Paper 2- Musclesas Effectors

Question 1

What is skeletal muscle

Answer 1

Attached to tendons by bone. It contracts in response to the release of the neurotransmitter.
Acetylcholine from a motor neurone burning about movement of a bone at a joint

Question 2

What is the structure of skeletal muscle

Answer 2

• many muscle fibres bound together by connective tissue
• they are long and thin containing several nuclei
• each muscle fibre is surrounded by a thin cell membrane called a sarcolemma and it’s nuclei are found just beneath
• cell contains cytoplasm called sarcoplasm which contains many mitochondria
• contains many myofirbrils which run parrallel to each other the length of the cell
• each myofibril is surrounded by sarcoplasmic reticulum
• each myofibril is made up of myofilaments containing 2 protiens called myosin and actin
• these myofilaments are arranged into contractile units called sarcomeres

Question 3

How is a myofibril viewed under a microscope

Answer 3

• often called strained muscle as under a light microscope dark bands are visible across the muscle fibres
• under an electron microscope, dark bands are visible across each myofibril. Each sarcomere has a distinctive banding pattern due to the presence or absence of the thick and think filaments

Question 4

What is the sliding filament theory of muscle contraction

Answer 4

• 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 H zone dissapears, the I band narrows, the A band is always the same

Question 5

What happens in the sliding filament theory

Answer 5

1) calcium ions diffuse into myofibrils from sarcoplasmic reticulum
2) calcium ions cause ,movement of tropomyosin on actin, exposing the myosin head binding sites
3) myosin heads attach to binding sites on actin forming actinomyosin cross bridges
4) hydrolysis of ATP on myosin heads causes myosin head to bend
5) the bending of the myosin heads move the actin molecule inwards over the myosin
6) attachment of new ATP molecule to each myosin head causes myosin heads to detach from actin sites and seperates it from the actin, returning it to the original shape
7) process repeats, moving the actin along the a bit more each time
8) If stimulation ceases, then calcium ions are pumped back into the sarcoplasmic reticulum and tropomyosin returns to its original position

Question 6

What is the role of ATP in providing energy during contraction

Answer 6

-active transport of calcium ions into the muscle fibre
- contraction by bending the head and breaking actinomyosin cross bridges
However a muscle fibre can only store enough ATP to allow a contraction for 3-4 secs
Regeneration of ATP by anaerobic respiration takes 10 secs and by aerobic even longer

Question 7

What is the role of phosphocreatine in providing energy during contraction

Answer 7

Muscle fibres can store phosphocreatine which is a molecule providing phosphate and ADP regenerating ATP in short term
Phosphocreatine can be regenerated utilising ATP when it can be supplied via respiration

Question 8

What is a slow twitch muscle fibre

Answer 8

• produces slow, sustained contractions over a long time
• slower speed of contraction
• slow to fatigue
• found in muscles of the legs and involved in maintaining posture

Question 9

What are the characteristics of a slow twitch muscle fibre

Answer 9

• specialised to use aerobic respiration energy system to regenerate atp
• many large mitochondria, some just under the sarcolemma to provide atp for active transport, and some deep between the myofibrils
• high conc of myoglobin which acts as an oxygen store, gives red colour
• large number of capillaries, good blood supply
• less extensive sarcoplasmic reticulum as less calcium ions required at one time
• less glycogen as glucose broken down fully via aerobic respiration

Question 10

What are fast twitch muscle fibres

Answer 10

Produce rapid, strong contractions as have faster speed of co traction, only sustained over a short period of time
Fast to fatigue due to build up of lactate

Question 11

Characteristics of fast twitch muscle fibres

Answer 11

• specialised to use phosphocreatine ATP / anaerobic respiration energy systems to regenerate ATP
• fewer, smaller mitochondria
• low concentration of myoglobin as anaerobic so little oxygen required
• fewer capillaries associated with fibres
• extensive sarcoplasmic reticulum as more calcium ions required at one time for rapid intense contraction
• more glycogen as more glucose required as anaerobic respiration heiress less atp per glucose