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Chapter 5 Skeletal and Muscular Systems 111
When complete, click on Save & Print, and a print-
able referral report will appear.
You’ll get a chance to practice this task in Case Study
9: Urgent Care Practicum.
To access Case Study 9, go to http://thepoint.lww.
com, log in using your username and password, search
for The Complete Medical Assistant, click on “Student
Resources,” nd the Harris CareTracker materials, and
click on “Case Study 9.”
Nervous System,
SpecialSenses, and
6
Endocrine System
Chapter Objectives
● Describe the structure of a neuron.
● Describe how neuron bers are built into a nerve.
● Explain the function of neurotransmitters in synapse
transmission.
● Explain the functions of the sympathetic and
parasympathetic nervous systems.
● Describe common disorders of the spinal cord and
spinal nerves.
● Explain the function of the three meninges.
● Describe the function of cerebrospinal uid.
● Identify the three subdivisions of the brain stem and
the function of each.
● List the 12 cranial nerves.
CAAHEP & ABHES Competencies
CAAHEP
● Describe structural organization of the human body.
● Identify body systems.
● List major organs in each body system.
● Describe the normal function of each body system.
● Identify common pathology related to each body
system including signs, symptoms, and etiology.
● Analyze pathology for each body system including
diagnostic measures and treatment modalities.
● Describe disorders that affect the brain and cranial
nerves.
● Explain the function of the special senses.
● Describe the major structures of the eye.
● Explain the processes involved in the sense of sight.
● Describe common disorders of the eye and vision.
● Describe the major structures of the ear.
● Explain the processes involved in the sense of hearing.
● Describe common disorders of the ear and hearing.
● Identify the glands of the endocrine system and the
hormones they produce.
● Describe the functions of hormones.
● Describe common disorders of the endocrine glands.
ABHES
● List all body systems, their structure, and functions.
● Describe common diseases, symptoms, and
etiologies as they apply to each system.
● Common diseases, diagnoses, and treatments.
● Identify diagnostic and treatment modalities as they
relate to each body system.
Chapter Terms
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 113
Acromegaly
Axon
Cataract
Cerebrum
Ceruminosis
Conjunctivitis
Dendrite
Diabetes mellitus
Epinephrine
Gigantism
Glaucoma
Incus
Malleus
Meninges
Abbreviations
ACTH
ADH
ALS
CNS
CSF
Case Study
Alicia, a college student, is attending her rst year
as a freshman at the state university. It is midterm
and she has been really spending a lot of hours
studying for her exams. Today, she woke up in her
dorm room and didn’t really feel well. She felt a
little achy and warm and decided to stay in bed for
awhile thinking she probably just needed a little
CT
CVA
EEG
FSH
GH
Myelin
Myopia
Nerve
Neurons
Neuropathy
Otitis media
Paraplegia
LH
MRI
MS
MTBI
PET
rest. She knew other classmates who had been
coughing and sneezing but just thought they were
coming down with a cold so she gured she had
caught a cold from one of them. She fell asleep and
when she woke up in a couple of hours, she knew
she was running a fever, she had a terric headache, and her neck felt tight and stiff.
Poliomyelitis
Quadriplegia
Reex
Sciatica
Seizure
Stapes
Synapse
PNS
PRL
T1DM
T2DM
TSH
In this chapter, we will explore the nervous system, including
the senses, and the endocrine system. Homeostasis is a concept of maintaining body functions within set limits. The
nervous, endocrine, and sensory systems play a major role
in helping the body maintain homeostatic balance. These
body systems are able to act on the changes detected in the
external and internal environments and make adjustments
in the body.
C
O
G
THE NERVOUS SYSTEM
The nervous system is the main coordination and communication system in the body. The system relies on
the brain, spinal cord, and the nerves throughout the
body to accomplish these functions. The brain acts as
the main communication center interpreting the senses
that are transmitted from the body’s nerves through
the spinal cord to the brain. A
nerve is composed of a
bundle of neuron bers. It is similar to an electrical cord
with numerous wires encased by an insulated covering.
