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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