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The Muscular System
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Slide 0
Introduction
• Muscular tissue enables the body and its
parts to move
 Movement caused by ability of muscle
cells (called fibers) to shorten or
contract
 Muscle cells shorten by converting
chemical energy (obtained from food)
into mechanical energy, which causes
movement
 Three types of muscle tissue exist in
the body
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Slide 1
Muscle Tissue
• Types of muscle tissue
 Skeletal muscle—also called striated
or voluntary muscle
 Is 40% to 50% of body weight (“red
meat” attached to bones)
 Microscope reveals crosswise stripes
or striations
 Contractions can be voluntarily
controlled
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Slide 2
(Cont’d…)
Muscle Tissue
(…Cont’d)
 Cardiac muscle—composes bulk of
heart
 Cardiac muscle cells branch
frequently
 Characterized by unique dark
bands called intercalated disks
 Interconnected nature of cardiac
muscle cells allows heart to contract
efficiently as a unit
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(Cont’d…)
Slide 3
Muscle Tissue
 Nonstriated muscle or involuntary muscle—
also called smooth or visceral muscle
 Lacks cross stripes or striation when seen
under a microscope; appears smooth
 Found in walls of hollow visceral structures
such as digestive tract, blood vessels, and
ureters
 Contractions not under voluntary control;
movement caused by contractions is
involuntary
 Function—all muscle cells specialize in
contraction (shortening)
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Slide 4
Structure of Skeletal Muscle
• Structure
 Each skeletal muscle is an organ
composed mainly of skeletal muscle
cells and connective tissue
 Most skeletal muscles extend from
one bone across a joint to another
bone
(Cont’d…)
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Slide 5
Structure of Skeletal Muscle
(…Cont’d)
 Parts of a skeletal muscle
 Origin—attachment to the bone that
remains relatively stationary or fixed
when movement at the joint occurs
 Insertion—point of attachment to
the bone that moves when a muscle
contracts
 Body—main part of the muscle
(Cont’d…)
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Slide 6
Structure of Skeletal Muscle
(…Cont’d)
 Muscles attach to the bone by tendons—
strong cords of fibrous connective tissue;
some tendons enclosed in synovial-lined
tubes and are lubricated by synovial fluid;
tubes called tendon sheaths
 Bursae—small synovial-lined sacs
containing a small amount of synovial fluid;
located between some tendons and
underlying bones
(Cont’d…)
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Slide 7
Structure of Skeletal Muscle
(…Cont’d)
• Microscopic structure
 Contractile cells called fibers—grouped
into bundles
 Fibers contain thick myofilaments
(containing the protein myosin) and thin
myofilaments (composed of actin)
(Cont’d…)
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Slide 8
Structure of Skeletal Muscle
(…Cont’d)
 Basic functional (contractile) unit called
sarcomere; sarcomeres separated from
each other by dark bands called Z lines
 Sliding filament model explains
mechanism of contraction
o Thick and thin myofilaments slide past
each other as a muscle contracts
o Contraction requires calcium and
energy-rich ATP molecules
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Slide 9
Functions of Skeletal Muscle
• Movement
 Muscles produce movement; as a
muscle contracts, it pulls the
insertion bone closer to the origin
bone; movement occurs at the joint
between the origin and the insertion
(Cont’d…)
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Slide 10
Functions of Skeletal Muscle
(…Cont’d)

Groups of muscles usually contract to
produce a single movement
o Prime mover—muscle whose contraction
is mainly responsible for producing a
given movement
o Synergist—muscle whose contractions
help the prime mover produce a given
movement
o Antagonist—muscle whose actions
oppose the action of a prime mover in
any given movement
(Cont’d…)
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Slide 11
Functions of Skeletal Muscle
(…Cont’d)
• Posture
 A specialized type of muscle contraction,
called tonic contraction, enables us to
maintain body position
 In a tonic contraction, only a few of a
muscle’s fibers shorten at one time
 Tonic contractions produce no movement
of body parts
(Cont’d…)
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Slide 12
Functions of Skeletal Muscle
(…Cont’d)
 Tonic contractions maintain muscle
tone called posture
 Good posture reduces strain on
muscles, tendons, ligaments, and
bones
