Muscle Contraction

Question 1

Describe the structure of skeletal muscle

Answer 1

• hierarchical bundles of fibres and fascicles enveloped in connective tissues/ fascia
• long cylindrical multinucleate cells (fused myoblasts)
• each cell (fibre) composed of myofibrils
• myofibrils consist of repeated sarcomeres = the functional unit of striated muscle
• sarcoplasmic reticulum to store calcium needed for contraction

Question 2

What is the sarcomere made up of?

Answer 2

• thick and thin filaments (actin and myosin)

Question 3

What is the I- band?

Answer 3

• only actin

Question 4

what is the A- band?

Answer 4

• both actin and myosin

Question 5

What is the H-zone?

Answer 5

• only myosin

Question 6

What do the z-discs do?

Answer 6

• anchor actin filaments

Question 7

What is the M-line?

Answer 7

• network of cytoskeleton

Question 8

Describe the structure of myosin filaments

Answer 8

• 2 heavy and 4 light polypeptide chains
• with 2 globular heads, neck, and long tail
• heads contain enzyme myosin ATPase

Question 9

Describe actin structure

Answer 9

• thin filaments of intertwined actin monomers
• nebulin - rodlike molecule around which actin wraps
• tropomyosin - protein that blocks myosin head deform binding to site on actin
• troponin - small globular protein that binds to tropomyosin to enable myosin heads to bind

Question 10

What is titin?

Answer 10

• molecular spring holding myosin in optimal position

Question 11

Describe filament theory

Answer 11

• myosin heads bind to sites on actin
• binding forms cross-bridge
• myosin neck bends and exerts force (power stroke)
• release and repeat to climb or ratchet up
• myofilaments stay the same length but slide past
• sarcomere shortens due to increasing overlap of myofilaments

Question 12

What is the full name for ATP

Answer 12

• Adenosine Triphosphate

Question 13

What is ATP?

Answer 13

• energy-rich nucleotide used as a common energy currency by all cells

Question 14

How is ATP regenerated?

Answer 14

• from the phosphorylation of ADP

Question 15

What are the three methods of ATP production in a muscle cell

Answer 15

• oxidative phosphorylation in mitochondria (aerobic respiration)
• phosphorylation catalysed by creatine kinase enzyme in cytosol
• glycolysis in the cytosol (anaerobic respiration)

Question 16

Describe oxidative phosphorylation?

Answer 16

• requires steady supply of o2
• uses blood-borne fuels (glucose, fatty acids)
• can also use glycogen in muscle fuel
• slow/limited by blood supply to muscles
• resting or moderate activity
• generates 30 ATP molecules

Question 17

Describe Glycolysis

Answer 17

• first step in the break down of glucose
• doesn’t require o2
• only 2 ATP molecules from glucose
• lactic acid by-product
• relied on in intense exercise

Question 18

Types of muscle fibres are classified based off what?

Answer 18

• velocity of shortening (fast/slow)
• main pathway used to from ATP (glycolytic/aerobic)
• type I = oxidative
• type II (fast)
• type IIa (fast oxidative/glycolytic)
  type IIb (fast glycolytic)

Question 19

Oxidative fibres have lots of what?

Answer 19

• myoglobin
• good capillary supply
• many mitochondria = darker in appearance
• red muscle

Question 20

What effects what type of muscle fibre is most prominent?

Answer 20

• genetics (species/breed)
• training
• age
• diet

Question 21

How does muscle force vary with length?

Answer 21

• actin-myosin crossbridge cycling generates force
• also causes sarcomeres to change length
• there is an optimal sarcomere length - maximal overlap of myosin heads with actin
• active force, developed by actin-myosin interactions
• also a passive force (titin, connective tissues within and around muscle fibres)
• total force is sum of the active and passive forces