PoH: Skeletal, Smooth and Cardiac Muscle

Question 1

Describe the 3 structural features of skeletal muscle

Answer 1

· Nuclei on peripheries
· Multinucleate
· Fibres are 10-100 micrometres diameter, up to 20cm long

Myoblasts in fetus, but not when born

Question 2

Describe the 4 features of skeletal muscle’s ultrastructure

Answer 2

· Bundles of muscle fibre in connective tissue sheathes with other tissue and fat
· Attached to bone by tendons
· Satellite cells replace damaged cells by differentiating into fibres. Other fibres undergo hypertrophy to compensate
· Is red as contains blood vessels to allow good blood supply to get energy and offload CO2

Question 3

Sketeletal muscle is made of bundles of what, which is made from what, which is made from what?

Answer 3

Muscle made of fascicles
Fascicles made of single muscle fibre (cells)
Fibres made of myofibrils

Question 4

What happens if bodybuilders gain muscle too quickly?

Answer 4

Ischemia (interruption of blood supply)

Question 5

What is the basic repeating unit that allows muscle to contract?

Answer 5

Sarcomere

Question 6

What are thin filaments in muscle called?

Answer 6

Actin

Question 7

What are thick muscle fibres called?

Answer 7

Myasin.

Question 8

How do actin and myasin interact?

Answer 8

Actin filaments are interdigitating (sliding between) myosin filaments

Question 9

Are cross-bridge heads found on actin or myosin?

Answer 9

Myosin

Question 10

What is the x-bridge head made of?

Answer 10

Actin binding sites
ATP binding site
Light chains
Heavy chains

Question 11

What shape do actin filaments form?

Answer 11

Hexagon

Question 12

What shape do myosin filaments form?

Answer 12

Triangle

Question 13

What is titin?

Answer 13

Makes sure myosin stays between actin filaments and doesn’t go too far from the Z lines. It acts like a guide spring or ropes

Question 14

When a muscle is shortened, what happens to A bands, I bands and the H zone?

Answer 14

A band - unchanged
I band - reduced
H zone - reduced

Question 15

What theory describes how muscle contract and relaxes?

Answer 15

Sliding-filament theory

Question 16

When muscle is contracted what happens to myosin and actin?

Answer 16

Myosin stays the same

Actin slides between, shortening the muscle.

Question 17

Name the 4 steps of the x-bridge cycle

Answer 17

1. Detachment
2. Hydrolysis
3. Cross bridge
4. Power stroke

The myosin heads latch onto the actin molecule binding sites, then flip and pull the sarcomere into a smaller contractive pattern

Question 18

Which molecule starts to rise to form the x-bridge?

Answer 18

Ca2+

Question 19

Contraction means the space between what gets smaller?

Answer 19

Z line and myosin

Question 20

When does actin detach?

Answer 20

When new ATP binds to myosin head

Question 21

What 3 molecules regulate the x-bridge cycle?

Answer 21

Troponin
Tropomyosin
Ca2+

Question 22

How do troponin, tropomyosin and Ca2+ regulate the x-bridge cycle?

Answer 22

· Tropomyosin partially covers the myosin binding site
· Troponin holds tropomysin in position (cooperative block) to block the myosin binding site
· Ca2+ binds to troponin
· Troponin alters shape, pulling tropomysin away
Ca2+ is removed, blocking the site again

Question 23

What can we measure to check for heart-attacks? It relates to x-bridge cycle

Answer 23

Cardiac troponin level

Question 24

What graph describes the %of muscle length vs the % of max isometric tetanic tension?

Answer 24

The length-tension relationship

Question 25

What’s the % of muscle length that generates the most amount of isometric tension?

Answer 25

Optimum length

Question 26

If you stretch muscle, what does it do to compensate?

Answer 26

Try to contract back. The more force, the stronger the contraction

Question 27

If muscle is overstretched, what’s happening to the muscle?

Answer 27

Actin and myosin no longer overlap, so x-bridge heads can’t bind to actin

it generates less tension

Question 28

If muscle’s filaments are too close together, what’s happening to the muscle?

Answer 28

Actin and myosin inteferes with each other and some binding sites are not easy to access for actin

Question 29

Describe agonist/antagonist and what makes it beneficial?

Answer 29

Another feature that makes muscles strong is their arrangement as a lever system – one muscle flexes and its antagonist extends. It amplifies muscle shortening velocity, producing increased manoeuvrability.

Question 30

Define excitation-contraction coupling

Answer 30

converting a command from a nerve cell into mechanical force (contraction in the muscle)

Question 31

How is calcium stored in muscle?

Answer 31

Sarcoplasmic reticulum