Lecture 4 - Skeletal Muscle Contraction

Question 1

What is connective tissues surrounding the entire muscle?

Answer 1

Epimysium

Question 2

What is made up of multiple fascicles?

Answer 2

Muscle

Question 3

What is connective tissue surrounding individual fascicle?

Answer 3

Perimysium

Question 4

What is a bundle of myofibers?

Answer 4

Fascicle

Question 5

What is delicate connective tissue around each myofiber?

Answer 5

Edomysium

Question 6

What is the cell membrane of each muscle fiber called?

Answer 6

Sarcolemma (=plasmalemma)

Question 7

What is an individual multinucleated muscle cell called?

Answer 7

Myofiber

Question 8

What is a chain of sarcomeres within a myofiber?

Answer 8

Myofibril

Question 9

What is actin and myosin filaments that make up a sarcomere called?

Answer 9

Myofilament

Question 10

What anchor actin filaments and are located at the end of a sarcomere?

Answer 10

Z discs (Z lines)

Question 11

What are composed entirely of actin and change their width during contraction?

Answer 11

I bands

Question 12

What are composed of actin and myosin and do not change their width during contraction?

Answer 12

A bands

Question 13

What are composed entirely of myosin and change their widths during contraction?

Answer 13

H bands

Question 14

What are responsible for the banding pattern characteristic of striated muscle?

Answer 14

Sarcomeres alignment

Question 15

Describe the sequences LEADING UP TO the sliding filament mechanism.

Answer 15

1) Action potential arrives
2) Voltage gated calcium channels open
3) Ach released into synaptic cleft
4) Opening of ligand gated sodium channels
5) Action potential occurs
6) Voltage gated T-tubules interact with ryanodine receptors on SR membrane
7) Opening of Ryanodine-sensitive calcium ion release channels
8) Ca2+ increases in cytosol
9) activation of sliding filament mechanism

Question 16

Describe the sequences after Calcium has been released in the cytosol to muscle contraction.

Answer 16

1) Calcium ions bind to troponin
2) Tropomyosin uncovers myosin binding sites on actin.
3) ATPase heads of myosin molecules split ATP and bind to actin.
4) Stored energy in myosin head causes deformation such that thick and thin filaments slide past one another.
5) A second ATP binds to myosin and causes it to release actin
6) process is repeated
7) contraction stops when ATP-dependent calcium pump sequesters calcium ions into SR.

Question 17

What causes conformational changes in the ryanodine receptors and are located on the sacrolemma T-tubules?

Answer 17

Dihydropyridine receptors (DHP)

Question 18

What open in response to conformational changes in the DHP receptors and allow calcium to flow into the cytosol from the SR?

Answer 18

Ryanodine receptors (RyRs or Ca2+ release channels)

Question 19

How many heads does each myosin molecule contain?

Answer 19

2

Question 20

Where is ATP required for muscle contraction? (3)

Answer 20

1) sliding filament mechanism (most)
2) pumping calcium from sarcoplasm back into SR
3) pumping sodium and potassium ions through the sarcolemma to reestablish resting potential.

Question 21

What type of contraction occurs when there is an increase in tension but not in length?

Answer 21

Isometric

Question 22

What type of contraction occurs when there is a change in muscle length? (2)

Answer 22

Isotonic contraction. Eccentric - lengthens, Concentric - shortens.

Question 23

What type of muscle has fewer mitochondria, primarily uses anaerobic respiration, and has a larger concentration of ATPase?

Answer 23

Fast(white), contract rapidly but have less endurance. Example: gastrocnemius

Question 24

What type of muscle has more mitochondria, primarily uses aerobic respiration, has more myoglobin, and smaller concentration of ATPase?

Answer 24

Slow(red), slow twitch fibers contract more slowly but have more endurance. Example: soleus