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Chapter 10:

Muscle Tissue
Muscle is one of the primary tissue types in the human body
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The body contains 3 types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle
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Cardiac muscle pumps blood through the
cardiovascular system
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Skeletal muscle) are organs composed mainly of skeletal muscle tissue, but they also contain
connective tissues, nerves, and blood vessels
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Skeletal
muscles attach directly or indirectly to bones
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Produce skeletal movement: pulls on tendons to move bones
2
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Support soft tissues: layers make up the abdominal wall and floor of the pelvic cavity, support the weight of
our visceral organs and shield internal organs

4
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Maintain body temperature: contractions use energy, and when energy is used, some of it is converted to
heat
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Store nutrients: when diet contains too few proteins, or calories, the contractile proteins in skeletal muscle are
broken down, and their amino acids released into the circulation
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Chapter 10:

10-2
A skeletal muscle contains muscle tissue, connective tissues,
blood vessels, and nerves

Organization of Connective Tissues
Each muscle has 3 layers of connective tissue: (1) an epiphysium, (2) a perimysium, and (3)
an endomysium
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It separates
muscle from nearby tissues and organs

Perimysium) divides the skeletal muscle into a series of compartments
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Within a fascicle the

Endomysium) delicate connective tissue, that surrounds the individual skeletal muscle cells
(muscle fibers) and loosely interconnects adjacent muscle fibers
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All these structures are in direct contact with the muscle fibers
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They usually attach muscle
to bone
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As a result, ant contraction of the muscle pulls on the attached bone
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An extensive vascular network
delivers the necessary oxygen and nutrients and carries away the metabolic wastes generated by active
skeletal muscles
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Axons) nerve fibers, extending from neurons
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They are also multinucleate: each contains 100s just internal to
the plasma membrane
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Striations are due to precise arrangements of thin (actin) and thick myosin) filaments
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The Sarcolemma and Tranverse Tubules

Sarcolemma) or plasma membrane of a muscle fiber, surrounds the sarcoplasm, or cytoplasm of
the muscle fiber
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Transverse tubules or T tubules) where the contraction signal is conducted through quickly so
all muscle fibers contract simultaneously
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Myofibrils
Myofibrils) hundreds to thousands of cylindrical structures in each muscle fiber
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Myofilaments) bundles of protein filaments contained in each myofibril
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The Sarcoplasmic Reticulum
Sarcoplasmic Reticulum) a membrane complex in skeletal muscles, that forms a tubular
network around each individual myofibril, fitting over it like lacy shirtsleeves
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Chapter 10:

Terminal cisternae) expanded chambers formed by fusion of SR tubules
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Even though the membranes
of the triad are tightly bound together, their fluid contents are separate and distinct
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Sarcomeres
Sarcomeres) bundles of myofibrils organized into repeating functional units
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Their interactions are responsible for muscle contractions
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Each sarcomere has dark bands called A bands and light bands called I bands
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the M line in the center of the A band, proteins connect the central portions of each thick filament to neighbor
thick filaments
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the H band a lighter region on either side of the M line, Contains thick filaments but no thin filaments
3
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Here 3 thick
filaments surround each thin filament, and 6 thin filaments surround each thick filament
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It extends from
the A band of one sarcomere to the A band of next sarcomere
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They consist of
proteins called actinins, which interconnect thin filaments of adjacent sarcomeres
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It helps keep thick and thin filaments in proper alignment and aids in restoring resting
sarcomere length after contraction
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F-actin, nebulin, tripomyosin, and troponin
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Chapter 10:

Nebulin) a long strand, which extends along the F-actin strand in the cleft between the rows of Gactin molecules
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Each G-actin molecule contains an active site, where myosin (in thick filaments) can bind
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It is a
double strand protein that covers 7 active sites
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Troponin) a molecule consisting of 3 globular subunits
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The 3rd subunit has a receptor that binds 2 calcium ions
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Cross-bridges) what myosin heads are known as when they interact during contraction with thin
filaments
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On either side strands of titn extend the length of the
thick filament
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When muscle cells contract they pull on the tendon fibers the way a line of people might pull on
a rope
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Chapter 10:

10-4
The nervous system communicates with skeletal muscles at the
neuromuscular junction
Electrical Impulses and Excitable Membranes
All cells in the body maintain a membrane potential due to unequal distribution of positive and
negative charges across their membrane
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In
cells, the inner surface of the plasma membrane is slightly negative compared to the outer surface
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Graded potential) the presence or absence of stimulation localized in the plasma membrane
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Excitable membranes) fibers in neurons and skeletal muscle, that permit rapid communication
between different parts of the cell
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The Control of Skeletal Muscle Activity
Skeletal muscle contractions begin with the release of their internal stores of calcium ions,
under control of the nervous system
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When the other cell is a skeletal muscle fiber, the synapse is known as a
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It is made up of an axon terminal
(synaptic terminal) of a neuron
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This coupling occurs at the triads
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The Contraction Cycle
The cycle is a series of molecular events that enables muscle contraction
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Tension Production by Muscle Fibers
The amount of tension produced by an individual muscle fiber ultimately depends on the
number of pivoting cross-bridges
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In summary skeletal muscle fibers contract most forcibly when stimulated over a narrow short
range of lengths
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The duration of a contraction can be extended by repeated stimulation, and muscle fiber undergoing such a sustained contraction produces more tension than it does in a single twitch
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Division of a single twitch phase
1
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2
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, the phase ends roughly 15msec after stimulation
3
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Trepps…

Treppe) a pattern of repeated stimulation constant in strength when happening immediately after the
relaxation phase
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Wave Summation…