Nervous System Divisions
The nervous system is divided into two parts, the central nervous system (CNS) and the peripheral nervous
system (PNS). The CNS is comprised of the brain and
spinal cord. The PNS includes the nerves that lie outside
of the CNS. This system includes the cranial nerves, carrying impulses to and from the brain, and the spinal
Case Question
A
F
F
she do?
As you read through the chapter, see if
you can gure out what might be causing Alicia’s symptoms. What should
114 Section II Anatomy and Physiology
Central nervous
system:
Brain
Spinal
cord
Peripheral nervous
system:
Cranial
nerves
Spinal
nerves
Neurons
The highly specialized cells of the nervous system are
called
neurons. Each neuron has a nucleus and thread-like
bers that extend out from the cell body carrying impulses
across the neuron. These bers are the dendrites and axons.
Dendrites—The neuron bers that conduct impulses
r
to the cell body. They function as the receptors in the
nervous system (receive the stimulus).
Axons—The neuron bers that conduct impulses
r
away from the cell body. Their function is to deliver
the impulses from one neuron to another neuron or
to a muscle or gland.
See Figure 6-2, which is a neuron with the dendrites,
axons, and myelin sheath.
Figure 6-1 Central nervous and peripheral nervous
systems. (Reprinted from Cohen BJ. Memmler’s
The Human Body in Health and Disease. 13th ed.
Philadelphia, PA: Wolters Kluwer; 2014.)
nerves, which carry messages to and from the spinal
cord. Figure 6-1 shows the division of the CNS and PNS
with the main structures of each system identied.
The Peripheral Nervous System
The PNS is further divided into the somatic nervous system, which is controlled voluntarily and the autonomic
nervous system, which functions involuntarily.
Somatic nervous system—Skeletal muscles act as the
r
effectors responding to the stimuli communicated
through the somatic nerves; an example of this action is
when your hand is pulled away quickly from a hot stove.
Autonomic nervous system—Also referred to as the vis-
r
ceral nervous system; the effectors are smooth muscle,
cardiac muscle, and glands, which function involuntarily;
numerous examples of autonomic action includes the
heart functioning without conscious control.
Dendrites
Cell body
Axon branch
Myelin
Muscle
Figure 6-2 A neuron with dendrite, axon, and myelin.
(Reprinted from Cohen BJ. Memmler’s The Human Body
in Health and Disease. 13th ed. Philadelphia, PA: Wolters
Kluwer; 2014.)
Nucleus
Node
Axon
covered with
myelin sheath
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 115
Neurons are also categorized by their function, relaying information to or from the central nervous system.
There are three types of neurons including sensory,
motor, and interneurons.
Sensory neurons—Called afferent neurons; they
r
conduct impulses to the spinal cord and brain, for
example, when your ngers feel the heat from the hot
stove, a signal is carried to the brain through afferent
neurons.
Motor neurons—Called efferent neurons; they con-
r
duct impulse from the brain and spinal cord to the
muscles and glands (the effectors) where action will
take place, for example, when you pull your hand
away from the hot stove.
Interneurons—Called central or association neurons;
r
they conduct impulses within the central nervous
system; they help us learn to avoid painful situations and assist during times of immediate response
to a stimulus, for example, helping to maintain
balance and coordination when responding to a
situation.
Myelin Sheath
C
O
G
THE SPINAL CORD
The spinal cord is the primary connection between the
spinal nerves and the brain. It is located in and protected
by the vertebral column. It extends from the upper cervical region to the lumbar region between the rst and
second lumbar vertebrae. The spinal cord is surrounded
by cerebrospinal uid (CSF) that acts as a cushion for
protection and carries nutrients and oxygen to the cord.
The spinal cord serves as the pathway for the sensory
and motor impulses traveling to and from the brain.
C
O
G
SPINAL NERVES
There are 31 pairs of spinal nerves that branch off of
the spinal cord. These nerves serve specic areas of
the body. The cervical spinal nerves are located in the
Myelin is a whitish, fatty substance that covers some of
the axons just like the insulation on an electrical cord.
