Animal Movement: Muscles

Question 1

What are striated muscles, list characteristics and examples in the body.

Answer 1

Striated muscles have a striped appearance due to the thick and thin filaments being arranged in organised arrays (stripes).
They are found in skeletal muscles (attached to the skeleton) i.e. hamstrings.

Question 2

What is the length in which thick myosin pulls along thin actin with each step to remain on the same plane?

Answer 2

36nm

Question 3

What is the degree of overlap (distance from Z-disc to Z-disc) between thick myosin and thin actin filaments called?

Answer 3

Sarcomere Length.

Question 4

What is the optimal sarcomere length for striated muscle?

Answer 4

2um

Question 5

Describe the sliding filament model.

Answer 5

1. ATP binds to thick myosin filaments and detaches from thin actin filaments.
2. Hydrolysis of ATP to ADP + P causes myosin to attach further down the actin filament.
3. The release of Phosphate (P) generates a power stroke in myosin, pulling the actin filament with it.
4. ADP is released and the cycle can then continue.

Question 6

What is a myofibril? Briefly describe.

Answer 6

The myofibril runs the length of the muscle cell and is a cylindrical structure encompassing all the sarcomeres.

Question 7

What is the advantage of sarcomeres being arranged parallel?

Answer 7

This is optimal for increased force, although has minimal shortening properties.

Question 8

What is the advantage of sarcomeres being arranged in a series (long)?

Answer 8

This has a greater capacity for shortening, although generates less force than parallel arrangements.

Question 9

The amount of force sarcomeres can generate is proportional to their cross-sectional area, what is the equation for this?

Answer 9

10 Newtons per cm-squared

Question 10

What are myofibres?

Answer 10

These are muscle cells, which are composed of bundles of myofibrils (which are composed of sarcomeres –> which are composed of thin and thick filaments in arrangement).

Question 11

What is the function of troponin and tropomyosin?

Answer 11

They are thin filament proteins that are bound together and lie on the actin filament. When Ca+ is present they roll out of the way to allow binding sites for myosin.
When Ca+ is low they move back to block binding sites.

Question 12

Explain the RELATIVE refractory period.

Answer 12

Once the muscle cell has partially repolarized, it is able to respond to a second stimulus, this period is sooner in skeletal as cardiac need to maintain a regular relaxed period for heart beats.

Question 13

What is an ABSOLUTE/EFFECTIVE refractory period?

Answer 13

This is the window in which muscles cannot be induced to contract again (by normal means) until the repolarization is nearly complete or has reached the “Relative” refractory period.

Question 14

What can be found more prevalently in fast-twitch muscles, and allows for the more effective flow of electrical impulses along the sarcomere to move deeper into the cell.

Answer 14

T-tubules (transverse tubules)

Question 15

What type of muscle (fast or slow twitch):
- are for endurance
- cannot supply a lot of power at once
- larger amounts of myoglobin and mitochondria
- primarily powered by oxidative phosphorylation

Answer 15

Slow-twitch

Question 16

What type of muscle (fast or slow twitch):
- are for bursts of strength and speed
- Fatigue quickly
- Have less myoglobin and mitochondria
- Greater ability for glycolysis than using oxygen

Answer 16

Fast-twitch

Question 17

What does excitation-contraction coupling in muscles with different speeds of contraction (slow, fast, faster) rely on?

Answer 17

Slow:
Ca2 + movement through (DHPR) is sufficient to trigger contraction.
Fast:
Increased reliance on the Sarcoplasmic Reticulum as a source of Ca2 +
Faster:
The SR and the t-tubules are localised to improve efficiency.