 Poor posture causes fatigue and may
lead to deformity
(Cont’d…)
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Slide 13
Functions of Skeletal Muscle
(…Cont’d)
• Heat production
 Survival depends on the body’s ability to
maintain a constant body temperature
 Fever—an elevated body temperature;
often a sign of illness
 Hypothermia—a reduced body
temperature
 Contraction of muscle fibers produces most
of the heat required to maintain normal
body temperature
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Slide 14
Fatigue
• Reduced strength of muscle contraction
• Caused by repeated muscle stimulation
• Repeated muscular contraction depletes
cellular ATP store and outstrips the ability of
the blood supply to replenish oxygen and
nutrients
(Cont’d…)
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Slide 15
Fatigue
(…Cont’d)
• Contraction in the absence of adequate oxygen
produces lactic acid, which contributes to
muscle soreness
• Oxygen debt—term used to describe the
metabolic effort to burn excess lactic acid that
may accumulate during prolonged periods of
exercise; the body is attempting to return the
cells’ energy and oxygen reserves to preexercise levels
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Slide 16
Role of Other Body Systems in
Movement
• Muscle functioning depends on the functioning
of many other parts of the body
• Respiratory, circulatory, nervous, muscular, and
skeletal systems play essential roles in
producing normal movements
• Multiple sclerosis, brain hemorrhage, and spinal
cord injury are examples of how pathologic
conditions in other body organ systems can
dramatically affect movement
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Slide 17
Motor Unit
• Stimulation of a muscle by a nerve impulse is
required before a muscle can shorten and
produce movement
• A motor neuron is the specialized nerve that
transmits an impulse to a muscle, causing
contraction
(Cont’d…)
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Slide 18
Motor Unit
(…Cont’d)
• A neurotransmitter junction is the
specialized point of contact between a nerve
ending and the muscle fiber it innervates
• A motor unit is the combination of a motor
neuron with the muscle cell or cells it
innervates
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Slide 19
Muscle Stimulus
• A muscle will contract only if an applied
stimulus reaches a certain level of
intensity
 A threshold stimulus is the minimal level of
stimulation required to cause a muscle fiber
to contract
• Once stimulated by a threshold
stimulus, a muscle fiber will contract
completely, a response called all or none
(Cont’d…)
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Slide 20
Muscle Stimulus
(…Cont’d)
• Different muscle fibers in a muscle are
controlled by different motor units
having different threshold-stimulus
levels
 Although individual muscle fibers always
respond all or none to a threshold
stimulus, the muscle as a whole does not
 Different motor units responding to
different threshold stimuli permit a
muscle as a whole to execute contractions
of graded force
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Slide 21
Types of Skeletal Muscle Contraction
• Twitch and tetanic contractions
 Twitch contractions are laboratory
phenomena and do not play a significant
role in normal muscular activity; they are a
single contraction of muscle fibers caused
by a single threshold stimulus
 Tetanic contractions are sustained and
steady muscular contractions caused by a
series of stimuli bombarding a muscle in
rapid succession
(Cont’d…)
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Slide 22
Types of Skeletal Muscle Contraction
(…Cont’d)
• Isotonic contractions
 Contraction of a muscle that produces
movement at a joint
 During isotonic contractions, the muscle
changes length, causing the insertion end
of the muscle to move relative to the point
of origin
 Most types of body movements such as
walking and running are caused by isotonic
contractions
(Cont’d…)
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Slide 23
Types of Skeletal Muscle Contraction
(…Cont’d)
• Isometric contractions
 Isometric contractions are muscle
contractions that do not produce
movement; the muscle as a whole does not
shorten
 Although no movement occurs during
isometric contractions, tension within the
muscle increases
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Slide 24
Effects of Exercise on Skeletal Muscles
• Exercise, if regular and properly
practiced, improves muscle tone and
posture, results in more efficient heart
and lung functioning, and reduces
fatigue
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(Cont’d…)
Slide 25
Effects of Exercise on Skeletal Muscles