This sheath of tissue protects and insulates the axon
ber. In the peripheral nervous system, the myelin is
actually cells called Schwann cells, which wrap around
the axon. In the peripheral nervous system, Schwann
cells are important to help neurons regenerate. In the
central nervous system, when the neurons are injured,
the damage is usually permanent. Within the CNS, the
myelinated axons are called white bers because of the
myelin’s color. The section of the brain and spinal cord
called white matter is made up of these white bers. The
gray matter is an area of the brain and spinal cord not
covered with these myelin bers.
The Synapse
Neurons rely on impulses that are passed from one to
another. The junction for that transmission is the syn-
apse
. The synapse allows transmission of the impulse
from the axon of one neuron to the dendrite of another
neuron. In order for the synapse to occur, chemicals
called neurotransmitters are required. The most common neurotransmitters are norepinephrine, serotonin,
dopamine, and acetylcholine.
There are some synapses controlled not by chemicals
but by electrical signals. For example, cardiac muscle is
activated by these electrical signals that travel directly
from one cell to another causing the heart muscle to
contract.
C1
C2
Cervical
C3
plexus
C4
C5
C6
Brachial
C7
C8
plexus
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
L1
L2
L3
L4
Lumbosacral
plexus
L5
S1
S2
S3
S4
S5
Figure 6-3 Spinal cord and spinal nerves. (Reprinted
from Cohen BJ. Memmler’s The Human Body in Health and
Disease. 13th ed. Philadelphia, PA: Wolters Kluwer; 2014.)
116 Section II Anatomy and Physiology
cervical (neck) region. The spinal nerves serve different
regions or structures of the body. The motor function of
the nerves as assigned as follows:
C1–C6: Neck exor muscles
r
C1–T1: Neck extensor muscles
r
C3, C4, C5: Supply diaphragm
r
C5, C6: Shoulder movement, raise arm, exion of
r
elbow, external rotation of the arm
C6, C7: Extends elbow and wrist, pronates wrist
r
C7, T1: Flex wrist, supply small muscles of the
r
hand
T1–T6: Intercostals and trunk above the waist
r
T1–L1: Abdominal muscles
r
L1–L4: Thigh exion
r
L2, L3, L4: Thigh adduction, extension of the leg at
r
the knee (quadriceps femoris)
L4, L5, S1: Thigh abduction, exion of the leg at
r
the knee (hamstrings), dorsiexion of foot, extension of toes
L5, S1, S2: Extension of leg at the hip (gluteus maxi-
r
mus), plantar exion of foot, and exion of toes
See Figure 6-3, which identies the location of the
spinal nerves.
The spinal nerves also receive messages from sensory
neurons located all over the skin except the face and
scalp. These skin regions are called dermatomes.
C
O
G
A reex is an involuntary response to a stimulus. The
nervous system is highly developed with the ability to
coordinate the responses. When a complete pathway is
formed from the stimulus to a response, it is called a
reex arc. An example is the knee-jerk response. When
REFLEXES
the physician taps the patellar tendon just beneath the
patella, the normal response is to move the lower leg
forward. The stimulus is the reex hammer striking the
tendon and the response is the movement of the leg. A
complete reex arc occurred from the beginning of the
stimulus when a message is sent to the brain, it is interpreted, then a message is returned to the nerve associated with that region and the leg moves. Another basic
response is when the eyes are closed when you see an
object approaching your eyes. Figure 6-4 demonstrates
how the physician examines a patient’s tendon reexes.
C
O
G
This is the nervous system that acts automatically without conscious awareness. This system regulates the
blood vessels, heart muscle, smooth muscle of the internal organs, and the glands. There are two divisions of
the autonomic nervous system, the sympathetic and the
parasympathetic.
THE AUTONOMIC
NERVOUS SYSTEM
Sympathetic Nervous System
This system acts as an accelerator for the body to
meet stressful situations, promoting the ght-or-ight
response. This is the response when faced with the decision to stay and ght the enemy or ee from the enemy
and run away. When we are faced with an emergency,
astressful situation, or when doing exercise, the sympathetic system affects the following:
Heart contractions—Increase rate and force
r
Blood pressure—Increases in response to constriction
r
of small arteries and more effective heartbeat
AB CD
Figure 6-4 Techniques for eliciting major tendon reexes. A. Biceps reex. B. Triceps reex. C. Patellar reex. D. Ankle
or achilles reex. (Reprinted from Kronenberger J, Ledbetter J. Lippincott Williams & Wilkins’ Comprehensive Medical
Assisting. 5th ed. Philadelphia, PA: Wolters Kluwer; 2016.)