Wave summation) the summation of twitches received before the relaxation phase has ended
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If the stimulation continues and the muscle is never allowed to relax completely, tension will
increase until it reaches a peak value 4x the maximum produced by treppe
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the tension produced by the stimulated muscle fibers
2
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The tension is transferred in turn to bones, which are moved against an external load
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The size of a motor
unit is an indication of how fine the control of a movement can be (neuron+less muscle fibers = finer
movement) Example is eye movement very precise)
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Recruitment) the smooth, but steady, increase in muscular tension produced by increasing the
number of active motor units
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Strong muscle tone makes the muscle appear to be firm and defined,
even at rest
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Isotonic contractions) when tension increases and the skeletal muscle's length changes
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1
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There are 2 types of isotonic contractions:
Concentric contraction: the muscle tension exceeds the load and the muscle shortens
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(you control the speed but can't stop the movement)

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Chapter 10:

Isometric contraction) the muscle as a whole does not change length, and the tension
produced never exceeds the load
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The heavier the load, the slower muscles
shorten and react
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When that muscle is contracting
each thick filament breaks down around 2500 ATP molecules per sec
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At rest a muscle fibers produce more ATP than it needs
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Creatine) a small molecule that muscle cells assemble from fragments of amino acids
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ATP Generation
Most cells in the body produce ATP through (1) aerobic metabolism in mitochondria and (2) glycolysis
in cytoplasm
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Chapter 10:

Glycolysis
Glycolysis) the anaerobic breakdown of glucose to pyruvate in the cytoplasm of a cell
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This process provides a net gain
of 2 ATP molecules and generates 2 pyruvate molecules from each glucose molecule
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underutilized pyruvate molecules produced through glycolysis are converted to lactic acid
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Glycolysis is a relatively inefficient way to generate ATP

Muscle Fatigue
Fatigued) when active skeletal muscle can no longer perform at the required level of activity
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depletion of metabolic reserves within the muscle fibers
2
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a decline in pH within the muscle fibers and the muscle as a whole, which decreases calcium
ion binding to troponin and alters enzyme activities
4
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Normal muscle function requires:
1
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a normal circulatory supply
3
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blood pH within normal limits

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Chapter 10:

The Recovery Period
Recovery period) conditions in the muscle fibers are returned to normal, pre-exertion levels
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The liver absorbs the lactate and converts it to pyruvate
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The Oxygen Debt
Oxygen debt or (postexertion oxygen consumption (EPOC) what the amount of oxygen
required to restore normal, pre-exertion conditions is called
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Active skeletal muscles release roughly 85% of
the heat needed to maintain normal body temperature
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Growth
hormone from the pituitary gland and testosterone stimulates the synthesis of contractile proteins and
the enlargement of skeletal muscles
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The 3 Types of Skeletal Muscle Fibers:
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Fast fibers) make up most of the skeletal muscles
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These produce powerful contractions
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Slow fibers) ½ the diameter of fast fibers
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They also contain myoglobin) red pigment
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They resemble fast fibers, for they

contain little myoglobin and are relatively pale
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(brief intervals)
Red muscles) muscles dominated by slow fibers (dark meat)
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a net effect resulting from muscle
fibers having more myofibrils and the myofibrils containing more thick and thin
filaments
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Chapter 10:

Physical Conditioning
Anaerobic endurance) the length of time muscular contraction can continue to be supported
by glycolysis and by the existing energy reserves of ATP and CP
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This conditioning improves an individual's power
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This does not promote muscle hypertrophy
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2 factors result in the improvement of aerobic endurance:
1
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Improvements in cardiovascular performance:

Cross-training is the combination of anaerobic and aerobic endurance
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Structural Characteristics of Cardiac Muscle Tissue
Like neurons and skeletal muscle fibers, cardiac muscle cells have excitable membranes
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The SR of cardiac muscle cells lack terminal cisternae, and its tubules contact the plasma membrane as well as the
T tubules
Cardiac muscle cells are almost totally dependent on aerobic metabolism for the energy they need to continue
contracting
Each cardiac muscle cell contacts several others at specialized sites known as Intercalated discs

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Chapter 10:

Intercalated discs--At the intercalated discs, the sarcolemmas of 2 adjacent cardiac muscle cells are extensively
intertwined and bound together by gap junctions and desmosomes
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Functional syncytium) the term given to cardiac muscle cells because they are physically,
chemically, and electrically connected to one another, and the entire tissue resembles a single,
enormous muscle cell
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It contracts without neural stimulation
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Specialized cardiac
muscle cells called pacemaker cells normally determine the timing of contractions
2
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3
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They also
have longer refractory periods and do not readily fatigue
4
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10-9
Smooth muscle tissue differs structurally and functionally from
skeletal and cardiac muscle tissue
Smooth muscle tissue) forms sheets, bundles, or sheaths around other tissues in almost every
organ
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In the gallbladder bile is
ejected into the digestive tract
Urinary system: smooth muscle tissue alters the rate of filtration in the kidneys
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In females, it moves
the oocytes (and possibly sperm) along the reproductive tract
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Chapter 10:

Structural Characteristics of Smooth Muscle Tissue
All 3 types of muscle tissue contain actin and myosin
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It is nonstriated muscle

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Thick filaments are scattered throughout the sarcoplasm of smooth muscle cells
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excitation-contraction coupling

2
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control of contractions

4
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Once in the sarcoplasm, the calcium ions interact with

Calmodulin) a calcium building protein
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Length-Tension Relationships
Plasticity) the ability to function over a wide range of lengths
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Smooth muscle can contract over a range 4x greater than that of skeletal muscle
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Smooth Muscle Tone
Both multiunit and visceral smooth muscle tissues have a normal background level of activity,
or smooth muscle tone

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