Discurso

The nucleus is large and usually spherical, containing a
prominent nucleolus. The nucleochromatin is invariably
pale, with little dense heterochromatin. In some neurons,
such as the cerebellargranule cells, the nucleoplasm may
show more differentiation and dense heterochromatin.
The nucleolus is vesiculated and clearly delineated
from the rest of the nucleoplasm. It usually contains
twotextures: the pars fibrosa, which are fine bundles
of filaments, and the pars granulosa, in which dense granules
predominate. An additional juxtaposed structure,
found in neurons of the female ofsome species, is the
nucleolar satellite, or sex chromatin, which consists of
dense but loosely packed, coiled filaments. The nucleus is
enclosed by the nuclear envelope, made up on the cytoplasmicside by the perikaryon inner membrane, which
sometimes is seen in continuity with the endoplasmic
reticulum (Fig. 1-5), and a more regular membrane on the
inner, or nuclear, aspect of the envelope.Between the two
is a clear channel of between 20 and 40 nm. Periodically,
the inner and outer membranes of the envelope come
together to form a single diaphragm, a nuclear pore
(Fig. 1-5). Intangential section, nuclear pores are seen as
empty vesicular structures, approximately 70 nm in diameter.
In some neurons, as in Purkinje cells, that segment
of the nuclear envelope which faces thedendritic pole is
deeply invaginated.
The perikaryon, or body of the neuron, is rich in organelles
(Fig. 1-4). It often stands out poorly from a homogeneous
background neuropil, most of which iscomposed
of nonmyelinated axons and dendrites, synaptic complexes
and glial cell processes. Closer inspection shows
that, like all cells, the neuron is delineated by a typical
triple-layered unitmembrane approximately 7.5 nm wide.
Among the most prominent features of the perikaryal
cytoplasm is a system of membranous cisternae, divisible
into rough or granular endoplasmic reticulum (ER),...