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 117
Blood vessels—Dilate to increase blood ow to the
r
skeletal muscles
Bronchial tubes—Dilate to allow increased respira-
r
tion, deliver more oxygen, and excrete more carbon
dioxide
Adrenal gland—Increases output of adrenaline, epi-
r
nephrine, a stimulating hormone. You may have
heard the saying “an adrenaline rush.”
Pupil of the eye—Dilates the pupil allowing for
r
increased distance vision
Parasympathetic Nervous System
This system acts as a balance providing the opposite
function of the sympathetic nervous system. It is sometimes referred to as the “rest and digest” system. It has
the effect on the following:
Heart rate—Slows the heart rate
r
Bronchial tubes—Constrict the tubes, lowering the
r
respiratory rate
Pupil of the eye—Constriction of the eye
r
Digestive and urinary system—Increase urine output
r
and activity of the digestive tract
C
O
G
THE CRANIAL NERVES
They supply the structures of the head and have specic functions. Table 6-1 is a list of the cranial nerves
and their function. You will notice that they are labeled
using a Roman numeral.
Study Skill
When you need to remember a list of items or structures in anatomy, it is easier if you put together a
pneumonic that uses the rst letter of each word to
make a statement that is easier to remember. You
can make your own statement something that is
one you will never forget. Here is one used to recall
the 12 cranial nerves On Old Olympus Tiny Tops A
Fin And German Viewed Amber Hops.
C
O
G
The brain is a main part of the central nervous system
(CNS). It is the control center of the nervous system where
information received from the body is interpreted, processed, and coordinated. Our ability to reason, learn, and
memorize information takes place in the brain. Thebrain
is located in the cranial cavity and is protected by the
skull bones. There are four main regions of the brain:
THE BRAIN
There are 12 pairs of cranial nerves that connect directly
to the cerebrum, brainstem, and cervical spinal cord.
Table 6-1
Cranial Nerve Function
I—Olfactory Nerve Carries smell impulses from receptors in the nasal mucosa to the brain
II—Optic Nerve Carries visual impulses from the eye to the brain
III—Oculomotor Nerve Controls the contraction of most of the eye muscles. These muscles are skeletal
IV—Trochlear Nerve Supplies one eyeball muscle
V—Trigeminal Nerve Great sensory nerve of the face and head; has three branches that carry general
VI—Abducens Nerve Sends motor impulses to an eyeball muscle
VII—Facial Nerve Controls the muscles of facial expression; includes special sensory bers for taste;
VIII—Auditory Nerve Carries sensory impulses for hearing and equilibrium from the inner ear; formerly
IX—Glossopharyngeal Nerve Contains sensory bers from the tongue (taste) and the pharynx (swallowing)
X—Vagus Nerve Longest cranial nerve; carries autonomic motor impulses to most of the organs in the
XI—Accessory Nerve Controls two muscles of the neck, the trapezius and sternocleidomastoid; supplies
XII—Hypoglossal Nerve Carries impulses controlling the tongue muscles
Cranial Nerves and Their Function
muscles and are under voluntary control
sensory impulses from the eye, the upper jaw, and the lower jaw (muscles of chewing)
contains secretory bers to salivary glands and lacrimal glands
called the auditory or acoustic nerve; also called the vestibulocochlear nerve
thoracic and abdominal cavities, including the muscles and glands of the digestive
system; contains somatic motor bers supplying the larynx
muscles of the larynx
Cerebrum—Largest part of the brain divided into a
r
right and left hemisphere.
118 Section II Anatomy and Physiology
Diencephalon—In the center of the brain between the
r
hemispheres and above the brain stem; the thalamus
and hypothalamus are located there.
Brain stem—Located in the region between the
r
diencephalon and the spinal cord; has three divisions including the midbrain, pons, and medulla
oblongata.
Cerebellum—Located behind the brainstem; the term
r
cerebellum means little brain.
See Figure 6-5, which demonstrates the major structures of the brain.
