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Chapter 20: The
Muscular System
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Chapter Objectives
• Location and function of smooth, cardiac & skeletal muscle.
• Typical structure of a skeletal muscle.
• The mechanism of muscle contraction.
• How muscles work together to produce movement.
• Main types of movements produced by muscles.
• The criteria for naming muscles.
• Roots pertaining to the muscular system.
• Main disorders that affect muscles.
• Superficial anterior and posterior muscles.
• Abbreviations pertaining to muscles.
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Key Terms
Normal Structure and Function
acetylcholine
(ACh)
A neurotransmitter that stimulates contraction of skeletal muscles
actin
One of the two contractile proteins in muscle cells; the other is myosin
antagonist
The muscle that opposes a prime mover; it must relax when the prime
mover contracts.
cardiac muscle
Involuntary muscle that makes up the wall of the heart
fascia
The fibrous sheath of connective tissue that covers a muscle; called
deep fascia to differentiate it from the superficial fascia that underlies
the skin (root: fasci/o); plural: fasciae
fascicle
A small bundle, as of muscle or nerve fibers
insertion
In a given movement, the point where a muscle is attached to a moving
part of the skeleton
muscle
An organ that produces movement by contracting; also the tissue that
composes such organs (root: my/o, muscul/o)
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Key Terms
Normal Structure and Function (cont’d)
myosin
One of the two contractile proteins in muscle cells; the other is actin
neuromuscular
junction (NMJ)
The point of contact, or synapse, between a branch of a motor
neuron and a muscle cell
origin
In a given movement, the point where a muscle is attached to a
stable part of the skeleton
prime mover
The muscle that carries out a given movement; agonist (AG-on-ist)
skeletal muscle
Voluntary muscle that moves the skeleton and maintains posture
smooth muscle
Involuntary muscle that makes up the wall of the hollow organs,
vessels, and ducts; visceral muscle
tendon
A fibrous band of connective tissue that attaches a muscle to a bone
(root: ten/o, tendin/o)
tonus
A state of steady, partial contraction of muscle that maintains
firmness; muscle tone (root: ton/o)
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Key Terms
Disorders
amyotrophic lateral
sclerosis (ALS)
A disease caused by degeneration of motor neurons resulting
in muscular weakness and atrophy; Lou Gehrig disease
chronic fatigue syndrome
(CFS)
A disease of unknown cause that involves persistent fatigue,
along with muscle and joint pain and other symptoms; may
be virally induced
dermatomyositis
A disease of unknown origin involving inflammation of
muscles as well as dermatitis and skin rashes
fibromyalgia syndrome
(FMS)
A disorder associated with widespread muscular aches and
stiffness and having no known cause
muscular dystrophy
A group of hereditary muscular disorders marked by
progressive weakness and atrophy of muscles
myasthenia gravis (MG)
A disease characterized by progressive muscular weakness;
an autoimmune disease affecting the neuromuscular junction
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Key Terms
Disorders (cont’d)
polymyositis
A disease of unknown cause involving muscle inflammation and
weakness
repetitive strain injury
Tissue damage caused by repeated motion, usually overuse of the
arm or hand in occupational activities such as writing, typing,
painting, or using hand tools; also called repetitive motion injury,
cumulative trauma injury, overuse syndrome
strain
Trauma to a muscle because of overuse or excessive stretch; if
severe, may involve tearing of muscle, bleeding, or separation of
muscle from its tendon or separation of a tendon from bone
tendinitis
Inflammation of a tendon, usually caused by injury or overuse; the
shoulder, elbow, and hip are common sites; also spelled tendonitis
tenosynovitis
Inflammation of a tendon sheath
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Key Terms
Diagnosis
creatine kinase (CK)
An enzyme found in muscle tissue; the serum level of CK
increases in cases of muscle damage; creatine phosphokinase
(CPK)
electromyography
(EMG)
Study of the electrical activity of muscles during contraction
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Supplementary Terms
Normal Structure and Function
aponeurosis
A flat, white, sheetlike tendon that connects a muscle with the part
that it moves
creatine
A substance in muscle cells that stores energy for contraction
glycogen
A complex sugar that is stored for energy in muscles and in the liver
isometric
Pertaining to a muscle action in which the muscle tenses but does
not shorten (literally: same measurement)
isotonic
Pertaining to a muscle action in which the muscle shortens to
accomplish movement (literally: same tone)
kinesthesia
Awareness of movement; perception of the weight, direction, and
degree of movement (-esthesia means “sensation”)
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Supplementary Terms
Normal Structure and Function (cont’d)
lactic acid
An acid that accumulates in muscle cells functioning without
enough oxygen (anaerobically), as in times of great physical
exertion. The lactic acid leads to muscle fatigue, after which it is
gradually removed from the tissues
motor unit
A single motor neuron and all of the muscle cells that its branches
stimulate
myoglobin
A pigment similar to hemoglobin that stores oxygen in muscle cells
oxygen debt
The period during which muscles are functioning without enough
oxygen. Lactic acid accumulates and leads to fatigue.
