Nervous tissue Shiping Ding Zhejiang University

1. Nervous tissueShiping DingZhejiang University

3. General characteristics: ---Components: • nerve cell: neuron, receive the stimulation, conduct the nerve impulse • glial cell: neuroglia, support, protect, insulate and nourish neurons ---Function: • Transmit impulses and thus communicate with different parts of the body through these impulses. • Works closely with endocrine system in communication within the body.

4. Neuron: The structural and functional cellular unit of nerve system Morphology of neuron: consists of cell body, dendrite and axon ---cell body:spherical, pyramidal fusiform or satellite in shape, 5um-150um, ---dendrite:arise from the cell body and branched like trees, usually shorter and thinker than axon ---axon:most neuron only have one, long thin cord-liked, arise from the axon hillock

5. structure of neuron cell body:perikaryon ---cell membrane: • unit membrane-irritability, receive stimuli, initiate and conduct nerve impulse • membrane proteins-ions channel and receptor • ---cell nucleus: • large and round, centrally- located, less heterochromatin, pale stained and appears empty, with a large, clear nucleolus • ---cytoplasm:

6. a. Nissl body: Present throughout the cytoplasm of the cell body and dendrites, but absent from the axon hillock and axon LM: basophilic spot-liked or granule-liked structure EM: parallel-arranged RER and free ribosome The number of Nissl bodies varies according to neuronal type and functional state. function:synthesis of proteins: structural protein enzymes related to the production of neurotransmitters

7. b.Neurofibril: LM: silver impregnation methods (silver preparation) thread-liked dark brown color fibril forming a network abundant in cell body, dendrites and axon EM: • neurofilament: 10 nm in diameter • microtubule: 25 nm in diameter function: • Support neurons as a cell skeleton • involving in intracellular transportation

8. c.other organelle • Golgi complex: well-developed • Mitochondria: scattered throughout the cytoplasm • pigment • Lipid droplets

9. dendrites: ---short branches ---structure: similar to cell body ---dendritic spine:numerous fine projections (places for formation of synapse) ---function: receive the information from other nerve cells axon: ---longer and thinner process, have a uniform diameter ---structure:no Nissl body,but have microtubule, neurofilament, microfilament, mitochondria, SER and vesicle • axon hillock: the beginning part of axon (no Nissl body) • axolemma • axoplasm ---function:initiate an impulse and conduct the impulses away from the parent cell body to other neurons or effector structures

10. Structure and function of neuron

11. axonal transports: A cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins and other cell parts( organelles) to and from a neuron’s cell body, through the cytoplasm of its axon. • slow anterograde: • cytoskeletal protein: microtubule, microfilament and neurofilament (0.1-0.4mm/d) • fast anterograde: • synaptic vesicles, enzymes and proteins( 100-400mm/d) • fast retrograde: • products of metabolism, intaking materials including protein or neurotrophic factors (100-400mm/d)

12. Classification of neuron ---According to number of processes • multipolar neuron • bipolar neuron • pseudounipolar neuron ---According to function • sensory neuron: receive exogenous and endogenous stimuli • motor neuron: conduct impulses to effector organs and control their function • interneuron: connect other neurons to form complex functional chains

13. synapse neuron • neuron nerve fiber neuroglia Synapse nerve efferent receptor

14. Synapse ---definition:the junctions between neurons or neuron and non-nerve cells ---classification: • chemical synapse:taking neurotransmitter as communicating medium • electrical synapse:exchange ions for communication, gap junction

15. ---structure of chemical synapse: L/M: The axon terminate in the form of a rounded enlargement, calledaxonal terminal or terminal button E/M: presynaptic element:axonal terminal • presynaptic membrane: axon plasmalemma • synaptic vesicle: store neurotransmitters • mitochondria synaptic cleft:the extracellular space between the presynaptic membrane and the postsynaptic membrane, 15-30nm postsynaptic element: • postsynaptic membrane: the plasmalemma at the contract point of the receiving neurons, -specific receptor molecules

16. The nerve impulse reaches the presynaptic element • The synaptic vesicle fuses with the presynaptic membrane and discharges the neurotransmitters into the synaptic cleft by exocytosis • The neurotransmitters diffuses across the cleft and combines with specific receptors in the postsynaptic membrane • This reaction induces an increase in the permeability of the postsynaptic membrane and cause a change in the membrane potential of the postsynaptic neurons, then conduct the stimuli from one neuron to other neuron

17. Glial cell (neuroglia) Form a framework to support neurons and influence their activities and metabolism

18. Glial cell in central nervous system Astrocyte: • large star-shaped • ovoid nucleus, large and pale • end feet: to form glia limitans or vascular feet - constitute blood brain barrier • Two forms: protoplasmic astrocyte fibrous astrocyte ---function • supporting, insulating and repairing • regulate the environment and movement of neuron • secret neurotrophic factor: nerve growth factor and glial cell line-derived neurotrophic factor protoplasmic astrocyte fibrous astrocyte

19. blood brain barrier Functional barrier: • The continuous endothelium of capillaries and the tight junctions between endothelial cell • a continuous basal membrane around the endothelium • The vascular foot processes of astrocytes surrounding the capillaries ----Function: • Regulates the diffusion of many substances between the blood and brain, such as antibiotics, chemical and bacterial toxic matter.

