muscles

Question 1

why is muscle often called striated?

Answer 1

dark bands are visible across the myofibrils within the
muscle fibres, separated into sarcomeres.

Question 1

structure of muscles

Answer 1

Skeletal muscle is composed of many muscle fibres bound together.
Each muscle fibre is a long thin single cell containing several nuclei.
Each muscle fibre is surrounded by a cell membrane called a sarcolemma.
The cell contains cytoplasm called sarcoplasm, which contains many mitochondria to produce ATP for muscle contraction, via aerobic respiration.
The cell also contains a large number of myofibrils which run parallel to each other along the length of the cell.
Each myofibril is surrounded by sarcoplasmic reticulum.
Each myofibril is made up of protein filaments, these are divided into myosin (thick) and actin (thin) filaments.
These myofilaments are arranged into repeating units called sarcomeres

Question 2

draw + label a sarcomere

Answer 2

Question 3

describe sliding filament theory (visual)

Answer 3

During muscle contraction each sarcomere shortens, bringing the Z lines closer together, as the actin and myosin filaments slide over each other increasing the amount they overlap (the darkest part of the sarcomere)

Question 4

describe sliding filament theory (6 marks)

Answer 4

1. Voltage gated calcium ion channels in the sarcoplasmic reticulum open and calcium ions diffuse into the myofibrils.
2. Calcium ions bind to troponin (protein) and cause tropomyosin (protein) to move exposing the myosin binding sites on the actin. Calcium ions also activate the enzyme ATP hydrolase, so ATP can be hydrolysed, to release energy.
3. Myosin heads bind to binding sites on the actin, forming actinomyosin bridges.
4. Energy released from the hydrolysis of ATP, causes the myosin head to move (the powerstroke), pulling the actin filament relative to the myosin filament.
5. The binding of a new ATP to the myosin head causes the myosin head to detach from the actin, breaking the actinomyosin bridge.
6. The myosin head moves back to its original position.
7. As long as calcium ions are present, the myosin head can bind again, further along the actin filament and perform another powerstroke.

Question 5

role of atp + phosphocreatine providing energy for muscle contraction

Answer 5

The muscle fibre can only store enough ATP to allow contraction for 3 or 4 seconds. Regeneration of ATP by anaerobic respiration takes about 10secs and by aerobic respiration even longer. Therefore the muscle fibre requires another method to regenerate of ATP to bridge this gap.
Muscle fibres have a store of phosphocreatine, which can donate a phosphate to ADP regenerating ATP quickly (also re-forming creatine in the process). When the muscle is relaxed, the phosphocreatine can be regenerated by adding a phosphate from ATP (made in aerobic respiration) back to creatine.

Question 6

describe slow muscle fibres

Answer 6

adapted for aerobic respiration
Produce slow sustained contractions over long time periods, but have a slower speed of contraction. They are used for endurance.
Muscles which contain many of this fibre type are slow to fatigue as delay onset of anaerobic respiration at lactic acid production.
in the muscles of the legs and those involved in maintaining posture.
1. Specialised to use aerobic respiration. So have lots mitochondria.
2. Closely associated with a large number of capillaries, to provide a large oxygen supply for aerobic respiration.
3. Less glycogen, as less glucose used in aerobic respiration to produce the same amount of ATP.
4. High concentration of myoglobin to store oxygen for aerobic respiration

Question 7

describe fast muscle fibres

Answer 7

adapted for anaerobic respiration
Produce rapid, strong contractions as have a faster speed of contraction, but only sustained over short time periods. Muscles which contain many of this fibre type fatigue quickly due to build up of lactic acid.
1. Have a store of phosphocreatine, to provide phosphate to generate ATP quickly in anaerobic conditions.
2. More glycogen as more glucose required to produce the same amount of ATP, as anaerobic respiration yields only 2 ATP per glucose.
3. Have thicker more numerous myosin fibres for more powerful contractions. 4. Have fewer mitochondria (as do less aerobic respiration). 5. Low concentration of myoglobin - as primarily anaerobic. 6. Fewer capillaries associated with fibres as less oxygen required (as less aerobic respiration