Lecture 17 Flashcards
What are functions of skeletal muscles?
Produce movement of body parts: simple motion or coordinated movement
Support soft tissues: support the weight and shield visceral organs
Maintain posture and body positions: allows standing position
Communication: speech, expression, and writing
Control of openings and passageways: voluntary control of movements of digestive and urinary tracts
Maintain body temperature: heat released through muscle contraction participants in control of body temperature
What are universal characteristics of muscles?
Responsiveness (excitability)
- capable of response to chemical signals, stretch or other signals and responding with electrical charges across the plasma membrane
Conductivity
- local electrical charge triggers a wave of excitation that travels along the muscle fiber
Contractility
- shortens when stimulated
Extensibility
- capable of being stretched
Elasticity
- returns to its original resting length after being stretched
How are the myofibril structure surrounded by connective tissues?
Also present in bundles of cells and surrounding muscle fibers
What is epimysium and perimysium?
Blood vessels and nerves bring nutrients and electrical activity needed for contraction
Some muscles have cells 50-60cm but some are about 5cm
How do myoblasts fuse to form skeletal muscle fibers?
Plasma membrane (sarcolemma) from invaginations contribute to propagation of nerve signal to cell contractile units Sarcolemma is rich in glycogen and packed with bundles of proteins that organize into myofibrils
What do myofibrils contain repeated units of?
Sarcomeres (functional unit)
- Many composed of thick and thin filaments
- Thick filaments lie in center while thin overlap between two sarcomeres
What is the Dark band?
Situated in center
Mainly composed of thick filament
What is Light band?
Mainly composed of thin filament
What are Z-lines?
Show one sarcomere
What is contraction?
Sliding of thick and thin filaments
How many myosin heads do thick filaments contain?
300
How often does each head cycle?
5 times/s
What is the thick filament mainly made of?
Myosin
- one domain is a myosin head (globular) and the myosin chain (rod)
How are thick and thin filaments organized?
In opposite directions
Where do proteins anchor onto?
Filaments and Z-line:
made of 15 000 amino acids
What do the spring-like structures?
Allows whole filament to stretch and recoil
What is protein essential for?
Extensibility and elasticity
What is thin filament mainly made of?
Actin
Very stable in length and state
Why is the Z-disc anchored to CapZ and tropomodulin?
Maintains uniformity across sarcomere, the length of filament
What does nebulin act as?
molecular ruler (repeat units contain binding sites for the actin): set actual length of actin
What is actin partly associated with?
troponin and tropomyosin
Why do myosin heads can bind to filaments of actin?
Operating movement that pulls filament of actin towards them in opposite directions - contraction
What are the steps of myosin heads binding to filaments of actin?
- Myosin rod and head attached to specific binding site on actin filament
- Myosin head needs to detach from binding site (ATP onto myosin head)
- ATP - ADP + Pi: ADP remains bound to hinge region
- Myosin head comes back to resting protein
- Myosin head moves to another binding site
- Pi released changes conformation at level of hinge, allowing thin filament to slide past thick filament. 300 heads simultaneously carrying out sliding at fast speed
- very powerful and rapid contraction
How is contraction initiated?
- Electrical signal from motoneuron to skeletal muscle
- At the neuromuscular junction, depolarization of membrane is triggered, activating voltage-gated Ca channels. This increases intracellular Ca then initiates release of neurotransmitter
- ACh will bind to receptors at postsynaptic membrane which triggers entry of Na then causes depolarization of sarcolemma. This initiates voltage-gated Ca channels so Ca is released at sarcoplasmic reticulum
- Ca finds its way to troponin
- TroponinC is capable of binding to Ca which triggers a change of conformation between complex of troponin and tropomyosin
- masking of myosin head binding site - Troponin and tropomyosin prevent myosin head from binding
- electrical signal
- binds
- initiates contraction (need to have mechanism to end)