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Flashcards in Physiology Deck (76)
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1
Q

What proteins make up the thick filament?

A

myosin heavy chain; 2 light chains/head

2
Q

**

Identify the thick and thin filaments.

A

*

3
Q

What innervates skeletal muscle?

A

motor neurons in ventral horn

4
Q

Each muscle fiber receives innervation from…

A

ONE motor neuron

5
Q

Small motor neuron cell bodies innervate…

These are a.k.a (fast/slow) motor units

A

few muscle fibers that generally have a small cross sectional diameter

*slow

6
Q

Large motor neuron cell bodies innervate…

These are a.k.a (fast/slow) motor units

A

many muscle fibers that generally have a large cross sectional diameter

*fast

7
Q

What are the components of a motor unit?

A

motor neuron

muscle fibers innervated by motor neuron

8
Q

What type of receptors are targeted by ACh at MEP?

A

nicotinic

9
Q

What type of channels are at the nerve terminal?

A

monovalent cationic channels

10
Q

What type of depolarizations are generated at the MEP?

A

graded

11
Q

How is an action potential generated at the MEP?

A
  1. many nicotinic receptors activated
  2. surrounding membrane depolarized
  3. Na channels activated
  4. AP initiated
  5. propagation along muscle fiber membrane (~unmyelinated axon)
12
Q

Why is AP propagation axial?

A

because muscle fiber has long length and small diameter

13
Q

What is the transverse tubule system?

A

invanginations of the cell membrane, which bring it in close contact with SR

14
Q

What is the “triad”?

A

close proximity of T-tubule, SR and intervening structure

15
Q

What causes a conformational change in the dihydropyridine receptor?

A

depol of T-tubule membrane

16
Q

What type of receptor is the ryanidine receptor? WHere is it?

A

voltage-dep Ca channal in SR

17
Q

What activates the ryanidine receptor?

A

conformational change in the dihydropyridine receptor

18
Q

What is the result of activation of the ryanidine receptor?

A
  1. channel opens

2. passive efflux of Ca from SR causes rapid increase of intracellular [Ca]

19
Q

What occurs when the t-tubule membrane repolarizes?

A
  1. dihydropyridine receptor returns to its normal conformation
  2. conf change causes the ryanidine receptor to close
  3. Ca actively pumped back into SR, which decreases IC Ca
20
Q

Sarcomeres are structural organizations of _____ proteins

A

myofibrillar

21
Q

What is an A band?

A

anisotropic

ordered hexagonal array of THICK filamentous proteins

22
Q

What is an I band?

A

isotropic

ordered hexagonal array of THIN filamentous proteins

23
Q

What is a Z line?

A

where thin filamentous proteins of the I band anchor

24
Q

From Z line to Z line =

A

a sarcomere

25
Q

What are the components of the myosin heavy chain?

A
  1. globular head

2. filamentous tail

26
Q

Directed outward in the thick filament:

A

globular myosin head

27
Q

Permits ATPase activity in globular head

A

light chain of thick filament

28
Q

What are the components of thin filaments?

A
  1. actin
  2. tropomyosin
  3. troponin
29
Q

What does actin form?

A

monomers form helical chains

30
Q

High affinity for myosin head

A

actin monomer

31
Q

Where is tropomyosin found?

A

along the length of thin filament, covering actin’s myosin-binding site

32
Q

What are the 3 types of troponin, and what do they do?

A

C = binds Ca

T = binds tropomyosin

I = maintains troponin conformation

33
Q

Why is it important for troponin to maintain its shape?

A

so tropomyosin can cover the myosin-binding site on actin in absence of Ca

34
Q

Structurally, low intracellular Ca results in:

A

tropomyosin blocks myosin-head binding site on actin

35
Q

Structurally, high intracellular Ca results in what process?

A
  1. Ca binds to troponin C
  2. conformational change in tropomyosin/troponin complex
  3. tropomyosin slides into the cleft between helical actin monomers
  4. myosin-head binding sites opens
  5. actin + myosin bind
36
Q

Cross-bridge Cycle:

A
  1. ATP binds to myosin head and myosin undergoes conf change, which causes the release of myosin from actin
  2. ATPase activity&raquo_space; ADP + P (=higher affinity of myosin head for actin)
  3. myosin binds to actin’s (+) side (different site)
  4. conformational change hinge, which pulls Z lines together for power stroke
37
Q

How is power stroke released?

A

power stroke changes affinity of myosin head (increased ATP affinity), which results in release of actin

38
Q

What is rigor mortis? (cause?)

