The brain is the most complex and highly of semi-permeable excitable
membranes which specialised of all mammalian organs. Under- can be
caused, rapidly and transiently, to under- standing the complexity of
its function remains go changes in permeability to small chemical man's
greatest challenge. The functional unit is molecules and to cations. The
highly specialised the neurone, or excitable nerve cell, making ana-
nature of the constituent cells, with their unique tomical and chemical
connections with other function and specificity, is c10sely related to
units in the system. Many of the essential bio- the structure of the
whole tissue. The underlying chemical connections of the nerve cell are
de- chemical processes cannot be discussed or seen pendent upon special
morphological features: in perspective without constant awareness of
synaptic contact is mediated by chemical mol- related aspects of
physiology and morphology. ecules, 'neuro-transmitters' which ensure the
The hrain is structurally extraordinarily com- continued propagation of
electrical impulses plex in its distinct anatomical regions, each of
through sequential units of the system. Also which is heterogeneous in
the types and struc- c10sely related to the morphology of the ner- tures
of the constituent cells. vous system is the chemical energy expended in
One aspect of the biochemical function of maintaining distribution
gradients of cations the brain can be seen in its efficient production
across cellular membranes. Chemical neuro- of the energy required to
support the unique pro- transmission results in an alteration in cation
cesses referred to above.
