Brain state

In chapter 6 we defined the internal state of a cell: a set of reciprocal dependences involving structure, metabolism and transport. Internal state became central part of our characterisation of "livingness". Similarly, "brain state" is an important part of our tentative characterisation of "mind".

Essentially, the structure of the human brain consists of neurones connected via synapses to form pathways or circuits50. Brain function consists of the activities of these circuits: ordered sequences of action potentials, neurotransmitter release events, and postsynaptic responses. Function obviously depends on structure. However, as we showed in chapter 16, structure also depends on function. Neuronal activities alter the strengths of synapses and they also forge new growth in axon termini and the formation of new connections, i.e. new circuits.

50 Anyone with a basic knowledge of anatomy knows this to be an oversimplification. Apart from neurones, brains also contain large numbers of glial cells, whose functions include regulation of neurotransmitter levels. Blood vessels abound. Also, there are spaces filled with cerebrospinal fluid, which act as shock absorbers as well as maintainers of fluid, electrolyte and nutrient balance. Protective fibrous sheets surround the whole organ. When we speak of "structure" in the text we mean only those aspects of structure that are directly relevant to brain function.


-*- Brain



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