Nervous tissue Shiping Ding Zhejiang University

Nervous tissue

Shiping DingZhejiang University

General characteristics:

---Components: • nerve cell: neuron, receive the stimulation,

conduct the nerve impulse• glial cell: neuroglia, support, protect, insu

late 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 branc

hed like trees, usually shorter 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 stim

uli, initiate and conduct nerve impulse• membrane proteins-ions channel and r

eceptor

• --- cell nucleus: • large and round, centrally- located, les

s 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 axonL/M: basophilic spot-liked or granule-liked structureE/M: parallel-arranged RER and free ribosomeThe number of Nissl bodies varies according to neuronal type and functional state.

function: synthesis of proteins:

structural proteinenzymes related to the production of neurotransmitters.

b.  Neurofibril: L/M:silver impregnation methods (silver

preparation)

thread-liked dark brown color fibril forming a network abundant in cell body, dendrites and axon

E/M: • neurofilament: 10 nm in diameter• microtubule: 25 nm in diameterfunction: • Support neurons as a cell skelet

on• involving in intracellular transpor

tation

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 f

or formation of synapse) ---function: receive the information from other nerve

cellsaxon: ---longer and thinner process, have a uniform diameter---structure: no Nissl body, but have microtubule, neu

rofilament, mitochondria, SER and vesicle• axon hillock: the beginning part of axon (no Nissl

body)• axolemma• axoplasm---function: initiate an impulse and conduct the impul

ses 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, microfilamen

t and neurofilament (0.1-0.4mm/d)

• fast anterograde: • synaptic vesicles, enzymes and proteins( 100-4

00mm/d)

• fast retrograde: • products of metabolism, intaking materials incl

uding protein or neurotrophic factors (100-400mm/d)

Classification of neuron---According to number of processes• multipolar neuron• bipolar neuron• pseudounipolar neuron

---According to function• sensory neuron: receive exogenous and endogenous sti

muli • motor neuron: conduct impulses to eff

ector organs and control their function• interneuron: connect other neurons to

form complex functional chains

•neuron

synapsesynapse

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 enla

rgement, called axonal terminal or terminal button

E/M: presynaptic element: axonal terminal• presynaptic membrane: axon plasmalemm

a• synaptic vesicle: store neurotransmitters• mitochondria synaptic cleft: the extracellular space betwee

n 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 limitan

s or vascular feet - constitute blood brain barrier

• Two forms: protoplasmic astrocyte fibrous astrocyte---function• supporting, insulating and repai

ring• regulate the environment and m

ovement of neuron• secret neurotrophic factor: nerv

e growth factor and glial cell line-derived neurotrophic factor

protoplasmic astrocyte fibrous astrocyte

blood brain barrierFunctional barrier:• The continuous endothelium of ca

pillaries 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 nerv

ous 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 nu

cleus

• surrounding the Neuron in ganglion for form a kind of cellular capsul

e

---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 PNSL/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

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 en

ding of oligodendrocyte’s processes• one oligodendrocyte can envelop man

y 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 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 axonsN-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

IndividualAxon surroundedBy myelin sheath

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

Nerve EndingStudy 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 30-140 μm in length and 40-60 μm in diameter.

• 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, m

esentery, ligament---function: feel deep or heavy pressur

e

c:Muscular spindles:

---structure: • fusiform• CT capsule• a few small muscle fibers- intrafusal m

uscle fiber• NF: roll up the muscle fiber

---distribution: skeletal muscle

---function: detect muscle length and chang

e in muscle length

Muscular spindles

d: Motor nerve ending:Efferent nerve endingLM:Plate-like mass with the terminal swellin

g of a nerve fiber---structure: EM• muscle F: rich in cytoplasm, nuclei an

d mito• presynaptic membrane: - synaptic ve

sicles- acetylcholine• synaptic cleft: • postsynaptic membrane: -acetylcholine receptor function: control the contraction of skeletal muscl

e fiber

Thank you for your attention!