Chapter 11 The Nervous System • MHR 389
produced each day is about 500 mL. The
cerebrospinal fl uid transports hormones,
white blood cells, and nutrients across the
blood-brain barrier for cells of the brain
and spinal cord. It also circulates between
two layers of the meninges, the arachnoid
and pia mater, and therefore acts as a
shock absorber to cushion the brain.
2
Identify the main structures of
the central nervous system, and
describe its general functions.
2
Explain how the blood-brain
barrier and the cerebrospinal fl uid
protect the brain and spinal cord.
2
Identify fi ve homeostatic
functions of the brain.
2
Identify the major structures in
the hindbrain, midbrain, and
forebrain, and the functions of
these structures.
• • •
• • •
The Structure and
Function of the Cerebrum
Each half of the cerebrum consists of an
internal mass of white matter and a thin,
outer covering of grey matter, called the
cerebral cortex. Compared to a falcon
with its keen eyesight or a dog with its
sense of smell, humans lack many sensory
capabilities. Due to the evolution of the
cerebral cortex, however, humans are
considered to have the most sophisticated
intellect and behaviour of all animals.
The cerebral cortex is responsible for
language, memory, personality, vision,
conscious thought, and other activities
that are associated with thinking and
feeling. The cerebral cortex is about 5 mm
thick and, as shown in Figure 11.27, is
highly convoluted. This allows it to fi t a
high concentration of grey matter within
the confi nes of the skull. Relative to a
smooth surface, the convolutions and
fi ssures greatly increase the surface area,
so that the cerebral cortex covers about
0.5 m
2
, or about the area of an open
newspaper.
Figure 11.27 The human cerebrum. What
are the functions of the right and left sides?
Why are there so many folds along the
surface of the cerebrum?
The right and left halves of the
cerebrum are called the cerebral
hemispheres. They are linked by a bundle
of white matter called the corpus
callosum. The corpus callosum sends
messages from one cerebral hemisphere
to the other, telling each half of the brain
what the other half is doing. Surgical
isolation of the hemispheres is
sometimes used to treat epilepsy, a
condition that causes uncontrollable
seizures. Scientists think that epilepsy
can be caused by an overload of
neurological electrical activities, so the
corpus callosum is cut to prevent the
spread of the epileptic seizures from
one hemisphere to the other.
Research indicates that, while every
cognitive function contains right-brain
and left-brain components, some
functions seem to have a dominant
hemisphere. In general, the right-brain,
or right cerebral hemisphere, is
associated with holistic and intuitive
thinking, visual-spatial skills, and artistic
abilities. The left-brain, or left cerebral
hemisphere, is linked to segmental,
sequential, and logical ways of thinking,
and to linguistic and mathematical skills.
This is why people who are right-brain
dominant process and learn information
differently from people who are left-
BiologyFile
Try This
Take two eggs and two
plastic containers that are
just large enough to contain
the eggs. Fill one of the
containers with water, and
place one egg inside. Put
the other egg in the other
container, without water.
Tightly close the lid of each
container, and shake the
containers. Which egg
broke? How does this model
demonstrate the function of
the cerebrospinal fl uid?
BiologyFile
FYI
In the 1800s, several
scientists promoted the
common misconception
that humans use only
10 percent of their brains.
Researchers now know
that the destruction of even
small areas of the brain can
have devastating effects on
behaviour and physiology.
On the other hand,
sometimes a different
part of the brain is able to
compensate for, or take over,
the functions of the injured
part. This can occur when
someone has a stroke that
damages the parts of the
brain that are predominantly
involved in speech. Other,
usually less active parts may
take over the speech
functions.
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