The Structure of the Nervous System
o There are 12 pairs of cranial nerves that arise from the brain stem and innervate
(mostly) the head.
Oh, Oh, Oh To Touch And Feel Very Green Vegetables AH!
Some-CN 1 – olfactory nerve
Say-CN II – optic nerve
Marry-CN III – oculomotor nerve
Money-CN IV – trochlear nerve
But-CN V – trigeminal nerve
My-CN VI – abducens nerve
Brother-CN VII – facial nerve
Say-CN VII – vestibulocochlear nerve
Bad-CN IX – glossopharyngeal nerve
Business-CN X – vagus nerve
Marry-CN XI- spinal accessory nerve
Money-CN XII- hypoglossal nerve
Some of the cranial nerves are part of the CNS, others are part of the
somatic PNS, and still others are part of the visceral PNS.
Many cranial nerves contain complex mixture of axons that perform
o The CNS does not come into direct contact with the overlying bone. It is protected by
a three membranes collectively called the meninges which consists of the dura
mater, arachnoid membrane, and the pia mater
a. Dura mater – in Latin means “hard mother,” an accurate description of the
dura’s leather like consistency. It forms a touch, inelastic bag that surrounds
the brain and spinal cord.
b. Arachnoid membrane – in latin “spider,” this meningeal layer has an
appearance and a consistency resembling a spider web.
While there is no space between the dura and arachnoid, if blood
vessels passing through the dura are ruptured, blood can collect here
and form what is called a subdural hematoma
The buildup of fluid in this subdural space can disrupt brain function by
compressing parts of the CNS. This disorder is treated by drilling a hole
within the skull and draining the blood.
c. Pia mater – in latin the “gentle mother,” is a thin membrane that adheres
closely to the surface of the brain. Along the pia run many blood vessels that
ultimately dive into the substance of the underlying brain.
The pia is separated from the arachnoid by a fluid-filled space referred
to as the subarachnoid space which is filled with salty clear liquid
called the cerebrospinal fluid (CSF)
Thus brain floats inside the head in this thin layer of CSF o The fluid-filled caverns and canals inside the brain constitute the ventricular system
– fluid that runs in this system is the CSF, the same fluid as the fluid in the
CSF is produced by a special tissue, called the choroid plexus, in the ventricles
of the cerebral hemispheres
CSF flows from the paired ventricles of the cerebrum to a series of connected,
unpaired cavities at the core of the bra