6 Responding to Change- Muscle Contraction Flashcards

1
Q

What do antagonistic pairs consist of and what do they allow?

A

-consist of an agonist & an antagonist
- are how skeletal muscles contract and relax to allow body movement

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2
Q

What attaches skeletal muscles to bones?

A

Tendons

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3
Q

What is the muscle that’s relaxing called?

A

The antagonist
Which muscle in a pair this is can vary depending on the movement

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4
Q

What is the muscle that’s contracting called?

A

Agonist
Which muscle in pair this varies depending on movement

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5
Q

What do skeletal muscles consist of?

A

Many bundles of muscle fibres - long, specialised cells

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6
Q

What is the sarcolemma and what does it fold inwards to?

A

-The membrane of muscle fibres
-Folds inwards to sarcoplasm (muscle fibre cytoplasm) at certain points

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7
Q

What are the inwards folds in muscle fibre sarcolemma called and what are they important for?

A
  • Transverse (t) tubules
  • very important in initiating muscle contraction
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8
Q

What is the sarcoplasmic reticulum and its importance?

A
  • An organelle in the sarcoplasm
  • store for calcium (Ca²+ ions); important in muscle contraction
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9
Q

What other organelles do muscle fibres contain and why?

A

-Mitochondria & nuclei
-Mitochondria provide lots of ATP to power muscle contraction

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10
Q

What are myofibrils and their function?

A
  • Cylindrical organelles, run along length of muscle fibres
  • site of muscle contraction
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11
Q

What are sarcomeres?

A

-Make up myofibril; multiple units running end-to-end along myofibril
-End of sarcomere = Z line

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12
Q

What are the 2 types of myofilaments sarcomeres are made up of and their function?

A

-Thick (made of myosin protein) & thin (made of actin protein)
-The two slide past each other → movement makes muscles contract

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13
Q

How are myosin and actin filaments arranged with each other?

A

-Myosin & actin filaments → arranged in alternating pattern in sarcomeres
-Thick myosin filaments overlap w/ thin actin filaments at each end

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14
Q

What is the A-band and the H-zone?

A
  • A-band = overlapping region between myosin and actin filaments
  • H-zone = region w/ only myosin filament
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15
Q

What is the M-line and the I-band?

A

M-line = middle of the sarcomere, where myosin and actin filaments overlap
I-band = region with only actin filament

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16
Q

What does the sliding filament theory explain?

A

How muscle contraction is coordinated in myofibrils

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17
Q

Sliding filament; how is the sarcolemma depolarised?

A

-Muscle contraction → initiated when an action potential arrives at muscle cells
-Action potential depolarises sarcolemma

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18
Q

Sliding filament; what causes the sarcomeres to contract?

A

-Depolarisation of sarcolemma causes myosin & actin filaments to slide over each other
-Sliding movement causes sarcomeres to contact

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19
Q

Sliding filament; what causes the whole muscle to contract?

A

-There’s multiple sarcomeres along myofibril length
-As many sarcomeres contract simultaneously, muscle fibres contract
-Contraction of fibres causes whole muscle to contract

20
Q

Sliding filament; what causes the muscle to relax?

A

-After muscle contracts, sarcomeres relax
-Filaments slide back over each other & muscle relaxes

21
Q

What feature allows the myosin and actin filaments to slide past each other in muscle contraction?

A

-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

22
Q

What binding sites are present on the myosin head/actin filaments?

A

-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

23
Q

What is tropomyosin and its function?

A

-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

24
Q

Why does ATP need to be made rapidly in muscle contraction?

A

It’s a very energetically demanding process

25
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
26
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
27
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
28
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
29
Contraction; What causes the influx of calcium ions into the sarcoplasm?
-Depolarisation of T-tubules stimulates sarcoplasmic reticulum (SR) -SR releases Ca²+ ions—> sarcoplasm
30
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
31
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
32
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
33
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.
34
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
35
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.
36
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
37
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
38
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
39
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.
40
What are the 2 types of skeletal muscle fibres?
Slow & fast twitch fibres
41
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
42
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
43
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
44
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)
45
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