6B - Muscle contraction Flashcards
What do muscles act in?
Antagonistic pairs
What is the type of muscle you use to move?
Skeletal muscle
What is a skeletal muscle?
The type of muscle you use to move.
What are the other names for a skeletal muscle?
Striated, striped or voluntary muscles.
What are skeletals attached to?
Bones
How are skeletal muscles attached to bones?
By tendons
What do tendons do?
Attach skeletal muscle to bone.
What do ligaments do?
Attach bones to other bones, to hold them together.
How do pairs of muscles move bones at a joint?
Contract and relax.
What are the bones of the skeleton described as?
Incompressible (rigid)
What is the benefit of the bones of the skeleton being incompressible (rigid)?
They act as levers, giving the muscles something to pull against.
What are muscles that work together to move a bone called?
Antagonistic pairs.
What is the agonist?
The contracting muscle.
What is the contracting muscle called in an antagonistic pair?
The agonist.
What is the antagonist?
The relaxing muscle.
What is the relaxing muscle called in an antagonistic pair?
The antagonist.
Why do muscles work in pairs?
Because they can only pull when they contract - they can’t push.
Explain how muscles work together to cause flexion at the elbow
The bicep contracts (agonist) and the tricep relaxes (antagonist).
This pulls the bone so your arm bends at the elbow.
Explain how muscles work together to cause extension at the elbow
The tricep contracts (agonist) and the bicep relaxes (antagonist).
This pulls the bone so your arm straightens at the elbow.
What do muscles act as?
Effectors
What are muscles stimulated to contract by?
Neurones
What is skeletal muscle made up of?
Large bundles of long cells, called muscle fibres.
What are muscle fibres?
Large bundles of long cells that make up a skeletal muscle.
What is the cell membrane of muscle fibres called?
The sarcolemma.
What is the sarcolemma?
The cell membrane of muscle fibres.
What do bits of the sarcolemma do?
Fold inwards across the muscle fibre and stick into the sarcoplasm.
What is the sarcoplasm?
A muscle cell’s cytoplasm.
What is a muscle cell’s cytoplasm called?
The sarcoplasm.
What are the inward folds of the sarcolemma that stick into the sarcoplasm called?
Transverse (T) tubules.
What are T tubules?
Transverse tubules - inward folds of the sarcolemma.
What do T tubules do?
Help to spread electrical impulses through the sarcoplasm so they reach all parts of the muscle fibre.
What is the network of internal membranes that runs through the sarcoplasm called?
The sarcoplasmic reticulum.
What is the sarcoplasmic reticulum?
The network of internal membranes that runs through the sarcoplasm.
What does the sarcoplasmic reticulum do?
Stores and releases calcium ions that are needed for muscle contraction.
What is the number of mitochondria like in muscle fibres?
They have lots of mitochondria.
Why do muscle fibres have lots of mitochondria?
To provide the ATP that’s needed for muscle contraction.
What does it mean that muscle fibres are multinucleate?
They contain many nuclei.
What is the word that describes muscle fibres as they contain many nuclei?
Multinucleate.
What are the long, cylindrical organelles in muscle fibres?
Myofibrils.
What are myofibrils?
Long, cylindrical organelles in muscle fibres.
What are myofibrils made up of?
Proteins.
What are myofibrils highly specialised for?
Contraction.
What kind of appearance do muscle fibres have?
A banded appearance.
Why do muscle fibres have a banded appearance?
Due to microfibrils made up of thick and thin myofilaments.
What do myofibrils contain?
Bundles of thick and thin myofilaments that move past each other to make muscles contract.
What are thick myofilaments made up of?
Myosin protein
What are thin myofilaments made up of?
Actin protein
Is actin thick or thin?
Thin
Is myosin thick or thin?
Thick
What do dark bands contain?
Thick myosin filaments and some overlapping thin actin filaments (A bands).
What do light bands contain?
Thin actin filaments only (I bands).
What is the A band?
Contains myosin and actin.
What is the I band?
Contains actin only.
What band contains actin and myosin?
