Start With 100 Billion Brain Cells Called
Neurons.
The brain is, by far, the most complex and mysterious
organ in the human body. Composed of over 100 billion cells
called neurons
(sensory
neuron and motor
neurons), this amazing structure is the center from which
all of our skills of higher reasoning originate -- creativity,
learning, imagination, planning, and, perhaps most notable of
all, our sense of identity. But how exactly does the physical
brain make the transcendental leap to that much more esoteric
concept, one's sense of self? How does the brain work -- and
is it separate from what we might call the mind? These questions
are still hotly debated in scientific, philosophic,religious,
and cultural circles the world over,and the answers to them
may well never be
fully understood. Yet with the advent of modern neuroscience and psychology,
much has come to be understood about the human brain.
A technical definition of the human brain
begins, most simply, with the manner in which it is assembled. Each
of its 100 billion neurons connects to 10,000 others, forging a grand
total of somewhere between 100-1000 trillion connections strung together
by 90 million meters of neural fibers. Yet all of this neural density
weighs between three to four pounds, and is set inside a cranium no
more than 1 1/2 liters in volume, and the cortex
(the brain's rippled gray-matter surface, the center of all higher
thought processes) is no greater in thickness and surface area than
a formal dinner napkin
If peeled apart, that cortical "dinner
napkin" would reveal six distinct layers, each containing millions
of interconnected neurons. Neurons on all layers communicate with
each other through electrical impulses sent from the nucleus of each
cell, down axons
and across to dendrites of the surrounding neurons. This, in turn,
allows the brain as a whole to
communicate with the body it controls.
Through neurons, the brain is able to receive information from
numerous sensory receptors throughout the body, decide which
of these sensory stimuli deserve attention, and send commands
to initiate or inhibit various responses. Interestingly, the
brain has far more capacity to respond to stimuli than it does
to receive those stimuli in
the first place; there are 10 times the number of feedback connections
as there are "bottom-up" or sensory-input connections. It is, perhaps,
this favoring of response over input that allows humans their remarkable
skills at adapting to new, unfamiliar situations -- their ability
to interpret and innovate.
Parts Of The Brain:
From Brain Stem To Cerebellum and From Cortex
To Frontal Lobe.
On a larger scale, the brain is made up of four distinct lobes
on both the left and right hemispheres. The frontal, temporal, parietal,
and occipital lobes each have primary processing functions, such
as cognition, hearing, sensory input, and vision respectively, but
they also serve act to regulate one another. Click
here to learn more about the Parts of the Brain.
Seeing Brain Function With MRI & PET Scans
A Window Into Brain Activity.
The study of brain functions has been greatly augmented in recent
years by the development of high-tech imaging techniques that allow
scientists to observe the living brain in action. Click here to learn more about MRI
and PET Scans.
Consciousness itself is clearly quite a controversial and subjective
topic. It is thought to involve both the modern neocortex found in
all higher mammals (cats, dolphins, elephants, etc) as well as certain
profoundly developed sections of the brain stem only found in humans.
Click here to learn more about
Consciousness.
