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Anatomy and
Physiology I
Seminar 6
Chapter 7
The Muscular System
Renita K. Holmes, MSN, RN
Kaplan University
Slide 2
INTRODUCTION
 Muscular
tissue enables the body and its
parts to move



Three types of muscle tissue exist in body (see
Chapter 3)
Movement caused by muscle cells (called
fibers) shortening, or contracting
Muscle movement occurs when chemical
energy (obtained from food) is converted into
mechanical energy
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MUSCLE TISSUE
 Types

of muscle tissue (Figure 7-1)
Skeletal muscle—also called striated or
voluntary muscle
 Microscope
reveals crosswise stripes or striations
 Contractions can be voluntarily controlled

Cardiac muscle—composes bulk of heart
 Cardiac
muscle fibers branch frequently
 Characterized by unique dark bands called
intercalated disks
 Interconnected nature of cardiac muscle fibers
allows heart to contract efficiently as a unit
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Muscle tissue
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MUSCLE TISSUE
 Types

of muscle tissue (cont.)
Nonstriated muscle, or involuntary muscle—also
called smooth or visceral muscle
 Lacks
cross stripes or striations 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 contraction is involuntary
 Function—all
muscle fibers specialize in
contraction (shortening)
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STRUCTURE OF SKELETAL MUSCLE
 Composition—mainly
striated muscle fibers
and connective tissue
 Most skeletal muscles extend from one
bone across a joint to another bone
 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
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STRUCTURE OF SKELETAL MUSCLE
 Composition


Muscles attach to 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
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STRUCTURE OF SKELETAL MUSCLE
 Microscopic



structure (Figure 7-3)
Contractile cells called fibers—grouped into bundles
Fibers contain thick myofilaments (containing the
protein myosin) and thin myofilaments (composed
of actin)
Basic functional (contractile) unit called sarcomere


Sarcomeres separated from each other by dark bands
called Z lines
Sliding filament model explains mechanism of
contraction


Thick and thin myofilaments slide past each other as a
muscle contracts
Contraction requires calcium and energy-rich ATP molecules
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Structure of skeletal muscle.
A: Each muscle organ has many
muscle fibers, each containing
many bundles of thick and thin
filaments.
The diagrams show the
overlapping thick and thin
filaments arranged to form
adjacent segments called
sarcomeres.
During contraction,
the thin filaments are pulled
toward the center of each
sarcomere, shortening the whole
muscle.
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Structure of skeletal muscle B, This electron micrograph shows that the
overlapping thick and thin filaments within each sarcomere create a pattern
of dark striations in the muscle.
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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
 Groups
of muscles usually contract to produce a
single movement



Prime mover—muscle whose contraction is mainly
responsible for producing a given movement
Synergist—muscle whose contractions help the prime
mover produce a given movement
Antagonist—muscle whose actions oppose the action
of a prime mover in any given movement
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AGONIST (Prime Mover) ANTAGONIST
Biceps
Triceps
Deltoids
Pectoralis Major
Latissimus Dorsi
Trapezius/Rhomboids
Rectus Abdominis
Erector Spinae
Iliopsoas
Gluteus Maximus
Quadriceps
Hamstrings
Hip Adductor
Gluteus Medius
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FUNCTIONS OF SKELETAL MUSCLE
 Posture

A specialized type of muscle contraction, called
tonic contraction, enables us to maintain body
position



In tonic contraction, only a few of a muscle’s fibers
shorten at one time
Tonic contractions produce no movement of body
parts
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
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FUNCTIONS OF SKELETAL MUSCLE
 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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FATIGUE
 Reduced
strength of muscle contraction
 Caused by repeated muscle stimulation
without adequate periods of rest
 Repeated muscular contraction depletes
cellular adenosine triphosphate (ATP)stores
(the energy storage molecules of the cell)
and outstrips the ability of the blood supply to
replenish oxygen and nutrients
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FATIGUE
 Contraction
in the absence of adequate
oxygen produces lactic acid, which
contributes to muscle soreness
 Oxygen debt—term used to describe the
metabolic effort required 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 pre-exercise levels
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ROLE OF OTHER BODY SYSTEMS IN
MOVEMENT
 Muscle
functioning depends on the
functioning of many other parts of the body
 Most muscles cause movements by pulling on
bones across movable joints
 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
pathological conditions in other body organ
systems can dramatically affect movement
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Slide 18
MOTOR UNIT (Figure 7-4)
 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
 A neuromuscular 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 fiber or fibers it
innervates
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A motor unit consists of
one motor neuron and the
muscle fibers supplied by
its branches.
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Motor neuron.
A motor unit consists of one
motor neuron and the
muscle fibers supplied by its
branches.
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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
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MUSCLE STIMULUS
 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 23
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
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The muscle responds to
a single stimulus (neural
stimulation or electric
shock) with a quick
contraction and
relaxation.
Together, this is called a
muscle twitch. A muscle
is made up of individual
muscle fibers
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Slide 25
If you increase the
frequency of the shock,
eventually the second
stimulus will be applied
before the first muscle
twitch is over, then the
second stimulus will
build upon the previous
contraction and add to
that response.
This is called twitch
summation
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As you continue to increase the frequency of shocks, eventually no relaxation
will be allowed and the muscle contraction will increase smoothly up to a
point of maximum strength where individual twitches are not observed. This
is called tetany. Tetany is the way by which normal muscle contractions
occur
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TYPES OF SKELETAL MUSCLE
CONTRACTION
 Isotonic




