Nervous tissue Shiping Ding Zhejiang University

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.

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 Neuron: The structural and functional cellular unit of nerve system

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:

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

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

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

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

Structure and function of neuron

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 ( mm/d) fast anterograde: synaptic vesicles, enzymes and proteins( mm/d) fast retrograde: products of metabolism, intaking materials including protein or neurotrophic factors ( mm/d)

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

neuron synapse nerve fiber neuroglia neuron nerve efferent receptor 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 Synapse

---structure of chemical synapse: L/M: The axon terminate in the form of a rounded enlargement, called axonal 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

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

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

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

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.

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

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

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

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

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, mm, represent a single Schwann cell

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

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

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.

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

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

Perineurium Nerve bundle Individual Axon surrounded By myelin sheath

1) Sensory nerve ending Afferent ending ① free 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 Nerve Ending Study by yourself!

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

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

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

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

Thank you for your attention!