neural tissue

Histology 1

Neural tissue

Dr. Arsalan Amiri

2016

Neural tissueConsist of :

- neuron

signal reception, processing and forwarding

- Glia

support, service

Neural tissueParts of the neuron:


1. Cell body:

- Perikaryon

- Nucleus

active, loose chromatin

- Cytoskeleton

mikrofilamentum 5 nm actin

neurofilamentum 7-10 nm (in axon)

mikrotubuli 20 nm α and β tubulin

MAP = microtubule associated protein

TAU-protein - microtubulus cross bridge


2. Dendrit

- structure ~ perikaryon

- different forms

- dendrit-tree

- function:

synapsis

stimulus reception


3. Axon (neurit)

- neurotubuli, microfilaments

- Function: stimulus propagation

- axonal transport:

anterograde - retrograde

- axon sheets


4. Telodendrons

(distal branch of a axon that can branch into axon terminals)

Function: stimulus uptake / transmission

intercalar - between nerve cells

terminal - neural to non-neural tissues

Neural tissue

Based on the number of processes:

- Multipolar (>99 %)

- Bipolar (eye, ear)

- Pseudounipolar (sensory ganglia)

- Unipolar

- Apolar

Neural tissue

Locations of cell body:

- CNS (brain and spinal cord) : grey matter(nucleus, cortex)

- PNS : ganglion (sensory or autonomic)

Neural tissue

Types of glia cell:

- Fibrous (astrocyte)

support (~c.t.)

brain-blood barrier

- Protoplasmic glia

neurotroph

- Oligodendroglia

axonal sheet

- Microglia

phagocytosis

- Ependyma

Neural tissue

Types of glia cell:

Neural tissue

- only the axon of the nerve cell is in the peripheral nerve , which together with its sheath makes the nerve fiber.

- Depending on the character of the sheath the nerve fiber may be myelinated or non-myelinated (the latter has only a Schwann-cell covering).

Neural tissue

The surrounding of the peripheral nerve fibers is given by connective tissue sheaths:

- Endoneurium

- Perineurium

- Epineurium

Peripheral nerve cross-section HE

- the nerve bundles (fascicles) that are surrounded by a dense sleeve, the perineurium.

- The external fibrous coat also filling the space between the bundles is the epineurium.

- (So the epineurial

tissue is found not only

on the surface but also

in the deeper regions!)


- In the perineurial sleeve, collagenous fibers and flattened c.t. cells joined by tight junctions, with basal lamina between the layers.

- The perineurium has an important role as a barrier to the passage of

macromolecules

and protect the nerve

from mechanical and

chemical traumas.


- In regions where the structure gets "fuzzy“, is due to the oblique cuts because of the slightly spiral course of the fibers.


- perineurium on the left.

- On the right, nerve fibers surrounded by a delicate c.t. (endoneurium), with reticular fibers, scattered fibrocytesand macrophages.

-Most nuclei belong

to the Schwann cells,

they are strongly

basophilic, oval or

crescent shaped.


- Most of the fibers seen here are myelinated fibers, they have a homogenous pale gray-blue inner center (axon) and a sheath with radial pattern (myelin sheath).

Peripheral nerve cross-section HE- The proteins of the sheath (myelin basic protein and proteolipid protein) precipitate during fixation and the lipid component is mostly removed during standard histological procedures, the remnant of them are the neurokeratinblocks arranged ina radial pattern.

- Sometimes the sheath

and the axon collaps

during fixation, then

the fiber shows as a

small compact dot with

an empty (white) ring

around it


- unmyelinated fibers: the axons are enveloped within simple clefts of the Schwann cells. These appear as pale eosinophilic regions with "bubbles“.


- unmyelinated fibers: the axons are enveloped within simple clefts of the Schwann cells. These appear as pale eosinophilic regions with "bubbles“.

-Schwann cell nuclei

around a few axons

attached to the

myelin sheath


- layers of perineurium:

1: cellular layer

2: fibrous layer

3: epineurium

The endoneurium shows better in this preparation

- the c.t. fibers are blue.

- The myelin sheath is pink

- the nuclei are red.

Peripheral nerve cross-section Azan

Peripheral nerve cross-section Azan

- layers of perineurium:

1: cellular layer

2: fibrous layer

3: epineurium

Peripheral nerve - Osmium

- cross-section

- Osmiumtetroxide stains fat

- it binds to membranes, so the myelin sheath appears in this preparation

as black rings.


- Territories with unmyelinated fibers show as lighter territories with delicate light brown meshwork.


-Preparations may differ in color-shades, may have golden-brown or white background, this is due to the slightly different procedures during preparation and has no specific importance.

Sensory ganglion HE

E. g. :

- spinal or intervertebral ganglion

- sensory ganglia of cranial nerves, like trigeminal ganglion

- pseudounipolar cells (40-100 µm).

- The peripheral process of these cells carries sensory information from the periphery, while the central process ends in the central nervous system (spinal cord, medulla oblongata).

- There is no synapse in these ganglia!

Sensory ganglion HE

-The cells are surrounded by satellite cells

(small glial cells, related to Schwann cells).

- The ganglion is supported by a c.t. framework

(reticular and collagenous fibers, fibrocytes).

Sensory ganglion HE

- The nerve cells have large nucleus with well visible nucleolus. Since the slide is 8-10 µm thick and the cells are up to 100 µm, often the cut of the actual cell does not contain the nucleus.

- In some cells brownish pigmentation is present, this is the lipofuscin.

- Between the cells

bundles of nerve fibers

are visible, these are

the axons of the

ganglion cells.

Sensory ganglion HE

- dark, large spots are lipofuscin on an electronmicroscopicphoto

Sensory ganglion Kelemen impregnation

- The silver impregnated slides are usually thick slides (30-100 µm) so moving the micrometer will reveal different structures clearly.

- Often the fiber turns around the cell several times, inside the satellite cell capsule.

(satellite cell-capsule appears

as a white ring)

Sensory ganglion Kelemen impregnation

- Due to aging and shrinkage the surface of the ganglion cells is often uneven.

- Only one process originates from the sensory ganglion cells and if the cut is not in the optimal plane it may be that you do not see that one either.

Vegetative ganglion AgNO3 impregnation

- multipolar nerve cells and their dendrites

- preganglionic fibers entering the ganglion may synapsewith them. The axons of these cells leave the ganglion as postganglionic fibers.

- cells are covered with

satellite cells

Vegetative ganglion AgNO3 impregnation

- the nuclei of satellite cells and also the nuclei of the connective tissue cells in-between them - show in pale gray color as the background of the reaction.

Thank you for your attention

neural tissue

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