In this laboratory we're going to look at nervous tissue and on neurons. I've
shown you this image before of a multipolar neuron, this neuron comes from
the anterior form of the spinal cord I wouldn't expect you to know that at this
point in time clearly but we don't have any trouble identifying the nucleus and
nucleolus and the cytoplasm, which is called the perikaryon in neurons, it's
the cytoplasm within the cell body of a neuron. The cytoplasmic nissl substance
which is all this granular apunctate staining, essentially consists of rough
endoplasmic reticulum and poly ribosomes, this stains basophilic and it occurs
in clumps because what you're going to learn later in the course is that the
substantial microtubule networks disrupt the continuous sheets of the rough
endoplasmic reticulum so that when a neuron cell body is stained
you see these clumps of material and this has given the name Nissl substance.
You can observe dendrites that are coming into this neuron cell body and
can maybe just barely see the axon hillock in this area. You'll notice that
the nissl substance is in the dendrites so there is rough ER in ribosomes in the
dendrite but the axon hillock appears unstained and that's because there is no
rough ER or ribosomes to speak of going down into the axon of the neurons. This
particular neuron is stained with toluidine blue, I don't really expect you
to know that and then you can see some various nuclei of supporting cells
around this multipolar neuron. Here are some more multipolar neurons that are
stained with the silver stain, neurons preferentially take up heavy metal and
you can notice a lot of neurofibrils on this slide. These are essentially
aggregates of neurofilaments in microtubules and these filaments run
throughout the cytoplasm in neurons. There is some more multipolar neurons
that are silver stained and again these are in the anterior
horn of the spinal cord. You wouldn't be expected to know that at
this point in time but you can see this network of neuropil or cytoplasmic
processes from these various neurons. Here are several peripheral nerves, the
section demonstrates two peripheral nerves actually in cross-section within
dense irregular connective tissue. You can identify axons within these nerves
and you can identify flattened cells of the perineurium. Nuclei associated with
the axons could be either nuclei of Schwann cells or cells that make up the
endoneurium and we'll talk about the endoneurium and perineurium later in
the course. Here are some more peripheral nerves, this is a section that's stained
with osmium and you can see myelinated axons and you can see the perineurium
like this and the epineurium like this. These dark staining cells are actually
fat cells or adipocytes. The endoneurium which are connective tissue sheets that
are around individual axons cannot really be delineated at this low
magnification. Here's another peripheral nerve this
time it's stained with H and E and you can identify individual myelinated axons you
can also see nuclei that could either be Schwann cells or fibroblasts and at this
magnification you can't really distinguish between the Schwann cells or
fibroblasts so here is a smaller nerve and a little bit larger nerve. Now that's
something I'd like to highlight for you right here where my pointer is, that's
the actual axon that's being wrapped with myelin. Here is a peripheral nerve
with some surrounding connective tissue, a lot of fat shown here, some small blood
vessels, maybe an artery and a little small vein here and then a larger artery
down here and in this larger artery which you can clearly identify something
called the tunica intima, the internal elastic lamina like so, the tunica
media which is mostly smooth muscle and then the tunica adventitia and
you're gonna come to appreciate that the tunica adventitia in these arteries
blends with the loose connective tissue around the nerve and you're gonna, I
think remember from gross anatomy often times that blood vessels and nerves run
together and that's what you're observing in this particular
histological preparation. This is a little bit higher power view in
longitudinal section of myelinated axons. You can see a nice myelinated axon
running like this, the dark arrow is highlighting a node of ranvier and you
can see the light blue staining connective tissue, this is a trichrome
stained slide and these trichrome stained slides the blue stained stains
connective tissue, this would be the endoneurium that's enveloping each
individual myelinated axon so let me review this for you one more time. This
would be the axon itself, the white area would be the myelin sheath which is kind
of dropped out in the histological preparation, the node of ranvier like so
and then the connective tissue that would make up the endoneurium. Here you
can see some nuclei and these nuclei may be a nuclei of Schwann cells or
fibroblasts, of course the Schwann cells are producing the myelin that wraps
around the axon and the fibroblast would be the connective tissue cells that are
making the endoneurium. This is a plastic section stained with toluidine
blue, can observe the node of ranvier at the dark arrowhead and you can also
identify the nucleus of the Schwann cell probably visible here and the upper left
portion of the field. In this particular preparation, the myelin stains are very
deep blue and the axons appear unstained. This is a low-power view of a spinal
ganglion and this micrograph, you can clearly see the dorsal root towards the
top of the field and the ventral root on the bottom of the field and perhaps the
spinal nerve over here on the right side the field. A higher power view of the
spinal ganglion, you can identify nerve cell bodies, these big cells of the nerve
cell bodies, maybe right here would be part of the axon hillock and some of
these nerve cell bodies, you can get a sense of the nucleus and nucleolus, you
can see the punctated staining of the cytoplasmic nissl substance and you
can see some smaller cells which would be supporting cells or satellite cells
around these ganglion. This is a fairly high power view of the cortex of the
cerebellum and you can clearly notice the white matter shown here and the gray
matter that's shown here and it's very easy to get your orientation in the
cerebellum, if you look at the gray matter
there are several distinct layers. There's a granular layer, a layer of
Purkinje cells shown here and the molecular layer and so you can always
tell your orientation of gray matter from white matter in the cerebellum by
looking for the Purkinje cell layer and you're going to come to appreciate that
the Purkinje cell layer is a layer of cells in the gray matter that's between
the molecular layer and the granular layer. Here is just a higher power view
of the Purkinje cells shown like this so a little bit of the granular layer on
the bottom and the molecular layer on the top and some of the Purkinje cells.
