The central nervous system is divided into
two parts: the brain and the spinal cord. The brain contains about 100 billion
nerve cells (neurons) and trillions of "support cells" called glial
cells. The spinal cord is about 43 cm long in adult women and 45 cm long in
adult men and weighs about 35-40 grams. The vertebral column, the collection of
bones (back bone) that houses the spinal cord, is about 70 cm long. Therefore,
the spinal cord is much shorter than the vertebral column.
The lateral sutface (left) and sagiital
transsection (right) of the human brain
From a top view,
notice how the brain is divided into two halves, called hemispheres. Each
hemisphere communicates with the other through the corpus callosum, a bundle of
nerve fibers. The surface of the both hemispheres is covered by the cerebral
cortex. The thickness of the cerebral cortex varies from 2 to 6 mm. In higher
mammals such as humans, the cerebral cortex looks like it has many bumps and
grooves. A bump or bulge on the cortex is called a gyrus and a groove is called
a sulcus. Lower mammals, such as rats and mice, have very few gyri and sulci.
Generally, the cortex consists of sensory area (visual, auditory, somatosensory
and olfactory), motor area (responsible for the motor control) and associative
cortex (responsible for mental process).
The cerebellum is
located behind the brain stem. In some ways, the cerebellum is similar to the
cerebral cortex: the cerebellum is divided into hemispheres and has a
cerebellar cortex that surrounds these hemispheres. Mainly
cerebellum responsible for movement, balance and posture.
The thalamus
receives sensory information and relays this information to the cerebral
cortex. The cerebral cortex also sends information to the thalamus which then
transmits this information to other areas of the brain and spinal cord.
The hypothalamus
is composed of several different areas and is located at the base of the brain,
below thalamus. The hypothalamus is responsible for some very important
functions first of all
- control of the body temperature and homeostais.
The brain stem is
a general term for the area of the brain between the thalamus and spinal cord.
Structures within the brain stem include the medulla, pons, tectum, reticular
formation and tegmentum. Some of these areas are responsible for the most basic
functions of life such as breathing, heart rate and blood pressure.
The limbic system
is a group of structures that includes the amygdala, the hippocampus,
mammillary bodies and cingulate gyrus. These areas are important for
controlling the emotional response to a given situation. The hippocampus is
also important for memory.
The
basal ganglia are a group of structures, including the globus pallidus, caudate
nucleus, subthalamic nucleus, putamen and substantia nigra,
that are important in coordinating movement.
