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AQA A-Level Biology 5-8 > 6.3 Skeletal Muscle Contraction > Flashcards

6.3 Skeletal Muscle Contraction Flashcards

1
Q

What is the gross structure of skeletal muscles?

A

Whole muscle
Bundle of muscle fibres
Single muscle fibres
Myofibril

Multinucleate

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2
Q

How are the long giant cells in muscle fibres formed?

A 
They form from the fusion of smaller cells
The sarcoplasm (cytoplasm) are full of myofibril - which are bundles of protein filaments that cause contraction
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3
Q

What initiates the muscle contraction - due to what?

A

The sarcolemma (cell surface membrane) allows an action potential to pass along

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4
Q

What are the prefixes for muscle?

A

Sarco and Myo

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5
Q

How do muscles work?

A

In antagonistic pairs against an incompressible skeleton

Using flexion and extension

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6
Q

What are slow twitch fibres used for?

A

Aerobic respiration

They contract more slowly and provide less powerful contractions but over a long period

Adapted for endurance

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7
Q

How are slow twitch adapted?

A

Large store of myoglobin
Rich supply of blood vessels
A lot of mitochondria

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8
Q

What are fast twitch fibres used for?

A

Anaerobic respiration

They contract more rapidly and provide more powerful contractions but over a shorter period

Adapted for intense exercise

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9
Q

How are fast twitch adapted?

A

Thicker and more myosin filaments
Higher concentration of enzymes (for anaerobic respiration)
Higher concentration of phosphocreatine - to generate ATP from ADP
Supply of glycogen

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10
Q

What is involved in the structure of myofibril?

A

Actin and myosin

They are darker where they overlap

Sarcomere 
A band
H zone
I band
M line 
Z line
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11
Q

What do all the sections of myofibril represent?

A 
A band - length of the myosin filament
H zone - myosin only
I band - actin only 
M line - middle of the sarcomere
Z line - ends of the sarcomere
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12
Q

How do you remember which band for the colours on a myofibril diagram?

A

LIght - I band - just actin

dArk - A band - length of myosin filament

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13
Q

What is the sliding filament theory?

A

When the muscle contracts the sarcomere becomes smaller

The filaments don’t change length they just slide past an overlap

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14
Q

What is a neuromuscular junction?

A

Like a synapse

Allows the muscle to contract when threshold is exceeded as sufficient acetylcholine is released

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15
Q

What is different about a neuromuscular junction to a cholinergic synapse?

A

The post synaptic membrane is muscular
The sarcolemma can transmit an action potential along it
The sarcolemma have T-tubials (a large indent in the cell surface membrane which brings the action potential directly to the sarcoplasmic reticulum

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16
Q

What is ‘actin’ actually made up of?

A

Actin
Tropomyosin
Troponin

17
Q

What is the first part of the sliding filament mechanism?

A

The tropomyosin prevents the myosin head from attaching to the binding site on the actin
Ca+ ions are released from the sarcoplasmic reticulum and binds to the troponin - changing the tertiary structure causing the tropomyosin to pull away from the binding sites on the actin
The myosin head attaches to the binding site on the actin which forms a
Cross Bridge!!!

18
Q

What is the second part of the sliding filament theory?

A

Due to the cross bridge the myosin head changes shape moving the actin filament along it
As a result ADP + Pi is released as it is no longer complementary
An ATP now fixes to the myosin head causing it to detach from the actin filament
ATP is hydrolysed back into ADP + Pi using ATP synthase so the myosin returns to its original shape
The myosin head reattaches to a binding site further along the actin - cycle repeats

19
Q

What are the 3 ways ATP can be produced for muscle contraction?

A

Aerobic respiration
Anaerobic respiration
ATP-phosphocreatine system

20
Q

What is the ATP-phosphocreatine system?

A

ADP + PCr -> ATP + Cr

Phosphocreatine during exercise provides a Pi molecule, which phosphorylates ADP to ATP, by turning into creatine

21
Q

During the sliding filament mechanism what is ATP hydrolysis needed for?

A

Releases energy to restore the original shape of the myosin head

Release energy to actively transport Ca2+ ions into the sarcoplasmic reticulum

Provides a source of phosphate to regenerate phosphocreatine stores when muscles are relaxed

AQA A-Level Biology 5-8 (13 decks)

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