Brain and Spinal Cord Protection
Due to the delicate nature of the brain and spinal cord,
there are three membranes, the meninges, and uid that
surround the structures to help protect and cushion
them from injury and trauma. The meninges are:
Pia mater—Innermost layer; pia means delicate or
r
soft and mater is Latin for mother; holds the blood
vessels that supply the oxygen and nutrients to the
brain and spinal cord.
Arachnoid—Middle layer or space that has web-like
r
bers resembling a spider web.
Dura mater—Outermost layer; hard, tough layer.
r
Cerebrospinal uid (CSF) is a clear liquid that surrounds the brain and spinal cord. It is produced in the
ventricles of the brain. In addition to cushioning the
brain and spinal cord, it carries nutrients to the cells and
transports waste from the cells
Cerebrum
As mentioned earlier, the cerebrum is divided into two
hemispheres, and each hemisphere is then divided into
four lobes. These lobes are the frontal, parietal, temporal, and occipital. These lie in the region of the skull
bones with the same names. Each hemisphere has an
outer covering called the cerebral cortex. This is where
specic body functions are processed including thought,
reasoning, and mental functions.
Each lobe of the cerebrum is assigned a specic function such as these general functions:
Frontal lobe—Primary motor area providing con-
r
scious control of skeletal muscles.
Parietal lobe—Primary somatosensory area allow-
r
ing processing of impulses from the skin such as pain
and temperature; stores memories so we can interpret
Corpus callosum
DIENCEPHALON:
Thalamus
Hypothalamus
(Pituitary gland)
ANTERIOR POSTERIOR
CEREBRUM
BRAIN STEM:
Midbrain
Pons
Medulla
oblongata
Spinal cord
CEREBELLUM
Figure 6-5 Cross-section view of the brain and major components. (Reprinted from
Cohen BJ. Memmler’s The Human Body in Health and Disease. 13th ed. Philadelphia, PA:
Wolters Kluwer; 2014.)
Chapter 6 Nervous System, SpecialSenses, and Endocrine System 119
what we touch identifying hot versus cold and hard
and soft.
Temporal lobe—Auditory reception area detecting
r
sound from the environment; speech recognition is
also located in this area.
Occipital lobe—Visual reception area allowing us
r
to see brightness and color; visual association so we
can identify various objects and differentiate a ower
from a person
A primary function of the brain is to store volumes
of memory. Memory is categorized into short-term
memory that allows us to store bits of information for
a few seconds or minutes and long-term memory that
allows us to recall information at a later time even years
later.
Diencephalon
This area of the brain houses the thalamus and hypothalamus. The thalamus is similar to a relay station sending
impulses to the particular areas of the cerebral cortex
where they will be processed. The hypothalamus helps
the body maintain homeostasis by controlling the body
temperature, water balance, our sleep pattern, appetite,
and some emotions including fear and pleasure.
Brainstem
The structures of the brain stem have very specic
responsibilities acting as a connection between the cerebrum and spinal cord:
Midbrain—Responds to reexes involving the eye
r
and ear; coordination of eye movement
Pons—Regulation of respiration and involuntary
r
reex actions
Medulla oblongata—Controls muscles of respiration;
r
regulates rate and force of the heartbeat; regulates
contraction of smooth muscle of the blood vessels
controlling blood ow and blood pressure
The motor function of the cerebral hemispheres is
designed to allow contralateral control, which means that
motor functions controlled in the right hemisphere will control the left side of the body and those controlled in the left
hemisphere will affect function of the right side of the body.
Cerebellum
The primary functions of the cerebellum include assisting with the coordination of voluntary muscles allowing
us to maintain our balance and helping us to maintain
muscle tone so we are ready to move as needed.
C
O
G
MEDICAL PROCEDURES
INVOLVING THE NERVOUS
SYSTEM
In order to treat the numerous medical conditions that
affect the nervous system structures and function, a
physician needs to do testing to determine the cause or
root of the problem. Let’s explore just a few of the common procedures that you may see ordered by physicians
treating patients with abnormal signs and symptoms of
the nervous system.
