The Structure of the Nervous System

consists of two parts of the nervous system that are

encased in bone:
the brain
the spinal cord

The brain lies entirely within the skull.

a variation on a plan that is common to the

brains of all mammals

to all mammals:
the cerebrum
the cerebellum
the brain stem

the brain
has two cerebral hemispheres, separated by the deep

sagittal fissure.
In general, the right cerebral hemisphere receives sensations from, and controls movements of the left side of the body.

the cerebrum.

contains as many neurons as both cerebral hemispheres

combined.

is primarily a movement control center that has extensive connections with the cerebrum and the spinal cord.

the left side of the cerebellum is concerned with movements of the left side of the body, and the right side of the cerebellum is concerned with movements of the right side.

from which the cerebral hemispheres and the cerebellum sprout.
is

a complex nexus of fibers and cells that in part serves to relay information from the cerebrum to the spinal cord and cerebellum, and vice versa.
is part of brain where vital functions are regulated, such as breathing, consciousness, and the control of body temperature.
damage to the brain stem is usually fatal.

the bony vertebral column

is attached to the brain stem

is the

major conduit of information from the skin, joints, and muscles of the body to the brain, and vice versa

A transection of the spinal cord results in anesthesia (lack of feeling) in the skin and paralysis of the muscles in parts of the body caudal to the cut.

communicates with the body via the spinal nerves
Each spinal nerve

attaches to the spinal cord by means of two branches, the dorsal root and the ventral root
the dorsal root contains axons bringing information into the spinal cord
the ventral root contains axons carrying information away from the spinal cord

PNS has two parts:
the somatic PNS
the visceral PNS.

nerves that innervate the skin, the joints, and the muscles

that are under voluntary control
The somatic motor axons derive from motor neurons in the ventral spinal cord.
The cell bodies of the motor neurons lie within the CNS, but their axons are mostly in the PNS
The somatic sensory axons enter the spinal cord via the dorsal roots
The cell bodies of sensory neurons lie outside the spinal cord in dorsal root ganglia

nervous system)
consists of the neurons that innervate the internal organs,

blood vessels, and glands
visceral sensory axons (afferent) bring information about visceral function to the CNS
visceral motor axons (efferent) command
the contraction and relaxation of smooth muscles
the rate of cardiac muscle contraction
the secretory function of various glands

cranial nerves that arise from the brain stem and innervate

(mostly) the head

Each cranial nerve has a name and a number associated with it

Some of the cranial nerves are part of the
CNS
somatic PNS
visceral PNS

meninges.
dura mater
arachnoid membrane
pia mater

The dura matter forms a tough,

inelastic bag that surrounds the brain and spinal cord.

membrane.
There is subarachnoid space between arachnoid membrane and pia matter.
Subarachnoid

space is filled with cerebrospinal fluid (CSF) .
The pia mater is a thin membrane that adheres
closely to the surface of the brain.

and canals inside the brain.
The fluid is cerebrospinal fluid (CSF).

CSF

is produced by choroid plexus in the ventricles of the cerebral hemispheres.

CSF flows from the paired ventricles to a series of connected, central cavities at the core of the brain stem.

subarachnoid space by way of small openings located near where

the cerebellum attaches to the brain stem.

In the subarachnoid space, CSF is absorbed by the blood vessels at arachnoid villi.

If the flow of CSF from the choroid plexus through the ventricular system to the subarachnoid space is impaired, the fluid will back up and cause a swelling of the ventricles. This condition is called hydrocephalus