Chapter 13
Nerves of Steel
© 2009 Delmar, Cengage Learning
The Functions of the
Nervous System
• The nervous system coordinates and
controls body activity.
• The nervous system detects and processes
internal and external information and
formulates appropriate responses.
© 2009 Delmar, Cengage Learning
The Structures of the
Nervous System
• Two major divisions of the nervous
system:
– The central nervous system (CNS) consists of the
brain and spinal cord.
– The peripheral nervous system (PNS) consists of
the cranial and spinal nerves, autonomic nervous
system,
and ganglia.
© 2009 Delmar, Cengage Learning
The Structures of the
Nervous System
• The basic unit of the nervous system is the
neuron.
• There are three types of neurons:
– sensory (also called afferent)
– associative
– motor (also called efferent)
© 2009 Delmar, Cengage Learning
Parts of the Neuron
• The neuron consists of the
following:
– a cell body (soma)
– dendrites
• Carry impulses toward the cell
body
• Combining form is dendr/o.
– an axon
• Carries impulses away from
the cell body
• Combining form is ax/o.
© 2009 Delmar, Cengage Learning
Supporting Role
• Neuroglia, or glial cells, are the supportive
cells of the nervous system.
– Hold together nerve cells
– The combining form gli/o means glue.
© 2009 Delmar, Cengage Learning
Supporting Role
• Neuroglial (glial) cells consist of the
following:
– Astrocytes
• Cover surfaces of capillaries
– Blood Brain Barrier
» Astrocytes and capillary walls
» Regulates passage of nutrition and chemicals to brain
– Microglia
• Phagocytic cells for fighting infection and for healing
© 2009 Delmar, Cengage Learning
– Oligodendrocytes
• Hold nerve fibers together
• Form myelin sheath in CNS
– Schwann cells
• Found outside CNS
• Form the neurilemma and a thin layer of myelin around nerve fibers
© 2009 Delmar, Cengage Learning
Surrounding Structures
• Myelin is a protective
covering over some nerve
cells including parts of the
spinal cord.
• Myelin serves as an electrical
insulator.
• Myelin is interrupted at
regular intervals along the
length of a fiber by gaps
called nodes of Ranvier.
© 2009 Delmar, Cengage Learning
The Gap
• The space between two neurons or between
a neuron and a receptor is the synapse.
– The combining forms for synapse are synaps/o and synapt/o.
– Chemical substances called neurotransmitters are released into the
space to allow information to be relayed.
© 2009 Delmar, Cengage Learning
Nerves
• A nerve is one or more bundles of impulsecarrying fibers that connect the CNS to
other parts of the body.
• Combining forms for nerve or nerve tissue
are neur/i and neur/o.
© 2009 Delmar, Cengage Learning
The CNS
• The central nervous system is made up of
the brain and spinal cord.
• The combining form for the brain is
encephal/o.
• The combining form for the spinal cord is
myel/o. (Remember, myel/o also means
bone marrow.)
© 2009 Delmar, Cengage Learning
The Meninges
• The meninges are a threelayered membrane that
surrounds the CNS.
– The combining forms for the
meninges are mening/o and
meningi/o.
– The three layers of
the meninges are the dura mater,
the arachnoid membrane, and the
pia mater.
© 2009 Delmar, Cengage Learning
The CSF
• Cerebrospinal fluid (CSF) is the clear,
colorless ultrafiltrate that nourishes, cools,
and cushions the CNS.
• CSF is made by the choroid plexus that
lines the ventricles of the brain.
© 2009 Delmar, Cengage Learning
The Brain
• The brain is the enlarged and highly developed
portion of the CNS that lies in the skull and is the
main site of nervous control.
– The cranium is the portion of the skull that encases the brain.
• Crani/o is the combining form for skull.
• Encephal/o is the combining form for brain.
© 2009 Delmar, Cengage Learning
The Brain Divisions
• The brain is divided into three main parts:
– Cerebrum is the largest part and is responsible for receiving and
processing information.
• cerebr/o
– Cerebellum is the second largest part that coordinates muscle activity.
