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physio exam 3 > Muscle physiology > Flashcards

Muscle physiology Flashcards

1
Q

Muscles contract (develop tension and shorten) to achieve what?

PMPE

A
  • purposeful movement (lift up object, walk)
  • manipulation of external objects (drive)
  • propulsion of contents through hollow internal organs (circulation, digestion) (heart pumping blood)
  • emptying contents of certain organs to external environment (urination, child birth) (food you eat moving through digestive system)
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2
Q

Based on location what are the types of muscle?

A

Skeletal, cardiac, smooth

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3
Q

How much body weight is composed of skeletal muscle in women? men?

A

in women 32% of the body weight is skeletal muscle, 40% in men

cardiac and smooth compose the other 10% of muscle

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4
Q

What are the types of muscle based on striations?

A

striated, unstriated

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5
Q

What are striated muscles, what do they look like under a light microscope?

A

striated muscles have dark and light bands under a light microscope; cardiac and skeletal muscles are striated

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6
Q

What are unstriated muscles?

A

They do not have banding; smooth muscles are unstriated

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7
Q

What are the two types of muscles based on control?

A

voluntary and involuntary

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8
Q

Which muscles are voluntary?

A

skeletal (somatic innervation) - we decide when to walk or pick up an object

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9
Q

Which muscles are involuntary?

A

cardiac and smooth (autonomic innervation) - heart beating

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10
Q

Why do men have more skeletal muscle than women?

  1. they work out more
  2. they have less body fat
  3. testosterone is responsible for it
A

3

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11
Q

What are skeletal muscles?

A

they are many muscle fibers that lie parallel to one another and are bundled together by connective tissue

muscle fiber = muscle cell

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12
Q

What are the two defining characteristics of skeletal muscles?

A

they are multinucleated and have multiple mitochondria

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13
Q

Why are skeletal muscles multinucleated?

A

During embryonic development multiple cells fuse together forming the skeletal muscles

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14
Q

What is the purpose of having multiple mitochondria in skeletal muscle?

A

production of energy which is needed for contraction

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15
Q

What is a tendon?

A

it is connective tissue that connects muscle to bone

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16
Q

What are the three layers of skeletal muscle?

A

epimysium
perimysium
endomysium

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17
Q

What is the epimysium?

A

connective tissue that covers the entire muscle

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18
Q

What is the perimysium?

A

tissue that covers a group of muscle fiber

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19
Q

What is the endomysium?

A

tissue that covers each muscle fiber

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20
Q

What are the contractile elements in a muscle cell/fiber?

A

myofibrils

they constitute 80% of myofibril volume

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21
Q

A muscle cell/fiber has a regular arrangement of thick and thin filaments, why are they referred to as thick and thin?

A

they differ in diameter

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22
Q

What is actin in a muscle cell?

A

the thin filaments

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23
Q

What is myosin?

A

a thick filament

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24
Q

Starting with a whole muscle what is the process of components?

A

whole muscle -> muscle fiber/cell -> myofibril -> thin filaments (actin) and thick filaments (myosin)

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25
Q

What are sarcomeres?

A

a functional unit of the myofibril

- the smallest unit that can perform contraction

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26
Q

Where are sarcomeres found?

A

between two z-lines

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27
Q

What do sarcomeres consist of?

A

actin and myosin

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28
Q

There are four regions of sarcomeres, what are they?

A
  • A band
  • H zone
  • M line
  • I Band
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29
Q

What is an a-band?

A

it is where myosin (thick) filaments are stacked along with parts of actin (thin filaments)

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30
Q

What is an H zone?

A

myosin in the center of the A band - devoid of actin!

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31
Q

What is the M line in a sarcomere?

A

it extends vertically down the center of the A band to provide support

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32
Q

What is an I band?

A

it has a section of actin (thin filaments) that doesn’t project into the A band

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33
Q

How do muscle cells increase in length as we age?

