The Muscular System
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Functions and Types of Muscles
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Smooth Muscle
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Located in the walls of hollow organs
and blood vessels
Involuntary contraction
Moves materials through organs and
regulates blood flow
Cylindrical cells with pointed ends
Each cell is uninucleate
Functions and Types of Muscles
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Cardiac Muscle
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Forms the heart wall
Fibers are uninucleated, striated,
tubular, and branched
Fibers interlock at intercalated disks,
which permit contractions to spread
quickly throughout the heart
Contraction does not require outside
nervous stimulation
Nerves do affect heart rate and
strength of contraction
Functions and Types of Muscles
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Skeletal Muscle
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Fibers are tubular, multinucleated,
and striated
Make up muscles attached to the
skeleton
Contraction is voluntary
Functions and Types of Muscles
o
Connective Tissue Coverings of Skeletal
Muscle
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Endomysium
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Thin layer of areolar connective tissue
Surrounds each skeletal muscle fiber
Perimysium – surrounds bundles of muscle
fibers (fascicles)
Epimysium
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Layer that surrounds the entire muscle
Becomes part of the fascia (separates muscles
from each other)
Collagen fibers extend from epimysium to form
tendons that attach muscles to bone
Functions and Types of Muscles
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Functions of Skeletal Muscles
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Support the body
Make bones and other body parts
move
Help maintain a constant body
temperature
Assists movement in cardiovascular
and lymphatic vessels
Help protect bones and internal
organs, and stabilize joints
Microscopic Anatomy
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Muscle fiber components
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Sarcolemma – plasma membrane
Sarcoplasm – cytoplasm
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Contains glycogen that provides energy for muscle
contraction
Contains myoglobin which binds oxygen until
needed
Sarcoplasmic reticulum – endoplasmic
reticulum
T (transverse) tubules
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Formed by the sarcolemma penetrating into the
cell
Come into contact with expanded portions of the
sarcoplasmic reticulum
Microscopic Anatomy
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Myofibrils and Sarcomeres
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Myofibrils run the length of the muscle fiber
Composed of numerous sarcomeres
Extends between two vertical Z lines
Contains two types of protein myofilaments
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Thick filaments – made up of myosin
Thin filaments – made up of actin, tropomyosin, and
troponin
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I band contains only thin filaments
A band in the center of the sarcomere contains
thick and thin filaments
H zone in the center of the A band has only
myosin filaments
Microscopic Anatomy
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Myofilaments
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Thick filaments
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Composed of several hundred of
molecules of myosin
Myosin molecules end in a cross-bridge
Thin filaments
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Two strands of actin
Double strands of tropomyosin coil of
each actin strand
Troponin occurs at intervals on the
tropomyosin strand
Microscopic Anatomy
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Sliding filaments
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Occurs when sarcomeres shorten (during
muscle contraction)
Actin filaments slide past the myosin
filaments
Thick and thin filaments remain the same
length
Contraction of Skeletal Muscle
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Neuromuscular junction
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Axon terminals
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Come into close proximity to the
sarcolemma
Have vesicles that contain acetylcholine
(Ach)
Synaptic cleft – a small gap that
separates the axon from the
sarcolemma
Fig 7.4
Contraction of Skeletal Muscle
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Steps involved in skeletal muscle
contraction
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Nerve signal arrives at the axon terminal
The synaptic vesicles release Ach
Ach binds to receptors on the sarcolemma
The sarcolemma generates a signal that
travels down the T tubules to the SR
The SR releases calcium
Calcium from the SR causes the filaments to
slide past one another
Contraction of Skeletal Muscle
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The Role of Actin and Myosin
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Myosin binding sites on actin
molecules
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Covered by tropomyosin when muscle is
relaxed
Released calcium combines with troponin
and myosin binding sites are exposed
Cross-bridges of myosin have two
binding sites
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One site binds to ATP
Second binding site binds to actin
Contraction of Skeletal Muscle
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Energy for Muscle Contraction
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ATP present before strenuous
exercise only lasts a few seconds
Muscles acquire new ATP in three
ways
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Creatine phosphate breakdown
Cellular respiration
Fermentation
Contraction of Skeletal Muscle
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Creatine Phosphate Breakdown
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Does not require oxygen (anaerobic)
Regenerates ATP by transferring its phosphate to
ADP
Fastest way to make ATP available to muscles
ATP produced only lasts about 8 seconds
TA 7.1
Contraction of Skeletal Muscle
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Cellular Respiration
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Usually provides most of a muscle’s ATP
Uses glucose from stored glycogen and fatty acids from
stored fats
Required oxygen
Myoglobin can make oxygen available to muscle
mitochondria
Carbon dioxide and water are end products
Heat is a by-product
Contraction of Skeletal Muscle
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Fermentation
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Anaerobic process
Produces ATP for short bursts of exercise
Glucose is broken down to lactate (lactic acid)
Contraction of Skeletal Muscle
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Oxygen Debt
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Occurs when muscles use
fermentation to supply ATP
Requires replenishing creatine
phosphate supplies and disposing of
lactic acid
Contraction of Smooth Muscle