You can actually see the nuclei and the nucleoli and you can get some ideas of
profiles of small blood vessels and in various positions on this slide and a
silver stained preparation, just a higher power view again of the Purkinje cells
and you can see some of the cytoplasmic processes coming off of these Purkinje
cells going into the molecular layer. This is a Golgi stained preparation of
the cerebrum and it's just to highlight these large pyramidal cells and various
protoplasmic astrocytes. On the pyramidal cells, you can notice the very large
apical dendrites. Just a thought question for you, on these pyramidal cells these
are all the dendrites so where might you expect the axon
to be, just some various profiles of protoplasmic astrocytes, perhaps a little
bit of a profile of a blood vessel on the bottom. This is located in grey
matter and this is a silver stain, another view of protoplasmic astrocytes.
Protoplasmic astrocytes are actually the largest of the glial cells and they tend
to possess relatively blunt cytoplasmic processes. I'm not going to expect you to
really differentiate between protoplasmic and fibrous astrocytes, you
can make a general rule though, protoplasmic astrocytes are found in
grey matter whereas fibrous astrocytes which are cells like this have found in
white matter. Fibrous astrocytes tend to have very fine filamentous cytoplasmic
processes. This is not a course in neurobiology so I'm not going to ask you
to really be able to distinguish protoplasmic versus fibrous astrocytes.
As you become more experienced, you'll be able to identify areas in the central
nervous system that are grey matter because those are the areas where you
find the cell bodies of neurons as opposed to the white matter where you
essentially are just finding the axons and no cell bodies. Here are some views of
oligodendrocytes, oligodendrocytes are small glial cells and they usually
found near nerve cell bodies and we believe that the oligodendrocytes
function like Schwann cells in that they myelinate axons within the central
nervous system, so for example here's an oligodendrocytes, here are some
individual cell bodies of neurons so so here here here some more
oligodendrocytes and you can get the impression that these oligodendrocytes
are putting out cytoplasmic processes that are wrapping around individual
neurons and one thing that's rather interesting within the central nervous
system, these oligodendrocytes may envelop
multiple neurons with myelin sheaths. These are small micro
glial cells, these are thought to be the macrophages within the central nervous
system. Here are some pigmented neurons, these
neurons are actually pigmented with melanin granules. These happen to be
within the locus coeruleus of the pons. Pigmented neurons are relatively rare in
the central nervous system but they are found in at the olfactory bulb, the
substantial nigra, maybe reticular formation and they're found in some
spinal and sympathetic ganglion. This particular cell is just meant to
demonstrate the pigmented neurons, I'm not going to ask you to locate what
specific region in the central nervous system these happen to be found within
but you can clearly see the neurons with melanin granules within them.
Here are some blood vessels that you can see in this region of the central
nervous system. Here is a meissner's corpuscle, meissner's corpuscles are
touch receptors that are located in the hairless regions of the skin, you find
them within into digitation between the dermis which is down here and the
epidermis here and I'll remind you since this skin, this is a stratified squamous
epithelium with keratin, the dermis is a irregular connective tissue that you can
see the meissner's corpuscle that i'm highlighting here. These touch receptors
consist of axons, perhaps of one to four different types of afferent nerves that
are not visible but these nerves are surrounded by an elaborate club shaped
capsule which is composed to fibroblasts and flat epithelial like cells and
nuclei of these cells tend to be located horizontally. The axons, once they enter
this capsule, lose the myelin sheath and they're going to branch extensively and
interdigitate processes among the epithelial like cells and this is just a
little bit higher magnification of the meissner's corpuscle and finally this
onion-like structure is a pacinian corpuscle, this is a
pressure receptor and in this case it's found at the junction between the dermis
and the hypodermis and so here's the hypodermis the fat and more of the
connective tissue in the dermis. This pacinian corpuscle has multiple layers
of concentrically arranged fibroblast like cells that comprise the capsule of
this structure. In real life, these concentric layers of cells are filled
with fluid right in the very middle, you can actually see the axon for this
receptor, you can see these nuclei that would be nuclei of fibroblasts which are
the cells that are making up these concentric rings of tissues that are
surrounding this axon. You can see some small blood vessels off to the side in
this image as well.