contractions
Contraction of a muscle that produces movement
at a joint because the muscle changes length
During concentric contractions, the muscle shortens
insertion end of the muscle to move toward the
point of origin
During eccentric contractions, the muscle lengthens
under tension, thus moving the insertion away from
the origin
Most types of body movements such as walking and
running are produced by isotonic contractions
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TYPES OF SKELETAL MUSCLE
CONTRACTION
 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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What is an isometric contraction? To understand, is when you perform
without moving force (or shortening or muscle lengthening). For
example, if you push a wall without moving, you’re doing strength and,
unless you do get a lot and move the wall … you perform a static
contraction. This is exactly an isometric contraction.
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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
 Muscles change in relation to the amount of
work they normally do
 Prolonged inactivity causes disuse atrophy
 Regular exercise increases muscle size,
called hypertrophy
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EFFECTS OF EXERCISE ON SKELETAL
MUSCLES
 Strength
training is exercise involving
contraction of muscles against heavy
resistance
 Strength training increases the number 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
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EFFECTS OF EXERCISE ON SKELETAL
MUSCLES
 Endurance
training is exercise that
increases a muscle’s ability to sustain
moderate exercise over a long period; 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 37
SKELETAL MUSCLE GROUPS
(Table 7-1)
 Muscles

of the head and neck (Figure 7-7)
Facial muscles
 Orbicularis
oculi
 Orbicularis oris
 Zygomaticus

Muscles of mastication
 Masseter
 Temporal


Sternocleidomastoid—flexes head
Trapezius—elevates shoulders and extends
head
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Slide 38
Muscles of the head and neck. Muscles that produce most facial
expressions surround the eyes, nose, and mouth. Large muscles of
mastication stretch from the upper skull to the lower jaw. These powerful
muscles produce chewing movements. The neck muscles connect the
skull to the trunk of the body, rotating the head or bending the neck.
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SKELETAL MUSCLE GROUPS
 Muscles
that move the
upper extremities



Pectoralis major—flexes upper
arm
Deltoid—abducts upper arm
Biceps brachii—flexes forearm
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Slide 40
Muscles that move the
upper extremities
Latissimus dorsi—
extends upper arm
Triceps brachii—
extends forearm
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SKELETAL MUSCLE GROUPS
 Muscles

of the trunk (Figure 7-8)
Abdominal muscles
 Rectus
abdominis
 External oblique
 Internal oblique
 Transversus abdominis

Respiratory muscles
 Intercostal
muscles
 Diaphragm
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Slide 43
Muscles of the trunk. A, Anterior view showing superficial
muscles. B, Anterior view showing deeper muscles.
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SKELETAL MUSCLE GROUPS
 Muscles




Iliopsoas—flexes thigh
Gluteus maximus—extends thigh
Adductor muscles—adduct thighs
Hamstring muscles—flex lower leg







Semimembranosus
Semitendinosus
Biceps femoris
Quadriceps femoris group—extend lower leg


that move the lower extremities
Rectus femoris
Vastus muscles
Tibialis anterior—dorsiflexes foot
Gastrocnemius—plantar flexes foot
Peroneus group—flex foot
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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
 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
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Flexion and extension of the elbow. A and B, When the elbow is flexed, the
biceps brachii contracts while its antagonist, the triceps brachii, relaxes.
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Flexion and extension of the elbow. B and C, When the elbow is
extended, the biceps brachii relaxes while the triceps brachii contracts.
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Flexion and extension of the knee. A and B, When the knee flexes,
muscles of the hamstring group contract while their antagonists in the
quadriceps femoris group relax.
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Flexion and extension of the knee. B and C, When the knee extends, the
hamstring muscles relax while the quadriceps femoris muscle contracts.
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Abduction means moving
a part away from the
midline of the body, such
as moving your arm out
to the side.
Adduction means moving
a part toward the midline,
such as bringing your arms
down to your sides from an
elevated position.
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Rotation is movement around a longitudinal axis. You rotate
your head and neck by moving your skull from side to side as
in shaking your head “no”
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Supination and pronation
refer to hand positions
that result from rotation of the
forearm.
Prone refers to the body as a
whole lying face down.
Supine means lying face up.
Supination results in a hand
position with the palm turned
to the anterior position (as in
the anatomical position), and
pronation occurs when you
turn the palm of your hand so
that it faces posteriorly
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Dorsiflexion and plantar
flexion refer to ankle
movements.
In dorsiflexion the
dorsum or top of
the foot is elevated with
the toes pointing upward.
In plantar flexion the
bottom of the foot is
directed downward so
that you are in effect
standing on your toes
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Inversion and eversion are also ankle movements.
Inversion moves turn the ankle so that the bottom of the foot faces toward
the midline of the body. Eversion turns the ankle in the opposite direction,
so that the bottom of the foot faces toward the side of the body
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QUESTIONS
OR COMMENTS
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