Chapter 7 Nervous tissue

1.  General description: ---Components: nerve cell: neuron Glial cell: neuroglial ---Function: Neurons : receive the stimulation, conduct the nerve impulse Glial cell: support, protect and insulate, nourish neurons

2.       Neuron The structural and functional cellular unit

shape of neuron: consists of cell body, dendrite and axon ---cell body: spherical, pyramidal fusiform or stellate in shape, 5um-150um ---dendrite: like branches of tree ---axon: long thin cord-liked

2) structure of neuron ①     cell body: ---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, so pale stained, with a large, clear nucleolus

---cytoplasm: perikaryon a.      Nissl body: LM: basophilic spot-liked or granule-liked structure EM: parallelly-arranged RER and free ribosome function: synthesis of proteins structural protein enzymes related to the production of neurotransmitters

b.  Neurofibril: LM: in silver impregnation methods(silver preparation), there are many thread-liked dark brown color structure to form a network.

EM: neurofilament: 10 nm in diameter microtubule: 25 nm in diameter function: supporting involving in intracellular transportation

c.       other organelle Golgi apparatus mitochondria pigment

②     dendrite: ---many, short and more branches ---structure: similar to cell body ---dendritic spine( places for formation of synapse) and spine apparatus(structure formed by 2-3 layers SER) ---function: receive the information

③    axon: ---thin, less branch ---structure: no Nissl body, but have microtubule, neurofilament, microfilament, mitochondria, SER and vesicle axon hillock: the beginning part of axon axolemma axoplasm ---function: initiate an impulse and conduct the impulse

* axonal transports: 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(100-400/d)

3) classification: ---According to number of processes multipolar neuron bipolar neuron pseudounipolar neuron ---According to length of axon Golgi type I neuron: long axon and large Golgi type II neuron: short axon

---According to function sensory neuron motor neuron interneuron ---According to the neurotransmitter or neuromodulator release by the neuron cholinergic neuron aminergic neuron peptidergic neuron aminoacidergic neuron

3. synapse

---definition: is the junctions between neurons or neuron and non-nerve cells ---classification: chemical synapse: taking neurotransmitter as communicating medium electrical synapse: gap junction

---structure of chemical synapse: LM: in silver preparation, there are many button-liked structures on the surface of dendrites and cell body, called synaptic button

EM: /presynaptic element: axonal terminal presynaptic membrane synapse vesicle: -round or flattened, 40-60nm -clear or with electron dense core

-contain neurotransmitters: acetylcholine, Ach norepinephrine, NE dopamine, DA -neuromodulator: peptides- change the reaction of neuron to neurotransmitter, modulate neurotransmitter substance P enkephalin vasoactive intestinal polypeptide, VIP

there are synapsin I mito, SER, microtubule and microfilament /synaptic cleft: 15-30nm /postsynaptic element: --postsynaptic membrane --receptors

Classification of chemical synapse: /According to function: excitatory synapse inhibitory synapse

/According to structure: type I: postsynaptic membrane is thicker than presynaptic membrane, with wide synaptic cleft(excitatory synapse) type II: there are less electron dense material attached on synaptic membrane, the thickness of postsynaptic membrane is same to presynaptic membrane(symmetrical synapse)

4. Glial cell(neuroglia)

1)  Glial cell in CNS (central nervous system) a. Astrocyte: /large stellate /round or ovoid nucleus, large and pale (euchromatin) /gliafilament: intermediate filament /end feet: to form glia limitans or vascular feet-constitute blood brain barrier

/classification fibrous astrocytes: -white matter, have long, thin and smooth processes -more glial filament- glial fibrillary acidic protein, GFAP

protoplasmic astrocyte: -gray matter, short, thick processes with more branch -less glial filament

/function: ⅰ.supporting, insulating and repairing ii. regulate the environment and movement of neuron iii. secret neurotrophic factor: nerve growth factor, NGF, ciliary neurotrophic factor, CNTP and glial cell line-drived neurotrophic factor, GDNF

b. Oligodendrocyte: ---structure: smaller, fewer process with a small round and dark stained N ---function: i. their processes form myelin-sheath of NF in CNS ii. inhibite growth of processes of neuron( secrete inhibiting factor- NI-35,NI-250 myelin-associated glycoprotein)

c. Microglia: ---structure: smallest, elongate shape or ovoid, with a small dark irregular N ---function: phagocytosis-mononuclear phagocyte system

d. Ependymal cell: ---structure: simple cuboidal or columnar epi apical: microvilli and cilia basal: long processes-tanycyte ---function: produce cerebrospinal fluid nerve stem cell in or under ependyma ---distribution: ventricle of brain and central canal of spinal cord

2) glial cell in PNS( peripheral nervous system) a.       Schwann cell: /envelop the axon end to end to form myelin-sheath in PNS and /produce NGF, CNTF and BDNF(brain derived neurotrophic factor) b.       Satellite cell (capsular cell): /one layer of flattened or cuboidal cell, with round, ovoid and dark N /surrounding the Neuron in ganglion

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

1)      MNF ① MNF in PNS LM: Axon myelin-sheath: HE: net-liked; OsO4(osmium tetroside) fixation and stain: black with Schmidt-Lantermann incisure neurilemma: cell membrane of Schwann and basement membrane * Ranvier node: narrow part, no myelin-sheath-saltatory conduction * internode: the segment of NF between two Ranvier nodes

EM: Schwann cell (neurilemmal cell) : Schwann cell →invagination and envelop the axon →form mesaxon → mesaxon become longer and longer →spiral around the fiber →to force the N and cytoplasm go to two side, inner and out edges connecting with incisure

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

2)      N-MNF ①N-MNF in PNS ---structure: thin axon and Schwann cell connect end to end no myelin-sheath and Ranvier node one Schwann cell envelops more axons ②N-MNF in CNS * nothing to envelop the axon-naked axon

3)      Nerve ---Nerve fiber gets together to form nerve efferent N afferent N mixed N ---structure: epineurium: DCT perineurium: -two layers: /outer layer- CT /inner layer-several layers of SSE- perineural epithelium(tight junction and basement membrane) endoneurium: thin layer of LCT

6. Nerve Ending

1) Sensory nerve ending ---peripheral processes of pseudounipolar neuron + other structure to form sensory receptor 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

② Encapsulated N ending ---have CT capsule a.       tactile corpuscle ---structure: oval CT capsule flattened cell-transverse arranged NF→lost myelin-sheath→spiral flattened cells ---distribution: dermal papillae, especially in tip of finger or toe, palms, soles and lips ---function: touch receptors

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 T, 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 F ---distribution: skeletal muscle ---function: detect muscle length and change in muscle length

2)      Motor nerve ending: muscular T and gland ①Somatic MNE: motor end plate, neuromuscular junction

---structure: EM muscle F: rich in cytoplasm, nuclei and mito presynaptic membrane: - synaptic vesicles- achtylcholine synaptic cleft: postsynaptic membrane: -synaptic gatter -junctional folds -type N receptor * motor unit: axon of one neuron and all skeletal muscle fiber controlled by it

② Visceral MNE ---lateral horn neuron→axon(preganglionic fiber) →ganglia neuron or nerve plexus→axon (postganglionic fiber) ---structure: NF are thin, no MS →form varicosity( round granules-liked vesicles) *vesicles: acetylcholine- round, Clear norepinephrine, NE- granules-liked glycine- flattened, clear ---distribution: smooth M, Cardiac M and gland