We often discuss the interaction between the central nervous system and
muscle action. We even discuss the relationship between nerve fibres and the
type of muscle fibre, because interchanging the nerves that feed slow and
fast twitch musce fibres interchanges the properties of the muscles fibre
themselves. However, in the context of exercise science, there is scant
discussion on what happens to central nerves as a result of motor learning
processes taking place in sports training.
For many decades, neuroscientists have generally supposed that the process by
which the brain achieves its phenomenal performance is fundamentally similar
to the digital manner in which electronic computers work. However, recent
research has shown that very sophisticated computation and learning occurs
even at the level of individual cells and their even smaller components. The
implications for current simplistic views of nervous management of motor
processes are enormous. Surely we need to be humbled by such findings and
realise that we have long way to go before we even vaguely understand motor
learning and the processes that really underlie strength, speed and power!
The following article in the "Scientific American" gives more details on this
topic:
Debunking the Digital Brain: Individual neurons contribute to the brain's
unmatched complexity
<http://www.sciam.com/explorations/020397brain/020397explorations.html>
Here are a few extracts from this interesting article:
<Individual neurons, it turns out, are not so simple after all: experiments
have shown that they can actually perform surprisingly complex calculations
and register fine discriminations. It is even possible that networks of
interacting molecules within an individual neuron might perform specific
computations, Christof Koch of the California Institute of Technology
reported in the January 16, 1997 issue of Nature. The organ of thought is
looking far more complex than scientists believed just a few years ago.
Koch's conclusions are based on studies of the precise electrical behavior of
cells in the brain. Neurons conduct signals in the form of tiny electrical
impulses, known as spikes. Messages travel from one neuron to another as
pulses of chemicals that are released at specialized junctions, or synapses;
there are trillions of such junctions in the human brain. How and when
synapses relay messages between neurons is crucially important in controlling
mental activity. Moreover, neuroscientists believe that learning occurs
through a change in the strength of certain synaptic connections. A
frequently-used synapse becomes stronger, whereas an infrequently used one
may grow weaker over time.
Researchers have long understood the basic division of function in the
neuron. One set of branch-like extensions from the cell bears incoming
synapses; another set of branches, usually located at the end of a long
threadlike extension, processes outgoing messages. In the traditional view of
the neuron, which goes back to experiments conducted in the 1940s, the cell
functions as a fairly simple on-off switch. A spike would be initiated in a
neuron if the total amount of stimulation at all the incoming excitatory
synapses exceeded some critical level. (Conversely, if the neuron received
enough inhibitory synaptic signals, it would stop producing spikes.)
Yet as Koch observes, scientists have discovered that neurons actually have
numerous electrically-active components in the incoming branches. These
active components, which include the NMDA receptor, a protein that spans the
neuronal membrane, modify the effect of incoming messages. For example, the
active components ensure that spikes received at synapses that are adjacent
to one another carry more weight than spikes received at widely-separated
synapses. Computer simulations show that active elements probably multiply
the influence of adjacent synapses, rather than merely adding them together
as the traditional neurologists had supposed. This finding adds a layer of
complication to the picture of how the brain works.
And the story gets still more involved. Koch notes that the conventional idea
that the timing of individual spikes is unimportant turns out to be quite
wrong. Researchers had generally supposed that the representation of
information in the brain depends essentially on the overall rate of firing of
the neurons. But experiments over the past few years have shown conclusively
that some cells in monkeys' brains can adjust the intervals between spikes in
increments as little as one hundredth of as second.>
------------------------
Dr Mel C Siff
Denver, USA
http://www.egroups.com/group/supertraining
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