A

decreased metabolism = decreased ATP; without ATP:

  1. myosin/actin cross-bridges cannot release
  2. no active pump for Ca into SR
39
Q

How do changes in muscle length relate to tension?

A

as length increases, passive tension increases

or as length decreases, passive tension decreases

40
Q

What is passive tension, at optimal length?

A

0

41
Q

Passive tension occurs in (presence/absence) of contractile activity

A

absence

muscle opposes increases in fiber length naturally

42
Q

Total tension =

A

active + passive

43
Q

What is optimal length?

A

the point at which every myosin binds every actin within a sarcomere

44
Q

If the sarcomere is too long (i.e. compared to optimal length)…

A

every myosin does not bind every actin

45
Q

If the sarcomere is too short (i.e. compared to optimal length)…

A

steric interaction hinders the optimal force

46
Q

Active tension results from (what two factors):

A

AP and fixed length

47
Q

When does a maximum active tension occur?

A

at a specific optimal sarcomere length

48
Q

An isometric twitch is generated in response to:

A

a single AP

49
Q

Maximal active tension occurs at skeletal muscle lengths when…

A

there is maximal overlap of thick and thin filaments

50
Q

In an isotonic contraction, ____ remains unchanged and _____ changes

A
  1. tension
  2. the muscle’s length

(wikipedia; I don’t get this at all)

51
Q

If the weight on a muscle fiber is the same as peak tension, distance (does/doesn’t) change.

A

doesn’t

52
Q

If the weight on a muscle fiber is less than peak tension, distance (does/doesn’t) change.

A

does

53
Q

As force (weight) increases, the initial velocity from the muscle moving the weight will (increase/decrease)

A

decrease

54
Q

_____ is at the x-intercept (where velocity = 0)

_____ is at the y-intercept (when force = 0)

A

isometric peak tension

maximum velocity of shortening

55
Q

Why does a fast motor unit have a greater isometric twitch tension?

A

there are more fibers with the unit, and a larger cross sectional area

56
Q

Why does a fast motor unit have a faster time to peak tension (TPT) and 1/2RT (time required to relax 1/2 peak tension)?

A

due to its Ca handling

57
Q

Why does a fast motor unit have a faster velocity (y-intercept)?

A

increased cross bridging

58
Q

At a given velocity, a fast motor unit generates greater ___ than a slow motor unit.

A

force

59
Q

At a given force, a fast motor unit generates greater ___ than a slow motor unit.

A

velocity

60
Q

How does the lower surface area of small motor neuron bodies affect depolarization?

A

fewer excitatory synapses are required for depolarization threshold to be met

61
Q

Excitatory inputs first recruit _____ for AP’s

A

small motor neurons

when a greater number of inputs, large motor neurons are activated for APs

62
Q

When large motor neurons are recruited, small motor neurons fire…

A

at a higher frequency

sorry, didn’t know how to ask this

63
Q

What type of motor neuron will activate fewer muscle fibers in a motor unit?

A

small

64
Q

An excitatory neuron will first activate few muscle fibers, which results in:

A

a smaller contraction; it then activates many fibers, resulting in a greater contraction

65
Q

When a muscle is stretched to longer lengths, what 2 things are reduced?

A
  1. the number of possible cross-bridges

2. active tension

66
Q

What happens to fast and slow motor units at a frequency of ~10Hz?

A

fast: generate tension and completely relax
slow: cannot completely relax before next stimulus

67
Q

What happens to fast and slow motor units at a frequency of ~20Hz?

A

fast: begin to sum tension
slow: reach a maximum GREATER than standard twitch tension (Tetanic Tension)

68
Q

Slow units produce tetanic contraction at a (higher/lower) frequency than fast units

A

lower

69
Q

Slow units produce a (higher/lower) tetanic force than fast units.

A

lower

70
Q

How do graded contractions generate greater force?

A

recruiting more motor units with a higher frequency of contraction

71
Q

Muscle fibers with a greater shortening velocity have more…

A

myosin ATPase activity

72
Q

ADP&raquo_space; ATP via…

A

creatine kinase (which removes P from creatine-P, forming creatinine)

73
Q

How can you determine when an elevated creatinine and BUN is due to muscle disease rather than kidney disease?

A

in muscle disease the CK and LDH will be elevated (but will be nml in kidney disease)

74
Q

Why are slow twitch fiber less likely to fatigue?

A

thet have a greater density of mitochondria = increased FA oxidation

75
Q

Slow + fast twitch fibers (in combo) support what type of muscle contraction

A

intense, short term contraction

76
Q

What type of fibers are glycogenolytic?

A

fast twitch