Nerve tissue. 1.Nerve tissue characteristics, histogenesis and classification 2.Neurons

Transcription

1 Nerve tissue 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 6.Neuroglial cells 7.Nerve endings: sensory (afferent) receptors effector (efferent) endings

2 main functions: sensing stimuli and creating, analyzing and integrating information regulates and controls body functions provides the unity with the environment properties: irritability Textus nervosus: capacity to respond to a stimulus generation of a nerve impulse conductivity capacity to transfer the response throughout the neuron by the plasma membrane Nerve tissue cells nerve and glial cells extracellular matrix Prof. Dr. Nikolai Lazarov 2

3 Classification of nervous system Prof. Dr. Nikolai Lazarov 3

4 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: cranial neuropore Е25 caudal neuropore Е27 Prof. Dr. Nikolai Lazarov 4

5 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

6 neuron more than 10 billion in the human NS cell body (perikaryon) axon Golgi type І and ІІ neurons dendrites Nerve cells Prof. Dr. Nikolai Lazarov 6

7 composition: Cell body perikaryon (Gr. peri, around + karyon, nucleus) a trophic and receptive center of the neuron diameter µm (4-120 µm) shape pyramidal, stellate, fusiform, flask-shaped etc. large, euchromatic nucleus with a prominent nucleolus organelles: Nissl bodies Golgi complex mitochondria microtubules neurofilaments lypofuscin and neuromelanin Prof. Dr. Nikolai Lazarov 7

8 axon (Lat. axis, axle or pivot) length 1 mm-100 cm structure: diameter µm 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 cm/day anterograde and retrograde flow Nerve processes Prof. Dr. Nikolai Lazarov 8

9 Nerve processes dendrites (Gr. dendron, tree) number variable, most frequently % 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

10 Basic neuronal types functional classes: morphological classes: pseudounipolar neurons bipolar neurons multipolar neurons motor (efferent) neurons sensory (afferent) neurons interneurons Prof. Dr. Nikolai Lazarov 10

11 Types of nerve fibers: unmyelinated µm diameter both in the CNS and PNS absence of nodes of Ranvier 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 m/sec velocity Nerve fiber: Nerve fibers axon sheath derived from cells of ectodermal origin: oligodendrocyte CNS Schwann cell PNS Prof. Dr. Nikolai Lazarov 11

12 myelination in humans: Myelin-forming cells: begin fetal period end 7 years regulation neuroregulin NRG1 Myelination oligodendrocytes CNS Schwann cells PNS myelin: lipids 70% proteins 30% in CNS MBP (myelin basic protein) P 0 peripheral axons PMP-22 peripheral axons myelin sheath: major dense lines intraperiod lines Prof. Dr. Nikolai Lazarov 12

13 Synapses synapse (Gr. synaptein, to join together) structure: presynaptic component, axon terminal presynaptic membrane presynaptic grid mitochondria synaptic vesicles (20-65 nm) transmitters C.S. Sherrington synaptic cleft (20-30 nm) postsynaptic membrane postsynaptic thickening receptors Prof. Dr. Nikolai Lazarov 13

14 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 Types of synapses Prof. Dr. Nikolai Lazarov 14

15 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 Neurotransmitters Prof. Dr. Nikolai Lazarov 15

16 Transporters: integral proteins Na + transport symporters Transmitter receptors: ionotropic transmitter-gated ion for ACh, GABA, Gly, SER for glutamate NMDA-receptors Transporters and receptors ion channels non-nmda-receptors (AMPA and kainate) metabotropic receptors G-protein-coupled receptors muscarinic ACh receptors α- and β-adrenergic receptors receptors for Glu, SER, GABA, neuropeptides tyrosine kinases receptor family guanylate cyclase receptors cytokine receptors autoreceptors Acetylcholinesterase (AChE) Prof. Dr. Nikolai Lazarov 16

17 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 17

18 central gliocytes neural tube: astrocytes oligodendrocytes ependymal cells microglial cells peripheral gliocytes neural crest: Schwann cells (neurolemmocytes) satellite cells of Cajal (syn: mantle cells or amphicytes) Neuroglia Glial cells glioblastic origin: central macroglia and microglia (in CNS) peripheral in PNS Prof. Dr. Nikolai Lazarov 18

19 astrocytes oligodendrocytes large light medium-sized small dark ¼ of the light cells myelin-forming cells in the CNS ependymal cells neural crest line the ventricles of the brain and central canal of the spinal cord absorption and secretion of cerebrospinal fluid (liquor) tanycytes (ependymal astrocytes) microglia 15% (Gr. astron star) protoplasmic fibrous astrocytes (Gr. oligos small) Central gliocytes 15% of the total cells of CNS non-dividing cells derived from monocytes role of macrophages (mononuclear phagocyte system in nervous tissue) Prof. Dr. Nikolai Lazarov 19

20 Peripheral gliocytes Schwann cells (neurolemmocytes) neural crest origin myelin-forming cells in the PNS maintenance of the axon integrity phagocytotic activity and cellular debris that allows for regrowth of PNS neuron satellite cells (amphicytes) in sensory and autonomic ganglia help regulate the external chemical environment Prof. Dr. Nikolai Lazarov 20

21 Sensory receptors classification 3 main groups Sherrington,, 1906: exteroceptors proprioceptors interoceptors by sensory modality: baroreceptors respond to pressure chemoreceptors chemical stimuli mechanoreceptors mechanical stress nociceptors pain perception thermoreceptors temperature (heat, cold or both) by location: cutaneous receptors in the skin muscle spindles in the muscles by morphology: free nerve endings encapsulated receptors C.S. Sherrington Prof. Dr. Nikolai Lazarov 21

22 four kinds of touch sensations: free nerve endings: unencapsulated light toucht (contact) cold heat pain unspecialized, detect pain most widely distributed, most numerous in the skin, mucous&serous membranes, muscle, deep fascia, viscera walls peritrichal endings of hair follicles tactile discs of Merkel: mechanoreceptors pressure and texture superficial layers of glabrous and hairy skin Sense of touch Prof. Dr. Nikolai Lazarov 22

23 tactile corpuscles of Meissner end bulbs (of Krause genital corpuscles Pacinian (Vater( Vater-Pacini) ) corpuscles vibration Golgi-Mazzoni corpuscles in the fingertips Encapsulated receptors Meissner glabrous skin Krause) responds to pressure, Ruffini endings responds to pressure neurotendinous organs (Golgi( tendon organs) neuromuscular spindles proprioceptors: intrafusal fibers extrafusal fibers Prof. Dr. Nikolai Lazarov 23

24 Effector nerve endings myoneural junction motor end plate: structure: myelinated axon collaterals ~50 axon terminals (boutons) synaptic vesicles ACh presynaptic membrane sarcolemma junctional folds postsynaptic membrane nicotinic ACh receptors autonomic effector endings: sympathetic adrenergic (NA) parasympathetic cholinergic (ACh) purinergic ATP and adenosine do not make specialized synaptic contacts Prof. Dr. Nikolai Lazarov 24

25 Thank you Prof. Dr. Nikolai Lazarov 25