Leaving staining for a moment and just finishing,
I just want to explain what resolving power means.
You've been looking at histological sections
in this lecture.
I've shown you some electron micrographs in
and I just want to define what resolving power is.
It's the ability of the microscope lens
or an optical system
to clearly distinguish 2 closely positioned objects.
It depends on a number of factors.
Resolution is a dependent on first of all,
the wavelength of light
or the wavelength of an electron beam,
depending on whether
you're using an electron microscope or a light microscope.
And it also depends on what we call
the numerical aperture
or some details about the optics used in our microscopes.
And I don't want to go into all the physics
of numerical aperture
and all the physics of resolution, but basically, if you look at the left-hand side,
the minimum distance you can discern between 2 resolvable objects
depends on the wavelength of light or the emission wavelength of an electron beam
and also on the denominator, the numerical aperture.
And quite clearly, you don't need to be a
mathematician, but if you look at that equation,
the smaller the wavelength is, the smaller
the resolving distance is.
So if you use a much smaller wavelength of
light such as electron beam,
then you're naturally going to resolve
distances between 2 points
that are very, very, very tiny or very closely related.
The human eye has a resolving power of only
about 0.2 mm or 200 µm.
Lower than that, an object just appears as a single object.
It doesn't appear as 2 separated individual
Light microscope gives us a resolution of
about 0.2 µm,
and the electron microscope, because it's got a much smaller wavelength
that the electron beam gives us a lot better resolution of around 1 nm.
So just finishing off.
If we look at these 2 last sections, on the
is a light microscope picture or image taken through an epithelial surface in the gut.
You've seen this before.
You can see at the top along line of cells,
they're columnar cells.
They've got elongated nuclei which reflects
the shape of the cells.
And under the light microscope, you can just see
at the very top the brush border, a very thin line
on the surface of these enterocytes or these
epithelial cells that represent microvilli.
You can't see details of these microvilli
because the resolving power is only 0.2 µm,
using a standard light microsoft.
If we use an electron microscope, our resolving
power is a lot higher.
We can resolve structures closer together
and on the right-hand side, you now clearly
see individual microvillus, collectively called
microvilli, projecting from the cell surface.
You can even see details of the glycocalyx
on the surface.
Fine detail, better resolving power,
it's a product of the wavelength of either
the light or the electron beam.
And lastly, here is a picture of a piece of
skeletal muscle on the left-hand side.
Under the light microscope, you can just make
out striations, but on the right-hand side,
using an electron microscope,
you not only see the striations,
but you see them in more detail.
In fact, you see details of the very dark
and light bands that characterize the basic
functional unit of skeletal muscle, and that
is the sarcomere.