Back to AI Flashcard MakerBiology /Biology IB HL - 11.2 Movement Part 4
What is the role of acetylcholine?
Acetylcholine initiates depolarization within the sarcolemma, which is spread through the muscle fibre via T tubules
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Key Terms
Term
Definition
What is the role of acetylcholine?
Acetylcholine initiates depolarization within the sarcolemma, which is spread through the muscle fibre via T tubules
What is the role of depolarisation?
Depolarisation causes the sarcoplasmic reticulum to release stores of calcium ions (Ca2+)
What is the role of calcium ions?
Calcium ions play a pivotal role in initiating muscular contractions
Why can binding not occur straight away?
On actin, the binding sites for the myosin heads are covered by a blocking complex (troponin and tropomyosin)
How are the myosin heads allowed to bind?
Calcium ions bind to troponin and reconfigure the complex, exposing the binding sites for the myosin heads
What happens when the actin is exposed?
The myosin heads then form a cross-bridge with the actin filaments
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| Term | Definition |
|---|---|
What is the role of acetylcholine? | Acetylcholine initiates depolarization within the sarcolemma, which is spread through the muscle fibre via T tubules |
What is the role of depolarisation? | Depolarisation causes the sarcoplasmic reticulum to release stores of calcium ions (Ca2+) |
What is the role of calcium ions? | Calcium ions play a pivotal role in initiating muscular contractions |
Why can binding not occur straight away? | On actin, the binding sites for the myosin heads are covered by a blocking complex (troponin and tropomyosin) |
How are the myosin heads allowed to bind? | Calcium ions bind to troponin and reconfigure the complex, exposing the binding sites for the myosin heads |
What happens when the actin is exposed? | The myosin heads then form a cross-bridge with the actin filaments |
What causes myosin to detach? | ATP binds to the myosin head, breaking the cross-bridge between actin and myosin |
What does ATP hydrolysis cause? | ATP hydrolysis (releasing ADP and inorganic phosphate) causes the myosin heads to change position and swivel, moving them towards the next actin binding site |
What happens once myosin has swivelled/changed shape? | The myosin heads bind to the new actin sites and return to their original conformation |
What causes the movement? | This reorientation drags the actin along the myosin in a sliding mechanism (a power stroke) |
What does the cycle cause? | The repeated reorientation of the myosin heads drags the actin filaments along the length of the myosin |
What change in appearance occurs to the sarcomeres? | As actin filaments are anchored to Z lines, the dragging of actin pulls the Z lines closer together, shortening the sarcomere |
What, overall, causes the muscle to contract? | As the individual sarcomeres become shorter in length, the muscle fibres as a whole contracts |
What change in appearance occurs to I bands after contraction? | When muscle fibres contract, actin filaments slide along the myosin, reducing the length of the lighter I bands |
What change in appearance occurs to H zone after contraction? | The movement of the actin filaments also reduces the width of the H zone |
What change in appearance occurs to the A bands? | the length of A bands do not change |
What type of protein is actin? | These are globular protein molecules |
What form does actin take in sarcomeres? (structure) | Many actin molecules link together to form a chain | Two actin chains twist together to form one thin filament |
What surrounds the actin filaments? | A fibrous protein known as tropomyosin is twisted around the two actin chains | Another protein known as troponin is attached to the actin chains at regular intervals |
What type of protein is myosin? | These are fibrous protein molecules with a globular head |
What is the role of the fibrous part of myosin? | The fibrous part of the myosin molecule anchors the molecule into the thick filament |
What is the structure of myosin? | In the thick filament, many myosin molecules lie next to each other with their globular heads all pointing away from the M line |
What enzyme is involved in muscle contraction? | The enzyme ATP hydrolase hydrolyses ATP into ADP and inorganic phosphate which causes the myosin heads to move back to their original positions | This is known as cocking of the myosin head or the recovery stroke |
What happens once the muscle relaxes? | When the motor neurone stops sending impulses to the muscle fibre, calcium ions are actively pumped back into the sarcoplasmic reticulum and the tropomyosin moves back to cover the binding sites on the actin | The muscle is now relaxed |
What is the M-line? | attachment for myosin filaments |