Grade 12 Exercise Science
Muscle Structure and Function Note
Properties of Muscle Fibre
1. Excitability/ Irritability
 ability to receive and respond to stimuli
2. Contractibility
 ability to shorten and thicken, or contract
3. Extensibility
 ability to stretch, or extend
4. Elasticity
 ability return to its original shape after contraction or extension
5. Conductivity
 ability to transmit nerve impulses
Muscle Types
1. Skeletal
 named for its location (attached to bones and moves the skeleton)
 it is striated (has striations, or alternating bands of light and dark bands visible
under microscope)
 it is voluntary because it can be made to contract and relax by conscious
control
2. Cardiac
 forms the bulk of the wall of the heart
 it is striated and involuntary
3. Smooth
 involved with internal processes
 located in the internal structures (e.g. blood vessels, the stomach, and the
intestines)
 it is non-striated and involuntary
Muscle Function
1. Motion
 walking, beating of the heart, churning food in stomach, etc.
2. Maintenance of posture
 contraction of skeletal muscles holds the body in stationary positions
3. Heat production
 skeletal muscle contractions produce heat which helps to maintain normal
body temperature
Grade 12 Exercise Science
Muscle Structure and Function Note
Connective Tissue Components
1. Fascia/ Epimysium
 a sheet or broad band of fibrous connective tissue beneath the skin or around muscles
and other organs of the body
2. Fasiculi or fasicules
 bundles of muscle fibres
3. Perimysium
 a fibrous connective tissue that covers the fasicules
4. Endomysium
 the fibrous connective tissue that wraps each individual muscle cell
5. Tendon
 a cord of connective tissue that attaches a muscle to a bone
 made of epimysium, perimysium, and endomysium
Muscle structure under a microscope
Muscle fibres
 skeletal muscle viewed under a microscope contains thousands of these elongated,
cylindrical cells
Sarcolemma
 the plasma membrane that covers each muscle fibre
Myofibrils
 found within each skeletal muscle fibre
 cylindrical structures which run longitudinally through the muscle fibre
 consist of two smaller structures called myofilaments
Myofilaments
 thin myofilaments and thick myofilaments
 do not extend the entire length of a muscle fibre
 they are arranged in compartments called sarcomeres
Sarcomeres
 separated by narrow zones of dense material called Z lines
 within a sarcomere is a dark area called the A band (thick myofilaments)
 ends of the A band are darker because of overlapping thick and thin myofilaments
 the light coloured area is called the I band (thin myofilaments)
 the combination of alternating dark A bands and light I bands gives the muscle fibre
its striated appearance
Grade 12 Exercise Science
Muscle Structure and Function Note
Thin myofilaments
 thin myofilaments are anchored to the Z lines
 composed mostly of the protein actin
 actin is arranged in two single strands that entwine like a rope
 each actin molecule contains a myosin- binding site
 thin myofilaments contain two other protein molecules that help regulate muscle
contraction (tropomyosin and troponin)
Thick myofilaments
 composed mostly of the protein myosin which is shaped like a golf club
 the heads of the golf clubs project outward
 these projecting heads are called cross bridges and contain an actin- binding site and
an ATP binding site
Sliding Filament Theory
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during muscle contraction, thin myofilaments slide inward toward the centre of a
sarcomere
sarcomere shortens, but the lengths of the thin and thick myofilaments do not change
myosin cross bridges of the thick myofilaments connect with portions of actin on thin
myofilaments
myosin cross bridges move like the oars of a boat on the surface of the thin
myofilaments
thin and thick myofilaments slide past one another
as thin myofilaments slide inward, the Z lines are drawn toward each other and the
sarcomere is shortened
myofilament sliding and sarcomere shortening result in muscle contraction
this process can only occur in the presence of sufficient calcium (Ca++) ions and an
adequate supply of energy (ATP)