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physio- exam 1 > muscle > Flashcards

muscle Flashcards

1
Q

from the largest unit to the smallest unit- list the organization of skeletal muscle

A

whole muscle

fascicle

muscle fiber (cell)

myofibril

sarcomere

filament

protein

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2
Q

thin filaments are composed of two intertwined helical chains of what?

A

actin molecules

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3
Q

Troponin contains a binding site for _____

A

calcium ions (Ca2+)

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4
Q

troponin is comprised of what 3 subunits?

A

TnC

TnI

TnT

(Remember: Troponin looks like a “TIC” on a tropomyosin strand)

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5
Q

tropomyosin binds to actin at what sites?

A

cross-bridge binding sites

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6
Q

what is meant by “protein isoforms”?

A

Same protein but slightly different amino acid sequence

eg- myosin heavy and light chians

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7
Q

a _______ is one functional unit of the contractile apparatus

A

sarcomere

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8
Q

what is a sarcomere composed of?

A

thick filaments, thin filaments and z-lines

does not include any other organelles

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9
Q

_______ ions play a pivotal role in the activation of skeletal muscle

A

calcium

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10
Q

what structure of the muscle cell is responsible for the cytoplasmic uptake and release of calcium ions?

A

sarcoplasmic reticulum

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11
Q

t/f: the duration for an AP and for the shortening of a muscle fiber is similar

A

False- the shortening of a muscle fiber takes place much slower than the action potential

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12
Q

low cytosolic calcium will lead to a ____ muscle

A

relaxed

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13
Q

the energized cross-bridge cannot bind to _____ when Ca2+ is low

A

actin

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14
Q

once cyctosolic calcium levels are increased, the _________ are exposed

A

cross-bridge binding sites

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15
Q

what is the “sliding filament theory”?

A

muscle shortens by a relative sliding of thick and thin filaments.

-the filaments do not change length

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16
Q

when a muscle fiber is shortened, which sections are reduced? which are unchanged?

A

I band and H zone are reduced in length

A band remains unchanged (length of thick filaments)

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17
Q

the “cross-bridge theory”

A

-thick and thin filaments on sarcomeres are not connected at rest

  • cross-links form between the 2 types of filaments when the Ca2+ levels increase
  • —-these links are called “cross-bridges”
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18
Q

how does the cross-bridge theory explain filament sliding?

A

sliding is due to repetitive cross-bridge cycles

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19
Q

what is one cycle of cross-bridging?

A
  • myosin head attaches to actin
  • conformational change in myosin
  • simultaneous sliding of thin filaments relative to thick filaments
  • detachment of myosin (thick) and actin (thin)
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20
Q

what is the source of energy for muscle contraction?

A

ATP

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21
Q

the concentration of ATP inside muscle cells is buffered by ____________

A

phosphocreatine (PCr)

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22
Q

what are the 3 sources of ATP in muscle cells?

A
  • Creatine phosphate (1 ATP)
  • Glycolysis (3 ATP)
  • Oxidative Phosphorylation (2 ATP)
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23
Q

what is the basic observation that led to the discovery of the Length-tension relationship?

A

the amount of tension (force) that a muscle can generate when it is activated depends on its length

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24
Q

at what percent of muscle length do we see the largest isometric tetanic tension?

A

100%

anything less than, or greater than, this will cause a decrease in maximum tension

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25
Q

what does the Load-velocity relationship show?

A

a muscle can shorten at a higher velocity when moving a lighter load

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26
Q

what are the 2 types of isotonic muscle contractions?

A

1) constant length isotonic contractions

2) constant load isotonic contractions

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27
Q

Isometric contractions produced by multiple stimuli can create what types of contraction?

A

Unfused and fused tetanus

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28
Q

A __________ is the set of muscle fibers innervated by branches of a single motorneuron

A

single motor unit

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29
Q

T/F: motorneurons innervate one muscle fiber

A

False- motor neurons can innervate multiple muscle fibers

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30
Q

what is the range of muscle fibers that a single motor neuron can control?

A

100 fibers (in the fingers) up to 2,000 (in the leg)

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31
Q

Slow muscle fibers, compared to fast fibers, are:

A

1) smaller in diameter
2) have smaller neuromuscular junctions
3) contain different sarcomere protein isoforms
4) contract more slowly
5) are more fatigue resistant

32
Q

slow fibers are referred to as ______ fibers

A

type 1

33
Q

muscles that are utilized for maintaining posture have a higher proportion of type ___ fibers, where as muscles for rapid tasks involving dexterity use type ___ fibers

A

posture- type 1

rapid/dexterity movements- type 2

34
Q

what is the difference between type 1 and type 2 fibers? type 3 fibers?

A

type 1- slow-oxidative fibers

type 2- fast-oxidative fibers

type 3- fast-glycolytic fibers

35
Q

what factors can contribute to skeletal muscle craps?

A
  • dehydration
  • metabolic- low sodium, magnesium, calcium, glucose, potassium
  • endocrine- Thyroid, adrenal insufficiency
  • pregnancy
  • drugs & toxins
36
Q

what is the most common form of muscular dystrophy? what population does it effect?

A

Duchenne muscular dystrophy

effects males (x-linked, recessive)

37
Q

what differentiates a cardiac sarcomere from a skeletal sarcomere?

A

thin filaments in cardiac sarcomeres are not all the same length

38
Q

which myosin heavy chain is found in both cardiac and skeletal muscle? which is found only in cardiac muscle?

