resemblance to a horse’s tail) that               tissue that rests on the outside of the brain and
    continues inferiorly to the sacrum and            spinal cord.
   The white matter of the spinal cord               Cerebrospinal Fluid
    functions as the main conduit of nerve                The space surrounding the organs of the
    signals to the body from the brain.                    CNS is filled with a clear fluid known as
   The grey matter of the spinal cord                     cerebrospinal fluid (CSF).
    integrates reflexes to stimuli.                       CSF is formed from blood plasma by
Nerves                                                     special structures called choroid plexuses.
   Nerves are bundles of axons in the                    he choroid plexuses contain many
    peripheral nervous system (PNS) that act               capillaries lined with epithelial tissue that
    as information highways to carry signals               filters blood plasma and allows the filtered
    between the brain and spinal cord and the              fluid to enter the space around the brain.
    rest of the body.
   Each axon is wrapped in a connective              Sense Organs
    tissue sheath called the endoneurium.             1.   Eye is the sense of sight.
    Individual axons of the nerve are bundled         2.   Ear is the sense of hearing.
    into groups of axons called fascicles,            3.   Nose is the sense of smell.
    wrapped in a sheath of connective tissue          4.   Tongue is the sense of taste.
    called the perineurium.                           5.   Skin is the sense of touch.
   Finally, many fascicles are wrapped
    together in another layer of connective           Eye
    tissue called the epineurium to form a
    whole nerve.                                          It allows you not only to view objects, but
   The wrapping of nerves with connective                 to see depth, color, size, and detail.
    tissue helps to protect the axons and to              The eye works by refracting and focusing
    increase the speed of their communication              light onto the retina.
    within the body.                                      When light strikes the retina, millions of
                                                           rhodopsin-containing rods, which are
Meninges                                                   responsible for night vision, convert the
                                                           light into electrical impulses, which are
The meninges are the protective coverings of               sent to the brain.
the central nervous system (CNS). They
                                                          The brain then translates what it receives
consist of three layers: the dura mater,
                                                           from the optic nerves so that we can
arachnoid mater, and pia mater.
                                                           understand what we see.
Dura mater : The dura mater, which means                  The retina also contains millions of cones
“tough mother,” is the thickest, toughest, and             that contain iodopsin and are used for
most superficial layer of meninges.                        bright light vision and color perception.
                                                           There are approximately 17 times more
Arachnoid mater : The arachnoid mater,                     rods than cones - about 120 million rods
which means “spider-like mother,” is much                  and 7 million cones - in the retina of each
thinner and more delicate than the dura mater.             eye.
                                                          The human eye is about 2.5 cm in
Pia mater : The pia mater, which means
“tender mother,” is a thin and delicate layer of