c. Meninges. The meninges are the three membranes that envelop the brain
and the spinal cord. The outermost layer is the dura mater. The middle layer is the
arachnoid, and the innermost layer is the pia mater. These three spinal meninges cover
the spinal nerves to the point where the spinal column goes through the intervertebral
foramen. The meninges offer protection to the brain and the spinal cord by acting as a
barrier against bacteria.
d. Cerebrospinal Fluid (CSF). The cerebrospinal fluid protects the brain
against injury. CSF circulates through the subarachnoid space (the area between the
arachnoid and pia mater), around the brain and spinal cord and through the ventricles of
the brain. In addition to protecting the brain, this clear fluid nourishes the central
nervous system and carries off wastes.
1-10. PERIPHERAL NERVOUS SYSTEM (PNS)
The peripheral nervous system (PNS) is composed of nerves that connect the
central nervous system to remote parts of the body, relaying and receiving messages
from these parts of the body. This system is a pathway to the brain for the five senses
which help us respond to the world around us. The peripheral nervous system is
divided into the cerebrospinal nervous system and the autonomic nervous system
a. Cerebrospinal Nervous System. This system is composed of 12 pairs of
cranial nerves. The cranial nerves are symmetrically arranged and attached to the
brain. Each cranial nerve leaves the skull through a foramen (an opening) at its base.
The nerves are numbered in the order in which they emerge from the opening and from
front to back. The numbered nerves along with the function of each nerve are given in