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Supplementary Terms
Symptoms and Conditions
asterixis
Rapid, jerky movements, especially in the hands, caused by
intermittent loss of muscle tone
asthenia
Weakness (prefix a- meaning “without” with root sthen/o meaning
“strength”)
ataxia
Lack of muscle coordination (from root tax/o meaning “order,
arrangement”); adjective: ataxic
athetosis
A condition marked by slow, irregular, twisting movements, especially
in the hands and fingers; adjective: athetotic
atrophy
A wasting away; a decrease in the size of a tissue or organ, such as
the wasting of muscle from disuse
avulsion
Forcible tearing away of a part
clonus
Alternating spasmodic contraction and relaxation in a muscle;
adjective: clonic
contracture
Permanent contraction of a muscle
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Supplementary Terms
Symptoms and Conditions (cont’d)
fasciculation
Involuntary small contractions or twitching of muscle fiber groups
(fasciculi)
fibromyositis
A nonspecific term for pain, tenderness, and stiffness in muscles
and joints
fibrositis
Inflammation of fibrous connective tissue, especially the muscle
fasciae; marked by pain and stiffness
restless legs syndrome
(RLS)
Uneasiness, twitching, or restlessness in the legs that occurs
after going to bed and often leading to insomnia; may be caused
by poor circulation or drug side effects
rhabdomyolysis
An acute disease involving diffuse destruction of skeletal muscle
cells (root rhabd/o means “rod,” referring to the long, rodlike
muscle cells)
rhabdomyoma
A benign tumor of skeletal muscle
rhabdomyosarcoma
A highly malignant tumor of skeletal muscle
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Supplementary Terms
Symptoms and Conditions (cont’d)
rheumatism
A general term for inflammation, soreness, and stiffness of muscles
associated with pain in joints (adjective: rheumatic, rheumatoid)
spasm
A sudden, involuntary muscle contraction; may be clonic (contraction
alternating with relaxation) or tonic (sustained); a strong and painful
spasm may be called a cramp (adjectives, spastic, spasmodic)
spasticity
Increased tone or contractions of muscles causing stiff and awkward
movements
tetanus
An acute infectious disease caused by the anaerobic bacillus
Clostridium tetani. It is marked by persistent painful spasms of
voluntary muscles; lockjaw
tetany
A condition marked by spasms, cramps, and muscle twitching caused
by a metabolic imbalance, such as low blood calcium caused by
underactivity of the parathyroid glands
torticollis
Spasmodic contraction of the neck muscles causing stiffness and
twisting of the neck; wryneck
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Supplementary Terms
Diagnosis and Treatment
Chvostek sign
Spasm of facial muscles after a tap over the facial nerve; evidence of
tetany
occupational
therapy
Health profession concerned with increasing function and preventing
disability through work and play activities. The goal of occupational
therapy is to increase the patient's independence and quality of daily
life.
physical therapy
Health profession concerned with physical rehabilitation and
prevention of disability. Exercise, massage, and other therapeutic
methods are used to restore proper movement
rheumatology
The study and treatment of rheumatic diseases
Trousseau sign
Spasmodic contractions caused by pressing the nerve supplying a
muscle; seen in tetany
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Supplementary Terms
Drugs
antiinflammatory
agent
Drug that reduces inflammation; includes steroids, such as cortisone,
and nonsteroidal antiinflammatory drugs
COX-2 inhibitor
Nonsteroidal antiinflammatory drug that does not cause the stomach
problems associated with other NSAIDs. Inhibits the cyclooxygenase
(COX)-2 enzyme without affecting the COX-1 enzyme, a lack of
which can cause stomach ulcers. These drugs are under study, and
some have been withdrawn from the market because of cardiac risk.
