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Flashcards in Muscle System Deck (48):
1

sarco-

flesh

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myo-

muscle

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mys-

muscle

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functions of muscle system

-movement
-maintain posture
-stabilizes joints
-generates heat

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types of tissue

-skeletal
-cardiac
-smooth

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anatomy of skeletal muscle

-fibers are enclosed by endomysium
-many endomysii are wrapped together by the perimysium
-one group of fibers wrapped in perimysium is called a fascicle
-all fascicles are wrapped together in epimysium
-blended into tendons or aponeuroses

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aponeuroses

layers of flat, broad tendons

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sarcolemma

plasma membrane of skeletal muscle

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myofibrils

long, ribbon-like organelles filling majority of cytoplasm

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sarcomere

basic unit of muscle (I and A bands)

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I and A bands

myofilaments
-give the appearance of striation

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2 types of myofilaments

-thick
-thin

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thick filaments

composed of myosin and ATP enzymes

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thin filaments

composed of actin and regulatory proteins

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sarcoplasmic reticulum

-surrounds each myofibril
-plays a role in storing and releasing calcium during contraction

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2 main functions of muscles

-irritability and contractility

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irritability

-receive and respond to stimuli

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contractility

shorten when stimuli is applied

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nerve stimulis

-muscle cells must be stimulated by nerve impulses to contract
-cells join at neuromuscular junctions
-gap b/w is called synaptic cleft
-when impulse reaches neuromuscular junction, a neurotransmitter is released
-neurotransmitter travels across synaptic cleft and attaches to sarcolemma
-if enough neurotransmitter reaches the sarcolemma, then Na ions rush into muscle cell and generate electrical current called action potential
-causes contraction

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neuromuscular junctions

-where muscle cells join
-don't touch, but very close

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synaptic cleft

gap between neuromuscular junctions
-filled w/ fluid

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motor unit

1 neuron and all skeletal muscles that it stimulates

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muscle contraction mechanism(sliding filament theory)

-when muscle fibers are activated by the nervous system, cross bridges attach and detach to myosin on the thin filaments and sliding begins
-powered by ATP
-contraction requires Ca until action potential ends, then Ca is stored into sarcoplasmic reticulum

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contraction of skeletal muscle

-skeletal muscles consist of thousands of muscle cells
-react with graded responses
-produced by changing frequency of muscle stimulation or changing # of muscle cells being stimulated

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graded responses

different degree of shortenings

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muscle twitches

single, brief, jerky contractions

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fused tetanus(complete tetanus)

muscles move through an accumulation of nerve impulsed

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unfused tetanus(incomplete)

steps leading to fused tetanus

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# of stimuli in contraction

force of muscle contraction depends on how many cells are stimulated
-when only a few cells are stimulated, contraction as a whole will be slight
-when all motor units are active, contraction is very strong

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ATP for contraction

-as muscles contract, the bonds of ATP are hydrolyzed to release needed energy
-muscles store only 4-6 seconds worth, so ATP must be regenerated

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3 pathways for ATP regeneration

-direct phosphorylation of ADP by creatine phosphate
-aerobic respiration
-anaerobic respiration

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direct phosphorylation of ADP by creatine phosphate

-CP transfers high energy phosphate to ADP molecule, resulting in ATP (yields 1 ATP per CP)
-anaerobic
-muscles store 5x as much CP as ATP; however, CP supplies are exhausted in about 15-20 seconds

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aerobic respiration

-glucose is broken down into CO2, H2O, and up to 36 ATP (per 1 glucose model)
-requires O2, amino acids, fatty acids
-slow process but allows muscles to contract for hours

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anaerobic glycolysis and lactic acid formation

-glycolysis breaks glucose into pyruvic acid and 2 ATP (per 1 glucose molecule)
-if O2 is not present then pyruvic acid is broken into lactic acid (yields 5% of ATP for aerobic respiration) (faster process and provides ATP for 30-60 seconds of strenuous muscle activity)

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muscle fatigue

inability of a muscle to contract even though it is being stimulated
-occurs bc of O2 debt
-depending on blood supply, lactic acid accumulation and low ATP, causes muscle to contract less and less effectively, then stop

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o2 debt

-person can't take up enough o2 fast enough to keep muscle supplied

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types of muscle contractions

isotonic
-isometric

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isotonic contraction

-myofilaments slide, causing muscle to shorten and movement occurs
-ex: bending knee, rotating arm, smiling

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isometric contractions

-myofilaments attempt to slide but are unable to due to immovable object and tension builds up
-ex: attempting to move 400 lbs alone or pushing against a wall

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adduction

movement of a limb toward the body midline

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circumduction

combination of flexion, extension, abduction, and adduction, where proximal end of limb is stationary and its distal end moves in a circle

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dorsiflexion

standing on heels

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plantar flexion

pointing the toe

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inversion

-turning the sole of the foot medially

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eversion

-turning the sole laterally

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opposition

movement of the thumb to touch the tips of the other fingers

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supination

rotating the forearm laterally so the palm faces anteriorly (anatomical position)

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pronation

rotating the forearm medially so the palm faces posteriorly