The two halves of the nervous system work together in order for
your body to properly communicate its sensations and needs. The
forebrain, midbrain, hindbrain, and spinal cord form the central
nervous system (CNS), which is one of two great divisions of the
nervous system as a whole. The brain is protected by the skull,
while the spinal cord, which is about 17 inches (43 cm) long, is
protected by the vertebral column. The other great division of
the human brain is the peripheral nervous system (PNS), which
consists of nerves and small concentrations of gray matter
called ganglia, a term specifically used to describe structures
in the PNS. Overall the nervous system is a vast biological
computing device formed by a network of gray matter regions
interconnected by white matter tracts. The brain sends messages
via the spinal cord to peripheral nerves throughout the body
that serve to control the muscles and internal organs. The
somatic nervous system is made up of neurons connecting the CNS
with the parts of the