20. Oligodendrocyte: ---structure: smaller, fewer process with a small round and dark stained nuclei ---function: their processes form myelin-sheath of nerve fibers in central nervous system (CNS) Microglia: ---structure: smallest neuroglial cells, with a small dark irregular nucleus ---function:phagocytosis - mononuclear phagocyte system

21. Ependymal cell: ---structure: • simple columnar epithelium • apical: microvilli and cilia • basal: long processes ---function: • produce cerebrospinal fluid ---distribution:ventricle of brain and central canal of spinal cord

22. Glial cell in peripheral nervous system (PNS) Schwann cell: envelop the axon end to end to form myelin-sheath in PNS Satellite cell(capsular cell): • one layer of flattened or cuboidal cell, with round, ovoid and dark nucleus • surrounding the Neuron in ganglion for form a kind of cellular capsule

23. Nerve fiber ---definition: a structure formed by axon and glial cell which can conduct the impulse to certain direction ---classification: • myelinated nerve fiber • unmyelinated nerve fiber

24. myelinated nerve fiber(MNF) 1) MNF in PNS L/M: • Axon • myelin-sheath:tubular sheath encloses the axon • neurolemma: cell membrane of Schwann cell and basement membrane Myelin is a complex of lipids and protein. • Ranvier node: narrow part, no myelin-sheath • internode: the segment of NF between two Ranvier nodes, 0.3-1.5 mm, represent a single Schwann cell

25. E/M: The myelin sheath is seen as a series of concentrically arranged light and dack lamellae---Schwann cell plasmalemma Schmidt-Lanterman cleft (incisure): area where the cytoplasm of the Schwann cells is present within the myelin sheath. Schmidt-Lanterman cleft

27. 2) MNF in CNS ---structure: • similar to that in PNS • myelin-sheath formed by flattened ending of oligodendrocyte’s processes • one oligodendrocyte can envelop many axons • no incisure and basement membrane

28. The function of the myelin sheath: • to provide an insulation layer around the axon • to speed up impulse conduction: nerve impulses jump from node to node across the intervening internodal segment of myelin sheath ( the axon directly exposed to the extracelluar fluidal ions at nodes of Ranvier, where depolarisation occurs) • The thicker the myelin sheath, the greater the internodal distance and conduction speed.

29. unmyelinated nerve fiber(N-MNF) N-MNF in PNS ---structure: • thin axon and Schwann cell which connect end to end • no myelin-sheath and Ranvier node • one Schwann cell envelops many axons N-MNF in CNS • naked axon , nothing to envelop the axon

30. Nerve (Study by yourself!) ---the aggregation of nerve fiber • efferent nerve • afferent nerve • mixed nerve ---connective tissue • epineurium • perineurium • endoneurium

31. Perineurium Nerve bundle Individual Axon surrounded By myelin sheath

32. Nerve EndingStudy by yourself! 1) Sensory nerve ending Afferent ending ①free nerve ending ---structure: NF→lose myelin-sheath → branch → distribute in epidermis, cornea, hair follicle epithelial cell and CT ---function: feel cold, hot, pain and slight touch

33. ② Encapsulated nerve ending ---have CT capsule a. tactile corpuscle: • encapsulated unmyelinatednerve endings, which consist of flattened supportive cells arranged as horizontal lamellae surrounded by a connective tissue capsule. The corpuscle is between 30-140 μm in length and 40-60 μm in diameter. • A single nerve fiber meanders between the lamellae and throughout the corpuscle.

34. b. lamellar corpuscle ---structure: • large , oval or spherical • capsule: several layers of flattened cell concentrically-arranged • bulb- cylindrical • NF →lost MS→enter the bulb ---distribution: subcutaneous tissue, mesentery, ligament ---function: feel deep or heavy pressure

35. c:Muscular spindles: ---structure: • fusiform • CT capsule • a few small muscle fibers- intrafusal muscle fiber • NF: roll up the muscle fiber ---distribution: skeletal muscle ---function: detect muscle length and change in muscle length Muscular spindles

36. d: Motor nerve ending: Efferent nerve ending LM: Plate-like mass with the terminal swelling of a nerve fiber ---structure: EM • muscle F: rich in cytoplasm, nuclei and mito • presynaptic membrane: - synaptic vesicles- acetylcholine • synaptic cleft: • postsynaptic membrane: -acetylcholine receptor function: control the contraction of skeletal muscle fiber

37. Thank you for your attention!