1. Muscle Structure and Function
Chapter 3
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2. 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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3. Types of Muscle Skeletal muscle Smooth muscle Cardiac 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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4. 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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5. 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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6. 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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7. Components of skeletal muscle
d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly
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8. Muscle Fibres Cylinder-shaped cells that make up skeletal muscle
Each fibre is made up of a number of myofilaments
Diameter of fibre ( 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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9. 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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10. Bending or straightening of elbow requires the coordinated interplay of the biceps and triceps muscles
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11. 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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12. High microscope magnification of sarcomeres within a myofibril
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13. Contractile Machinery: Crossbridge formation and movement
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
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
Longitudinal section of myofibril
b) Contraction
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14. Contractile Machinery: Optimal Crossbridge formation
Longitudinal section of myofibril
Sarcomeres should be optimal distance apart
For muscle contraction: optimal distance is ( 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
c) Powerful stretching
d) Powerful contraction
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