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
- 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
- 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
- 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
- These neurotransmitters
alter the effective strength of the signal which can pass
- 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.