Muscles II: Microscopic Anatomy/Sarcomere Flashcards
components of muscle fiber
sarcolemma, sarcoplasm, sarcoplasmic reticulum
two main structures unique to muscle fibers
t-tubules, sarcoplasmic reticulum
t-tubules
deep invaginations of the sarcolemma that extend into the sarcoplasm
t-tubules purpose
carry impulses from sarcolemma to help stimulate contraction. bring sarcolemma close to sarcoplasmic reticulum and all regions of the cell
where do t-tubules open to?
the outside of the muscle fiber
do t-tubules contain extracellular fluid?
yes
sarcoplasmic reticulum
internal membrane complex
purpose of sarcoplasmic reticulum
stores calcium used to initiate contraction
cisternae of sarcoplasmic reticulum
enlargend portion of calcium storage that released calcium when action potential travels down the transverse tubules eliciting muscle contraction
triad
structure made up of two terminal cristae and one t-tubule
purpose of triad
link between sarcolemma and sacroplasmic reticulum at all regions to have synchronous release of calcium (allows muscles to contract forcefully)
myofibrils
cylindrical structure within the muscle fibers that run the length of the cell
myofilaments
strands of protein that allow for contraction
2 types of myofilaments
thick, thick filaments
thick filaments are composed of
myosin
myosin 2 strands
intertwined tails and globular head
what do heads of the myosin form?
cross bridges
myosin contain binding site for
actin, ATP binding
thin filaments extend toward ____ of thick filament, heads extend ______ outwards toward thin filament
middle, outward
thin filaments composed of
2 f-actin twisted around each other (filamentous)
g-actin shape
spherical
each actin strand is made of
g-actin (globular)
2 regulatory proteins that are part of the thin filament
tropomyosin, troponin
tropomyosin
threadlike protein covering part of actin
troponin
attaches to acting and tropomyosin and can bind calcium
sarcomere regions
M line, A band, H zone, I band
M line
line of protein that anchors to thick filaments/myosin filaments
A band
everywhere thick filaments occur
H zone
where thick filaments and no thin filaments
I band
only thin filaments around Z disc
sarcomere
overlapping thick and thin filaments forming the structural ad functional units within a myofibril
one sarcomere spans from one _____ to the next
z-line/disc
z-discs
specialized proteins perpendicular to the myofilaments and anchor thin filaments
what parts of the muscle shorten as the two sides come closer?
sarcomere, myofibril, muscle fibers
z bands contraction change
move closer together
m band contraction change
remains stable
why does the m bands remain stable during contraction?
actin is being pulled on by myosin
H zone contraction change
gets narrower
I zone contraction change
gets narrower
what led to the sliding filament theory of muscle contraction?
electron microscopy
sliding filament theory
muscles contract when sarcomeres shorten and muscle fibers slide past each other
M line cross section
thick filaments and accessory proteins anchored to them
H zone cross section
only thick filaments made of myosin
A band cross section
thick filaments and thin filaments interspersed
I band cross section
only thin filaments supporting proteins
eg of supporting proteins
connectin
connectin purpose
helps align thick and thin filaments within sarcomere
z-disc cross section
thin filaments and accessory proteins anchoring the thin filaments to the z-disc
