Muscles & Movement (Edexcel A Level Biology (A) SNAB): Flashcards
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Why does effective movement need both muscle and an incompressible skeleton?
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Why does effective movement need both muscle and an incompressible skeleton?
Muscles only produce movement by pulling on a structure that does not bend or shorten.
Bone provides this rigid structure.
Define tendon.
A tendon is strong connective tissue that connects muscle to bone and does not stretch when the muscle contracts.
Define ligament.
A ligament is strong connective tissue that connects bone to bone, holding the skeleton together.
Why must muscles work in antagonistic pairs?
Muscles can only contract (pull), not push.
So one muscle pulls a joint one way and its partner pulls it back.
Define antagonistic muscle action.
Antagonistic muscle action is when two muscles at a joint pull in opposite directions, one contracting as the other relaxes.
Which muscles contract and relax to raise the lower arm?
The biceps contracts and the triceps relaxes.
What is the difference between a flexor and an extensor?
A flexor bends a joint when it contracts (e.g. the biceps).
An extensor straightens a joint when it contracts (e.g. the triceps).
What stimulates a muscle to contract?
Nerve impulses from a motor neurone.
Muscles are effectors in the nervous system.
Tendons connect muscle to bone, whereas connect bone to bone.
Tendons connect muscle to bone, whereas ligaments connect bone to bone.
True or False?
A muscle can actively push a bone back into position.
False.
Muscles can only pull — the antagonistic partner pulls the bone back.
Why do tendons not stretch when a muscle contracts?
So that the force of contraction is transmitted to the bone.
A stretchy tendon would absorb the force instead of moving the bone.
Which muscles contract and relax to lower the lower arm?
The triceps contracts and the biceps relaxes.
Why are muscle fibres described as multinucleated?
Each muscle fibre contains many nuclei.
This is why they are called fibres rather than single cells.
What are the muscle-fibre names for the cell membrane, cytoplasm and endoplasmic reticulum?
Cell membrane = sarcolemma.
Cytoplasm = sarcoplasm.
Endoplasmic reticulum = sarcoplasmic reticulum.
Define myofibril.
A myofibril is a bundle of actin and myosin filaments within a muscle fibre that slide past each other during contraction.
What are the thick and thin filaments of a myofibril made of?
Thick filaments are made of myosin.
Thin filaments are made of actin.
Why do muscle fibres contain many mitochondria?
To carry out aerobic respiration.
This generates the ATP needed for muscle contraction.
What is stored in the sarcoplasmic reticulum, and why?
Calcium ions.
They are released to trigger muscle contraction.
How do fast twitch fibres differ from slow twitch fibres in how they respire?
Fast twitch rely on anaerobic respiration.
Slow twitch rely on aerobic respiration.
What type of activity are fast twitch fibres suited to, and why?
Short bursts of high-intensity activity.
They contract rapidly but fatigue quickly due to lactate build-up.
Why do slow twitch fibres appear dark red?
They contain lots of myoglobin (and haemoglobin).
This red pigment stores oxygen for aerobic respiration.
What type of activity are slow twitch fibres suited to?
Sustained, endurance activity such as posture and walking.
They fatigue slowly.
Define myoglobin.
Myoglobin is a red pigment in muscle that acts as an oxygen store and speeds up oxygen uptake from the blood.
Slow twitch fibres have a denser network of , giving a good supply of oxygen and glucose.
Slow twitch fibres have a denser network of capillaries, giving a good supply of oxygen and glucose.
True or False?
Human back muscles have a high proportion of slow twitch fibres.
True.
They must contract for long periods to hold the skeleton erect, which suits slow twitch fibres.
Define sarcomere.
A sarcomere is the repeating unit of a myofibril, between two Z discs, that shortens during muscle contraction.
What is the sliding filament theory?
Muscle contracts as actin and myosin filaments slide over one another.
The filaments themselves stay the same length; the sarcomere shortens.
What is released from the sarcoplasmic reticulum when an action potential arrives?
Calcium ions.
What do calcium ions do to troponin and tropomyosin?
Calcium binds to troponin, making it change shape.
This moves tropomyosin, exposing the myosin binding sites on actin.
Define cross-bridge.
A cross-bridge is the attachment formed when a myosin head binds to an exposed binding site on an actin filament.
What happens during the power stroke of muscle contraction?
The myosin heads bend, releasing ADP and phosphate.
This pulls the actin filaments towards the centre of the sarcomere.
What causes the myosin head to detach from actin?
ATP binds to the myosin head.
This changes its shape so it releases from the actin.
What is the role of ATPase in muscle contraction?
It hydrolyses ATP into ADP and phosphate.
The energy released moves the myosin head back to its original position (recovery stroke).
What happens when muscle stimulation stops?
Calcium ions are actively transported back into the sarcoplasmic reticulum.
Tropomyosin again blocks the binding sites, so no cross-bridges form and the muscle relaxes.
Calcium ions bind to , causing it to change shape and move tropomyosin off the binding sites.
Calcium ions bind to troponin, causing it to change shape and move tropomyosin off the binding sites.
True or False?
During contraction, the actin and myosin filaments themselves get shorter.
False.
The filaments stay the same length — they slide over each other, shortening the sarcomere.
How does the sliding filament theory explain rigor mortis?
After death there is no ATP to detach the myosin heads from actin.
So the cross-bridges stay attached and the muscles remain contracted.
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