A band
What band contains actin only?
I band
What is a myofibril made up of?
Many short units called sarcomeres.
What do sarcomeres make up?
A myofibril.
What are the ends of each sarcomere marked with?
A z-disc/line
What is the middle of each sarcomere called?
M-line
What is the M-line?
The middle of the myosin filaments/sarcomere.
What is the z-disc?
Marks the end of a sarcomere.
What is the H-zone?
Contains myosin only.
What band/zone contains myosin only?
H-zone
What is the actin anchored to?
Z-disc
What is the length between 2 Z-discs called?
Sarcomere
Tropomyosin
Forms long threads that wraps around the actin.
What is muscle contraction explained by?
The sliding filament theory.
What does the sliding filament theory explain?
Muscle contraction.
What happens to the sarcomere during muscle contraction?
It gets shorter.
Why does the sarcomere shorten during muscle contraction?
As the I band slides into the H band.
What happens to the I band during muscle contraction?
Gets shorter
What happens to the A band during muscle contraction?
Does not change
What happens to the H zone during muscle contraction?
Gets shorter
What does the simultaneous contraction of lots of sarcomeres means?
Means the myofibrils and muscle fibres contract.
What happens to the sarcomeres as the muscle relaxes?
They return to their original length.
What is a motor unit?
All the muscle fibres supplied by a single motor neurone.
What do myosin filaments have so they can move back and forth?
Globular heads that are hinged.
What do the globular heads that are hinged on myosin filaments allow?
Allow the filament to move back and forth.
What does each myosin head have a binding site for?
Actin and ATP.
What do actin filaments have binding sites for?
Myosin heads.
What are the binding sites for myosin heads on actin filaments called?
Actin-myosin binding sites.
Where is tropomyosin found?
Between actin filaments.
What does tropomyosin help?
Helps myofilaments move past each other.
What are the actin-myosin binding sites in resting muscles blocked by?
Tropomyosin.
What does tropomyosin do in resting (unstimulated) muscles?
Blocks the actin-myosin bind site.
What happens when tropomyosin blocks the actin-myosin binding site?
The myofilaments can’t slide past each other because the myosin heads can’t bind to the actin-myosin binding site on the actin filaments.
Explain how muscle contraction is triggered
1) AP from a motor neurone stimulates a muscle cells and depolarises the sarcolemma. Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum.
2) This causes the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm.
3) Calcium ions bind to a protein attached to tropomyosin, causing the protein to change shape. This pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament.
4) This exposes the binding site allowing the myosin head to bind.
5) The bond formed when a myosin head binds to an actin filament is called an actin-myosin cross bridge.
6) Calcium ions also activate the enzyme ATP hydrolase which hydrolyses ATP to provide energy for muscle contraction.
7) The energy released from ATP causes the myosin head to bend, which pulls the actin filament along in a kind of rowing action.
8) Another ATP molecule provides the energy to break the actin-myosin cross bridge, so the myosin head detaches from the actin filament after it’s moved.
9) The myosin head then reattaches to a different binding site further along the actin filament. A new crossbridge is formed and the cycle is repeated.
10) Many cross bridges form and break very rapidly, pulling the actin filament along - which shortens the sarcomere, causing the muscle to contract.
11) The cycle will continue as long as calcium ions are present.
What bond is formed when a myosin head binds to an actin filament?
An actin-myosin cross bridge.
What happens to the calcium ions when the muscle stops being stimulated?
They leave their binding sites and are moved by active transport back into the sarcoplasmic reticulum.
What does the calcium ions leaving their binding sites and are moved by active transport back into the sarcoplasmic reticulum cause?
Causes tropomyosin molecules to move back, so they block the actin-myosin binding sites again.
When don’t muslces contract?
When no myosin heads are attached to actin filaments (so there are no actin-myosin cross bridges).
What happens to the sarcomere when the muscle stops contracting and how/why?
The actin filaments slide back into their relaxed position, which lengthens the sarcomere.
What provides the energy for muscle contraction?
ATP and phsophocreatine.
