to Brain Activity
Excerpts from "The Human Brain "
eeg is important for studying not just normal brain activity but brain
disorders as well, such as epilepsy.
In epilepsy there is a miniature brain storm of certain groups of brain
cells that can lead to convulsions. This virtual explosion of electricity
can be detected on an EEG used subsequently by neurologists to locate
where damaged brain tissue lies.
Not only does the EEG show what brain waves look like but it shows how
imagine that a signal - an electrical impulse - travelling at some 220
miles per hour, arrives at the end of the axon, and hence at the synapse.
soon as the action potential, the electrical signal, invades the end of
the axon, it creates the right conditions by which acetylcholine is released
into the synapse.
Once released acetylcholine diffuses easily through the watery salty liquid
outside all neurons, (the extracellular fluid) crossing the synapse as
readily as a boat might cross a river
The original electrical signal, which was converted to a chemical one,
now needs to be converted back to an electrical impulse.
Within our brains there are some hundred billion neurons. To get an idea
of just how big a hundred billion is, the Amazon rain forest offers an
appropriate analogy. The Amazon rain forest stretches for 2,700,000 square
miles and it contains a hundred billion trees. There are about as many
trees as neurons in the brain. But the metaphor need not stop there: if
we now consider the huge number of connections between neurons, then we
could say that there are about as many as leaves on the trees in the Amazon
It is virtually impossible to imagine on a global scale the fervour of
chemical and electrical activity, even if only 10 per cent of our hundred
billion neurons were signalling at any one moment.
brain is built up from single neurons in increasingly complex circuits.
Between ten thousand and one hundred thousand neurons make contact with
any particular neuron. In turn any particular neuron will become one of
many thousands of inputs for the next cell in the
network. If we took a peice of brain the size of a match head alone there
could be up to a billion connections on that surface.