ULTIMATE COMPUTING - Quantum Consciousness Studies

Cytoskeleton/Cytocomputer 113
Figure 5.22: Amoeboid movement in a time-lapse series by U. P. Roos at the
University of Zurich. 1a) Probing lamellipodia (arrow-heads) in direction #a of
cell movement. Retraction fiber (arrow) shows trailing end of cell. b)
Cytoplasm has flowed to fill out lamellipodia. c) Finger-like filopodia (arrow)
probe direction. d) Cytoplasm advances, moving cell. With permission from U.
P. Roos (1984).
Using the electron microscope, Lazarides and Revel (1979) described the
lamellipodium as a somewhat irregular sheet of cytoplasm about one tenth of a
micrometer (100 nanometers) thick. It is decorated along the edge by small
protrusions resembling stubby fingers which attach themselves to the surface of
the dish, and can quickly extend several times their initial length into rod-like
filopodia. These are highly dynamic structures that can change from a fluid state
to a rigid one in less than a second by virtue of the sudden assembly of actin
filaments. Growing from the cell surface, they provide spatial guides between
which the cell membrane and cytoplasm flows to form the ruffle. The filopodia
either attach themselves to the substrate and become rigid, or melt back into the
cell. The cell adheres to the surface below it at only a few distinct sites, rather like
a hand contacting a table top only with finger tips. Permanent contacts of the
ruffle with substrate result in adhesion plaques; as the cell moves the plaques are
continuously formed and broken. In addition to their role in cell adhesion and
motility, the ruffles and particularly the filopodia serve a sensory function. In the
developing embryo when the filopodium of one migrating nerve cell makes
contact with the surface of another, the cells stop moving toward each other.
Similarly, when the filopodium of a cell spreading in tissue culture touches the