A

Beta chain- both cardiac and skeletal

Alpha chain- not normally found in skeletal muscle
found in the masseter muscle

39
Q

_____ is not present in cardiac sarcomeres, which is one striking difference between cardiac and skeletal muscle

A

Nebulin

40
Q

while skeletal muscles attach to tendons, cardiac muscle cells are attached how?

A

end-on-end to each other

41
Q

what is the physical connection between cardiac muscle cells?

A

the intercalated disk

42
Q

________ are found in intercalated disks, which allow the rapid and direct transmission of action potentials between adjacent cells

A

gap junctions

43
Q

T/F: gap junctions use neurotransmitters to allow the rapid transmission of AP’s between cardiac muscle cells

A

FALSE- they are “electrical synapses” and do not involve chemical transmitters

44
Q

what is different about the AP between cardiac and skeletal muscle cells?

A

the cardiac AP has a “plateau” phase, which increases the refractory period between firing

45
Q

T/F: the speed of tension development in cardiac and skeletal muscle is roughly the same

A

FALSE- cardiac muscle cells produce tension much slower than skeletal muscle

46
Q

what is the purpose of the long refractory period in the Cardiac muscle AP?

A

it prevents the heart from undergoing a tetanic contraction, which could prevent the heart from functioning

47
Q

what ion influx is responsible for the “plateau” phase of the cardiac AP?

A

Calcium

-the calcium influx keeps the membrane potential higher, thus leading to the plateau, and the extended AP time

48
Q

how is Ca2+ removed from a cardiac cell after an action potential has been reached?

A

Ca-ATPase pump

Na/Ca exchanger- moves Na into the cell and Ca out

49
Q

which mechanism of Ca2+ removal is shared between skeletal and cardiac muscle?

A

the Calcium-ATPase pump (Ca-ATPase)

50
Q

T/F: smooth muscle cells are very small, and there is relatively little sarcoplasmic reticulum

A

True

51
Q

smooth muscle cells have “_________” which are homologous to the Z lines of sarcomeres in striated muscle

A

dense bodies

52
Q

all nerual innervation to smooth muscle is from the ______________, meaning it is normally involuntary

A

autonomic nervous system

53
Q

T/F: smooth muscle has a lesser range of cell lengths over which force can be generated (when compared to striated muscle

A

False- it has a greater range

54
Q

why is there virtually no fatigue in smooth muscle?

A

its rate of ATP splitting by myosin is 10-100 times lower than skeletal muscle

55
Q

what is the role of MLCK? (myosin light chain kinase)

A

binds to Ca-calmodulin and causes the contraction of myosin

phosphorylates myosin in order to contract

56
Q

_________, that dephosphorylates smooth muscle myosin, is continuously active.

A

Phosphatase

57
Q

what does dephosphorylation of myosin prevent?

A

prevents reattachment of myosin to actin

58
Q

what are the sources of Calcium ions for the activation of smooth muscle?

A

1) sarcoplasmic reticulum
2) extracellular fluid

Note: the inward positive charge flow during smooth muscle Action Potential is carried by CALCIUM ions (not sodium)

59
Q

T/F: neurotransmitters are the only mechanism for smooth muscle control

A

False

  • pacemaker potential
  • neurotransmitters
  • hormones
  • local factors (pH, oxygen level, nitric oxide, stretch)
60
Q

how is calcium removed from smooth muscle cells? (hint: 3 mechanisms)

A

1) Calcium pump in the sarcolemma
2) Na/Ca exchanger
3) Sarcoplasmic reticulum

61
Q

what are the 2 types of smooth muscle?

A
  • Single-unit

- Multi-unit

62
Q

which type of smooth muscle is activated by stretch?

A

single-unit

63
Q

how wide is the neuromuscular cleft?

A

400 angstroms

twice the diameter of a synaptic vesicle

64
Q

what is the aptitude of a motor endplate potential?

A

Amplitude: 10 mV (remember: AP 130 mV)

65
Q

what is Nebulin? what is it used for by scientists?

A

Nebulin = thin filament protein – possibly a molecular ruler, to determine thin filament length.

66
Q

Ca2+ ions are sequestered (taken up) by the _____________ of the Sarcoplasmic Reticulum to cause relaxation.

A

fenestrated collar (central portion)

67
Q

what is a motor unit?

A

a single motoneuron and all of the of the muscle fibers it innervates

68
Q

Fast and slow fibers differ with respect to what?

A

to the relative contribution of the three pathways for ATP production.

69
Q

which type of muscle fiber, type 2a or 2b, is smaller?

A

2a

70
Q

what enzyme is constantly active in smooth muscle, and prevents contraction?

A

phosphatase

71
Q

Activation of smooth muscle results when the ______ activity is greater than the _______ activity.

A

the MLCK activity is greater than the phosphatase activity.

72
Q

actin in smooth muscle can be dephosphorylated and remain attached in a _____ state with no movement of the cross-bridges.

what does this cause?

A

“rigor”

leads to a maintenance of force with very little ATP consumption, very high economy

73
Q

General characteristics of single-unit smooth muscle:

A

Electrical synapses (gap junctions)

Spontaneously active

Stretch-activated

Innervation is primarily restricted to pacemaker cells

(smooth muscle in intestinal tract, uterus, small diameter blood vessels.)

74
Q

general characteristics of multi-unit smooth muscle:

A

Each cell activated independently

Not spontaneously activated

Gap junctions are rare

(smooth muscle in large arteries, large airways.)

75
Q

Ca2+ ions are released from __________ of the SR to initiate contraction.

A

lateral sacs (terminal cisterna)

physio- exam 1 (8 decks)

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