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In cross section the 9 + 2 axoneme of the cilium stands out. The
plasma membrane (pm) covers the axoneme and is continuous with
the plasma membrane covering the cell body. Each doublet tilts inward
to the tangent of the axonemal cylinder. Two arms, an inner arm and
outer arm, extend from the complete microtubule of each doublet. These
arms have ATPase activity and are called dyneins. They cause one
doublet to slide against the adjacent doublet. Other protein links
(spokes) in the axoneme are elastic and induce the characteristic
bending of the cilium and prevent excess sliding as the doublets slide
past each other. EM taken on 7/15/67 by R. Allen with Philips 200 TEM.
Neg. 19,200X. Bar = 0.2µm.
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