3.8 Muscle structure

Question 1

How do muscles act in antagonistic pairs?

Answer 1

1 muscle contracts and the other relaxes.

Question 2

What is the skeletal muscle structure?

Answer 2

Muscle fibre
Myofibril
Myosin/actin

Question 3

How has each muscle cell been formed from several cells?

Answer 3

The plasma membrane separating them has broken down.

Question 4

What are the basic repeating units of myofibrils?

Answer 4

Sarcomere

Question 5

What are the 2 proteins found in myofibril?

Answer 5

Actin
Myosin

Question 6

What is actin + structure?

Answer 6

• A globular protein
• Forms a thin filament
• Anchored into the Z lines
• 2 chains of actin molecules twisted around each other
• Linked together to form long chains

Question 7

What is myosin + structure?

Answer 7

• A fibrous protein
• Forms a thick filament
• ‘Tails’ of myosin form the M line in the sarcomere
• Myosin molecules lie side by side

Question 8

Epimysium vs Perimysium in muscles

Answer 8

The epimysium is the fibrous tissue envelope that surrounds skeletal muscle.

Perimysium the sheath of connective tissue surrounding a bundle of muscle fibres.

Question 9

Why do muscle fibres have multiple nuclei?

Answer 9

Each muscle fibre has been formed from several cells; the plasma membranes separating them have broken down.

Question 10

What is the cytoplasm and endoplasmic reticulum called in muscle fibre?

Answer 10

Sarcoplasm
Sarcoplasmic reticulum

Question 11

What is the sarcomere?

Answer 11

The section in between 2 Z-lines

Question 12

What is the A band in skeletal muscles?

Answer 12

• Consists of both actin and myosin
• Contains the H zone in the centre

Question 13

What is the I band in skeletal muscles?

Answer 13

• Contains only actin, so appear light
  Contain Z line in the centre

Question 14

What is the H zone in skeletal muscles?

Answer 14

• Central strip in the A band
• Contain thick myosin filaments, so lighter than the rest of the A band.