonal ending (terminal) synapse axolemma axoplasm: ribosomes – occasionally absence of rER and GA axonal transport: slow stream – 0.2 µm/day anterograde flow fast stream – 10-40 cm/day anterograde and retrograde flow Prof. Dr. Nikolai Lazarov 8 Nerve processes . dendrites (Gr. dendron, tree) number – variable, most frequently 5-15 80-90% of the surface . structure: short, dendritic tree dendrite spines dendritic cytoplasm: Nissl bodies mitochondria neurofilaments microtubules absence of Golgi complex Prof. Dr. Nikolai Lazarov 9 Basic neuronal types . morphological classes: . functional classes: pseudounipolar neurons motor (efferent) neurons bipolar neurons sensory (afferent) neurons multipolar neurons interneurons - 99% of all neurons in adults anaxonic (amacrine) neurons Prof. Dr. Nikolai Lazarov 10 Peripheral nerves . Peripheral nerves: o Nerve fibers: axon sheath derived from cells of ectodermal origin: oligodendrocyte – CNS Schwann cell – PNS o Connective tissue components: endoneurium perineurium epineurium Prof. Dr. Nikolai Lazarov 11 Nerve fibers – types . Types of nerve fibers: unmyelinated – 0.1-2 µm diameter both in the CNS and PNS absence of nodes of Ranvier 0.5-2 m/sec conduction velocity myelinated – 1-20 µm both in the CNS and PNS mesaxon nodes of Ranvier internodal segment – 1-2 mm Schmidt-Lanterman clefts 4-120 m/sec velocity Prof. Dr. Nikolai Lazarov 12 Nerve impulse . Nerve impulse: resting potential -70 mV action potential – membrane depolarization nerve impulse propagation Prof. Dr. Nikolai Lazarov 13 The Nobel Prize in Physiology or Medicine 1963 was awarded jointly to Sir John Carew Eccles, Alan Lloyd Hodgkin and Andrew Fielding Huxley "for their discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane". Prof. Dr. Nikolai Lazarov 14 Synaptic communication . synapse (Gr. synaptein = to join together) C.S. Sherrington 1857-1952 0.6x109 synapses per mm3 60000 synapses over one pyramidal neuron one pyramidal nerve cell – 600 neurons NB: The human brain contains roughly 90 billion neurons, which transmit information across roughly 150 trillion synapses! Prof. Dr. Nikolai Lazarov 15 Synapses . synapse (Gr. synaptein, to join together) . structure: presynaptic component, axon terminal presynaptic membrane presynaptic grid mitochondria synaptic vesicles – (20-65 nm) transmitters synaptic cleft (20-30 nm) postsynaptic membrane postsynaptic thickening receptors Prof. Dr. Nikolai Lazarov 16 Types of synapses . way of transmission: electrical synapses chemical synapses . contacting structures: axosomatic synapses axodendritic axoaxonic dendrodendritic somatodendritic etc. morphologically: asymmetrical (type I) – Glu symmetrical (type IІ) – GABA . functionally: excitatory synapses inhibitory synapses . atypical synapses: reciprocal dendrodendritic serial synapses “ribbon” synapse synaptic glomeruli Prof. Dr. Nikolai Lazarov 17 Neurotransmitters . neurotransmitters – criteria . neuromodulators . types of neurotransmitters: classical transmitters amino acids biogenic amines other major transmitters – ACh neuroactive peptides (neuropeptides) . atypical neural messengers: arachidonic acid derivatives purines adenosine, ATP gaseous – NO, CO . postsynaptic effect: excitatory acetylcholine glutamate aspartate inhibitory monoamines GABA and glycine Prof. Dr. Nikolai Lazarov 18 Transporters and receptors . Transporters: . Acetylcholinesterase (AChE) integral proteins – Na+ transport symporters . Transmitter receptors: ionotropic – transmitter-gated ion channels for ACh, GABA, Gly, SER for glutamate • NMDA-receptors • non-NMDA-receptors (AMPA and kainate) metabotropic receptors G-protein-coupled receptors • muscarinic ACh receptors • - and -adrenergic receptors • receptors for Glu, SER, GABA, neuropeptides tyrosine kinases receptor family guanylate cyclase receptors cytokine receptors autoreceptors Prof. Dr. Nikolai Lazarov 19 Arvid Carlsson, Paul Greengard and Eric Kandel for their discoveries concerning "signal transduction in the nervous system" Arvid Carlsson, Department of Pharmacology, Göteborg University, Sweden, is rewarded for his discovery that dopamine is a brain transmitter of great importance for our ability to control movements that has led to the realization that Parkinson's disease is caused by a lack of dopamine in certain parts of the brain. Paul Greengard, Laboratory of Molecular and Cellular Science, Rockefeller University, New York, USA, is rewarded for his discovery of how dopamine and a number of other transmitters exert their action in the nervous system. Eric Kandel, Center for Neurobiology and Behavior, Columbia University, New York, USA, is rewarded for his discoveries of how the efficiency of synapses can be modified, and which molecular mechanisms that take part. Prof. Dr. Nikolai Lazarov 20 Thank you… Prof. Dr. Nikolai Lazarov 21 .
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