6 Responding to Change- Muscle Contraction Flashcards
What do antagonistic pairs consist of and what do they allow?
-consist of an agonist & an antagonist
- are how skeletal muscles contract and relax to allow body movement
What attaches skeletal muscles to bones?
Tendons
What is the muscle that’s relaxing called?
The antagonist
Which muscle in a pair this is can vary depending on the movement
What is the muscle that’s contracting called?
Agonist
Which muscle in pair this varies depending on movement
What do skeletal muscles consist of?
Many bundles of muscle fibres - long, specialised cells
What is the sarcolemma and what does it fold inwards to?
-The membrane of muscle fibres
-Folds inwards to sarcoplasm (muscle fibre cytoplasm) at certain points
What are the inwards folds in muscle fibre sarcolemma called and what are they important for?
- Transverse (t) tubules
- very important in initiating muscle contraction
What is the sarcoplasmic reticulum and its importance?
- An organelle in the sarcoplasm
- store for calcium (Ca²+ ions); important in muscle contraction
What other organelles do muscle fibres contain and why?
-Mitochondria & nuclei
-Mitochondria provide lots of ATP to power muscle contraction
What are myofibrils and their function?
- Cylindrical organelles, run along length of muscle fibres
- site of muscle contraction
What are sarcomeres?
-Make up myofibril; multiple units running end-to-end along myofibril
-End of sarcomere = Z line
What are the 2 types of myofilaments sarcomeres are made up of and their function?
-Thick (made of myosin protein) & thin (made of actin protein)
-The two slide past each other → movement makes muscles contract
How are myosin and actin filaments arranged with each other?
-Myosin & actin filaments → arranged in alternating pattern in sarcomeres
-Thick myosin filaments overlap w/ thin actin filaments at each end
What is the A-band and the H-zone?
- A-band = overlapping region between myosin and actin filaments
- H-zone = region w/ only myosin filament
What is the M-line and the I-band?
M-line = middle of the sarcomere, where myosin and actin filaments overlap
I-band = region with only actin filament
What does the sliding filament theory explain?
How muscle contraction is coordinated in myofibrils
Sliding filament; how is the sarcolemma depolarised?
-Muscle contraction → initiated when an action potential arrives at muscle cells
-Action potential depolarises sarcolemma
Sliding filament; what causes the sarcomeres to contract?
-Depolarisation of sarcolemma causes myosin & actin filaments to slide over each other
-Sliding movement causes sarcomeres to contact
Sliding filament; what causes the whole muscle to contract?
-There’s multiple sarcomeres along myofibril length
-As many sarcomeres contract simultaneously, muscle fibres contract
-Contraction of fibres causes whole muscle to contract
Sliding filament; what causes the muscle to relax?
-After muscle contracts, sarcomeres relax
-Filaments slide back over each other & muscle relaxes
What feature allows the myosin and actin filaments to slide past each other in muscle contraction?
-Myosin filaments—> have globular heads; move back and forth
-Movement of globular heads—> allows actin & myosin filaments to slide past each other in muscle contraction
What binding sites are present on the myosin head/actin filaments?
-2 binding sites on each myosin head; one binds to actin, another to ATP
-Also binding site for myosin heads on actin filaments; actin-myosin binding site
What is tropomyosin and its function?
-Protein located on actin filaments
-Plays important role in muscle contraction as blocks actin-myosin binding site when muscle fibres—> at rest
-When muscle fibres= stimulated, tropomyosin protein is moved so myosin heads can bind to actin-myosin binding site
-When actin + myosin bind, can slide past each other—> muscle contracts
Why does ATP need to be made rapidly in muscle contraction?
It’s a very energetically demanding process