Topic 7: Muscles and joints

Question 1

Describe the structure and function of smooth muscle

Answer 1

• non striated
• spindle shaped
• uninuclear fibres
• involuntary
• in walls of internal organs

Question 2

Describe the structure and function of cardiac muscle

Answer 2

• striated
• branched
• uninuclear fibres
• involuntary
• walls of the heart

Question 3

Describe the structure and function of skeletal muscle

Answer 3

• striated
• tubular
• multinuclear fibres (cells)
• voluntary
• attached to skeleton

Question 4

What is a tendon?

Answer 4

joins muscles to bones

• white fibrous tissue
• bundles of collagen fibres
• inelastic

Question 5

What is a ligament?

Answer 5

elastic tissue that holds bones to bones

Question 6

What is cartilage?

Answer 6

tissue at the ends of bones, made of chondrocytes and collagen, to prevent bone erosion

• elastic
• shock absorber

Question 7

How do muscles allow movement?

Answer 7

antagonist pairs which work in opposite directions:

• flexor (reduces angle)
• extensor (straightening)

Question 8

What is a synovial joint?

Answer 8

bones separated by synovial fluid, allowing free movement

Question 9

Describe the structure of a section of skeletal muscle

Answer 9

bundles of muscle fibres with myocytes (single muscle cells)

Question 10

Describe the structure of a myocyte

Answer 10

• multi-nucleate
• made up of contractile myofibrils
• sarcolemma, sarcoplasm, sarcoplasmic reticulum
• sarcosomes (mitochondria) for ATP

Question 11

What are myofibrils?

Answer 11

bundles of myofilaments, which are repeated chains of sarcomeres

Question 12

What is the thick filament in myofibrils?

Answer 12

myosin

Question 13

What is the thin filament in myofibrils?

Answer 13

actin

Question 14

What are A bands?

Answer 14

dark bands contain thick myosin and overlapping thin actin

Question 15

What are I bands?

Answer 15

light bands containing only thin actin filaments

Question 16

What is the Z line?

Answer 16

sarcomeres are joined here

Question 17

What is the M line?

Answer 17

middle of the myosin filaments

Question 18

What does the H zone contain?

Answer 18

only thick myosin filaments

Question 19

What is the sliding filament theory?

Answer 19

myosin and acting slide over each other, shortening the length of the sarcomere

Question 20

What happens to the I band in contraction?

Answer 20

gets shorter

Question 21

What happens to the A band in muscle contraction?

Answer 21

stays the same

Question 22

What happens to the H zone in contraction?

Answer 22

gets shorter

Question 23

What happens when muscles are relaxed?

Answer 23

• no Ca2+ so tropomyosin blocks the myosin binding site on actin
• myofilaments can’t slide past each other as heads can’t bind

Question 24

How is muscle contraction triggered?

Answer 24

• nerve impulse reaches axon terminals at neuromuscular junction
• depolarises sarcolemma and spreads to sarcoplasm
• neurotransmitter released and binds to receptors on muscle cells
• Ca2+ released from sarcoplasmic reticulum

Question 25

How do muscles contract?

Answer 25

1 - Ca2+ binds to troponin and pulls tropomyosin away from binding site
2 - Myosin head (ADP + Pi) attaches to actin, forming cross bridge
3 - Pi released, causing power stroke: myosin pulls on actin
4 - ADP released
5 - ATP binds to myosin head and cross-bridge detaches
6 - Myosin ATPase hydrolyses ATP to ADP + Pi so it has energy