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A brief account of the construction of the brain and how it works

It is difficult to imagine how many cells there are in the brain – 100 billion neurons and up to 5 times as many supporting or glial cells.

Neurons: There are many different types of neuron. These are cells that consist of a cell body, up to 0.1 mm in diameter, and processes. Extended from the cell body is one long process, called the axon, and several smaller processes, called dendrites. The axon can be up to a metre or more long. Each neuron can have contact, called synapses, with thousands of other neurons.

Glial cells: Glial cells are astrocytes, microglia and oligodendrocytes.
Astrocytes consist of a cell body approximately 0.015 mm in diameter. Long slender processes extend in all directions from the cell body. The name, astrocyte or asgroglial cell, derives from the cell resembling a star when looked at through a microscope, after staining. The processes extend towards and surround the synapses, neuronal cell bodies as well as the blood vessel walls, forming contact with other astrocyte processes. Thus these cells are arranged in large cell formations with contact between the different cells.

The microglial cell acts as the cleaner of the nervous system, intimately involved in immunological processes. These cells are small with tiny processes which continuously move around, probing the extracellular milieu of the nervous system. The microglial cells become activated at the first sign of infection, inflammation or any other damage.

The oligodendrocyte produces a myelin sheath, which is made up of lipids and proteins that surround the neuronal processes. Within the myelin sheath, electrical impulses are moved along the neuronal processes extremely rapidly.

There is extensive continuous signalling between all the cells and even the astrocytes are active.

The figure shows the brain (below to the left) with its pleated surface, neuronal and glial couplings (above) and the contacts of the astrocytes towards a blood vessel, the so called blood-brain barrier (top to the right). In addition, the figure illustrates a coupling between two neuronal processes, a so called synapse which is surrounded by astrocyte processes (below to the right).

Illustration by Eva Kraft, Gothenburg.

The brain works as a whole

There are regions in the brain which are dedicated to performing different functions, for example to register and process light or sound information, while other regions are responsible for movements and sensibility.
All regions in the brain must work together in order for the most advanced brain functions to become activated − “The brain works as a whole”.

Illustration by Eva Kraft, Gothenburg.

Currently, we know very little about the ways that mental processes are performed within the brain. The regulation of sensory influx has been studied with regard to vision and hearing. There are special units that process visual information comprised of neuronal circuits that recognise straight lines and horizontal and vertical structures. There are similar units for other signal types, but also other, more adaptable ones. Such units can be unconsciously activated in order to suppress background noise or prevent it from reaching conscious hearing. For instance, when a low frequency fan which has been working for a few hours is turned off, we become relaxed. This indicates that the unconscious mental process of suppressing the background noise requires energy.

It is also possible to recruit, shape and/or activate such units consciously. In a similar way to unconscious suppression of background noise etc., active and conscious suppression requires energy as well. Mental functions which have been formed under normal conditions function optimally in similar conditions. Should the conditions change, the precision of the functions could be impaired, which may lead to increased uncertainty in the processes and thereby also increased energy consumption.

Page Manager: Pontus Sundén|Last update: 9/10/2010
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