Muscle Contraction Flashcards
Features of skeletal muscle contraction:
> Muscles act in antagonistic pairs and is used to move bones at joints.
Voluntary muscles which attach to bone via inelastic tendons
What are sarcomere?
Protein filaments that slide over each other
1 muscle fibre =
1 cell
How are the muscle fibres bound together in a skeletal muscle?
By connective tissue, which is continuous with the tendons
Within each muscle fibre there are also numerous….
myofibrils
What do myofibrils consist of?
Bundles of thick (myosin) and thin (actin) filaments
What protein are thick filaments made up of?
Myosin
What protein are thin filaments made up of?
Actin
On an electron microscope, what are the end lines of a sarcomere marked by?
Z lines - the distance between the two Z lines is a sarcomere
The M line (on a Electron Microscope image) is…
where the thick myosin are anchored (near the middle)
The A band (on a Electron Microscope image) is…
where thin and thick filaments overlap (the dark area/bands)
The I band (on a Electron Microscope image) contains…
only thin filaments (at the ends near the Z line)
The H zone (on a Electron Microscope image) contains…
only thick filaments ( middle bit where the M line is)
The thick myosin filaments are held by the…
M line
The thin actin filaments are held by the…
Z line
During contraction, the …….. filaments are pulled over the ……….. filaments to make the ……… contract and the muscle …………
Actin
Myosin
Sarcomere
Shorten
The A band stays the same length during contraction but just gets…
darker
How are the cross bridges formed between the thick and thin filaments?
The myosin heads have a specific shape to be able to bind to the actin filaments and form the bridges
What is each actin filament made up of?
Tow helical strands of globular actin molecules which twist round each other to form an actin filament
What is Tropomyosin?
A fibrous protein which is wrapped around the filaments to prevent the myosin heads from binding and forming cross bridges.
How is Tropomyosin moved to allow the Myosin Heads to form cross bridges with the actin filaments?
Calcium ions bind to Troponin which moves the Tropomyosin exposing the binding area for myosin heads
What is the role of ATP in the contraction of a myofibril?
Hydrolysis of ATP causes:
- formation of a cross bridges
- Causes myosin heads to move
- It breaks the cross bridges to allow a power stroke to occur
How does the action potential that has moved across through the muscle fibre via T tubules cause calcium ions to be released?
It opens the calcium ion channels on the sarcoplasmic reticulum and calcium ions flood into the muscle cytoplasm down a diffusion gradient (this caused tropomyosin to be moved so myosin heads can bind)
Give three similarities between neuromuscular junctions and a cholinergic synapse
- Both have acetylcholine
- Both have receptors that ACh binds to causing an influx of sodium ions
- Both use a sodium-potassium pump to repolarise the axon
- Both use enzymes to break down the neurotransmitter
What is the role of calcium ions in the contraction of a myofibril?
- Calcium ions activate ATP hydrolase in the myosin head to provide ATP for the power stroke
- Calcium ions diffuse into myofibrils from sarcoplasmic reticulum
- Calcium ions move Tropomyosin by binding to Troponin
- Exposes the actin binding sites
Give two ways in which ATP is a suitable energy source for cells to use
> ATP is resynthesized quickly
ATP does not leave the cell
ATP is an immediate source of energy
Releases small manageable amounts
What happens to the I band during contraction?
Becomes narrower
Give some features of the slow twitch fibres
- Less sarcoplasmic reticulum so calcium ions remain in their sarcoplasm for longer
- Have more mitochondria which provide ATP
- Have more myoglobin than fast twitch
