Lecture 18 Muscle Physiology Flashcards
Types of muscle
skeletal- striated, voluntary
cardiac- striated, involuntary
smooth- nonstriated, involuntary
Levels of structure
muscle
fascicle- bundle of muscle fibers
muscle fiber (=cell)
myofibril- bundle of protein filaments w/in the muscle fiber
myofilaments - thick(myosin) & thin (actin)
Muscle bone joint systems
muscle actions (flexion & extension)
agonist
antagonist
Sarcomere
functional unit of muscle contraction
A band, I band, Z disk, H zone, M line
Thick filaments
mysoin bundles
myosin head - forms crossbridges with thin filament
actin binding site
ATP binding site
Thin filaments
actin chains (F-actin)
myosin binding sites
regulatory proteins: tropomyosin & troponin
twice as many as thick
Sarcolemma
plasma membrane of muscle fiber
forms muscle action potentials
T tubules
invaginations of sarcolemma
carry APs deep into the muscle fiber
contain extracellular fluid
sarcoplasmic reticulum (SR)
intracellular membrane system, stores Ca2+ terminal cisterns
terminal cisterns
enlarged ends of SR, in close contact with T tubules
Sliding filament mechanism
thin filaments slide across thick filaments toward the center of the sarcomere
thick and thin filaments do not change in length, only in extent of overlap
During the contraction of the sarcomere
A band remains constant
I band and H zone shorten
Z disks move closer together
Contraction-Relaxation cycle
Ca+ is released from SR and binds to troponin then;
- Myosin head binds to actin - forms crossbridge
- power stroke - myosin head rotates, Pi and ADP are released
- ATP binds to myosin - releases crossbridge (releases actin)
- ATP hydrolysis - energizes myosin head; ADP and Pi are still attached to myosin
relaxed muscle
myosin heads energized (stage 4) but A-M binding sites blocked
Rigor state
myosin heads stuck to actin; ATP is required for crossbridges to detach
