Chapter 7
The Muscular System
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 1
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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 2
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 are branched
• Has dark bands called intercalated disks
• Cardiac muscle fiber interconnections allow heart to
contract efficiently as a unit
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 3
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 4
MUSCLE TISSUE (cont.)

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 structures, such as digestive
tract, blood vessels, etc.
• Contractions not under voluntary control

Function—all muscle fibers specialize
in contraction (shortening)
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 5
STRUCTURE OF SKELETAL MUSCLE

Muscle organs—mainly striated muscle fibers and
connective tissue



Connective tissue forms “wrappers” around each muscle fiber,
around fascicles (groups) of muscle fibers, and around the entire
muscle; fascia surrounds muscle organs and nearby structures
Most skeletal muscles extend from one bone across a joint
to another bone
Regions of a skeletal muscle (Figure 7-2)
• 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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 6
STRUCTURE OF SKELETAL
MUSCLE (cont.)

Muscle organs (cont.)
• Muscles attach to bone by tendons—strong cords
or sheets of fibrous connective tissue that extend
from the muscle organ; some tendons enclosed
in synovial-lined tubes (tendon sheaths) and are
lubricated by synovial fluid
• Bursae—small synovial-lined sacs containing a small
amount of synovial fluid; located between some
tendons and underlying bones
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 7
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 8
STRUCTURE OF SKELETAL
MUSCLE (cont.)

Muscle organs (cont.)

Microscopic structure and function (Figure 7-3)
• Contractile cells are called muscle fibers; connective tissue holds
muscle fibers in parallel groupings
• Fibers of the cytoskeleton form cylinders that contain thick
myofilaments (containing myosin) and thin myofilaments
(containing mainly 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 to contract
– Contraction requires calcium and energy-rich ATP molecules
(Figure 7-4)
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 9
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 10
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 11
FUNCTIONS OF SKELETAL MUSCLE

Movement

Muscles produce movement by pulling on bones
as a muscle contracts
• The insertion bone is pulled 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—mainly responsible for producing a given
movement
• Synergist—helps the prime mover produce a given
movement
• Antagonist—opposes the action of a prime mover in a given
movement
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 12
FUNCTIONS OF SKELETAL
MUSCLE (cont.)

Posture

A continuous, low-strength muscle contraction
called tonic contraction (muscle tone) enables us to
maintain body position
• Only a few of a muscle's fibers shorten at one time
• Produce no movement of body parts
• Maintain muscle tone called posture
 Good posture favors best body functioning
 Skeletal muscle tone maintains good posture by
counteracting the pull of gravity
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 13
FUNCTIONS OF SKELETAL
MUSCLE (cont.)

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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 14
FUNCTIONS OF SKELETAL
MUSCLE (cont.)

Fatigue





Reduced strength of muscle contraction
Caused by repeated muscle stimulation without adequate periods
of rest
Repeated muscular contraction depletes cellular ATP stores and
outstrips the ability of the blood supply to replenish oxygen and
nutrients
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
• Labored breathing after strenuous exercise is required to “pay the
debt”
• This increased metabolism helps restore energy and oxygen
reserves to pre-exercise levels
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 15
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 moveable 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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 16
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
Neuromuscular junction (NMJ)—point of contact
between a nerve ending and the muscle fiber
Motor unit—combination of a motor neuron with
the muscle fibers it controls (Figure 7-6)
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 17
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 18
MUSCLE STIMULUS

A muscle will contract only if an applied stimulus reaches a
certain level of intensity



Threshold stimulus—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
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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 19
TYPES OF SKELETAL MUSCLE
CONTRACTION

Twitch and tetanic contractions

Twitch contractions are laboratory phenomena and
not normal muscle activity; they are a single
contraction of muscle fibers caused by
a single threshold stimulus
 Tetanic contractions are sustained muscular
contractions caused by stimuli hitting a muscle in
rapid succession
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 20
TYPES OF SKELETAL MUSCLE
CONTRACTION (cont.)

Isotonic contractions

Contractions that produce movement at a joint because
the muscle changes length
 Concentric contractions—the muscle shortens at the
insertion end of the muscle to move toward the point of
origin
 Eccentric contractions—the muscle lengthens under
tension, thus moving the insertion away from the origin
 Most types of body movements (walking, running, etc.)
are produced by isotonic contractions
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 21
TYPES OF SKELETAL MUSCLE
CONTRACTION (cont.)

Isometric contractions

Contractions that do not produce movement;
the muscle as a whole does not shorten
 Although no movement occurs, tension
within the muscle increases
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 22
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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 23
EFFECTS OF EXERCISE ON
SKELETAL MUSCLES (cont.)

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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 24
EFFECTS OF EXERCISE ON
SKELETAL MUSCLES (cont.)

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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 25
MOVEMENTS PRODUCED BY SKELETAL MUSCLE
CONTRACTIONS (Figures 7-7 through 7-9)









Flexion—decreases an angle
Extension—increases an angle
Abduction—away from the midline
Adduction—toward the midline
Rotation—around an axis
Circumduction—move distal end of a part in a circle
Supination and pronation—hand positions that result
from twisting the forearm
Dorsiflexion and plantar flexion—foot movements
(upward and downward ankle movement)
Inversion and eversion—foot movements (sideways)
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 26
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 27
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 28
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 29
SKELETAL MUSCLE GROUPS
(Table 7-1)

Muscles of the head and neck (Figures 7-10
and 7-11)

Facial muscles
• Orbicularis oculi
• Orbicularis oris
• Zygomaticus
 Muscles of mastication
• Masseter
• Temporal
 Sternocleidomastoid—flexes head
 Trapezius—elevates shoulders and extends head
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 30
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 31
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 32
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 33
SKELETAL MUSCLE GROUPS (cont.)

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
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 34
SKELETAL MUSCLE GROUPS (cont.)

Muscles of the trunk (Figure 7-12)


Abdominal muscles
• Rectus abdominis
• External oblique
• Internal oblique
• Transversus abdominis
Respiratory muscles
• Intercostal muscles
• Diaphragm
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 35
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 36
SKELETAL MUSCLE GROUPS (cont.)

Muscles that move the lower extremities








Iliopsoas—flexes thigh
Gluteus maximus—extends thigh
Adductor muscles—adduct thighs
Hamstring muscles—flex lower leg
• Semimembranous
• Semitendinosus
• Biceps femoris
Quadriceps femoris group—extend lower leg
• Rectus femoris
• Vastus muscles
Tibialis anterior—dorsiflexes foot
Gastrocnemius—plantar flexes foot
Peroneus group—flex foot
Mosby items and derived items © 2012 by Mosby, Inc., an affiliate of Elsevier Inc.
Slide 37