Electron microscopy

Within the last few decades, many new discoveries in neuro-scientific histology have become possible because of the introduction of the electron microscope (usually abbreviated to EM) and its use in the electron microscopy. This microscope uses an electron beam instead of light; and electromagnetic fields instead of lenses. the Electron Microscope magnifies objects up to 100,000 times.

The structure of the cell or cells as seen with the EM is known as ultrastructure. For electron microscopic studies small bits of tissues are set very rapidly after removal from the animal body. Special fixatives are required (the most frequent being glutaraldehyde).

Very thin areas are required, and for this function, tissues need to be inserted in the press that is harder than wax. Epoxy resins (e.g., Araldite) are used. The microtomes used for reducing sections are much more sophisticated versions of traditional microtomes and are called ultramicrotomes.

 
Thin areas prepared in this way are also very helpful in light microscopy. They reveal a lot more detail than is seen in conventional paraffin areas. Before sections are examined under an electron microscope they are generally treated with solutions comprising uranium or lead, to boost the contrast of the image.

Osmium tetroxide acts both as a fixative and staining agent and has been thoroughly used for planning cells for electron microscopy. In conventional EM studies (or transmission electron microscopy) images are shaped by electrons passing through the section.

Wide use is also made of scanning electron microscopy where the images are made by electrons reflected off the top of the tissue. The surface appearances of cells are seen, and three-dimensional images may also be obtained.

 
Especially useful details of some tissue (e.g., membranes) can be acquired by freezing tissue and then fracturing it to see the fractured surface.

Who invented these microscopes?

The invention of these types of microscopes begins with the discovery of Louis De Broglie who stated that the electron beam has a wave-like nature similar to light.

Max Knoll and Ernst Ruska in 1931 invented the first transmission microscope in Berlin. Max Knoll also build a house scanning microscope. In 1935 James Hiller and Albert Prebus made the first commercial Transmission microscope. In 1975 the Cambridge instrument company produces first commercial scanning microscope in England

How does the electron microscope work?

If you ever used a compound light microscope then you have the basic idea that how the microscopes work. In the ordinary light microscope, there is a light source at the bottom that shines upward through a slice. To observe the image a person will see through an eyepiece lens. From this, we conclude that there are four essential parts in the ordinary light microscopes that are

1. Light source
2.  Specimen
3.   Lenses that magnify the image
4.   Eyepiece lens

Electron microscope also has these four parts but these four parts are slightly different in the electron microscope. The modification of the parts of the electron microscopes are

1.  In an ordinary microscope, we use a light source but in an electron microscope, it is replaced by a beam of a fast moving electron.

2.  There is also a modification to the specimen in these microscopes and that is the specimen is held inside the vacuum chamber from which air has been pumped out. In the electron microscope, we put the specimen in a vacuum chamber because electrons do not travel very in the air.

3.  The magnifying lenses are replaced by coiled shaped electromagnets. In the light microscope, the magnifying glasses refract the light and produce magnification while in the electron microscope the same function is done by the coiled shaped electromagnets.

4.  In ordinary microscopes, we use the eyepiece lens to see the object but in the electron microscope, the image is formed as a photograph.

That the basic principle of an electron microscope but there are different types of electron microscopes and all works in different ways. On the basis of functions The three main types of electron microscopes,

1. Transmission electron microscope
2.  Scanning microscope
3.   Scanning tunneling electron microscope

In Scanning microscopes beam of electrons pass over the specimen and produce a magnified image while in the transmission microscope the beam of electron goes right through the specimen.

Histochemistry

In many cases, the chemical character of mobile and intercellular constituents can be dependant on the utilization of staining techniques. Lipids and sugars (glycogen) present in cells are easily demonstrated.

The existence of several enzymes can be determined by placing sections in solutions comprising the substrate of the enzyme, and by watching the product produced by the action of the enzyme on a substrate. The merchandise is sometimes noticeable or can be made visible using appropriate staining agents.

For enzyme studies, the utilization of frozen areas is vital. Good frozen areas can be acquired by using cryostats (mentioned previously).

Immunocytochemistry

Specific molecules within cells can be discovered in tissue sections stained with antibodies specific to the molecules. The technique allows chemical substances to be localized in cells with great accuracy.

Such studies have greatly improved our knowledge of chemical substance transformations occurring within cells.

Autoradiography

Many molecules (e.g., proteins) injected into an animal become incorporated into the tissue of the pet. It is sometimes possible to displace a standard amino acid with a radioactive alternative.

For instance, if a radioactive isotope of thymidine is injected, it becomes incorporated in proteins in place of normal thymidine. The sites of the existence of the radioactive material can be dependant on covering tissue areas with a photographic emulsion.

Radiations rising from radioactive materials react on the emulsion. After the right interval, the emulsion is ‘developed’. Grains of silver are seen under the microscope at sites where in fact the radioisotope was present.

summary

Electron microscopy is a type of microscopy that can be done through a special type of microscope called an electron microscope.  An electron microscope is a type of microscope in which a beam of the electron is used instead of light. there are many types of electron microscopes but the two important among them are scanning electron microscopes and transmission electron microscopes. scanning tunneling microscope is also the type of electron microscope.