module 9 muscles Flashcards
skeletal muscles
75% water, 20% protein, 5% organic and inorganic compounds
2-60 cm long
fusiform
pennate
sarcolemma
membrane enclosing each muscle fiber
fasciculi
muscle fibers grouped together
endomysium
connective tissue surrounding sacrolemma of each muscle fiber
perimysium
connective tissue surrounding fasciculi, between fasciculi
epimysium
connective tissue surrounding entire muscle
tendon and bone attachement
by sharpy fibers, continuous with perimysium
motor unit
functional unit
greater innervation ratio: increased endurance
less innervation: more precise movement
slow oxidative (red) (9)
postural muscles low ATPase activity slow hight fatigue resistance high oxidative capacity anaerobic enzyme content: low many mitochondria, capillaries low glycogen content small fiber diameter
fast glycolytic (white)
ocular muscles high ATPase activity low fatigue resistance low oxidative capacity high anaerobic enzyme content few mitochondria and capillaries high glycogen content large fiber diameter
myofibril
functional unit of contraction
repeating sarcomere
contractile proteins: filaments
actin: tropomysin and troponin bound to it
myosin: larger, “thick filaments”
A band
middle of sarcomere
end to end of myosin
contains myosin and actin
i band
ends of sarcomere
contains just actin
M line
middle of sarcomere
Z line
ends between sarcomeres
H band
very middle of sarcomere
contains only myosin
sliding filament theory
muscle shortening accomplished by increased amount of overlap of actin and myosin filaments
Steps of sliding filament
Excitation: action potential
- active site on actin is exposed as Ca binds troponin
Coupling
- the myosin head forma s cross bridge with actin
Contraction
- power stroke: myosin head bends, and ADP and phosphate are released
Relaxation (requires ATP)
- new molecule of ATP attaches to the myosin head, causing bridge to detach
- ATP hydrolyzed to ADP and phosphate, which returns the myosin to the “cocked position”
Steps in contraction initiation
- ACh released from Motor end plate, binding to receptors
- action potential reaches T tubule
- sarcoplasmic reticulum released Ca
- active-site exposure, cross-bridge binding
- contraction begins
steps that end contraction
- ACh removed by AChE
- sarcoplasmic reticulum recaptures Ca
- active sites covered, no cross-bridge interaction
- contraction ends
- relaxation occurs, passive return to resting length.
Role of Ca in muscle contraction
myosin heads prevented form binding to actin by tropomysin, which lies on top of binding site
- tropomysin controlled by troponin
- in abscense of Ca troponin induces tropomysin to cover binding site
- Ca presence, tropinin allows tropomysin to move and uncover binding site.
aging and bones
bone loss
stiff, brittle, decreased strength
bone remodel time is lengthened and rate of mineralization slows down.
-by age 70 women have lost 50% of mass
females: bone density loss accelerated by menopause: loss of estrogen
males: bone density loss occurs at later age and much slower rate than women
- absolute risk for fx is the same in men and women of same age.
aging and joints
cartilage becomes more stiff, rigid, and fragile
decreased range of motion
