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 fibres 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?
-Ask up myofibril; multiple units running end-to-end along myofibril
-End of sarcomere = Z line
What are the 2 types of myofilaments and their function?
-Sarcomeres → made from 2 types of myofilaments; 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
How does aerobic respiration make ATP for muscle contraction?
-Makes ATP via oxidative phosphorylation
-Requires oxygen
-Mainly used for extended periods of low-intensity muscle use
How does anaerobic respiration make ATP for muscle contraction?
-Makes ATP by glycolysis & lactate fermentation; makes lactate, build up can cause fatigue
-Mainly used in short periods of high-intensity muscle use
What is phosphocreatine and how does it make ATP for muscle contraction?
-Molecule that can supply ATP for muscle contraction
-In intense muscular effort, phosphocreatine donates phosphate to ADP—> makes ATP, sustains muscle contraction
-In low periods of muscle activity, ATP can phosphorylate creatine—> phosphocreatine; short supply made, anaerobic process, makes no lactate
Contraction; How is depolarisation of the sarcolemma and then the sarcoplasm caused?
- Muscle contraction initiated when action potential arrives at neuromuscular junction from motor neurone
-Action potential causes depolarisation of sarcolemma and spreads along T-tubules—> sarcoplasm
Contraction; What causes the influx of calcium ions into the sarcoplasm?
-Depolarisation of T-tubules stimulates sarcoplasmic reticulum (SR)
-SR releases Ca²+ ions—> sarcoplasm
What is the role of tropomyosin and what occurs due to it in the muscle contraction process?
-Ca²+ ions bind → protein attached to tropomyosin (protein blocking actin-myosin binding site)
-binding of Ca²+ ions causes protein to change shape
-Altering protein causes tropomyosin to be moved. Actin-myosin binding site no longer blocked by tropomyosin
How is the actin-myosin cross bridge formed?
-Actin-myosin binding site no longer blocked by tropomyosin so myosin head can now bind to actin filament
-bond between the 2 is called the actin-myosin cross bridge
How is ATP hydrolase activated and what is its role in muscle contraction?
-Ca²+ ions also activate ATP hydrolase (enzyme hydrolysing ATP → ADP + inorganic phosphate)
-Process releases energy that can power muscle contraction
How does the bending of the myosin heads occur and what does this lead to and why?
-Ca²+ ions activate ATP hydrolase—>ATP hydrolysed, energy released.
-energy released causes myosin head to bend.
-movement of myosin head causes actin filament to slide past myosin filament.
-actin filament pulled by myosin head due to actin-myosin cross bridge.
How is the actin-myosin bridge broken and what does this result in?
-After actin filament has slid past myosin filament, actin-myosin cross bridge= broken (driven by energy from ATP)
-myosin head no longer attached to actin filament
How is the actin-myosin cross bridge reformed?
-myosin head bends back to OG position after it’s released from actin binding site.
-myosin forms new cross bridge w/ binding site further along actin filament.
How does the forming/breaking cycle of the actin-myosin bridges lead to muscle contraction?
-cycle of forming + breaking actin-myosin cross bridges occurs quickly & continuously.
-As actin filaments are pulled past myosin filaments, overall result= shortening of sarcomere; causes muscle contraction
Halting contraction; how are calcium ions removed?
-If action potentials—> no longer stimulating muscle cells, release of Ca2+ ions by sarcoplasmic reticulum (SR) will stop.
-Ca2+ ions= transported back into SR by active transport
Halting contraction; why does tropomyosin move and what does this cause?
-Removal of Ca²+ ions= protein attached to tropomyosin undergoes conformational change.
-protein changes shape—> causes tropomyosin to shift so it’s blocking actin-myosin binding sites.
-Myosin heads can no longer bind to actin filaments
Halting contraction; what causes the sarcomere to lengthen and what does this mean?
-Myosin heads can no longer bind to actin filaments.
-actin filaments return to resting position.
-sarcomere lengthens again; muscle no longer contracting.
What are the 2 types of skeletal muscle fibres?
Slow & fast twitch fibres
How do slow and fast twitch muscle fibres differ in location?
-Slow twitch fibres; found in muscles used for posture, eg back & neck
- fast twitch fibres; found mainly in muscles like arms & legs
How do slow and fast twitch muscle fibres differ in adaptation to function?
-slow twitch fibres; adapted for endurance & slow movements over long time periods. Are long & thin. Fatigue slowly, contract slowly
- fast twitch fibres; adapted for fast/strong movement over short time periods. Are short & wide. Fatigue quickly, contract quickly
How do slow and fast twitch fibres differ in energy source?
- slow twitch fibres; rely on energy released via aerobic respiration
- fast twitch fibres; rely on energy released via anaerobic respiration
What is the cell structure of slow twitch fibres?
- Lots of mitochondria to maintain aerobic respiration
- lots of capillaries to supply muscle fibres with oxygen
-Low levels of glycogen
-Low levels of phosphocreatine - large stores of myoglobin (pigment storing oxygen) so appear reddish
- less sarcoplasmic reticulum (contains calcium ions)
What is the cell structure of fast twitch fibres?
-fewer mitochondria
-fewer capillaries
-high levels of glycogen
-high levels of phosphocreatine
-small stores of myoglobin
-more sarcoplasmic reticulum
