Specimen Nr. 08

Specimen:

Neuromuscular synapse (Rat)

Staining:

TEM

Magnification:

30 000x

Important structures :

1.Myelinated axon (slice)
2.End of myeline sheath
3.Schwann cell
4.Presynaptic end of a motor neuron
5.Mitochondria
6.Postsynaptic sarcolemma
7.Invaginations of postsynaptic sarcolemma
8.Synaptic cleft with basement membrane
9.Nucleus of skeletal striated muscle cell
10.Myofibrils of skeletal striated muscle cell
11.Endoneurium
Das Bild zeigt eine neuromuskuläre Synapse. Am linken oberen Bildrand erkennt man den Anschnitt eines markhaltigen Axons, dessen Schwann’sche Zelle mit sog. Taschen, die Zytoplasma enthalten, endet. Am rechten unteren Bildrand ist eine quergeschnittene Skelettmuskelzelle mit Zellkern und Myofibrillen zu sehen. Die präsynaptische Endigung enthält viele Mitochondrien. Das postsynaptische Sarkolemm ist eingefaltet. Der synaptische Spalt und die Falten werden von einer Basalmembran ausgefüllt. Zwischen den Myofibrillen und dem postsynaptischen Sarkolemm findet man zahlreiche Mitochondrien und reichlich Glykogen.

Legende:

Myelinated axon (slice)
End of myeline sheath
Schwann cell
Presynaptic end of a motor neuron
Mitochondria
Postsynaptic sarcolemma
Invaginations of postsynaptic sarcolemma
Synaptic cleft with basement membrane
Nucleus of skeletal striated muscle cell
Myofibrils of skeletal striated muscle cell
Endoneurium

Synoptic impulse transmission[ju]

Depolarization of the presynaptic membrane (1) induces a brief opening of calcium channels (2). The flow of calcium ions leads to exocytosis of the synaptic vesicles (3) and, thereby, to a release of the neurotransmitter into the synaptic gap junction (4). The neurotransmitter binds to the receptors (5) and causes a depolarization of the post-synaptic membrane (6).

Transmission electron microscope (TEM)

The sections for examination under the transmission electron microscope are about 0.1µm thick. They are referred to as ultra-thin sections.

To obtain such ultra-thin sections, the tissues are embedded in plastic polymers like epon (instead of paraffin, which is used for examination under the light microscope) after fixation and dehydration. Ultra-thin sections are not stained with dyes, but contrasted with heavy-metal salts. The heavy-metal salts lead to a different electron scatter and thereby create a differentiated blackening of the photographic negative. A common method of creating contrast results with 5% uranyl acetate and lead citrate.

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Myelinated axon (slice)
End of myeline sheath
Schwann cell
Presynaptic end of a motor neuron
Mitochondria
Mitochondria
Postsynaptic sarcolemma
Invaginations of postsynaptic sarcolemma
Synaptic cleft with basement membrane
Nucleus of skeletal striated muscle cell
Myofibrils of skeletal striated muscle cell
Endoneurium

HistoNet2000 - Help

1. Organization of the screen surface

Right side: histologic specimen
Left side: information about the specimen (above) and general program functions (below)

2.Histologic specimen

Pull the mouse across the histologic specimen for training purposes. A small square with exclamation marks (dynamic labels) will appear where there is an important structure. You should then decide what structure this could be. To check your result, simply click the appropriate square, and the correct label will appear. The option “marked” allows you to see all labels for all structures simultaneously. These can be removed by clicking “unmarked”. This reactivates the dynamic labels.

3. Complementary information

Info: general information about the specimen, as well as a list of the dynamic labels
Drawing: schematic drawing of the specimen
Staining: information about the staining method for this specimen
Knowledge: short texts with basic histologic information, presently deactivated

4. General Program Functions

Home: returns you to the “start” page
Tutor: how to contact the HistoNet Team
Help: Instructions for Use appear
Exit: closes down the HistoNet program
Boxes: goes back to the other specimen of a topic
VM: provides virtual microscopy

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