muscle structure_and_function

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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