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MUSCULAR SYSTEM
Part 3:
Muscle Structure & Contraction
OBJECTIVES
 Describe the structure of skeletal muscle
 Name the major parts of skeletal muscle
fiber and describe the major functions of
each
 Describe the neural control of skeletal
muscle fiber contraction
 Identify the major events in muscle fiber
contraction
 Describe how muscle may become
fatigued and oxygen debt
MUSCLE IN GENERAL
 Is made up of hundreds to thousands of
single, _______________ muscle cells
 A large amount of connective tissue, blood
vessels and nerves are also present
 Muscle cells are soft and easy to injure
 Connective tissue covers and supports each
muscle fiber and reinforces the muscle as a
whole
LAYERS OF CONNECTIVE TISSUE
IN MUSCLE
 There are 3 major layers of connective
tissue
… _________________
… _________________
… _________________
MUSCLE TISSUE
 The health of a muscle depends on a
__________________________________________
 Each skeletal muscle fiber has a nerve
ending that controls its activity
 Active muscles use a lot of energy and need a
continuous supply of oxygen and nutrients
 Muscles produce large amounts of metabolic
waste that must be removed through veins
SKELETAL MUSCLE COMPONENTS
 It is made up of elongated cells called muscle
fibers
 Each muscle cell has a special membrane
called the ________________
 Skeletal muscle fibers are grouped into dense
bundles called _____________
 Between each fiber is the endomysium
 These fascicles are bound together by
connective tissue called the perimysium
 The fascicles & perimysium are wrapped in the
epimysium or deep fascia
Fascicle
MICROSCOPIC STRUCTURE
 A skeletal muscle fiber contains bundles
of threadlike structures called
myofibrils
 Each myofibril is made up of two types
of protein filaments: thick ones and thin
ones
 Thick filaments are made of the protein
_________
 Thin filaments are made of the protein
_____________
MICROSCOPIC STRUCTURE
 Myosin and actin filaments are
arranged to form an overlapping
pattern, giving striated muscle tissue
its striped appearance
 Thin actin filaments are anchored at
their endpoints to a structure called the
__________
 The region from one Z line to the next is
called a ________________
THE STRUCTURE OF CONTRACTION
 The sarcomere is the functional unit of
muscle contraction
 As a muscle contracts, myosin filaments
and actin filaments “slide” past each
other, _____________ the sarcomere
 Myosin filaments have extensions shaped
like oval “heads,” called ________________
 Actin filaments look like a twisted strand
of beads
THE STRUCTURE OF CONTRACTION
1. When a ___________stimulates a muscle to
contract, the myosin filaments’ heads attach to
points between the beads of the actin filaments
2. The myosin heads then bend inward, pulling
the actin with them
3. The myosin heads then let go, bend back into
their original position, attach to a new point on
the actin filament, and pull again
4. The __________ shortening of sarcomeres along
the length of a muscle fiber causes the whole
fiber, and thus the muscle, to contract
REQUIREMENTS OF MUSCLE
CONTRACTION
REQUIREMENTS OF MUSCLE
RELAXATION
WHY THE NEED FOR ATP?
 Muscle cells must have
______________________________________________
 Without ATP,
_____________________________________________
 Muscle contraction is an ____________________:
either the fibers contract or they remain relaxed
QUESTION?
How, then, are you able to
contract your muscles tightly
enough to lift a dumbbell or
gently enough to lift a pen?
SIMPLE MUSCLE CONTRACTION
ANIMATION
SLIDING FILAMENT THEORY
MUSCLE CONTRACTION STEPS IN-DEPTH
1. An action potential arrives at the
sarcolemma of the muscle fiber
2. Acetylcholine is released, depolarizing the
sarcolemma so that Na+ ions flood into the
fiber
3. Action potential is then transmitted via Ttubules to sarcoplasmic reticulum (SR)
… The sarcoplasmic reticulum is a special type
of smooth endoplasmic reticulum found only
in smooth and striated muscle
4. Ca++ ions are released from the SR into the
sarcoplasm (cytoplasm of muscle cells)
MUSCLE CONTRACTION STEPS IN-DEPTH
5. Ca++ ions are bound by troponin
6. ATP binds to myosin heads
7. Tropomyosin (actin binding protein) shift
from actin binding site
8. Actin-myosin crossbridge formation
9. Repeated formation & breaking of
crossbridges resulting in sliding of
filaments and sarcomere shortening
MUSCLE RELAXATION STEPS IN-DEPTH
1. Acetylcholine is destroyed by the enzyme
cholinesterase making the membrane no
longer permeable to sodium ions
2. Sarcolemma & T-tubules are repolarized
3. Ca2+ transported (active, ATP used) back
into the sarcoplasmic reticulum.
4. Low concentration of Ca2+ ]in the
sarcoplasm causes Ca2+ to leave troponin
MUSCLE RELAXATION STEPS IN-DEPTH
5. Actin-myosin crossbridge formation
is terminated
6. Return of tropomyosin to actin
binding site
7. Mg2+ complex formed with ATP
8. Passive sliding of filaments
returns the sarcomeres to the
resting state