How is ATP continually generated?
Aerobic respiration
Anaerobic respiration
ATP-Phosphocreatine (PCr) System
How is ATP continually generated by aerobic respiration?
Most ATP generated via oxidative phosphorylation in the mitochondria.
When does aerobic respiration work?
When there is oxygen.
What is aerobic respiration good for?
Long periods of low-intensity exercise.
How is ATP continually generated by anaerobic respiration?
ATP is made rapidly by glycolysis.
What is the end product of glycolysis and what is this converted to in anaerobic respiration?
Pyruvate - converted to lactate by lactate fermentation.
How is pyruvate converted to lactate in anaerobic respiration?
By lactate fermentation.
What can lactate do in the muscles and what does this cause?
Can quickly build up in the muscles and cause muscle fatigue.
What is anaerobic respiration good for?
Short periods of hard exercise, e.g. a 400m sprint.
How is ATP continually generated by the ATP-Phosphocreatine system?
ATP is made by phosphorylating ADP - adding a phosphate group taken from PCr.
Where is PCr found?
Stored inside cells.
How long is it before PCr runs out?
After a few seconds.
What is the ATP-PCr system good for?
Short bursts of vigorous exercise, e.g. a tennis serve.
Is the ATP-PCr system aerobic or anaerobic?
Anaerobic
Apart from being anaerobic, what is the ATP-PCr also described as being?
Alactic - it doesn’t form any lactate.
Equation showing how the ATP-PCr system generates ATP
ADP + PCr –> ATP + Cr
What does PCr stand for?
Phosphocreatine
What does Cr stand for?
Creatine
What does some of the Cr produced by the generation of ATP by the ATP-PCr system get broken down into and then what happens to it?
Gets broken down into creatinine which is removed from the body via the kidneys.
When can creatinine levels be higher?
In people who exercise regularly and those with high muscle mass.
What might high creatinine levels indicate?
Kidney damage.
What are the types of muscle fibres?
Fast and slow twitch.
What are the properties of slow twitch muscle fibres?
- Contract slowly.
- Muscles used for posture, e.g. those in the back, have a high proportion of them.
- Good for endurance activities, e.g. maintaining posture, long-distance running.
- Can work for a long time without getting tired.
- Energy’s released slowly through aerobic respiration.
- Lots of mitochondria and blood vessels supply the muscles with oxygen.
- Reddish colour because they’re rich in myoglobin.
What is myoglobin?
A red-coloured protein that stores oxygen.
What type of muscle fibre contract slowly?
Slow twitch
What type of muscle fibre is found in high proportions in the muscles used for posture?
Slow twitch
What type of muscle fibre is good for endurance activities?
Slow twitch
What type of muscle fibre can work for a long time without getting tired?
Slow twitch
What type of muscle fibres energy is released through aerobic respiration?
Slow twitch
What type of muscle fibre has lots of mitochondria and blood vessels supplying the muscles with oxygen?
Slow twitch
What type of muscle fibre is reddish in colour because they’re rich in myoglobin?
Slow twitch
What are the properties of fast twitch muscle fibres?
- Contract very quickly.
- Muscles you use for fast movement, e.g. those in the eyes and legs, have a high proportion of them.
- Good for short bursts of speed and power, e.g. eye movement, sprinting.
- Get tired very quickly.
- Energy’s released through anaerobic respiration using glycogen (stored glucose).
- Few mitochondria or blood vessels.
- Whitish in colour because they don’t have much myoglobin (so can’t store much oxygen).
What type of muscle fibre contracts very quickly?
Fast twitch
What type of muscle fibre is used for fast movement?
Fast twitch
What type of muscle fibre is good for short bursts of speed and power?
Fast twitch
What type of muscle fibre gets tired very quickly?
Fast twitch
What type of muscle fibres energy is released through anaerobic respiration using glycogen?
Fast twitch
What type of muscle fibre have few mitochondria or blood vessels?
Fast twitch
What type of muscle fibre are whitish in colour because they don’t have much myoglobin?
Fast twitch