• cerebell/o
– Brainstem connects the cerebral hemispheres with the spinal cord and
supports basic life functions.
© 2009 Delmar, Cengage Learning
The Spinal Cord
• The spinal cord is the
continuation of the medulla
oblongata of the brainstem.
– The combining form for spinal cord
is myel/o.
• The spinal cord passes through an
opening in the occipital bone
called the foramen magnum.
• The spinal cord carries the tracts
that influence the innervation of
the limbs and the lower part of the
body and is the pathway for
impulses going to and from the
brain.
© 2009 Delmar, Cengage Learning
The Discs
• The spinal cord is housed
within vertebrae to protect it
from injury.
• The vertebrae are protected
from each other by
intervertebral discs located
between the vertebrae.
• Intervertebral discs are layers of
fibrocartilage that form pads
separating and cushioning the
vertebrae from each other.
© 2009 Delmar, Cengage Learning
The PNS
• The peripheral nervous system consists of cranial and spinal nerves, the
autonomic nervous system, and the ganglia.
– The cranial nerves are 12 pairs of nerves that originate from the undersurface of the brain.
– The spinal nerves arise from the spinal cord and supply sensory and motor fibers to the body
region associated with their emergence from the spinal cord….31 pairs
© 2009 Delmar, Cengage Learning
Cranial Nerves
•
•
•
•
•
•
Olfactory
Optic
Oculomoter
Trochlear (eye movement, proprioception)
Trigeminal (head/face, chewing movements)
Abducens abduction of eye)
•
•
•
•
Facial (expression, saliva, taste)
Acoustic (hearing, balance, equilibrium)
Glossopharyngeal (swallowing)
Vagus
– Slows heart
– Increases peristalsis
• Accessory
– shoulder movements,
– turning head,
• Hypoglossal (tongue movements)
© 2009 Delmar, Cengage Learning
Spinal Nerves
• Named after corresponding vertebrae
• Supply sensory and motor fibers to the
region of the body in the area where
they emerge from spinal cord
© 2009 Delmar, Cengage Learning
The ANS
• The autonomic nervous system is that
part of the peripheral nervous system
that innervates smooth muscle, cardiac
muscle, and glands.
• There are two divisions of the ANS:
– sympathetic: “fight or flight”
– parasympathetic: maintains normal body function
• “rest and restore”
© 2009 Delmar, Cengage Learning
Sympathetic
• Dilate pupils
• Accomadates eyes to distance
• Dilates bronchial tubes
• Heart rate increases
• Blood vessels constrict
(skin and viscera)
• Blood to muscles
• GI and bladder relax
• Sphincter muscles contract
(prevent leakage)
© 2009 Delmar, Cengage Learning
Parasymapthetic
•
•
•
•
•
•
•
Constricts pupils
Near objects vision
Constricts bronchial tubes
Slower heart rate
Dilates blood vessels
GI contractions increase
Relaxation of sphincter muscles
© 2009 Delmar, Cengage Learning
© 2009 Delmar, Cengage Learning
Diagnostic Procedures
• Myelography
– Diagnostic study of the spinal cord
– Injection of contrast dye
– Myelogram is produced-record of the spinal cord
after dye is injected
© 2009 Delmar, Cengage Learning
© 2009 Delmar, Cengage Learning
• Pupillary Light Reflex
–
–
–
–
Response of pupil to a bright light source
PLR
Light shone in one eye causes both eyes to constrict (normal)
Used to assess neurological damage
© 2009 Delmar, Cengage Learning
© 2009 Delmar, Cengage Learning
• Cerebrospinal Fluid Tap
–
–
–
–
Insert needle/ catheter
Obtain fluid from cisterna magnum
(subarachnoid space between cerebellum and medulla)
Or Lumbosacral area
© 2009 Delmar, Cengage Learning
© 2009 Delmar, Cengage Learning
Medical Terms for the
Nervous System
• Additional terms for nervous system tests,
pathology, and procedures can be found in
the text.
• Review StudyWARE to make sure you
understand these terms.
© 2009 Delmar, Cengage Learning