NERVOUS TISSUE.

Man Bahadur Paudyal

Objective

• To describe the nervous tissue • To describe the compnent of nervous tissue.

NERVOUS TISSUE

• Nervous tissue Consists of:- Neuron Supporting cells(neuroglia)

Nervous system 1. central nervous system:- brain and spinal cord 2. peripheral nervous system:- cranial and spinal nerve.

• Neurons : transmit electrical impulses from one site in the body to another, and receive and process information

• Neuroglia : are non-conducting cells that are in intimate physical contact with neurons .

Neurons –Functional unit of nervous system - It Consists of:• Cell body• Processes

• It is basically a cell nucleus surrounded by cytoplasm. •Nuclei of nerve cells are: large, round and euchromatic with a single prominent nucleolus.•Centrioles- absent.•Cytoplasm of nerve cell bodies is abundantly supplied with: - masses of RER ,numerous Golgi bodies, lysosomes

Cell body(perikaryon or soma)

Cell body.....

•Nissl substance:-(nissl bodies / granules):-granular material, composed of rough endoplasmic reticulum. protein synthesis – high•Neurofibrils:- microflaments and microtubules) •Pigment granules:- neuromelanin( substantia nigra) lipofuscin(resudual bodies – lysosomes)

Aggregation of cell body-- within CNS– k/a--nuclei outside CNS—k/a–ganglia

PROCESSES (NEURITES)

Two types:-• Axon• Dendrites

Axon:-• long, cylindrical process up to 1m• nissl substance absent• axon hillock• impulse:- away from cell body.• telodendria.• terminal boutons.• commenly refer to as nerve fibers

Initial segment

telodendria

Dendrites

•Numerous, Highly branched•Irregular•Terminate near the cell body.•Nissl granules – present•Impluse- towards the cell body

Gray matter:- cell body of neuron unmyelinatedWhite matter:- myelinated fibers

Aggregation of cell body-- within CNS– k/a--nuclei outside CNS—k/a–ganglia

Types of neuronea. According to the shape of cell bodyb. According to variation in axon

a.According to the shape of cell body:- shape of the cell body dependent on the number of processes arrising from it. 3 types:-

1. Multipolar neurones:- many processes arises form the cell body eg:- motor neurone

2.Bipolar neurone single dendrites and axon eg:- olfactory neuron, retina.

3.Unipolar neurone single dendrite and the axon arise form common stem of the cell body.

Eg:- dorsal root ganglian.

According to variation in axon

2 types

Golgi type I:- • long axon and connect remote regions

Golgi type II:-(microneurons)• short axon and end near the cell body.• Inhibitory in function.

Myelinated and non myelinated nerve fibers

PNS:- schwann cellCNS:- oligodendrocytes.

Non myelinated:- • Small diameter axon• simple envolop by the cytoplasm

Myelinated fibers:-• large diameter fiber , • concentric layers .

Peripheral nerve•Afferent and efferent nerve fiber•1or more bundle(fascicles) of nerve fibersWithin fascicle, each nerve fibers with its investing schwann cell:- endoneurium

Each fascicle is surrounded -- tough Collagenous tissue with flat epithlial Cell-- perineurium

If >1 fascicles, further layer of loose collagenous tissue – epineurium.

Supporting cell ( neuroglia)

•Non neural cell.•Highly branches cell that occupy the space between neurones•Mechanical and metabolic support.

In CNS – neuroglial cells are 1. astrocytes 2. oligodendrocytes 3. microglia 4. ependymal cells

In PNS:- neuroglial cells are 1. schwann cell 2. satellite cell

Astrocytes•Most numerous glial cell•Long branched processes

•Some processes terminate in adjacent non-synaptic region of neuron•Some terminates upon the BM of capillaries( perivascular feet)Which covers most surface of capillary BM forming BBB

Some process invest between CNS and inner most layer of meninges(pia mater)— impermeable barrier glia limitants

2 types

1. Fibrous astrocyte:-• white matter• Few straight cytoplasmic processes microtubules and intemediate filament– prominent.

2. Protoplasmic astrocyte:-• grey matter• numerous short , highly branch cytoplasmic process.

Oligodendrocytes olios– few, dendron– tree.

•Small number of short , branching process.•Myelination of axon in CNS.(4th mts)•Upto 50 axon•Aggregate closely around nerve cell bodies.•Large cell, with Small rounded condense nuclei Cytoplasm unstain( clear halo around nuclei)

oligodendrocyte

Microglia:-

•Small cell, •mesenchymal in origin.•Elongated nuclei, •little cytoplasm which forms, highly branch process•Becomes active after damage phagocytes.

Ependyma

•Epithelial lining of ventricles and spinal canal•Cuboidal to low columnar, and tightly bounded at luminal surface•Luminal surface cilia present•Donot rest on BM which ramify with process of astrocytes.

Ependymal

Schwann cell ( lemnocytes, peripheral glial )

•Responsible for myelination of axon•Wraps itself as spirally around a short segment of axon•Myelinate single axon.

Satellite cell( capsular gliocytes)•Flat cell that surround the cell bodies of neuron of PNS ganglia.•Regulate exchange of material between neuron cell bodies and interstitial fluid

Ganglion

Collection of cell body in PNS.2 types.

1.Sensory2.Autonomic

Sensory:- unipolar• fibers passes centrally • ganglion cell located peripherally• nerve cell body– surrounded by rounded satellite cell• cover on the outside by connective tissue capsule.

Autonomic ganglion•Multipolar•Neuron are scattered througout the ganglion•Nerve fiber are non myelinated and thinner so, less conspicious than sensory• satellite cell present but not well define•Nissl subs are better define.•Outside by connective tissue capsule.

Thank you