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Smooth muscle fibers contain thick
and thin filaments
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Filaments are not arranged into
myofibrils that create striations
Thin filaments are anchored to the
sarcolemma or dense bodies
When contracted, the elongated
cells become shorter and wider
Contraction occurs very slowly
Contractions can last for long
periods of time without fatigue
Muscle Responses in the Laboratory
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All-or-none law – a muscle fiber
contracts completely or not at all
A whole muscle shows degrees of
contraction
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Muscle twitch – a single contraction that
lasts only a fraction of a second
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Latent period
Contraction period
Relaxation period
Summation – increased muscle contraction
Tetanic contraction – maximal sustained
contraction
Muscle Responses in the Laboratory
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Fatigue
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Muscle relaxes even though
stimulation continues
Reasons for fatigue
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ATP is depleted (oxygen debt)
Accumulation of lactic acid in the
sarcoplasm inhibits muscle function
ACh may become depleted
Muscle Responses in the Body
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Motor unit
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A nerve fiber together with all of the muscle
fibers it innervates
Obeys the all-or-none law
Recruitment
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As the intensity of nervous stimulation
increases, more motor units are activated
Results in stronger muscle contractions
Tone
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Some muscle fibers are always contracting
Important in maintaining posture
Muscle Responses in the Body
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Athletics and muscle contraction
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Size of muscles
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Atrophy – a decrease in muscle size
Hypertrophy – an increase in muscle size
Slow-twitch fibers (Type I fibers)
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Tend to be aerobic
Have more endurance
Have many mitochondria
Dark in color because they contain
myoglobin
Highly resistant to fatigue
Muscle Responses In the Body
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Fast-twitch fibers (Type II fibers)
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Tend to be anaerobic
Designed for strength
Light in color
Have fewer mitochondria, little or no
myoglobin, and fewer blood vessels than
slow-twitch fibers
Vulnerable to accumulation of lactic acid
and can fatigue easily
Skeletal Muscles of the Body
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Basic Principles
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Origin – attachment of a muscle to
the immovable bone
Insertion – attachment of a muscle to
the bone that moves
Prime mover – muscle that does most
of the work in a movement
Synergist – muscles that assist the
prime mover
Antagonists – muscles that work
opposite one another to bring about
movement in opposite directions
Skeletal Muscles of the Body
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Naming Muscles
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Size
Shape
Direction of fibers
Location
Attachment
Number of attachments
Action
Skeletal Muscles of the Body
o Muscles of the Head
• Muscles of Facial
Expression
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Frontalis
Orbicularis oculi
Orbicularis oris
Buccinator
Zygomaticus
• Muscles of Mastication
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Masseter muscles
Temporalis muscles
Fig 7.13
Skeletal Muscles of the Body
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Muscles of the Neck
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Swallowing
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Tongue and buccinators
Suprahyoid and infrahyoid muscles
Palatini muscles
Pharyngeal constrictor muscles
Muscles that move the head
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Sternocleidomastoid
Trapezius muscles
Skeletal Muscles of the Body
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Muscles of the Trunk
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Muscles of the thoracic wall
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External intercostal muscles
Diaphragm
Internal intercostal muscles
Muscles of the abdominal wall
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External and internal obliques
Transversus abdominis
Rectus abdominis
Skeletal Muscles of the Body
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Muscles of the Shoulder
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Muscles that move the scapula
Trapezius
Serratus anterior
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Muscles that move the arm
Deltoid
Pectoralis major
Latissimus dorsi
Rotator cuff muscles
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Supraspinatus
Infraspinatus
Teres minor
Subscapularis
Fig 7.15
Skeletal Muscles of the Body
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Muscles of the Arm
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Biceps brachii
Brachialis
Triceps brachii
Muscles of the Forearm
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Flexor carpi and extensor carpi
Flexor digitorum and extensor
digitorum
Skeletal Muscles of the Body
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Muscles of the Hip and Lower Limb
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Muscles that move the thigh
Iliopsoas
Gluteus maximus
Gluteus medius
Adductor group muscles
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Pectineus
Adductor longus
Adductor magnus
Gracilis
Skeletal Muscles of the Body
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Muscles that move the leg
Quadriceps femoris group
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Rectus
Vastus
Vastus
Vastus
femoris
lateralis
medialis
intermedius
Sartorius
Hamstring group
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Biceps femoris
Semimembranosus
Semitendinosus
Skeletal Muscles of the Body
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Muscles that move the ankle and foot
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Gastrocnemius
Tibialis anterior
Fibularis longus
Fibularis brevis
Flexor and extensor digitorum longus
Effects of Aging
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Muscle mass and strength tend to
decrease
Endurance decreases
Exercise at any age can stimulate
muscle buildup
Homeostasis
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Cardiac muscle contraction forces blood into
the arteries and arterioles
Smooth muscle in arteries and arterioles help
maintain blood pressure
Smooth muscle contraction moves food along
the digestive tract and assists in the voiding of
urine
Skeletal muscles protect internal organs and
stabilizes joints
Skeletal muscles are active during breathing
Heat produced by skeletal muscle contraction
helps maintain normal body temperature
Skeletal muscle contraction allows us to
relocate our bodies