Muscle Contractile Mechanisms Flashcards
What is the function of muscle?
-Provides movement to skeleton and hollow organs
-Provides structure to skeleton and hollow organs when under pressure
-Allows for voluntary and involuntary control of muscle and associated functions over different time scales
What is included in the organised apparatus in striated muscle?
-z band
-Light or I band
-Dark or A band
What is a z band?
Attachment site for actin
What is a light or I band?
-Non-superimposed length of actin
What is a dark or A band?
Entire length of myosin
What is the organisation level of myosin and actin in striated muscle?
-Myosin and actin filaments are highly organised
What is a unit of striation called? What line to what line is it?
-unit of striation is called the sarcomere
-Z line to Z line
What happens to striated sarcomere during contraction?
-When relaxed, little overlap
-When contracted, increased overlapped
-During contraction:
-Myosin length stays the same
-Actin moves across myosin
What is the organisation like in smooth muscle and what does this organisation allow?
-myosin and actin filaments are disorganised:
-interact at dense bodies
-Disorganisation allows for more 3D contraction like in hollow organs
What is G-actin?
A globular protein
What does actin bind and contain?
-Binds ATP
-Contains ATPase activity
What is F-actin?
A helical protein
What does F-actin use to make filaments?
-Uses ATP to make filaments
What sites do actin filaments contain that allow interactions with myosin?
-Filaments contain active actin binding sites which allow interactions with myosin
what type of muscle contain tropomyosin?
-Striated muscle not smooth muscle contains tropomyosin
What does tropomyosin do and what does this prevent?
-Tropomyosin covers active actin binding sites at rest
-Prevents myosin interactions
What makes up the troponin system in striated muscle and what is this system essential for?
-In striated muscle, actin also contains the troponin system
-Tnl, TnC, TnT
-Essential for modulating actin-myosin interactions
Where is myosin II found?
-Myosin II found in muscle
How many heavy chains does myosin have and what do they form?
-2 heavy chains
-Both intertwined
-Forms head domain
What do the heavy chains of myosin bind?
-Binds ATP and ADP, ATPase activity
What do the heavy chains of myosin bind to?
-Binds to active actin binding sites
How many light chains does myosin have?
-4 light chains-2 per head
What do light chains in myosin modulate?
Modulates myosin-actin interactions
-Especially in smooth muscle(smooth muscle contraction
What initiates muscle contraction? And what does this lead to?
-Rise in concentration of Ca2+ in cytosol of muscle cells is central of initiating muscle contraction
-Rise in Ca2+ concentration leads to removal of tropomyosin from active actin binding sites allowing myosin heads to interact with actin
What is the extracellular concentration of Ca2+?
-Extracellular concentration in Ca2+ is high(1-2mM)
What is the resting intracellular cytosolic concentration of Ca2+?
-Resting intracellular cytosolic concentration of Ca2+ is kept very low(100nM)
What is the concentration of Ca2+ in intracellular SR?
-Concentration of Ca2+ in intracellular SR Ca2+ stores is high (0.5-1mM)
What is a rise in Ca2+ concentration produced by?
-Rise in Ca2+ concentration are produced by Ca2+ influx + Ca2+ release from SR I
How do actin and myosin interact to produce muscle contraction following rise in cytosolic Ca2+ concentration?
- Myosin heads hydrolyse ATP and become reoriented and energised
a. ADP/Pi alongside the myosin head have a high affinity for actin - Myosin heads bind to actin, forming crossbridges
a. Myosin head-actin is 90 degrees cocked - Myosin crossbridge rotate toward centre of the sarcomere(power stroke)
a. Myosin head-acting is 45 degrees cocked - As myosin heads bind ATP, the crossbridges detach from actin
a. ATP and myosin head have a low affinity for actin
-All is like a rowing action
What are the 3 sources of ATP for the sliding filament hypothesis?
- Aerobic
- Anaerobic
- Phosphocreatine
What happens in rigor mortis?
- Rise in Ca2+ causes removal of tropomyosin from actin-myosin binding site
- Loss of ATP production prevents detachment of actin-myosin filaments which causes stiffness of muscles (Rigor)
