Something in the cell itself may align some quantum forces and these
cells are in our test tubes. There probably soon will be no need to
appeal to the impossibility dogma and Penrose's main fears will become
extinguished.
Microtubules are cylindrical molecules made by gluing together 13
strands of the protein, tubulin, to make a tube 25 nanometres across,
with a central channel about 15 nanometres wide. Each microtubule is
covered by a fuzz of protein stubs, known as MAPs (microtubule
associated proteins), and these can be used to hook clusters of
microtubules together into larger lattices. Both microtubules and MAPs
seem to be capable of a certain amount of movement, meaning that they
can be woven into plastic structures, able to give and bend.
The structural properties of microtubule assemblies make them a
valuable building material within cells. For example, a bundle of 20
microtubules form the beating, hair-like cilia that coat the surface
of many small single-celled animals, allowing them to swim. However
the main use for microtubules appears to be to make an internal
skeleton for cells-an intricate scaffolding that gives a cell its
shape but also can deform and bend enough to allow it to move.
The existence of the microtubule cytoskeleton was discovered only
relatively recently in the 1970s-previously the fixative chemicals
used in electron microscopy was having the unfortunate effect of
dissolving the tubules-so biologists still have much to learn about
what the cytoskeleton does and how it operates. Yet biologists believe
that it not only holds a cell in shape but also plays an important
role in cell metabolism, acting as a piping system or an internal
highway to move plasma and other essential cell products about the
cell. Some have suggested microtubules might do this by using their
MAP spurs to drag cell protoplasm along, hand over hand, in a
miniature bucket brigade running up the sides of a tubule.
There is also evidence that the cytoskeleton could serve as a
primitive brain. Biologists have long been puzzled how a simple single-
celled animal, like the slipper-shaped paramecium, could behave so
intelligently when it has no nervous system. A paramecium is
surprisingly nimble as it swims about in pond-bottom detritus,
twisting in and out of tight spaces in search of its dinner. Somehow
the protozoan manages to respond swiftly to information coming in from
a light-sensitive eyespot and its touch-sensitive cilia to co-ordinate
its swimming action. Several biologists have speculated that the
cytoskeleton could serve as the communication and information
processing link needed to organise such relatively complex behaviour.
This suggestion that the cytoskeleton could be a "brain within a
brain" has particularly excited the quantum theorists. In casting
around for a suitable cell structure to operate as a go-between,
connecting the sub-atomic realm with the macroscopic world of firing
brain cells, some theorists had considered that the membranes at the
synaptic junctions between nerve cells might be the site of quantum
interactions. Others had wondered whether the ion channels down the
flanks of neurons could be ruled by quantum effects. But quickly,
microtubules began to look a far better bet. While microtubules are
not unique to neurons, they are found there in particular abundance (a
fact that does not surprise neurologists given that nerve cells are so
metabolically-active and microtubules seem essential to metabolic
activity). Furthermore, the speed at which microtubules can switch
state between relaxation and contraction is believed to be of the
order of a nanosecond. This may be slow by the usual time scales of
quantum events, but it is about a million times faster than the cell
firing events usually believed to underlie consciousness and so at
least appears to get the biology of the system within striking
distance of a quantum explanation.
http://www.dichotomistic.com/mind_readings_quantum%%20mind.html
