Page 92 - Atlas of Histology with Functional Correlations

differences between cilia (singular, cilium) and microvilli (singular, microvillus).

Both cilia (1) and microvilli (2) project from the apical surfaces of certain cells
in the body. The cilia (1) are long, motile structures, with a core of uniformly
arranged microtubules (3) in longitudinal orientation. The core of each cilium
contains a constant number of nine microtubule doublets located peripherally
and two single microtubules in the center. Each cilium is attached to and extends

from the basal body (4) in the apical region of the cell. Instead of nine
microtubule doublets, the basal bodies exhibit nine microtubule triplets and no
central microtubules.

In contrast to cilia, microvilli (2) are smaller, shorter, closely packed finger-

like extensions that greatly increase the surface area of certain cells. Microvilli
(2) are nonmotile and exhibit a core of thin microfilaments called actin. The
actin filaments extend from the microvilli (2) into the apical cytoplasm of the
cell to form a terminal web, a complex network of actin filaments.

FIGURE 2.7 ■ Cilia and microvilli. ×20,000.

FIGURE 2.8 | Nuclear Envelope and Nuclear

Pores

A high-magnification electron micrograph illustrates in detail part of a nucleus
(8) and the surrounding membrane, the nuclear envelope (3), which consists of
an outer nuclear membrane (3a) and an inner nuclear membrane (3b).

Between the two nuclear membranes (3a, 3b) is a space. The outer nuclear

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