  1. sarcomeres become longer
  2. new muscle cells are made in the body replacing older ones
  3. more sarcomeres are added on existing muscles
A

3

34
Q

What is a thick filament composed of?

A

several HUNDRED myosin molecules (thick filaments)

35
Q

What is the structure of myosin?

A

myosin is composed of two identical subunits (shaped like a golf club), the heads form cross bridges and the tail ends are intertwined, oriented toward the center

36
Q

What is a cross bridge in a thick filament(myosin)

A
  • it is formed by the heads of myosin that associate with actin
  • they can be seen under an electron microscope
  • they extend from thick to thin filaments
  • they attach to actin binding sites
  • they possess myosin ATPase (break atp to ADP +Pi and release energy) activity
37
Q

What are the three components of thin filaments?

A

actin, troponin and tropomyosin

38
Q

What is the structure of actin?

A

joined into two twisted strands to form filament backbone, each molecule has a binding site for a myosin cross bridge

39
Q

What is the structure of tropomyosin?

A

thread-like, covers the actin binding sites, preventing their association with myosin cross bridges

40
Q

What is the structure of troponin?

A

it has three polypeptide units for binding to tropomyosin, actin and Ca2+ ions

41
Q

How are troponin and tropomyosin similar?

A

they are regulatory proteins which regulate skeletal muscle contraction

42
Q

Actin and myosin are contractile proteins, but do they actually undergo a contraction?

A

no

43
Q

What is G-actin?

A

globular, think of individual pearls - free actin molecules with a binding site for attachment with myosin cross bridge

44
Q

What is f-actin?

A

g-actin joined together, two twisted strands - an actin helix (pearl necklace/two strands of peals)
f = filament

45
Q

What does tropomyosin cover?

A

the sites responsible for binding to myosin (the actin binding sites)

46
Q

If tropomyosin is covering the sites on actin molecules does a muscle contraction occur? Why or why not?

A

No because the cross bridges of myosin cannot associate with actin

47
Q

When calcium if present in the muscle fiber what happens?

A

Troponin can bind to the calcium and cause a conformational change which causes tropomyosin to slip away which exposes the actin binding sites

48
Q

What is a power stroke?

A

When actin bends inwards and brings about a contraction

49
Q

What is the mechanism of skeletal muscle contraction?

A

The sliding filament mechanism

50
Q

What is the sliding filament mechanism?

A
  • cycles of cross bridge binding and bending pull thin filaments inward (power stroke)
  • z-lines come closer, sarcomere shortens and so the muscle shortens (contracts)
    • the h-zone and i-band decrease, A band is unaffected
51
Q

During muscle contraction do actin and myosin change?

A

NO they stay the same they just come closer together - slide on top of eachother

52
Q

What are the repeated cycles of muscle contraction?

A

binding, power stroke, detachment, binding etc

53
Q

What happens during muscle contraction?

A
  • binding: myosin cross bridge binds to actin molecule
  • power stroke: myosin cross bridge bends, pulling the actin inward
  • detachment: the cross bridge detaches at the end of a power stroke and returns to original conformation
54
Q

The process of muscle contraction is synchronous, true or false?

A

FALSE it is asynchronous, all cross bridges are not simultaneously binding with actin and performing power strokes at the same time

Think of climbing a rope, you do not let go with both hans at the same time

55
Q

During skeletal muscle contraction, what exposes actin cross bridge binding sites?

A

troponin and tropomyosin

56
Q

What causes actin cross bridge binding sites to be exposed during muscle contraction?

A

it is a response to increase in Ca2+

57
Q

In what direction is a power stroke directed towards?

A

the center of the thick filament

58
Q

During a power stroke how many thin filaments are pulled inwards simultaneously?

A

all 6 thin filaments

59
Q

Where does the calcium come from that causes a skeletal muscle contraction?

