Muscles Flashcards
Striated muscle
cardiac
skeletal
Smooth
blood vessels, vas deferens, airways, uterus
Skeletal muscles
multi-nucleated
increase fibre size during growth
muscle cells are replaced after injury by
satellite cells
Myosin
Thick
Z line/ cross bridge movement
Actin
thin filament
Cross bridge binds to actin
cross bridge moves
ATP binds to Myosin causing cross-bridge to detach
hydrolysis of ATP energizes cross-bridge
What covers the myosin binding site
tropomyosin
Tropomyosin is held in place by
troponin
Calcium can bind to troponin and..
alter its shape - troponin will pull tropomyosin away
If calcium is removed, tropomyosin will be able to…
block the myosin binding site again
Motor unit =
Motor neurones + motor fibres
Contraction with constant length
isometric
contraction with shortening length
isotonic
contraction with increasing length
lengthening
Latent period is the
time before excitation-contraction occurs
contraction time occurs between
start of tension and time when we have peak tension
Contraction time depends on
calcium
less overlap of filaments = less
tension
too much overlap of filaments =
they begin to interfere with each other
hydrolysis of ATP energises
X-bridges
ATP in contractions
ATP binds to myosin
dissociated bridges bound to actin
new cycle may begin
Fatigue prevents muscles using up
ATP - which could cause rigor (muscles would not be able to activate new X-bridge cycles)
Factors causing fatigue
contraction failure
increase in lactic acid
increase in ADP and Pi inhibiting the X-bridge cycle (delaying myosin detachment from actin filaments)
FAST fibres means myosin has
high ATPase
slow = low ATPase
oxidative fibres have…
lots of mitochondria
therefore increased oxidative phosphorylation
Glycolytic fibres have…
few mitochondria
lower blood supply
3 types of muscle fibre
slow oxidative
fast oxidative
fast glycolytic
Slow oxidative
resist fatigue
fast oxidative
intermediate resistance to fatigue
fast glycolytic
fatigue quickly
an increase in load gives a need for an increase in
activation of more motor units
exercise causes
hypertrophy
aerobic exercise gives an increase in
mitochondria
fibre diameter
vascularisation
exercise type determines the..
type of muscle fibres you have
Smooth muscle
spindle-shaped
mononucleated
myosin and actin - like skeletal muscle
HOWEVER
filaments are arranged diagonally across cells and are anchored to membranes
Smooth muscle X-bridge cycle activation
increase in calcium
calcium binds to calmodulin
calcium-calmodulin binds to Myosin Light Chain Kinase
kinase phosphorylates myosin X-bridges with ATP
phosphorylated X-bridges bind to actin filaments
CONTRACTION AND TENSION
Sources of Cytosolic Ca2+
Sarcoplasmic reticulum
extracellular calcium
calcium removed from cytosol by pumping back into SR and out of cell by calcium ATPases
in skeletal muscle one action potential releases enough calcium to…
saturate all troponin sites
