Muscle Contractions Flashcards
describe skeletal muscles
- 40mm
- multinucleated
- striated
describe cardiac muscle
- 100um
- uninucleated
- branched
describe smooth muscle
- 30-100um
- non-striated
- mono-nucleated
what is a contraction?
the interaction of actin and myosin using Ca2+ and ATP
how is skeletal muscle organised?
in bundles called fascicles made of fibres
what is the function of the sarcoplasmic reticulum?
stores Ca2+
what is actin and myosin sometimes referred to?
- actin: thin filament
- myosin: thick filament
what proteins are also associated with actin?
- tropomyosin: blocks the active site of actin
- troponin C: binds to Ca2+
- troponin T: binds to tropomyosin
describe the structure of myosin
- has a head and tail
- head has 2 domains:
1) binds to ATPase which allows it to flex
2) binds to actin
how is movement activated?
- ATP hydrolysis occurs which provides energy for the myosin to bind to actin, creating a cross bridge
- cross bridge bends, pulling the thin myofilament inward into the low energy configuration
- cross bridge detaches which requires ATP and returns into it’s original configuration
- cross bridge then binds to more distal actin molecule and cycle repeats
how do you initiate the sliding filament mechanism?
- influx of Ca2+ from the sarcoplasmic reticulum sallows Ca2+ to bind to troponin-c
- this causes troponin T to bind to tropomyosin with pulls the tropomyosin out of the active site on actin
- this means that actin is free to bind to myosin
how is Ca2+ released from the sarcoplasmic reticulum?
-Ach binds to the nAchR
-this leads to the Na+ channel opening
-the influx of Na+ leads to depolarisation down the t tubules
when the AP reaches the dihydropyridine protein (DHP) in the t tubule, it conforms
-the DHP binds to ryanodine receptor (RYR), the calcium release channel
-this conforms the RYR, causing Ca2+ to be released from the sarcoplasmic reticulum
cardiac muscles do not have RYRs, so how do they cause an influx of Ca2+?
- cardiac muscles have Ca2+ channels
- an influx of Ca2+ causes Ca2+ to be released from the SR
=calcium induced calcium release (CICR)
how is the contraction of smooth muscle different to skeletal muscle?
- they do not have t tubules and have an irregular myolfilament arrangement
- contraction proteins interact in a mesh
- SM wring out instead of getting shorter
- contains calmodulin and not troponin
- myosin is in a different isoform than in SKM (MYHII bc MYHI)
how do smooth muscle get an influx of Ca2+?
-through receptor mediated Ca2+ stores or by the production of a diffusible messenger (IP3)
