TOPIC 4 - Muscle Flashcards
What is the function and structure of skeletal muscle?
- For voluntary movement of bones that underpins locomotion
- striated (striped) in appearance
How is a contraction initiated in skeletal muscle?
- Acetylcholine released at neuromuscular junction initiates an action potential in the sarcolemma
- Wave of depolarization passes along the sarcolemma & through the T-tubule network to reach interior of the cell.
- Depolarization triggers an increase in intracellular calcium
- Contraction occurs
What is the function and structure of cardiac muscle?
Cardiac muscle is specific to the heart
- has a striated appearance
What is the function and structure of smooth muscle?
- mechanical control of organ systems, blood vessel and airway diameter.
- is multiunit and unitary
The appearance is non-striated
What are the steps in cross-bridge formation and contraction of the sarcomere?
- ATP binds to myosin head making actin-myosin complex dissociate.
- ATP is hydrolysed –> causing myosin heads to return to their resting conformation.
- A cross bridge forms and myosin binds to a new position on actin.
- Pi is released.
- A conformational change in the myosin head causes the power stroke. The filaments slide past each other.
- ADP is released.
Cycle repeats when interacts with ATP.
What happens in excitation-contraction coupling?
- it increase calcium in skeletal muscle
Depolarisation activates L-type calcium channels in the t tubule membrane.
And causes a mechanical tethering between L-type ca channles in the T-tubule and ca release channels (ryanodine receptors) in the SR membrane.
- The Ca2+ release channels in the SR open and Ca moves into cytoplasm.
What does smooth muscle lack?
Smooth muscle lacks T-tubules and triad structures.
instead has shallow invaginations - caveolae.
Also has no troponin.
What happens when calcium is removed from the cytoplasm?
It terminates muscle contraction
How does smooth muscle contract?
It has NO troponin - but has calponin and caldesmon which inhibit interaction between actin and myosin.
- There is contraction when ca2+ stimulates calmodulin.
- causes mysoin light chain kinase to be activated - phosphorlates the MLC.
- Removes inhibitory effects of calponin and caldesmon facilitating cross bridge formation and contraction.
What is the difference betweeb slow and fast muscle fibres?
slow fibres - half the diameter of fast fibres - take longer to contract after nerve stimulation.
Fast fibres - take 10msec or less to contact - contract quickly after never stimulation.
What is the mechanism of botulinum toxins (botulism)?
It is the most common cause of food poisoning - leads to muscle weakness, paralysis leading death.
- 1st symptoms: dry mouth, double vision
- 2nd symptoms: gastrointestinal (diarrhea, vomiting)
- 3rd symptoms: paralysis of limbs, respiratory muscles
clinical use = botox
What is the diffrence between aerobic and anaerobic exercise?
Aerobic = sustained, low level exercise
- slow fibres stimulated
- conversion of llx into lla.
- makes 38 ATP molecules
Anaerobic = brief, intense exercise
- fast fibres stimulated
- makes 2 ATP and lactic acid.
When we exercise intially rely on stored energy and anaerobic glycolysis.
Where does immediate stage energy release come from in muscle cells?
from reseves of ATP and phosphocreatine (PCr).
ATP -> ADP + Phosphate + energy
ADP + PCr -> ATP + creatine
As ADAP accumulates: ADP + ADP -> ATP + AMP
What is muscle fatigue?
It is the inability to maintain the desired power output.
- force and velocity of muscle shortening declines.
