PACK 27: MUSCLE CONTRACTION

Question 1

What are the three types of muscle in the body?

Answer 1

• Skeletal muscle
• Smooth muscle
• Cardiac muscle

Skeletal muscle is voluntary, smooth muscle is involuntary, and cardiac muscle is myogenic.

Question 2

What is the primary function of skeletal muscle?

Answer 2

Used for locomotion

Skeletal muscle contracts rapidly and fatigues quickly.

Question 3

What is the structure of myofibrils as viewed under an electron microscope?

Answer 3

Display repeated light and dark bands

Dark bands (A bands) consist of thick myosin filaments and overlapping thin actin filaments.

Question 4

What are the components of a sarcomere?

Answer 4

• Z lines
• A bands
• I bands
• H zones
• M lines

The distance between Z lines defines a sarcomere.

Question 5

What is the role of myosin in muscle contraction?

Answer 5

Forms thick filaments and creates actinomyosin bridges with actin filaments

Myosin heads change angle to pull actin filaments.

Question 6

What happens to the distance between Z lines during muscle contraction, and why?

Answer 6

Distance between Z lines shorter

This is due to the sliding of actin filaments over myosin filaments.

Question 7

What triggers the release of acetylcholine at the neuromuscular junction?

Answer 7

An action potential reaches the neuromuscular junction

Acetylcholine binds to receptors on the muscle cell membrane.

Question 8

What is the sliding filament theory?

Answer 8

Myosin heads pull actin filaments over myosin filaments to contract the sarcomere

This involves the formation and breaking of actinomyosin bridges.

Question 9

Fill in the blank: ATP hydrolysis provides the energy for the _______.

Answer 9

Power stroke

The power stroke is when myosin heads pull actin filaments.

Question 10

What is rigor mortis and why does it occur?

Answer 10

Muscles stiffen due to lack of ATP production after death

Existing cross bridges stay in place without ATP to detach myosin heads.

Question 11

Describe the role of calcium ions in muscle contraction.

Answer 11

Calcium ions bind to troponin, causing tropomyosin to move and expose myosin binding sites on actin

This allows cross bridge formation between actin and myosin.

Question 12

What is the function of phosphocreatine in muscle contraction?

Answer 12

Provides phosphate to regenerate ATP

Phosphocreatine is used for immediate energy supply during short bursts of activity.

Question 13

What distinguishes slow twitch fibers from fast twitch fibers?

Answer 13

• Slow twitch: sustained contractions, more mitochondria
• Fast twitch: rapid powerful movements, fewer mitochondria

Fast twitch fibers fatigue quickly while slow twitch fibers are more resistant to fatigue.

Question 14

What is the source of ATP for fast twitch fibers?

Answer 14

Glycolysis (anaerobic)

Fast twitch fibers rely on quick energy release.

Question 15

What is the structural difference between fast and slow twitch fibers?

Answer 15

• Fast fibers: large diameter, fewer capillaries
• Slow fibers: small diameter, more capillaries

This affects their oxygen supply and endurance capabilities.

Question 16

True or False: The neuromuscular junction can be both excitatory and inhibitory.

Answer 16

False

The neuromuscular junction is only excitatory.

Question 17

What happens to muscle contraction when nervous stimulation ceases?

Answer 17

Calcium ions are actively transported back into the sarcoplasmic reticulum

This causes tropomyosin to block myosin binding sites and the muscle relaxes.

Question 18

What are the three stages of ATP supply during muscle contraction?

Answer 18

• ATP hydrolysis
• ATP/Phosphocreatine system
• Glycolysis
• Oxidative Phosphorylation

Each stage provides energy for different durations and intensities of muscle activity.