SSB Histology Lab IV
Nerve Cells and Glia
SSB Week 4
►►► NOTE: Slide numbers may differ from box to box. If you don't have the slide listed, ask your colleagues.
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Slide 23, Spinal cord.
(EASY) Distinguish white matter from gray matter.
Locate the principal gray-matter regions (dorsal horn,
ventral horn).
(EASY) Associate functional ascending and descending
pathways with particular white matter regions. Dorsal
columns are easy (set off by the dorsal horns), but note
the absence of any markers for particular lateral and
anterior tracts.
(THOUGHTFUL) Determine the approximate level of
the cord section(s) on your slide. Recall that dorsal
columns must be larger in size at higher levels, as more
axons join the tracts at each level. The ventral horn area
is larger in regions serving the upper or lower limbs.
Slide 21. Cerebellar cortex.
The layers of the cerebellar cortex are conspicuous, so
begin by noting the outer "molecular layer" (where nerve
cell bodies are rare), the large cell bodies of the "Purkinje
cell layer", the densely-packed nuclei of the "granule cell
layer", and the underlying white matter.
(EASY) Find blood vessels in both white and gray
matter.
(EASY) Distinguish nerve cell bodies from glia. Nerve
cell bodies have noticable cytoplasm and nuclei that are
large, round, and relatively euchromatic. Glia generally
have inconspicuous (i.e., invisible) cytoplasm and small,
oval, heterochromatic nuclei.
(HARDER) Try to distinguish astrocyte nuclei from
oligodendrocyte nuclei. (You will not be tested on this
distinction.) Note that the nuclei of oligos are smaller and
more heterochromatic than those of astrocytes. Oligos
may be more numerous in white matter.
[For a later lab (week 7): Imagine the complete shape,
including dendrites and axons, of the neurons comprising
the visible layers of the cerebellar cortex. Think about
afferent and efferent axons, as well as the functional
connections locally within the cerebellum.]
Slide 20, Cerebral cortex, pre- and postcentral gyri.
This specimen spans the central sulcus, containing
portions of both precentral gyrus and postcentral gyrus.
The connective tissue in between (i.e., within the sulcus)
is called arachnoid and includes some fairly large blood
vessels.
(EASY) Find blood vessels within the cortex.
(EASY) Distinguish nerve cell bodies from glia.
Note that both vessels and nerve cell bodies may be
surrounded by clear space, an artifact that is relatively
common in nervous tissue due to tissue shrinkage.
(HARDER) Distinguish astrocyte nuclei from
oligodendrocyte nuclei. (Use the same criteria to
distinguish these cell types as in spinal cord, above.)
[For a later lab (week 7): Determine which gyrus is
which. Try to visualize the six layers of the cortex, and
what sorts of connections are typical of each layer. Think
about the synapses occurring in the cortex, with their
associated afferent and efferent axons.]
(EASY) Find blood vessels within the cerebellum.
(EASY) Distinguish nerve cell bodies from glia. Nearly
all of the nuclei in the molecular layer belong either to
glial cells or to capillary endothelium. But note that
within the densely-packed small nuclei of the granular
cell layer, granule cells (small neurons) and glia cannot be
readily distinguished.
Slide 22, Golgi stain, cerebral or cerebellar cortex.
A Golgi stain can, potentially, reveal great detail about
the shapes of cells in central nervous tissue, not only
neuronal dendrites and axons but also glial cell processes.
But the stain is quirky and our samples are not fine
examples of the art. The really large, irregular dark
patches are just masses of crystalized stain. Blood vessels
may also look like big, dark blobs. Nevertheless, with
some patience and care (i.e., thoughtful and diligent
searching), you may be able to find a nice example of a
nerve cell on which you can see dentritic spines, or an
astrocyte with end feet contacting a capillary.