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Muscular System
Chapter 8
Introduction
• Muscles are responsible for movement
– Contraction & relaxation
• Muscles make up 40 – 50 % of a human’s
total body weight
Characteristics of Muscle Tissue
• Excitability
– Can receive & respond to stimuli
• Contractility
– Can shorten & thicken
• Extensibility
– Can be stretched
• Elasticity
– Can return to its original shape
Functions of Muscle Tissue
• Motion
• Maintenance of posture
• Heat production
Kinds of Muscle Tissue
• Skeletal Muscle
• Cardiac Muscle
• Smooth Muscle
The Muscular System
• Muscle tissue = all contractile tissue
• Muscular system =
– Skeletal muscle tissue
– Connective tissue
Skeletal Muscle Tissue
• Fascia
– Sheet or band of
fibrous connective
tissue around muscles
and other organs
• Fascia of skeletal
muscle
– Surrounds muscle
– Subdivides muscle
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Structural Organization of Skeletal
Muscle
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Tendons
• Cord of connective
tissue that attaches
a muscle to the
periosteum of a
bone
• Extensions of
fascia
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Nerve & Blood Supply
• Each skeletal muscle is well-supplied with nerves and blood
vessels
– Related to contraction
• Contraction requirements
– Stimulation by impulse from a nerve cell
– Energy
– Waste products eliminated
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Skeletal Muscle Fiber
• Muscle fibers =
elongated cells
– Sarcolemma
– Sarcoplasm
– Sarcoplasmic
reticulum
– T tubules
• Muscle fibers consist
of myofibrils
• Extend length
of fiber
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Histology of Skeletal Muscle Tissue
• Myofibrils consist
of myofilaments -
proteins that cause
contraction
– Thick filaments
– Thin filaments
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Myofilaments
• Myofilaments do not
extend entire length of
fiber.
• Stacked in
compartments =
sarcomeres
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Thick and Thin Filaments
• Thin filaments
– Composed mostly of actin
– Contain tropomyosin and
troponin
– Double-stranded
coil
• Thick filaments
– Composed mostly
of myosin
– Rod-shaped (tail)
with head
• Cross bridges
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Contraction – Sliding Filament Theory
• Thin filaments slide
inward
• Sarcomere shortens
• Lengths of myofilaments
do not change
• Sliding of myofilaments
and shortening of
sarcomeres causes the
shortening of muscle
fibers
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuromuscular Junction
• Contraction requires a stimulus from a neuron
• An axon comes into close contact with a muscle membrane =
neuromuscular junction
• Small vesicles in end of axon release acetylcholine (Ach)
• Acetylcholine transmits nerve impulse to the muscle fiber
– Initiates contraction
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Physiology of Contraction –
Relaxed Muscle
• Sarcoplasm is low in
calcium
• ATP is bound to
myosin cross bridges
• Tropomyosintroponin complex is
attached to actin
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Physiology of Contraction –
Muscle is Stimulated
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Nerve impulse reaches neuromuscular junction
Neuron releases ACh
Electrical charge travels along sarcolemma
Electrical charge travels down T tubules
Electrical charge travels to S.R.
S.R. releases calcium into sarcoplasm
Physiology of Contraction –
Activation of Myosin
• Calcium binds to troponin
– Frees receptor sites of actin for myosin cross bridge
• Cross bridges attach to actin
• Calcium acts as an enzyme
– Breaks down ATP to ADP + P
• Myosin cross bridges move
• Sarcomere shortens
• Muscle shortens
Physiology of Contraction –
Relaxation of Muscle
•
•
•
•
Nerve impulse ends
ACh is broken down by acetylcholinesterase
Calcium is actively transported back into S.R.
ADP + P = ATP
– Binds to cross bridges
•
•
•
•
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Myosin cross bridges separate from actin
Binding sites on actin are covered
Thin myofilaments slip back to resting position
Sarcomeres return to resting length
Muscle fiber returns to resting length
Physiology of Contraction
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Disorders
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Fibrosis
Fibrositis
Fibromyalgia
Muscular dystrophy
Myasthenia gravis
Abnormal Contractions
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Spasm
Cramp
Convulsion
Fibrillation
Tic
Anatomy of the Muscular
System
How Skeletal Muscles Produce
Movement
• Exert force on tendons
• Attached to articulating bones forming a joint
• When muscle contracts, one bone moves toward
the other
• Attachments
– Origin = attachment to stationary bone
– Insertion = attachment to moveable bone
– Belly = fleshy portion of muscle between
tendons
Group Actions
• Agonist or prime mover
– Causes desired action
• Antagonist
– Effect is opposite to agonist
• Synergist
– Assists agonist
Naming of Skeletal Muscles
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Direction of muscle fibers
Location
Size
Number of origins
Shape
Origin & insertion
Action
Muscles of the Anterior Trunk and
Shoulder
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Sternocleidomastoid
Pectoralis major
Rectus abdominus
External oblique
Deltoid
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Muscles of the Posterior Trunk and
Shoulder
• Trapezius
• Latissimus Dorsi
• Deltoid
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Muscles of the Arm
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Deltoid
Biceps brachii
Brachioradialis
Triceps brachii
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Muscles of the Forearm
– Flexors - anterior side
– Extensors – posterior side
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Muscles of the Anterior Thigh
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Gracilis
Adductor longus
Sartorius
Quadriceps
• Rectus femoris
• Vastus lateralis
• Vastus medialis
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Muscles of the Posterior Thigh
– Gluteus maximus
– Hamstrings
• Biceps femoris
• Semitendinosis
• Semimembranosis
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Muscles of the Anterior and Lateral
Leg
– Tibialis anterior
– Peroneus longus
– Extensor
digitorum longus
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Muscles of the Posterior Leg
– Gastrocnemius
– Soleus
– Achilles tendon
(nonmuscular)
Human Anatomy, 3rd edition
Prentice Hall, © 2001