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Microscopic Anatomy, Organization, & Classification of Skeletal Muscle

Vocabulary to help you describe the structure of skeletal muscle from gross to microscopic levels.

AB
sarcoplasmmuscle cell cytoplasm
sarcolemmaplasma membrane of muscle cell
myofibrilsstrands of muscle cells that have a striped appearance & take up most of the cell volume
actincontractile protein (thin fibers) making up a myofibril
myosincontractile protein (thick fibers) making up a myofibril
sarcomeresfound in chains, make up the myofibrils; each sarcomere contains myosin and actin arranged in a regular array
sarcoplasmic reticulum (SR)system of tubules around each myofibril that releases and sequesters calcium ions
T tubulesinvaginations of the sarcolemma that run between the terminal cisternae of the SR/ function in electrical stimulation of cells
sliding filament theorythe thin filaments are pulled toward the sarcomere centers by cross bridge (myosin head) activity of the thick filaments
troponinprotein in the thin filament that inhibits the attachment of myosin heads to actin
tropomyosina rod-shaped protein that spirals around actin and blocks the actins active site
cross bridge attachmentsite of attachment of myosin heads to exposed binding sites on actin
working strokemyosin head pivots, changing from high-energy configuration to bent, low-energy shape which pulls on thin filament
cross bridge detachmentATP binds to myosin head, and actin lets go of myosin
"cocking" of myosin headhydrolysis of ATP to ADP and Pi bu ATPase provides energy to return myosin to high-energy position
rigor mortisdeath rigor (illustrates that cross bridge detachment is ATP driven, b/c cross bridge detachment is impossible and the body becomes stiff (peaks @ 12 hours)
action potentialelectrical current needed for muscle contraction
motor neuronsnerves that stimulate skeletal muscles to contract
neuromuscular junctionsinterface between the nerve and muscle cells (an axonal ending)
synaptic cleftspace between the end of the axon and the muscle cell (filled w/ gel-like substance of glycoproteins)
synaptic vesiclessmall membranous sacs containing a neurotransmitter called acetylcholine (ACh)
motor end platetroughlike part of the muscle fiber's sarcolemma that helps form the neuromuscular junction, have millions of ACh receptors
polarizedstate that a resting sarcoplasmic membrane is in (negative inside the cell membrane)
depolarizationchange in membrane potential (inside of cell membrane becomes positive)
repolarizationmuscle returns to its polarized state
refractory periodperiod when a muscle fiber cannot be stimulated again (during repolarization)
all or none responsemuscle fibers contract to the full extent of their ability or not at all
Acetylcholinesterase (AChE)enzyme that destroys ACh so that continued contraction will not occur
myasthenia gravisdrooping eyelids, muscle weakness, involves a shortage of ACh receptors
curarearrowhead poison (So. Amer. natives) binds to ACh receptors and blocks ACh attachment
myogramapparatus that gives a graphic recording of muscle contraction
muscle twitchreponse of a muscle to a single brief threshold stimulus
tetanus (normal)all evidence of muscle relaxtion disappears, contractions fuse into a smooth, sustained contraction, leads to muscle fatigue
tetanus (bacterial disease)causes a tetanic state to occur much longer than normal
muscle toneslightly contracted state, keeps muscles firm and ready to respond, stabilizes joints, maintains posture
isotonic contractionsmuscle changes in length and moves the load
isometric contractionstension continues to increase but the muscle neither shortens nor lengthens
glycolysis"sugar splitting", anaerobic stage of cellular respiration, occurs in the cell's cytoplasm, results in a net of 2 ATP
aerobic respirationconsists of the citric acid cycle and the electron transport chain, yields 36 ATP
muscle fatiguestate of physiological inability to contract (deficit of ATP)
contracturestate of continuous contraction (i.e. rigor mortis, or writer's cramp)
oxygen debtthe extra amount of oxygen that must be taken in by the body for restorative processes to occur
peristalsissmooth muscle contraction (i.e. bladder)
gap junctionscell connections found in smooth muscles, allow big sheet of muscle to contract as one
pacemaker cellscells that signal other cells what "pace" to take when contracting
hyperplasiaability of smooth muscle to divide their numbers (i.e. at puberty the uterus gets larger)
myoblastsmesoderm cells that make muscle cells
Duchenne muscular dystrophymost common and serious form, sex-linked recessive disease expressed in mostly males, results in respiratory death around 20s
RICEacronym for rest, ice, compression, and elevation/ standard treatment for pulled muscle
strainpulled muscle
spasminvoluntary muscle twitch, i.e. tic of the eye
myopathyany disease of muscle
myalgiamuscle pain from any muscle disorder
crampsustained spasm or tetanic contraction of an entire muscle
Calcium channel blockersdrugs that interfere with the transport of Calcium across plasma membrane thus inhibiting muscle contraction, i.e. muscle relaxer


Mrs. Hammond

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