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There are ______ Human skeletal muscles
600
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What are the levels of the fascia?
- Superficial
- deep
- epimysium
- perimysium
- endomysium
- tendons
- aponeuroses
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Epimysium...
- Covers whole muscle belly
- blends into connective tissue that separates muscles
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Perimysium...
- a slightly thicker layer of connective tissue
- surrounds a bundle of cells called a fascicle
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Endomysium...
- A thin layer of areolar tissue surrounding each cell
- allows room for capillaries and nerve fibers
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Where is Deep Fascia found?
Between adjacent muscles
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Where is Superficial Fasscia (Hypodermis) found?
- Between skin and muscle
- *contains adipose tissue*
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Most skeletal muscles span _____ and are attached to bone in at least two places
joints
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When muscles contract the ______ bone, the muscle's insertion moves toward the _______ bone (The muscles origin)
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Muscles attach in what two ways?
- Directly: epimysium of the muscle is fused to the periosteum of a bone
- Indirectly: connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis
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Each muscle is served by one ____, an _____, and one or more ______
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Each skeletal muscle fiber is supplied with a _______ ending that controls _________
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__________ require continuous delivery of oxygen and nutrients via arteries
Contracting fibers
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Wastes must be removed via
veins
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Describe a muscle fiber
- A long, cylindrical cell with multiple nuclei just beneath the sarcolemma
- Fibers are 10 to 100 mm in diameter, and up to hundreds of centimeters long
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Each cell is a _________ produced by fusion of embryonic cells
syncytium
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Sarcoplasm has numerous _________ and a unique oxygen-binding protein called ________
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Muscle Fibers contain ______, ______, ___________, and _________
- organelles
- myofibrils
- sarcoplasmic reticulum
- T tubules
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Myofibrils are
densly packed, rodlike contractile elements
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______ make up most of the muscle volume
Myofibrils
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The arrangement of myofibrils within a fiber is such that a
perfectly aligned repeating series of dark A bands and light I bands is evident
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What is the smallest contractile unit of a muscle
Sarcomere
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A Sarcomere is
the region of a myofibril between two successive Z discs
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Sarcomeres are composed of
Thick and thin myofilaments made up of contractile protein
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Thick myofilaments extend...
the entire length of an A band
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Thin myofilaments extend..
across the I band and partway into the A band
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What is a Z-disc?
a coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another
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Thick filaments are composed of the protein ____
myosin
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Each ___________ has a rodlike tail and two globular heads
Tails:
Heads:
myosin molecule
two interwoven, heavy polypeptide chains
Two smaller, light polypeptide chains called cross bridges
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Thin filaments are chiefly composed of the protein ____
actin
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Each _______ is a helical polymer of globular subunits called G actin
actin molecute
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The subunits of actin molecule contain the active cites to which _______ attach during contraction
myosin heads
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_________ and ________ are regulatory subunits bound to actin
Tropomyosin and troponin
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Sarcoplasmic Reticulum is
an elaborate, smooth enodplasmic reticulum that mostly runs longitudinally and surrounds each myofibril
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Sarcoplasmic Reticulum functions in the regulation of ____________ levels
intracellular calcium
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Elongated tubes called _________ penatrate into the cell's interior at each A band-I band junction
T Tubules
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_________ associate with the paired terminal cisternae to form _____
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T Tubles are continuous with the ______
sarcolemma
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T Tubules conduct _____ to the deepest regions of the muscle
impulses
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The impules conducted by T Tubules signal for the release of ______ from adjacent terminal cisternae
Ca2+
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______ and __________ provide tightly linked signals for muscle conraction
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A double zipper of ___________________ protrudes into the intermembrane space
integral membrane proteins
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T tubule proteins act as __________
voltage sensors
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SR foot proteins are receptors that regulate ____ release from the SR cisternae
Ca2+
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At low intracellular Ca2+ concentration:
- Tropomyosin blocks the binding sites on actin
- Myosin cross bridges cannot attach to binding sites on actin
- The relaxed state of the muscle is enforced
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At higher intracellular Ca2+ concentrations
- Additional calcium binds to troponin ( inactive troponin binds two Ca2+)
- Calcium- activated troponin binds an additional two Ca2+ at a separate regulatory site
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Contraction
refers to the activation of mysoin's cross bridges (force- generating sites)
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_______ occurs when the tension generated by the cross bridge exceeds forces opposing shortening
shortening
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________ ends when cross bridges become inactive, the tension generated declines, and relaxation is induced
contraction
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Contraction of ______-- and ___________ is similar
- mucle fibers (cells)
- muscles (organs)
-
Two types of muscle contractions are
- Isometric contraction
- Isotonic contraction
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An isometric contraction is
increasing mucle tension (Muscle does not shorten during contraction)
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Isotonic contraction is
decreaseing muscle length (muscle shortens during contraction
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A motor unit is a __________ and all the muscle fibers it supplies
motor neuron
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The number of muscle fibers per motor unit can vary from
four to several hundred
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Muscles that control fine moevemnts (fingers, eyes) have
small motor units
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Factors Affecting Muscle Tension
- Frequency of stimulation
- Length of fibers
- Number of fibers contracting
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Amount of tension production by muscle fibers depends on
number of cross bridges formed
-
Skeletal muscle contracts most forcefully over
a narrow ranges of resting length
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What is a twitch?
Cycle of contraction, relaxation produced by a single stimulus
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What is a Treppe?
Repeated stimulation after relaxation phase has been completed
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What is summation?
Repeated stimulation BEFORE relaxation phase has been completed
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Wave summation=
one twitch is added to another
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Incomplete tetanus=
muscle never relaxes completely
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Complete tetanus=
relaxation phase is eliminated
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What is a Myogram?
The record of a muscle contraction
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What are the 3 periods of a myogram?
- Latent
- Contraction
- Relaxation
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Where is internal tension generated?
inside contracting muscle fibers
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Where is external tension generated?
in extracellular fibers
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Muscle tone _______ bones and joints
stabilizes
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All the muscle fibers are ______ by one neuron
innervated
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Precise control of movement is determined by ______ and ______ of motor unit
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