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88 Cards in this Set
- Front
- Back
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What are the 3 types of muscle?
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skeletal, cardiac, and smooth
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What two kinds of myofilaments are necessary for muscle contraction?
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actin and myosin
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Sarcolemma
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muscle plasma membrane
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Traits of Skeletal Muscle
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-Packaged in skeletal muscles that attach to and cover the bony skeleton
-Has obvious stripes called striations -Is controlled voluntarily (i.e., by conscious control) -Contracts rapidly but tires easily -Is responsible for overall body motility -Is extremely adaptable and can exert forces ranging from a fraction of an ounce to over 70 pounds |
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Traits of Cardiac Muscle Tissue
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Occurs only in the heart
Is striated like skeletal muscle but is not voluntary Contracts at a fairly steady rate set by the heart’s pacemaker Neural controls allow the heart to respond to changes in bodily needs |
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Traits of Smooth Muscle Tissue
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Found in the walls of hollow visceral organs, such as the stomach, urinary bladder, and respiratory passages
Forces food and other substances through internal body channels It is not striated and is involuntary |
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Functional Characteristics of Muscle Tissue
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Excitability, or irritability – the ability to receive and respond to stimuli
Contractility – the ability to shorten forcibly Extensibility – the ability to be stretched or extended Elasticity – the ability to recoil and resume the original resting length |
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Muscle Functions
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Skeletal muscles are responsible for all locomotion
Cardiac muscle is responsible for coursing the blood through the body Smooth muscle helps maintain blood pressure, and squeezes or propels substances (i.e., food, feces) through organs Muscles also maintain posture, stabilize joints, and generate heat |
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Endomysium –
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fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber
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Perimysium –
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fibrous connective tissue that surrounds groups of muscle fibers called fascicles
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Epimysium –
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an overcoat of dense regular connective tissue that surrounds the entire muscle
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How many nerves, arteries and veins in each muscle?
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Each muscle is served by one nerve, an artery, and one or more veins
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How are nutrients delivered?
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Contracting fibers require continuous delivery of oxygen and nutrients via arteries
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What happens when Skeletal muscles contract?
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When muscles contract the movable bone, the muscle’s insertion moves toward the immovable bone, the muscle’s origin
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Direct Attachment
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epimysium of the muscle is fused to the periosteum of a bone
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Indirect Attachent
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connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis
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Microscopic Anatomy of a Skeletal Muscle Fiber
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Each fiber is a long, cylindrical cell with multiple nuclei just beneath the sarcolemma.
Fibers are 10 to 100 m in diameter, and up to hundreds of centimeters long Each cell is a syncytium produced by fusion of embryonic cells |
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What is in a Muscle Fiber?
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Fibers contain the usual organelles, myofibrils, sarcoplasmic reticulum, and T tubules
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What is in Sarcoplasm?
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Sarcoplasm has numerous glycosomes and a unique oxygen-binding protein called myoglobin
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What are Microfibrils?
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Myofibrils are densely packed, rodlike contractile elements
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How are Microfibrils arranged?
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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 a sarcomere?
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The smallest contractile unit of a muscle
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Where are Sarcomeres found?
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The region of a myofibril between two successive Z discs
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what is the banding pattern of a sarcomere?
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Thick filaments – extend the entire length of an A band
Thin filaments – extend across the I band and partway into the A band Z-disc – coin-shaped sheet of proteins (connectins) that anchors the thin filaments and connects myofibrils to one another |
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Why are M lines darker?
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M lines appear darker due to the presence of the protein desmin
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What are T Tubules?
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T tubules are continuous with the sarcolemma
They conduct impulses to the deepest regions of the muscle These impulses signal for the release of Ca2+ from adjacent terminal cisternae |
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In order to contract, a skeletal muscle must:
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Be stimulated by a nerve ending
Propagate an electrical current, or action potential, along its sarcolemma Have a rise in intracellular Ca2+ levels, the final trigger for contraction |
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Linking the electrical signal to the contraction is:__________
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excitation-contraction coupling
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Skeletal muscles are stimulated by?
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motor neurons of the somatic nervous system
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Each axonal branch forms a neuromuscular junction with:
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a single muscle fiber
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When a nerve impulse reaches the end of an axon at the neuromuscular junction:
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Voltage-regulated calcium channels open and allow Ca2+ to enter the axon
Ca2+ inside the axon terminal causes axonal vesicles to fuse with the axonal membrane |
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What is Action Potential?
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A transient depolarization event that includes polarity reversal of a sarcolemma (or nerve cell membrane) and the propagation of an action potential along the membrane
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What is depolarization?
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Initially, this is a local electrical event called end plate potential
Later, it ignites an action potential that spreads in all directions across the sarcolemma |
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A motor unit is?
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a motor neuron and all the muscle fibers it supplies
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Muscles that control fine movements (fingers, eyes) have:
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small motor units
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How are muscle fibers distributed in motor units?
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Muscle fibers from a motor unit are spread throughout the muscle; therefore, contraction of a single motor unit causes weak contraction of the entire muscle
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Muscle tone is:
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the constant, slightly contracted state of all muscles, which does not produce active movements
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Muscle tone serves what purpose?
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Keeps the muscles firm, healthy, and ready to respond to stimulus
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How do spinal reflexes account for muscle tone?
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Activating one motor unit and then another
Responding to activation of stretch receptors in muscles and tendons |
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isotonic contraction
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In isotonic contractions, the muscle changes in length (decreasing the angle of the joint) and moves the load
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What are the two types of isotonic contractions?