Example is celecoxib (Celebrex)
muscle relaxant
A drug that reduces muscle tension; different forms may be used to
relax muscles during surgery, to control spasticity, or to relieve
musculoskeletal pain
nonsteroidal
antiinflammatory
drug (NSAID)
Drug that reduces inflammation but is not a steroid; examples include
aspirin, ibuprofen, naproxen, and other inhibitors of prostaglandins,
naturally produced substances that promote inflammation
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Abbreviations
Ach
Acetylcholine
ALS
Amyotrophic lateral sclerosis
CFS
Chronic fatigue syndrome
C(P)K
Creatine (phospho)kinase
CTS
Carpal tunnel syndrome
EMG
Electromyography, electromyogram
FMS
Fibromyalgia syndrome
MG
Myasthenia gravis
MMT
Manual muscle test(ing)
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Abbreviations (cont’d)
NMJ
Neuromuscular junction
OT
Occupational therapy/therapist
PRICE
Protection, rest, ice, compression, elevation
PT
Physical therapy/therapist
RLS
Restless legs syndrome
ROM
Range of motion
RSI
Repetitive strain injury
RTC
Rotator cuff
SITS
Supraspinatus, infraspinatus, teres minor, subscapularis (muscles)
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Types of Muscles
• Smooth
– Walls of hollow organs and ducts
– Operates involuntarily
– Responsible for peristalsis
• Cardiac
– Myocardium of heart wall
– Functions involuntarily
– Responsible for pumping of heart
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Types of Muscles (cont’d)
• Skeletal
– Attaches to bones
– Responsible for voluntary movement
– Maintains posture
– Generates large portion of body heat
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Roots Pertaining to Muscles
Root
Meaning
Example
Definition of Example
my/o
muscle
myositis*
inflammation of muscle
muscul/o
muscle
musculature
muscle arrangement in a part or
the whole body
in/o
fiber
inotropic
acting on (muscle) fibers
fasci/o
fascia
fasciodesis
binding (suture) of a fascia to a
tendon or other fascia
* Note addition of s to this root before the suffix –itis.
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Roots Pertaining to Muscles
Root
Meaning
Example
Definition of Example
ten/o, tendin/o tendon
tenostosis
ossification of a tendon
ton/o
tone
cardiotonic
having a strengthening action on
the heart
erg/o
work
ergonomics
study of the efficient use of
energy during work
kin/o-, kine,
kinesi/o,
kinet/o
movement
kinesis
movement (adjective: kinetic)
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Muscle Structure
• Fibers held together in
fascicles
• Fascia covers muscle
• Tendons attach
muscles
to bones
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Muscle Action
• Skeletal muscles stimulated by motor neurons of nervous
system
• Acetylcholine released
– Prompts contraction
• Requires actin and myosin to interact
• ATP and calcium needed for this response
• Partial contraction = tonus
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Muscle Action (cont’d)
• Muscles work in pairs at joints to produce movement
– Prime mover = contraction
– Antagonist = relaxation
• Point of origin = muscle attachment point to stable part
of skeleton
• Point of insertion = muscle attachment point to moving
part of skeleton
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Neuromuscular Junction
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Origins and Insertions
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Naming of Muscles
• Named by:
– Location
– Direction of fibers
– Size
– Shape
– Number of attachment heads
• Indicated by suffix -ceps
– Its action
• Indicated by suffix -or
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Superficial Muscles, Anterior
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Superficial Muscles, Posterior
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Clinical Aspects of the Muscular System
• Myopathy = disorder of the muscles
• Techniques for diagnosing:
– Study of muscle in action
– Electromyography (EMG)
– Serum assay of enzymes released in damaged
muscles
• Creatine kinase
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Muscular Dystrophy
• Group of hereditary diseases
– Most common is Duchenne muscular dystrophy
• Progressive, noninflammatory degeneration of muscles
• Muscles tissue weakens and wastes away
– Gradually replaced with connective tissue and fat
• May co-exist with:
– Cardiomyopathy (disease of cardiac muscle)
– Mental impairment
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Polymyositis
• Inflammation of skeletal muscle
– Dysphagia
– Cardiac problems
• Cause unknown
– May be related to viral infection or autoimmunity
• Often associated with other systemic diseases
– Rheumatoid arthritis
– Lupus erythematosus
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Polymyositis (cont’d)