A
  • Ach is released at NMJ (efferent) -> generation of AP in muscle -> role of t tubules and sarcoplasmic reticulum
60
Q

What is excitation contraction coupling?

A

A series of events that are linked to muscle contraction, Ca2+

61
Q

What are transverse tubules?

A

they are dips of surface membrane into muscle fiber at the junction of the A-band and I-band, the action potential travels down them rapidly inducing permeability changes in the sarcoplasmic reticulum

62
Q

What is the sarcoplasmic reticulum?

A

a modified endoplasmic reticulum, it forms a network around myofibrils, has lateral sacs (terminal cisternae) which store Ca2+ that is release by action potentials

63
Q

Put the process of skeletal muscle contraction in order:

a. Calcium binds to troponin, moves tropomyosin aside
b. AP at NMJ releases Ach which binds to receptors at MEP
c. myosin cross bridges attach to actin, power stroke
d. Calcium actively taken up by SPR in absence of AP
e. AP generated and propagated across muscle and down T tubule
f. AP in T tubule releases calcium from SPR
g. tropomyosin slips back, actin slips back to resting position

A

b, e, f, a, c, d, g

64
Q

how does a contraction stop?

A

when there is no more calcium present the muscle relaxes

65
Q

What is the role of ATP in a skeletal muscle contraction?

A

myosin cross bridge has ATPase activity (ATP -> ADP + Pi), Mg2+ is important (cofactor to split atp to adp + pi),
ADP and Pi bound to myosin, energy used stored in cross bridge, power stroke on binding site of actin -> ADP + Pi released

66
Q

What is rigor mortis?

A

stiffness of death

67
Q

When does rigor mortis begin?

A

3-4 hours after death

68
Q

How long does it take rigor mortis to complete?

A

12 hours

69
Q

What causes rigor mortis?

A

the inability of actin-myosin complex to dissociate due to lack of ATP

70
Q

What happens to calcium during death?

A

all of the calcium in lateral sacs is released which leads to a power stroke but there is no more fresh ATP present so muscles remain in a contracted state - rigor mortis

71
Q

What are the two main steps of skeletal muscle contraction?

A
  • calcium returns into sarcoplasmic reticulum

- contractile activity outlasts electrical activity

72
Q

How is calcium returned to the SPR during muscle relaxation?

A
  • absence of Ach at NMJ terminates action potential at muscle cell
  • calcium actively taken up by SPR via Ca2+ ATPase pump (carrier protein - energy is required!!)
  • troponin- tropomyosin complex slips back
  • actin-myosin no longer able to bind at cross bridges
  • actin slips back to resting position (tropomyosin covers binding sites again)
73
Q

Why does muscle contractile activity outlast the electrical activity?

A

because an action potential only lasts 1-2msec while a muscle contraction lasts for 100 msec (50-msec contract, 50 msec relax) there is a latent period between action potential and muscle contraction

  • important for contractions of variable strength
74
Q

What type of contraction does a single action potential produce?

A

a brief, weak contraction: twitch too short and too weak to be useful (not able to perform any work)

75
Q

How do muscles work together to produce useful contractions of varying strength (what two factors do they adjust)?

A
  • number of muscle fibers contracting within a muscle: depend on extent of motor unit recruitment
  • tension developed by each fiber: frequency of stimulation, length and thickness of fiber, extent of muscle fatigue
76
Q

What is a motor unit?

A

one motor neuron and innervated muscle fibers distributed evenly

77
Q

What does muscle tension depend on?

A

The size of the muscle (larger muscle = more tension)
The extent of the motor units involved
Size of motor units (fine vs. coarse)

78
Q

How is muscle fatigue prevented?

A

by asynchronous recruitment of motor units (shifts)

shifts prevent fatigue of the entire muscle

79
Q

What do small motor units control?

A

small muscles which cause small increases in tension = fine movement

80
Q

What do large motor units control?

A

large muscles which cause large increases in tension -> coarser movement

physio exam 3 (6 decks)

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