Skeletal Muscle Flashcards
Epimysium
connective tissue surrounding entire muscle
Muscle
made up of multiple fascicles
Perimysium
connective tissue surrounding individual fascicle
Fascicle
A bundle of myofibers
Endomysium
Delicate connective tissue around each myofiber
Sarcolemma
also called (plasmalemma) cell membrane of muscle fiber
myofiber
muscle cell, individual multinucleated muscle cell
myofibril
a chain of sarcomeres within a myofiber
Myofilament
actin and myosin filaments that make up a sarcomere
Sarcolemma
Plasmalemma containing T-tubules
T-tubules
invaginations of carloemma, two per sarcomere
Sarcoplasmic reticulum
Endoplasmic reticulum
Sarcomere
basic contractile unit consisting of an I band (actin), an A band (myosin + actin), a Z disc indicating sarcomere separation, and an H band consisting of just myosin
Z discs
anchor actin filaments
located at each end of a sarcomere
I bands
composed entirely of actin
width changes during contraction
A bands
composed of actin and myosin
width does not change during contraction
H bands
composed entirely of myosin
width changes during contraction
Titin
the protein that helps keep the actin and myosin’s side by side relationship stable. act as a framework
After acetylcholine triggers an action potential at the sarcolemma…
voltage gated ion channels on T-tubules (dihydropyrodine channels) interact with ryanodine-sensitive calcium ion release channels
When voltage gates on _____ _______ are depolarized, they interact with _____ ______ on ______ ______
T-tubules, ryanodine receptors on SR membrane
Ryanodine receptor channels =
calcium ion sensitive, located in SR cisternae
Ryanodine receptors
release calcium in cytosol, which binds to troponin
Calcium binds to
troponin, which moves tropomyosin from myosin binding sites on actin
Where would you find ATPase in the sarcomere?
on myosin: splits ATP in order to bind to actin
ATP’s role in muscle contraction (2)
ATP used to connect to actin; ATP used to disconnect from actin
Power Stroke
this is the “event” caused by the potential energy stored up in myosin from cleaving ATP to ADP+P(i) earlier
Cycle of “power stroke” beginning at ATP binding to myosin
ATP binds to myosin to release actin from a previous cycle. Afterward myosins ATPase cleaves a P bond, leaving behind ADP+P(i) on the myosin head
when calcium comes along and causes conformational exposure of the actin binding sites, the myosin is “cocked and loaded”–contains the potential energy needed– and can perform the POWER STROKE, cycle continues
“Big picture” beginning at sarcolemma depolarization
Sarcolemma depolarizes—> T-tubule depolarizes —> DHP receptor undergoes conformational change —> causes Ryanodine receptors to change conformation —> causes Ryanodine receptor calcium channels to release traces amount of calcium —-> triggers SR to release tons of calcium into cytoplasm for sarcomere contractions
Ryanodine Receptors are located—>
on the cisternae of the sarcoplasmic reticulum
facilitated diffusion followed by active transport to return calcium to SR
Dihydropyridine (DHP) receptors are located —->
on sarcolemma t tubules
voltage gated
ATP in muscle contraction: where/how
Largely used for contraction (myosin/actin interactions),
pumping calcium ions from sarcoplasm BACK into sarcoplasmic reticulum
pumping sodium and potassium ions through the sarcolemma to reestablish resting potential
Concentration of ATP in muscle fiber
4 mmol, enough to maintain contractions for 1-2 seconds
Rephosphorylation: how
Energy derived from phosophcreatine, glycolysis, oxidative metabolism
Muscle Contractions: two types, plus describe them
Isometric: occurs when tension increases but muscle length does not
Isotonic: Muscle length changes in two ways
a) eccentrically: muscle length increases
b) concentrically: muscle length shortens
Muscle Fiber Types: White
Also called fast: more mitochondria, less myoglobin, primarily utilizes anaerobic respiration
Muscle Fiber Types: RED
Also called slow: less mitochondria, more myoglobin, primarily utilizes aerobic respiration
Fiber and Fibril Regeneration
Myofiber cannot be regenerated after birth, but myofibrils can. So mass can increase.
“Dark fibers”
soleus
“light fibers”
gastrocnemius
a neuron and the myofibers it innervates constitute
a motor unit
What happens when a neuron interfacing a myofiber fires a signal?
all the myofibers in the motor unit contract. All or none.
Summation
Before calcium ions have returned to SR, an additional release of calcium can occur: total amount of Ca increases, each additional “spike” adds to the effects of the last one.
Tetany
Too many spikes, not enough time. The muscle remains at maximal contraction
