Unit 3.3: Muscle Contraction Mechanism Flashcards
What is muscle tension?
Force created by contracting muscle where the load is a weight or force that opposes the contraction
What was the early theory of muscle contraction?
Myosin shortened when active and stretched back when at rest
Why did they reject the early theory of muscle contraction?
They saw that the A-band (myosin) remained the same length during muscle contraction
What is the sliding filament theory?
At rest, ends of thick and thin filaments slightly overlap
When contracting, they remain the same length and slide past each other towards the M-line, bringing the Z-disks closer to each other
How do the actin filaments move?
Thin filaments are propelled along by the heads of the myosin molecules
What is the power stroke?
When myosin releases Pi and swings back, pulling actin filament closer to the M-line
What would happen if all the crossbridges released together?
Thin filaments would slip back into their original positions and the contraction would not occur
What stops muscles from contracting whenever ATP is available?
Actin filament is associated with the 2 regulatory proteins troponin and tropomyosin
What are the 2 positions of tropomyosin?
- “off” position: blocking binding site for the myosin head
2. “on” position: allows free zccess to actin
What position is tropomyosin at rest?
“off” position
What regulates the activity of tropomyosin?
Troponin
What regulates troponin activity?
Troponin C, one of 3 subunits of troponin
How is troponin activated?
Ca2+ binds to troponin, causing a conformational change in troponin, this moved tropomyosin to the “on” position
What regulates muscle contraction? how?
Concentration of Ca+ in the cytosol
High levels = contraction
Low levels = relaxation
What is excitation-contraction coupling?
Series of electrical and mechanical events in a muscle which leads to muscle contraction
What are 3 ways that muscles use ATP?
Ca2+ removed from cytosol by Ca2+-ATPase
Na+/K+ moved in/out of the cell by Na-K ATPase
Myosin:Actin interaction uses ATP
What is the main energy currency in the cell?
ATP
What are the differences between glycolysis and oxidative metabolism?
Glycolysis: 2 ATPs, lactic acid (toxic products)
Oxydative metabolism: 30ATPs, no toxic products
What is creatine phosphate?
High energy phosphate molecule
What does creatine phosphate do in muscles?
Provide rapid source of energy for the muscle
Easily donates iP to ADP to make ATP (provided a limited supply of ATP)
Use to buffer ATP over VERY short time scales
How do you make ATP with CrP?
What is it catalyzed by?
CrP + ADP = ATP + Cr
Catalyzed by creatine kinase (CK)
Where do resting muscles store energy?
CrP
What is a twitch?
single contraction-relaxation cycle
What is the latent period?
Short delay between AP and beginning of muscle tension
What are the 3 types of muscle fibers?
- Slow-twitch fibres (type 1)
- Fast-twitch oxidative-glycolytic fibres (types IIA)
- Fast-twitch glycolytic fibres (types IIX)
What does oxidative/glycolytic refer to?
Main source of ATP
Why does oxidative fibers appear red?
Presence of myoglobin (oxygen-carrying heme protein)
What does fast/slow refer to?
Rate of myosin ATPase activity
What is twitch duration determined by?
Rate of removal of Ca2+ from the cytosol
what are short twitch useful for? long twitches?
short: rapid, small muscle contraction (typing)
long: long sustained movements (lifting heavy loads)
Which type of muscle has the highest rate of Ca2+ removal from the cytosol?
Fast twitch muscles
