Muscle

Question 1

What is a DNA unit?

Answer 1

volume of cytoplasm controlled by one nucleus

Question 2

What is a fibril enveloped by?

Answer 2

sarcoplasmic reticulum (loosely)

Question 3

What is the structural hierarchy of a fascicle?

Answer 3

• endomysium surrounds fibers
• fibers made up of fibrils
• fibrils made up of thin & thickfilaments

Question 4

What causes tropomyosin to change shape so that actin can bind to myosin?

Answer 4

calcium binding at all 4 sites on TnC

Question 5

What does TnT do

Answer 5

joins troponin and tropomyosin

Question 6

Which filaments are longer?

Answer 6

thick

Question 7

Why doesn’t the A band change length?

Answer 7

it is the length of the myosin filament, which does not change length during contraction

Question 8

Why does the sarcomere change length?

Answer 8

because the Z lines get pulled toward M plate during contraction

Question 9

Why does the H band change length?

Answer 9

• it’s the region of myosin filament that does not overlap with actin filament (center of sarcomere)
• the myosin heads bring the actin filaments closer to the M plate which makes region of non-overlap smaller

Question 10

What is the I band?

Answer 10

region of actin filament that is not overlapping myosin

Question 11

What binds myosin filaments to z-disks?

Answer 11

titin

Question 12

Which protein appears to prevent sarcomere from overstretching?

Answer 12

titin

Question 13

Which protein appears to anchor sarcomeres to adjacent structures and maintains overall structural integrity?

Answer 13

dystrophin

Question 14

What binds the thin filaments to z-disks and what protein reinforces that attachment?

Answer 14

actinin; nebulin

Question 15

What protein regulates the length of the thin filaments?

Answer 15

tropomodulin

Question 16

Which proteins hold thick filaments in register at the M line?

Answer 16

c-proteins and myomesin

Question 17

What is the cause and manifestation of myasthenia gravis? How is it treated?

Answer 17

• dysfunction of nicotinic receptors at NMJ
• commonly affecting respiration and ocular muscles
• therapy to elevate Ach or immunosuppressants (steroids)

Question 18

What is meant by isometric contraction?

Answer 18

muscle contracts but does not shorten & fails to move load

Question 19

What is meant by isotonic contraction?

Answer 19

muscle shortens as tension remains constant (force greater than load)

Question 20

What is meant by eccentric contraction?

Answer 20

muscle lengthens (extends) as tension remains constant

Question 21

What is a motor unit?

Answer 21

motor neuron and all the muscle cells innervated by it

Question 22

What are plaques in smooth muscle?

Answer 22

point at which thin filaments attach to myocyte membrane

Question 23

Describe single-unit smooth muscle.

Answer 23

• fibers will contract uniformly (due to gap junctions)
• force of contraction varies with calcium concentration
• visceral muscle

Question 24

How can single-unit muscle be induced to contract?

Answer 24

• a variety of chemicals (e.g. hormones)

- mechanical stimulation (stretch)

Question 25

What are varacosities?

Answer 25

where neurotransmitter is released through into the wide synaptic cleft

Question 26

Describe multi-unit smooth muscle.

Answer 26

• fibers are innervated independently of each other

- force of contraction varies with recruitment of fibers

Question 27

Where can single-unit smooth muscle be found?

Answer 27

• GI tract
• bladder and ureters
• most arteries (not in large, elastic arteries)

Question 28

Where can multi-unit smooth muscle be found?

Answer 28

• intrinsic muscles of eye

- some portions of reproductive tracts

Question 29

What are the names of the two voltage-gated calcium channels in skeletal muscle contraction?

Answer 29

• DHP

- ryanodine receptors