Biology of the Brain - Key Points

The Brain - General Features

• The brain is the most complex structure in the known Universe!
• It possesses many highly specialized component parts each associated with specific tasks, for example memory and vision.
• The functioning of the human brain not only allows us to sense our environment and coordinate movements but also gives rise to attributes such as consciousness.
• The latter is difficult to define but includes such attributes as a sense of past and future, an inner voice and self-awareness. Intelligence appears to be the outward sign of a conscious being.
• It is the result of millions of years of evolution - the distant origins of the human brain can be seen in simple reptiles and mammals.

The Human Cortex

• The most striking feature of the human brain is seen in the cortex. This is the folded, hemispherical structure which constitutes the bulk of the visible brain.
• It is not present in reptiles.
• The cortex is relatively recent. It is perhaps one hundred thousand years old and is the part of the brain most closely associated with our ability to form complex representations of the external world, to reason logically and to use language.
• It is much more dominant in humans than in any other species.
• Regions of the cortex control vision, our auditory senses, voluntary movement and touch sensations. It is also crucial for long term memory.

Neurons and Networks

• The central nervous system is composed of something like one hundred billion nerve cells or neurons.
• Each nerve cell or neuron possesses a single axon along which it can pass electrical signals to other neurons. Incoming signals are carried by a neuron's dendrites which form a tree-like structure around the neuron.
• Neurons are about one micron (1 millionth meter) in diameter. The dendrites are perhaps ten times this in length while the axon varies from a millimeter up to one meter in length.
• The signal from one neuron reaches another at the junction of axon and dendrite -- the synaptic gap.
• The typical voltages associated to these signals are small (tens of millivolts) and travel at about two hundred miles an hour (100 meters per second)
• Typically neurons can only fire once every millisecond (one thousandth of a second)
• Different patterns of electrical firing activity are associated with different brain functions.

Learning and Connections

• The brain is both robust (able to function in the event of severed connections and/or dead neurons) and plastic - able to adapt to new memories and functions.
• This is due to ability of the brain to form new connections between neurons. These connections take place at synapses and are mediated by the release of neurotransmitter chemicals.
• These neurotransmitters alter the effective strength of the signal which can pass between neurons.
• During our early years and during any kind of learning process these connections form and change their strengths.
• The power of the brain as a computational device derives from the complex network of neural pathways and the simultaneous processing capability of all the neurons.