9.3 Muscle Fiber Anatomy Flashcards
long, cylindrical cells with multiple nuclei
Skeletal muscle fibers
muscle fiber plasma membrane
Sarcolemma
muscle fiber cytoplasm
Sarcoplasm
many of these in the sarcoplasm; used for glycogen storage
Glycosomes
many of these in the sarcoplasm; used for O2 storage
Myoglobin
densely packed, rod-like elements
Myofibrils
stripes formed from repeating series of dark and light bands along length of each myofibril
Striations
dark regions
A bands
lighter region in middle of a dark A band
H zone
line of protein (myomesin) that bisects H zone vertically
M line
lighter regions
I bands
coin-shaped sheet of proteins on midline of light I band
Z disc (line)
smallest contractile unit (functional unit) of muscle fiber
-contains A band with half of an I band at each end
Sarcomere
orderly arrangement of actin and myosin myofilaments within a sarcomere
Myofilaments
thin filaments
-extend across I band and partway in A band
Actin myofilaments
thick filaments
- extend length of A band
- connected at M line
Myosin myofilaments
network of smooth endoplasmic reticulum tubules surrounding each myofibril
- functions in regulation of intracellular Ca2+ levels
- stores and releases Ca2+
Sarcoplasmic reticulum
tube formed by a protrusion of sarcolemma deep into cell interior
-penetrate cell’s interior at each A-I band junction between terminal cisterns
T tubules
area formed from terminal cistern of one sarcomere, T tubule, and terminal cistern of neighboring sarcomere
Triad
when an electrical impulse passes by, T tubule proteins change shape, causing SR proteins to change shape, causing release of calcium into cytoplasm
Triad relationships
during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more
Sliding filament model of contraction
the activation of cross bridges to generate force
Contraction
form when myosin heads bind to actin, causing sliding (contraction) process to begin
Cross bridges
