Muscles (7.2)

Question 1

Describe the structure of a microfibril

Answer 1

Microfibrils consist of functional units called sarcomeres which are made of two proteins called actin and myosin

Question 2

Describe the structure of a sarcomere

Answer 2

Sarcomeres are contractile and consist of two proteins called actin (thin filament) and myosin (thick filament)

Question 3

Explain the role calcium ions in muscle contraction

Answer 3

Calcium ions are released for the sarcoplasmic reticulum after an action potential passes through. These move tropomyosin bands from blocking binding sites on actin. These enables myosin heads to bind to the sites creating a cross bridge

Question 4

Describe the sequence of events from the arrival of a nerve impulse at the neuromuscular junction to the contraction of a muscle

Answer 4

Action potential arrives at neuromuscular junction and causes the depolarization of the membrane. Depolarization sent across the membrane and causes the release of calcium ions from the sarcoplasmic reticulum into the sarcomere

Question 5

Explain what would need to happen in order to get a muscle to relax following a contraction

Answer 5

The release of ADP + P causes the myosin head to change shape and pulls the myosin fibre over the actin fibre. ATP then binds to the free myosin head releasing it from the actin binding site. ATP is then is then hydrolysed into ADP + P causing the myosin head to return to its normal shape