(…Cont’d)
• Effects of Exercise on Skeletal Muscles
 Muscles undergo changes related to
the amount of work they normally do
 Prolonged inactivity causes disuse
atrophy
 Regular exercise increases muscle
size, called hypertrophy
(Cont’d…)
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Slide 26
Effects of Exercise on Skeletal Muscles
(…Cont’d)
 Strength training is exercise involving
contractions of muscles against heavy
resistance
 Strength training increases the numbers
of myofilaments in each muscle fiber, and
as a result, the total mass of the muscle
increases
 Strength training does not increase the
number of muscle fibers
(Cont’d…)
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Slide 27
Effects of Exercise on Skeletal Muscles
(…Cont’d)
 Endurance training is exercise that
increases a muscle’s ability to sustain
moderate exercise over long periods; it is
sometimes called aerobic training
 Endurance training allows more efficient
delivery of oxygen and nutrients to a
muscle via increased blood flow
 Endurance training does not usually
result in muscle hypertrophy
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Slide 28
Skeletal Muscle Groups
• Muscles of the head and neck
 Facial muscles
 Orbicularis oculi
 Orbicularis oris
 Zygomaticus
(Cont’d…)
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Slide 29
MAJOR MUSCLES
HEAD AND NECK
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Slide 30
Skeletal Muscle Groups
(…Cont’d)
 Muscles of mastication
 Masseter
 Temporal
 Sternocleidomastoid—flexes head
 Trapezius—elevates shoulders and
extends head
(Cont’d…)
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Slide 31
MAJOR MUSCLES
BACK
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Slide 32
MAJOR MUSCLES
UPPER EXTREMITIES
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Slide 33
Skeletal Muscle Groups
(…Cont’d)
• Muscles that move the upper extremities





Pectoralis major—flexes upper arm
Latissimus dorsi—extends upper arm
Deltoid—abducts upper arm
Biceps brachii—flexes forearm
Triceps brachii—extends forearm
(Cont’d…)
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Slide 34
MAJOR MUSCLES
ABDOMEN
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Slide 35
Skeletal Muscle Groups
(…Cont’d)
• Muscles of the trunk
 Abdominal muscles
 Rectus abdominis
 External oblique
 Internal oblique
 Transversus abdominis
 Respiratory muscles
 Intercostal muscles
 Diaphragm
(Cont’d…)
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Slide 36
MAJOR MUSCLES
LOWER EXTREMITIES
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Slide 37
MAJOR MUSCLES
PELVIS/ LOWER EXTREMITIES
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Slide 38
Skeletal Muscle Groups
(…Cont’d)
• Muscles that move the lower extremities




Iliopsoas—flexes thigh
Gluteus maximus—extends thigh
Adductor muscles—adduct thighs
Hamstring muscles—flex lower leg
 Semimembranosus
 Semitendinosus
 Biceps femoris
(Cont’d…)
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Slide 39
Skeletal Muscle Groups
(…Cont’d)
• Muscles that move the lower extremities
 Quadriceps femoris group—extend
lower leg
 Rectus femoris
 Vastus muscles
 Tibialis anterior—dorsiflexes foot
 Gastrocnemius—plantar flexes foot
 Peroneus group—flex foot
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Slide 40
Types of Movements Produced by
Skeletal Muscle Contractions
• Flexion—movement that decreases the angle
between two bones at their joint: bending
• Extension—movement that increases the
angle between two bones at their joint:
straightening
(Cont’d…)
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Slide 41
Types of Movements Produced by
Skeletal Muscle Contractions
(…Cont’d)
• Abduction—movement of a part away
from the midline of the body
• Adduction—movement of a part toward
the midline of the body
• Rotation—movement around a
longitudinal axis
(Cont’d…)
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Slide 42
Types of Movements Produced by
Skeletal Muscle Contractions
(…Cont’d)
• Supination and pronation—hand
positions that result from rotation of the
forearm; supination results in a hand
position with the palm turned to the
anterior position; pronation occurs when
the palm faces posteriorly
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(Cont’d…)
Slide 43
Types of Movements Produced by
Skeletal Muscle Contractions
(…Cont’d)
• Dorsiflexion and plantar flexion—foot
movements; dorsiflexion results in
elevation of the dorsum or top of the
foot; during plantar flexion, the bottom
of the foot is directed downward
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Slide 44
The End
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Slide 45