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Flashcards in 11. Muscle Contraction Deck (27)
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What is the role of ATP in muscle contraction? (Helping the filaments slide over each other)

-Energy source
-Enable the formation of cross-bridges
-Release myosin heads from their binding sites


What is the role of calcium ions in muscle contraction?

-Cause myosin to hydrolyse ATP
-Cause change in shape of tropinin
-Cause tropomyosin to detach from actin filament/ expose binding site


Name the protein found in the H zone



What happens to the width of the A band when the muscle contracts?

Stays the same


What happens to the width of the I band when the muscle contracts?



Suggest two functions of energy released by mitochondria in the synaptic knob

-Active transport of ions/ ionic pump (reject A.T of ACh)
-Synthesis of acetylcholine/ reform vacuole
-Reabsorption of ACh from cleft
-Movement of vesicles to membrane
- Synthesis of acetylcholinesterase


Describe how the appearance of a muscle fibre would change when the fibril is stimulated by the neurotransmitter

-Shortening of terminal light bands
-Central H zone disappears/ reduced
-Overall shortening of fibril/ sarcomere


Describe how the stimulation of a muscle by a nerve impulse starts the cycle of contraction (myosin heads moving along actin)

-Bind to/ displace tropomyosin
-Reveal actin binding site
-Myosin binds to exposed sites on actin
-Crossbridges formed
-Activates ATPase


*Graph- Time taken for phosphocreatine to reform against age. As age increases, the time taken for the regeneration of phosphocreatine increases.*

Use your knowledge of fast muscle fibres to explain the data.

-Phosphocreatine takes longer to reform as people get older (from graph)
-Fast muscle fibres used for rapid./ brief/ powerful/ strong contractions
-Phosphocreatine used up rapidly during contraction to make ATP
-Anaerobic respiration involved
-(As people get older) Slower metabolic rate/ slower ATP production/ slower respiration
-ATP used to reform phosphocreatine
-Lots of phosphocreatine in fast fibres


What are the three types of muscle and where are they found?

-Cardiac muscle- exclusively found in the heart
-Smooth muscle- found in the walls of the blood vessels and the gut
-Skeletal (striated muscle)- is the bulk of body muscle in most vertebrates. Attached to bone and is under conscious, voluntary control


What is a myofobril?

Tiny muscle fibres making up striated muscle.


How are myofibrils arranged in skeletal muscle?

Small units bundled into progressively larger ones


What are the two types of protein filament that myofibrils are made up of

-Actin- thinner, two strands twisted around one another

-Myosin-thicker, long rod shaped fibres with bulbous heads that project to the sides


What are the two different bands and why are they different colours?

-Isotropic (I) bands- light bands because actin and myosin do not overlap in these regions

-Anisotropic (A) bands- dark bands because actin and myosin filaments overlap in this region


What is a H zone?

A lighter region at the centre of the anisotropic band


What is a Z line? What is the distance between 2 Z lines called?

The part at the centre of each isotropic band.
The distance between 2 adjacent Z lines is called a sarcomere.


What happens to the sarcomere when the muscle contracts?

It shortens


Describe the differences between fast and slow twitch fibres.

>Contract more slowly
>Provide less powerful contractions over a longer period
>Adapted for aerobic respiration to avoid build up of lactic acid
>Large store of myoglobin- stores oxygen
>Supply of glycogen to provide a source of metabolic energy
>Rich supply of blood vessels to deliver oxygen and glucose
>Numerous mitochondria to produce ATP

>Contract more rapidly
>Produce more powerful contractions over a shorter period
>Thicker, more numerous myosin filaments
>Higher concentration of enzymes that are involved in ANAEROBIC respiration
>Store of phosphocreatine- rapidly regenerate ATP from ADP in anaerobic conditions


Why are there many neuromuscular junctions in a muscle?

If there was only one neuromuscular junction, there would be a wave of contraction across the muscle so the movement would be slow as not all the fibres would contract simultaneously.

There are many neuromuscular junctions spread throughout the muscle to ensure that there is simultaneous contraction so that contractions are powerful and rapid when stimulated by an action potential.


What is a motor unit?

All muscle fibres supplied by a single motor neurone and act together as a single functional unit


How does the arrangement of motor units benefit control of movement?

Gives control over how much force is needed for an action.
If slight force is needed then only a few motor units are stimulated whereas if a large force is needed then many motor units can be stimulated.


How does the body make sure that the muscles are not overstimulated?

Acetylcholinesterase breaks down acetylcholine to make sure there is not continuous stimulation of the muslcle at inappropriate times.


Give evidence using changes in the sarcomere for the sliding filament theory, as opposed to the theory that the filaments themselves contract during muscle contraction.

-I band becomes narrower
-Z lines move closer together- the sarcomere shortens
-The H zone becomes narrower
-A band remains the same width- A band is only made uo of myosin so this shows that the myosin doesn't change length or contract during muscle contraction.


Describe the series of events that occur during muscle contraction that are explained by the sliding filament theory.
3 stages:
-Muscle stimulation
-Muscle contraction
-Muscle relaxation

-Action potential arrives at the neuromusclular junction, causing calcium ion channels to open and Ca2+ ions to flood into the synaptic knob.
-Calcium ions cause synaptic vesicles to fuse with the pre synaptic membrane and release a neurotransmitter through exocytosis
-Acetylcholine diffuses across and binds to receptors on the post synaptic membrane, causing it to depolarise

-Action potential travels deep into the fibre through a system of T tubules, branching thoughout the cytoplasm
-Tubules are in contact with the endoplasmic reticulum of the muscle which has actively absorbed calcium ions from the cytoplasm of the muscle
-Action potential opens Ca2+ channels on the endoplasmic reticulum and calcium ions flood into the cytoplasm of the muscle
-Calcium ions cause tropomyosin molecules that were blocking the acting binding sites to move, exposing the binding sites as the tropomyosin pulls away
-ADP molecule is attached to the myosin heads mean they are in a state to bind to the actin filament and form a CROSS BRIDGE
-Once attached, the myosin heads change their angle, pulling the actin filament along and releasing the molecule of ADP
-ATP attaches to the myosin head, causing it to detach from the actin filament
-Calcium ions activate ATPase which hydrolyses ATP to ADP, providing the energy for the myosin head to return to its original position
-Myosin head once more with an attached ADP binds further along the actin filament and the cycle continues until the stimulation ceases.

-When nervous stimulation ceases, calcium ions are actively transported back into the endoplasmic reticulum, using energy from ATP
-Reabsorption of Ca2+ allows the tropomyosin to move to continue blocking the actin binding sites
-Myosin heads unable to form cross bridges so contraction ceases.


What is the role of ATP in muscle contraction?

-Movement of myosin heads
-Re absorption of calcium ions into the endoplasmic reticulum through active transport


What is the role of phosphocreatine?

-Serves as a reserve supply of phosphate
-In anaerobic conditions, ADP can combine with the phosphate provided by the phosphocreatine to form ATP
-Phosphocreatine replenished using ATP when the muscle is relaxed


(3 marks)
People who have McArdle’s disease produce less ATP than healthy people. As a
result, they are not able to maintain strong muscle contraction during exercise. Use
your knowledge of the sliding filament theory to suggest why.

1. Attachment/cross bridges
between actin and myosin;
2. ‘Power stroke’ / movement of
myosin heads / pulling of
3. Detachment of myosin
4. Myosin heads move back/to
original position / ‘recovery