Lumbar puncture—Also called a spinal tap, is an
r
invasive procedure that involves inserting a needle
into the space between vertebrae to withdraw a small
amount of cerebrospinal uid for analysis. The physician is testing for the presence of inammation
or infection. Figure 6-6 shows the positioning of a
Third lumbar vertebra
Dura mater
Subarachnoid space
Cauda equina
Figure 6-6 Spinal location and patient position used to perform a lumbar puncture. The L3 to L5 spaces
are just below the line connecting the anterior and superior iliac spines. (From Taylor C, Lillis CA, LeMone P.
Fuldamentals of Nursing. 2nd ed. Philadelphia, PA: Lippincott; 1993:543.)
120 Section II Anatomy and Physiology
patient for a lumbar puncture and the location in the
spine where the uid is extracted.
CT scan—Computed tomography; provides images
r
of the brain and bones, used to visualize abnormalities such as tumors or structural deformity.
MRI—Magnetic resonance imaging; provides more
r
detail of the brain and structures than those visible on the CT scan, used to visualize tumors and
hemorrhage.
PET scan—Positron emission tomography; visualizes
r
the brain in action.
EEG—Electroencephalograph is used to measure the
r
electrical activity of the brain, the brain waves; may
be used to study sleep disorders.
C
O
G
There are many conditions that can affect the structures
and function of the nervous system. A general term used
to describe any disease of the nervous system is
athy
neuropathy, which is a condition affecting the nerves
outside of the central nervous system. The term neuralgia is used as a general term to describe nerve pain and
can be an associated symptom with any nerve condition.
Here are some of the nervous system disorders affecting
the overall body:
r
r
r
r
r
DISORDERS OF THE
NERVOUS SYSTEM
neurop-
. More specically, a patient may have peripheral
Multiple sclerosis (MS)—An autoimmune disease
that causes loss of the myelin sheath around the axon;
results in a disruption in the nervous system communication process; one of the most common, chronic
CNS diseases in young adults, affecting women more
than men.
Amyotrophic lateral sclerosis (ALS)—Progressive,
degenerative disorder that destroys the motor neurons; muscles waste away (atrophy) and motor control is lost eventually, affecting the ability to talk,
swallow, and breathe; often referred to as Lou Gehrig
disease, the famous baseball player.
Poliomyelitis—Called polio, is a viral disease of the ner-
vous system; may only have minor symptoms however
in small amount of cases will spread to the motor neurons of the spinal cord causing paralysis of the limbs.
Spinal cord injuries—Caused from trauma, fracture,
and dislocation of vertebrae, herniation of vertebral
disks, or tumors; may result in paralysis in varying
degrees:
Monoplegia—Paralysis of one limb
Paraplegia—Paralysis of both lower limbs
Hemiplegia—Paralysis of one side of the body
Quadriplegia—Paralysis of all four limbs
Sciatica—Compression of the sciatic nerve of the
lower back causing pain, numbness, and tingling
from the lower back continuing down the leg
Figure 6-7 Shingles caused by the herpes zoster virus.
(Reprinted from Kronenberger J, Ledbetter J. Lippincott
Williams & Wilkins' Comprehensive Medical Assisting.
5thed. Philadelphia, PA: Wolters Kluwer; 2016.)
Bell palsy—Partial facial paralysis caused by inam-
r
mation of the VII facial nerve
Herpes zoster, commonly known as shingles, is sometimes associated with disorders of the nervous system
because the virus that causes this condition lies dormant along a nerve. The virus, which is the same one
that causes chicken pox, becomes reactivated years later
and causes intense nerve pain and a severe skin rash.
Figure6-7 is a photo of a person with herpes zoster.
Disorders of the Central
NervousSystem
In addition to general nervous system disorders, there
are some conditions that are more specically associated
with the brain and spinal cord, the CNS.
Seizure—Results from abnormal electrical activity in
r
the brain that might be due to infection, trauma, or
high fever; causes uncontrollable muscle contractions.
Epilepsy—The recurrence of seizures; in most cases,
r
the cause is idiopathic, which means unknown source
or origin.
Meningitis—Infection or inammation of the meninges
r
usually caused by a virus or bacteria (meningococcus);
symptoms include headache, stiff neck, nausea, and
vomiting