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Flashcards in Physiology Deck (76):
1

What proteins make up the thick filament?

myosin heavy chain; 2 light chains/head

2

**
Identify the thick and thin filaments.

*

3

What innervates skeletal muscle?

motor neurons in ventral horn

4

Each muscle fiber receives innervation from...

ONE motor neuron

5

Small motor neuron cell bodies innervate...
These are a.k.a (fast/slow) motor units

few muscle fibers that generally have a small cross sectional diameter

*slow

6

Large motor neuron cell bodies innervate...
These are a.k.a (fast/slow) motor units

many muscle fibers that generally have a large cross sectional diameter

*fast

7

What are the components of a motor unit?

motor neuron
muscle fibers innervated by motor neuron

8

What type of receptors are targeted by ACh at MEP?

nicotinic

9

What type of channels are at the nerve terminal?

monovalent cationic channels

10

What type of depolarizations are generated at the MEP?

graded

11

How is an action potential generated at the MEP?

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

Why is AP propagation axial?

because muscle fiber has long length and small diameter

13

What is the transverse tubule system?

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

14

What is the "triad"?

close proximity of T-tubule, SR and intervening structure

15

What causes a conformational change in the dihydropyridine receptor?

depol of T-tubule membrane

16

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

voltage-dep Ca channal in SR

17

What activates the ryanidine receptor?

conformational change in the dihydropyridine receptor

18

What is the result of activation of the ryanidine receptor?

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

19

What occurs when the t-tubule membrane repolarizes?

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

Sarcomeres are structural organizations of _____ proteins

myofibrillar

21

What is an A band?

anisotropic

ordered hexagonal array of THICK filamentous proteins

22

What is an I band?

isotropic

ordered hexagonal array of THIN filamentous proteins

23

What is a Z line?

where thin filamentous proteins of the I band anchor

24

From Z line to Z line =

a sarcomere

25

What are the components of the myosin heavy chain?

1. globular head
2. filamentous tail

26

Directed outward in the thick filament:

globular myosin head

27

Permits ATPase activity in globular head

light chain of thick filament

28

What are the components of thin filaments?

1. actin
2. tropomyosin
3. troponin

29

What does actin form?

monomers form helical chains

30

High affinity for myosin head

actin monomer

31

Where is tropomyosin found?

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

32

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

C = binds Ca

T = binds tropomyosin

I = maintains troponin conformation

33

Why is it important for troponin to maintain its shape?

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

34

Structurally, low intracellular Ca results in:

tropomyosin blocks myosin-head binding site on actin

35

Structurally, high intracellular Ca results in what process?

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

Cross-bridge Cycle:

1. ATP binds to myosin head and myosin undergoes conf change, which causes the release of myosin from actin
2. ATPase activity >> 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

How is power stroke released?

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

38

What is rigor mortis? (cause?)

decreased metabolism = decreased ATP; without ATP:
1. myosin/actin cross-bridges cannot release
2. no active pump for Ca into SR

39

How do changes in muscle length relate to tension?

as length increases, passive tension increases
(or as length decreases, passive tension decreases)

40

What is passive tension, at optimal length?

0

41

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

absence
(muscle opposes increases in fiber length naturally)

42

Total tension =

active + passive

43

What is optimal length?

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

44

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

every myosin does not bind every actin

45

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

steric interaction hinders the optimal force

46

Active tension results from (what two factors):

AP and fixed length

47

When does a maximum active tension occur?

at a specific optimal sarcomere length

48

An isometric twitch is generated in response to:

a single AP

49

Maximal active tension occurs at skeletal muscle lengths when...

there is maximal overlap of thick and thin filaments

50

In an isotonic contraction, ____ remains unchanged and _____ changes

1. tension
2. the muscle's length

(wikipedia; I don't get this at all)

51

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

doesn't

52

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

does

53

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

decrease

54

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

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

isometric peak tension

maximum velocity of shortening

55

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

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

56

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)?

due to its Ca handling

57

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

increased cross bridging

58

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

force

59

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

velocity

60

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

fewer excitatory synapses are required for depolarization threshold to be met

61

Excitatory inputs first recruit _____ for AP's

small motor neurons

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

62

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

at a higher frequency

(sorry, didn't know how to ask this)

63

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

small

64

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

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

65

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

1. the number of possible cross-bridges
2. active tension

66

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

fast: generate tension and completely relax

slow: cannot completely relax before next stimulus

67

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

fast:begin to sum tension

slow: reach a maximum GREATER than standard twitch tension (Tetanic Tension)

68

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

lower

69

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

lower

70

How do graded contractions generate greater force?

recruiting more motor units with a higher frequency of contraction

71

Muscle fibers with a greater shortening velocity have more...

myosin ATPase activity

72

ADP >> ATP via...

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

73

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

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

74

Why are slow twitch fiber less likely to fatigue?

thet have a greater density of mitochondria = increased FA oxidation

75

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

intense, short term contraction

76

What type of fibers are glycogenolytic?

fast twitch