Download Muscle

CHAPTER 3
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LEARNING OBJECTIVES
• To describe muscle’s macro and micro structures
• To explain the sliding-filament action of muscular
contraction
• To differentiate among types of muscle fibres
• To describe group action of muscles
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TYPES OF MUSCLE
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The human body is comprised of 324 muscles
Muscle makes up 30-35% (in women) and 42-47% (in men) of
body mass.
Three types of muscle:
Skeletal muscle
Cardiac muscle
Smooth muscle
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A. SKELETAL (STRIATED)
MUSCLE
• Connects the various parts of the skeleton through one or more
connective tissue tendons
• During muscle contraction, skeletal muscle shortens and moves
various parts of the skeleton
• Through graded activation of the muscles, the speed and smoothness
of the movement can be gradated
• Activated through signals carried to the muscles via nerves (voluntary
control)
• Repeated activation of a skeletal muscle can lead to fatigue
• Biomechanics: assessment of movement and the sequential pattern of
muscle activation that move body segments
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B. SMOOTH MUSCLE
• Located in the blood vessels, the respiratory
tract, the iris of the eye, the gastro-intestinal
tract
• The contractions are slow and uniform
• Functions to alter the activity of various
body parts to meet the needs of the body at
that time
• Is fatigue resistant
• Activation is involuntary
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C. CARDIAC MUSCLE
• Has characteristics of both skeletal and
smooth muscle
• Functions to provide the contractile
activity of the heart
• Contractile activity can be gradated
(like skeletal muscle)
• Is very fatigue resistant
• Activation of cardiac muscle is
involuntary (like smooth muscle)
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Components of skeletal muscle
d) myofibril
c) muscle fibre
b) muscle fibre bundle a) Muscle belly
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MUSCLE FIBRES
• Cylinder-shaped cells that make up skeletal muscle
• Each fibre is made up of a number of myofilaments
• Diameter of fibre (0.05-0.10 mm)
• Length of fibre (appr. 15 cm)
• Surrounded by a connective tissue sheath called Sarcolemma
• Many fibres are enclosed by connective tissue sheath Perimycium to
form bundle of fibres
• Each fibre contains contractile machinery and cell organelles
• Activated through impulses via motor end plate
• Group of fibres activated via same nerve: motor unit
• Each fibre has capillaries that supply nutrients and eliminate waste
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MUSCLE TEAMWORK
• Agonist (prime mover):
- the muscle or group of muscles producing a desired effect
• Antagonist:
- the muscle or group of muscles opposing the action
• Synergist:
- the muscles surrounding the joint being moved
• Fixators:
- the muscle or group of muscles that steady joints closer to the body axis so
that the desired action can occur
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BENDING OR STRAIGHTENING OF ELBOW REQUIRES
THE COORDINATED INTERPLAY OF THE BICEPS AND
TRICEPS MUSCLES
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CONTRACTILE MACHINERY:
SARCOMERES
• Contractile units
• Organized in series ( attached
end to end)
• Two types of protein
myofilaments:
- Actin:
thin filament
- Myosin: thick filament
• Each myosin is surrounded by
six actin filaments
• Projecting from each myosin
are tiny contractile myosin
bridges
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Longitudinal section of myofibril
(a) At rest
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HIGH MICROSCOPE MAGNIFICATION OF SARCOMERES
WITHIN A MYOFIBRIL
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CONTRACTILE MACHINERY:
CROSSBRIDGE FORMATION AND
MOVEMENT

Cross bridge movement:
- similar to the stroking of the oars and
• Cross bridge formation:
movement of rowing shell
- a signal comes from the motor
- movement of myosin filaments in relation
nerve activating the fibre
- the heads of the myosin filaments to actin filaments
- shortening of the sarcomere
temporarily attach themselves to
- shortening of each sarcomere is additive
the actin filaments
Longitudinal section of myofibril
b) Contraction
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CONTRACTILE MACHINERY:
OPTIMAL CROSSBRIDGE
FORMATION
Longitudinal section of myofibril
• Sarcomeres should be optimal
distance apart
• For muscle contraction: optimal
distance is (0.0019-0.0022 mm)
• At this distance an optimal number
of cross bridges is formed
• If the sarcomeres are stretched
farther apart than optimal distance:
- fewer cross bridges can form 
less force produced
• If the sarcomeres are too close
together:
- cross bridges interfere with one
another as they form  less force
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produced
c) Powerful stretching
d) Powerful contraction
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