Making sense of the brain's mind-boggling complexity isn't easy. What we do know is that it's the organ that makes us human, giving people the capacity for
art, language, moral judgments, and rational thought. It's also responsible for
each individual's personality, memories, movements, and how we sense the
world.
All this comes from a jellylike mass of fat and protein weighing about 3
pounds (1.4 kilograms). It is, nevertheless, one of the body's biggest organs,
consisting of some 100 billion nerve cells that not only put together thoughts
and highly coordinated physical actions but regulate our unconscious body
processes, such as digestion and breathing.
The brain's nerve cells are known as neurons, which make up
the organ's so-called "gray matter." The neurons transmit and gather
electrochemical signals that are communicated via a network of millions of nerve
fibers called dendrites and axons. These are
the brain's "white matter."
The cerebrum is the largest part of the brain, accounting
for 85 percent of the organ's weight. The distinctive, deeply wrinkled outer
surface is the cerebral cortex, which consists of gray matter.
Beneath this lies the white matter. It's the cerebrum that makes the human
brain—and therefore humans—so formidable. Whereas animals such as elephants,
dolphins, and whales have larger brains, humans have the most developed
cerebrum. It's packed to capacity inside our skulls, enveloping the rest of the
brain, with the deep folds cleverly maximizing the cortex area.
The cerebrum has two halves, or hemispheres. It is further divided into four
regions, or lobes, in each hemisphere. The frontal lobes,
located behind the forehead, are involved with speech, thought, learning,
emotion, and movement. Behind them are the parietal lobes,
which process sensory information such as touch, temperature, and pain. At the
rear of the brain are the occipital lobes, dealing with vision.
Lastly, there are the temporal lobes, near the temples, which
are involved with hearing and memory.
Movement and Balance
The second largest part of the brain is the cerebellum,
which sits beneath the back of the cerebrum. It is responsible for coordinating
muscle movement and controlling our balance. Consisting of both grey and white
matter, the cerebellum transmits information to the spinal cord and other parts
of the brain.
The diencephalon is located in the core of the brain. A
complex of structures roughly the size of an apricot, the two major sections are
the thalamus and hypothalamus. The thalamus
acts as a relay station for incoming nerve impulses from around the body that
are then forwarded to the appropriate brain region for processing. The
hypothalamus controls hormone secretions from the nearby pituitary
gland. These hormones govern growth and instinctual behavior such as
eating, drinking, sex, anger, and reproduction. The hypothalamus, for instance,
controls when a new mother starts to lactate.
The brain stem, at the organ's base, controls reflexes and
crucial, basic life functions such as heart rate, breathing, and blood pressure.
It also regulates when you feel sleepy or awake.
The brain is extremely sensitive and delicate, and so requires maximum
protection. This is provided by the surrounding skull and three tough membranes
called meninges. The spaces between these membranes are filled with fluid that
cushions the brain and keeps it from being damaged by contact with the inside of
the skull.