• If skin involved known as dermatomyositis
• Symptoms
– Erythema
– Dermatitis
– Lilac-colored rash
• Diagnosis
– Enzyme studies
– EMG
– Muscle biopsy
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Fibromyalgia Syndrome
• Widespread muscle aches
• Tenderness
• Stiffness
• Fatigue
• Sleep disorders
• Difficult to diagnose
• Treatment
–
Exercise program
–
Pain relievers, muscle relaxants, antidepressants
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Chronic Fatigue Syndrome
• Persistent fatigue of no known cause
• Associated with:
–
Impaired memory
–
Sore throat
–
Painful lymph nodes
–
Muscle and joint pain
–
Headaches
–
Sleep problems
–
Immune disorders
• Often occurs after viral infection
• No consistent successful treatments
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Myasthenia Gravis
• Acquired autoimmune disease
– Antibodies interfere with muscle stimulation at
neuromuscular junction
– Progressive loss of muscle power
• Especially in:
• External eye muscles
• Other facial muscles
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Amyotrophic Lateral Sclerosis
• Lou Gehrig disease
• Progressive degeneration of motor neurons, leads to
muscular atrophy
• Signs:
– Weakness
– Cramping
– Muscle twitching
• Eventually leads to death
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Stress Injuries
• Include:
–
Accidental injuries
–
Damage caused by overexertion or repetitive motion (RSI)
• Damage to soft tissue:
–
Muscle strain
–
Inflammation
–
Tearing of ligaments and tendons
–
Bursitis
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Stress Injuries (cont’d)
• Tendonitis = inflammation of tendon, tendon sheath, and
synovial membrane at joint
• Signs: pain, fatigue, weakness, stiffness, numbness,
ROM
• Treatment: rest, elevation, ice packs, bracing,
medications
– If more severe: steroid injections, ultrasound for
deep heat, strength exercises, surgery, PT
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Common Upper Extremity Conditions
• Rotator cuff
• Epicondylitis
• Carpal tunnel syndrome
• Trigger Finger
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Common Lower Extremity Conditions
• Hamstring strain
• Shin splint
• Achilles tendonitis
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Pretest
1. The neuromuscular junction is between a muscle and a :
(a) gland
(b) neuron
(c) bone
(d) gonad
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Pretest
1. The neuromuscular junction is between a muscle and a :
(a) gland
(b) neuron
(c) bone
(d) gonad
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Pretest
2. In the muscular system, the opposite of the origin is
the:
(a) counterorigin
(b) prime mover
(c) diaphragm
(d) insertion
Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins
Pretest
2. In the muscular system, the opposite of the origin is
the:
(a) counterorigin
(b) prime mover
(c) diaphragm
(d) insertion
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Pretest
3. The quadriceps femoris muscle forms the anterior part
of the:
(a) neck
(b) back
(c) thigh
(d) abdomen
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Pretest
3. The quadriceps femoris muscle forms the anterior part
of the:
(a) neck
(b) back
(c) thigh
(d) abdomen
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Pretest
4. The opposite of flexion is:
(a) rotation
(b) antiflexion
(c) relaxation
(d) extension
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Pretest
4. The opposite of flexion is:
(a) rotation
(b) antiflexion
(c) relaxation
(d) extension
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Pretest
5. The opposite of abduction is:
(a) adduction
(b) circumduction
(c) periduction
(d) pronation
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Pretest
5. The opposite of abduction is:
(a) adduction
(b) circumduction
(c) periduction
(d) pronation
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Pretest
6. The band of connective tissue that attaches a muscle to
a bone is a:
(a) cartilage
(b) bursa
(c) tendon
(d) diaphysis
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Pretest
6. The band of connective tissue that attaches a muscle to
a bone is a:
(a) cartilage
(b) bursa
(c) tendon
(d) diaphysis
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Pretest
7. Polymyositis is inflammation of many:
(a) sense organs
(b) muscles
(c) glands
(d) bones
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Pretest
7. Polymyositis is inflammation of many:
(a) sense organs
(b) muscles
(c) glands
(d) bones
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Pretest
8. The word kinesis means:
(a) movement
(b) bending
(c) stretching
(d) pain
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Pretest
8. The word kinesis means:
(a) movement
(b) bending
(c) stretching
(d) pain
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