muscles Flashcards
what is the organization of skeletal muscle?
myofilaments -> sarcomeres -> myofibrils -> muscle fiber -> fascicle (bundle of muscle fiber) -> muscle
epimysium
dense collagenous connective tissue that surrounds entire muscle
perimysium
collagenous connective tissue that surrounds bundles of muscle fibers called fascicles
endomysium
fine sheath of connective tissue composed of reticular fiber that surrounds individual muscle
myotendinous junction
finger-like extensions of the muscle fibers insert into the connective tissue of the tendon
basal lamina
specialized layer of extracellular matrix that supports and separates epithelial cells from the underlying connective tissue
how does the basal lamina provide structural support to the cell?
it binds to the myofiber via dystroglycan-containing complex
how does basal lamina connect to the actin (cytoskeleton)?
basal lamina -> transmembrane protein alpha-dystroglycan then beta -> dystrophin -> actin
myofibers
long, cylindrical and striated
multinucleated with nuclei located at the periphery (at the edge)
myofibrils
aligned in parallel
separated by mitochondria and sarcoplasmic reticulum
composed of filaments called myofilaments
sarcoplasmic reticulum
smooth endoplasmic reticulum
forms an interconnected network of tubules
surrounds each myofibrils
forms chambers called terminal cisternae on either side of the t-tubules
terminal cisternae
chamber formed by SR on either side of the t-tubules
when is Ca2+ stored and released?
stores Ca2+ when muscle is at rest
released in the sacroplasm when muscle is stimulated
t-tubules
deep invagination of sacrolemma
perpendicular to the length of myofiber
how many terminal cisternae are next to the t-tubule?
two tc and a single t-tubule form a triad junction
how are Ca2+ released?
action potential runs along the sarcolemma, reaches the T-tubules, and activates DHPRs.
DHPRs are mechanically coupled to RyRs, which release Ca²⁺ from the sarcoplasmic reticulum into the sarcoplasm, where it initiates muscle contraction.
which side does the myosin head face and why?
it faces outwards because the actin binding site and myosin ATPase site is on it (for contraction to occur)
what happens when Ca2+ is at low concentration?
myosin binding sites on actin are masked by tropomyosin