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concentric and eccentric
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Concentric contractions –
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the muscle shortens and does work
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Eccentric contractions –
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the muscle contracts as it lengthens
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Isometric Contractions
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Tension increases to the muscle’s capacity, but the muscle neither shortens nor lengthens
Occurs if the load is greater than the tension the muscle is able to develop |
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What is the source of muscle energy?
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ATP is the only source used directly for contractile activity
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As soon as available stores of ATP are hydrolyzed (4-6 seconds), they are regenerated by:
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The interaction of ADP with creatine phosphate (CP)
Anaerobic glycolysis Aerobic respiration |
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What happns during Anaerobic Glycolysis
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When muscle contractile activity reaches 70% of maximum:
Bulging muscles compress blood vessels Oxygen delivery is impaired Pyruvic acid is converted into lactic acid |
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During Anaerobic Glycolysis lactic acid:
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Diffuses into the bloodstream
Is picked up and used as fuel by the liver, kidneys, and heart Is converted back into pyruvic acid by the liver |
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Muscle fatigue –
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the muscle is in a state of physiological inability to contract
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Muscle fatigue occurs when:
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ATP production fails to keep pace with ATP use
There is a relative deficit of ATP, causing contractures Lactic acid accumulates in the muscle Ionic imbalances are present |
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For a muscle to return to a resting state:
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Oxygen reserves must be replenished
Lactic acid must be converted to pyruvic acid Glycogen stores must be replaced ATP and CP reserves must be resynthesized |
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How much energy released in muscle activity is useful as work
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Only 40% of the energy released in muscle activity is useful as work
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How much is heat?
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The remaining 60% is given off as heat
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Aerobic exercise results in an increase of:
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Muscle capillaries
Number of mitochondria Myoglobin synthesis |
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Resistance exercise (typically anaerobic) results in:
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Muscle hypertrophy
Increased mitochondria, myofilaments, and glycogen stores |
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Smooth Muscle lacks...
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the coarse connective tissue sheaths of skeletal muscle, but have fine endomysium
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Smooth Muscle is organized in ____ layers of ______ fibers.
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Organized into two layers (longitudinal and circular) of closely apposed fibers
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Smooth muscle is found in the wall of _____ _______. (Except the _____)
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hollow organs (except the heart)
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Peristalsis –
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alternating contractions and relaxations of smooth muscles that mix and squeeze substances through the lumen of hollow organs
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How does smoth muscle contact?
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When the longitudinal layer contracts, the organ dilates and contracts
When the circular layer contracts, the organ elongates |
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Smooth muscle lacks ________ junctions.
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neuromuscular
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Innervating nerves have bulbous swellings called ________.
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varicosities
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Varicosities release neurotransmitters into wide synaptic clefts called ___________ junctions.
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diffuse junctions
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Microscopic Differences of Smooth Muscle from skeletal muscle.
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SR is less developed than in skeletal muscle and lacks a specific pattern
T tubules are absent Plasma membranes have pouchlike infoldings called caveoli There are no visible striations and no sarcomeres |
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In smooth muscle there is no:
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Troponin complex
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Smooth muscles are ______ and ________ without external stimuli
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self-excitatory depolarize
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Unique characteristics of smooth muscle include:
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Smooth muscle tone
Slow, prolonged contractile activity Low energy requirements Response to stretch |
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stress-relaxation response
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Smooth muscle responds to stretch only briefly, and then adapts to its new length
The new length, however, retains its ability to contract |
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Certain smooth muscles can divide and increase their numbers by undergoing ___________.
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hyperplasia
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The cells of single-unit smooth muscle, commonly called _______ muscle
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visceral
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Traits of visceral muscle:
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Contract rhythmically as a unit
Are electrically coupled to one another via gap junctions Often exhibit spontaneous action potentials Are arranged in opposing sheets and exhibit stress-relaxation response |
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Multiunit smooth muscles are found:
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In large airways to the lungs
In large arteries In arrector pili muscles In the internal eye muscles |
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Muscle tissue develops from embryonic mesoderm called ______.
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myoblasts
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Multinucleated skeletal muscles form by _______ of myoblasts
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fusion
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Cardiac and smooth muscle myoblasts do not fuse but develop _______ _________ at an early embryonic stage
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gap junctions
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As muscles are brought under the control of the somatic nervous system, the numbers of ____ and ______ fibers are also determined
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fast and slow fibers
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can cardiac and skeletal muscle reproduce through mitosis?
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Cardiac and skeletal muscle become amitotic, but can lengthen and thicken
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How does muscle development occur?
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Development occurs head-to-toe, and proximal-to-distal
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Peak natural neural control of muscles is achieved by ___________.
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mid-adolescence
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Women’s skeletal muscle makes up ___% of their body mass
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36%
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Men’s skeletal muscle makes up ___% of their body mass
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42%
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The difference between men and women's muscle mass is due primarily to the male sex hormone _________.
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testosterone
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By age 80, _____% of muscle mass is lost (sarcopenia)
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50% of muscle mass is lost
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With age, Muscles become ______ and more ________.
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stringier and more sinewy
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Sarcopenia can be reversed by _______ _______
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Regular exercise
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_______________may block distal arteries, leading to intermittent claudication and causing severe pain in leg muscles
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Atherosclerosis
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Atrophic Muscular Diseases
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muscular dystrophies
post poliomyelitis syndrome |
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Infections of the muscles
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HIV, tetanus, Lyme’s, influenza
trichinosis, gangrene(myopathic) |
