Intro to Muscle

Question 1

What is the I band?

Answer 1

Thin filament, actin

Question 2

What is the A band?

Answer 2

Thick filament, myosin

Question 3

What is the length-tension relationship?

Answer 3

. Force of contraction of sarcomere depends on overlap between actin and myosin filaments
. At full stretch, not many myosin heads have access to actin, so the force of contraction is weak
. At optimum length, all the myosin heads have access to the actin filament

Question 4

Which muscle types are striated? Why are they described this way?

Answer 4

Skeletal and cardiac muscle are striated. It is the Z-lines which create the striped appearance.

Question 5

Which type of muscle has fibres in syncytium and which has single mono or di-nucleated cells with limb-like extensions?

Answer 5

. Skeletal muscle has fibres in syncytium
. Cardiac muscle has single mono or di-nucleated cells with limb-like extensions which connect cells together by intercalated discs.

Question 6

Describe smooth muscle contraction.

Answer 6

Actin filaments are pulled across each other in an antiparallel way so that the muscle length shortens dramatically and also increases in diameter

Question 7

Why can smooth muscle contract further than striated muscle?

Answer 7

The thick filaments hit the Z-lines in striated muscle

Question 8

What is EC coupling?

Answer 8

. Excitation- Contraction Coupling

. Steps between AP and actin-myosin interaction

Question 9

Describe EC Coupling in striated muscle

Answer 9

.AP travels along sarcolemma, runs down T-tubules, then causes release of calcium ions from sarcoplasmic reticulum
. Calcium binds to troponin on actin and moves tropomyosin out of the myosin binding site

Question 10

Describe EC Coupling in smooth muscle

Answer 10

. AP triggers influx of calcium through membrane
. Calcium binds to calmodulin, which causes phosphorylation of myosin via light chain kinase
. This frees the myosin heads to bind to actin