Post on 26-Mar-2015
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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 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
Smooth muscle
Cardiac 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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d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly
Components of skeletal muscle
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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
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 formation:
- a signal comes from the motor nerve activating the fibre - the heads of the myosin filaments temporarily attach themselves to the actin filaments
Cross bridge movement: - similar to the stroking of the oars and movement of rowing shell- movement of myosin filaments in relation to actin filaments- shortening of the sarcomere- shortening of each sarcomere is additive
b) Contraction
Longitudinal section of myofibril
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Contractile Machinery:Optimal Crossbridge formation
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 produced
Longitudinal section of myofibril
c) Powerful stretching
d) Powerful contraction