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MSS - MSK Exam 3 > Excitation Contraction Coupling > Flashcards

Excitation Contraction Coupling Flashcards

1
Q

innervation of skeletal muscle

A

somatic motor neurons

ventral horn of spinal cord
-except cranial nerves

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2
Q

motor unit

A

motor neuron and all muscle fibers it innervates

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3
Q

synapse vs NMJ?

A
  • two excitable cells
  • chemical messengers
  • change in membrane potential both graded potentials

differences:

  • synapse is junction of two neurons, NMJ is not
  • one-to-one transmission at NMJ, neuron requires summation of multiple EPSPs
  • NMJ always excitatory, neuron NO
  • inhibition can only occur in neurons (not NMJ)
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4
Q

active zone

A

dense spot over which synaptic vesicles are clustered

  • fusion of vesicles and release of ACh occurs
  • oriented directly over secondary postsynaptic clefts between adjacent postjunctional folds
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5
Q

postjunctional folds

A

where there are lots of receptors

-folds increase SURFACE AREA

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6
Q

type of receptor in skeletal muscle?

A

nicotinic acetylcholine receptors

high density expression at crests of postjunctional folds

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7
Q

acetylcholinesterase

A

high concentration associated with synaptic basal lamina (basement membrane)

terminates synaptic transmission**
hydrolyzes acetylcholine > choline + acetate

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8
Q

neurotransmitter at NMJ?

A

acetylcholine

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9
Q

acetylcholine

A

vesicles produced in cell body and fast axonal transport sends them to nerve terminal
-microtubule mediated

vesicles for ACh (and other non-peptides) travel down axon empty
-vesicle destined contain peptide neurotransmitters travel down axon with presynthesized peptide precursors inside

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10
Q

site of ACh synthesis and uptake?

A

nerve terminal

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11
Q

choline acetyltransferase

A

synthesizes ACh from choline and acetyl CoA

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12
Q

ACh-H+ exchanger

A

allow ACh uptake by synaptic vesicle
-antiport of ACh into cell and H+ out of cell

  • driven by vesicular proton electrochemical gradient
  • positive voltage and low pH inside
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13
Q

synaptobrevin

A

v-snare

essential for transmitter RELEASE
forms complex with SNAP-25 and syntaxin
-helps drive vesicular fusion

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14
Q

synaptotagmin

A

Calcium receptor of vesicle

-detects rises in calcium and triggers exocytosis of docked vesicles

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15
Q

syntaxin and snap 25

A

t-snares

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16
Q

vesicle fusion?

A

snap-25 and syntaxin on membrane coil around synaptobrevin on the vesicle to bring vesicle closer to presynaptic membrane

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17
Q

exocytosis of neurotransmitter?

A

synaptotagmin is calcium sensor

calcium triggers vesicle fusion and exocytosis

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18
Q

tetanus toxin

A

endoproteinase that digests synaptobrevin

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19
Q

botulinum B, D, F, G

A

endoproteinase that digests synaptobrevin

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20
Q

botulinum A, E

A

cleave SNAP-25

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21
Q

botulinum toxin C1

A

cleave syntaxin

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22
Q

acetylcholine receptor?

A

ionotropic, nicotinic AcHR channel

non-selective cation channel at muscle endplate

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23
Q

what happens when ACh binds receptor?

A

allows influx of multiple cations (non-specific)

-to raise Vm above threshold

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24
Q

threshold at membrane with ACh receptor?

A

-50mV

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25
Q

opening of AChR channel?

A

Na+ and K+ become equally permeable

increase normally low permeability of sodium relative to K+

Vm shifts to value between Ek and Ena
-80 > +50

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26
Q

end-plate potential

A

for action potential
-due to increased sodium permeability relative to potassium

type of graded potential

is an EPSP

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27
Q

will you run out of ACh?

A

no, there’s a lot at the end of the neuron in vesicles

-can maintain high rate of AP transmission without significant loss of function

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28
Q

termination of neurotransmitter action

A

enzymatic destruction removes ACh from NMJ synaptic cleft

ACETYLCHOLINESTERASE
-two step reaction

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29
Q

MEPP

A

??

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30
Q

myofibril

A

contractile element

contain thick and thin filaments

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31
Q

striations

A

ordered arrangements of thick and thin filaments

32
Q

sarcomere

A

z line to z line

33
Q

what changes during contraction of sarcomere?

A

A band no change
H zone gets smaller
I band decreases in width
sarcomere shortening

34
Q

thick filament

A

2 myosin heavy chain

regions:
rod (tail)
hinge (arm)
head

2 alkali light chains
2 regulator light chains

35
Q

rod of thick filament

A

alpha helices

36
Q

heads of thick filaments

A

form cross-bridges binding actin on thin filament

37
Q

binding sites on heavy chain?

A

2 important sites**
actin site
myosin ATPase site

both on heads of heavy chains

38
Q

actin site

A

for cross-bridge formation

39
Q

myosin ATPase site

A

for binding and hydrolyzing ATP

40
Q

myosin light chain

A

alkali and regulatory

stabilizing and rate of ATP hydrolysis regulation

41
Q

thin filaments

A

F-actin

-globular actin polymerizes to alpha helix of F-actin

42
Q

how many actin monomers in one turn?

A

13

43
Q

regulatory proteins of thin filament

A

tropomyosin and troponin

44
Q

tropomyosin function?

A

blocks the myosin binding site at rest on actin

45
Q

troponin

A

interacts with one tropomyosin molecule

46
Q

tropomyosin

A

interacts with 7 actin monomers

47
Q

what allows regulated actin-myosin interaction?

A

troponin, tropomyosin, and actin interactions

48
Q

structure of tropomyosin?

A

2 alpha helices coiled around each other

regulate binding of myosin heads to myosin binding site on actin

49
Q

components of troponin

A

troponin T
troponin C
troponin I

50
Q

troponin T

A

TnT, TNNT

bind to single tropomyosin molecule

51
Q

troponin C

A

TnC, TNNC

bind calcium

52
Q

troponin I

A

TnI, TNNI

bind to actin and inhibit contraction

53
Q

when calcium binds troponin?

A

tropomyosin slips away from its blocking position between actin and myosin

allows cross bridge to form and muscle contraction can occur

54
Q

titin

A

largest known protein
tethered from M line to Z line

appears to be involved in elastic behavior of muscle by maintaining resting length

mutation affects the length of muscle cell

55
Q

T-tubule?

A

action potential originating at sarcolemma propagate to the cell interior via these specialized membrane invaginations

56
Q

location of T-tubules

A

extend into muscle fiber and surround myofibrils at junction of A and I bands

57
Q

sarcoplasmic reticulum

A

stores calcium

58
Q

triad

A

t-tubule with 2 cisternae of sarcoplasmic reticulum

59
Q

dihydropyridine receptor?

A

L-type Ca2+ channel

responds to change in voltage
-causes conformation in ryanodine receptor

60
Q

ryanodine receptor

A

located in SR membrane
-cluster at portion of SR membrane that faces T tubules

release stored Ca2+ from SR

61
Q

calcium role?

A

does not directly interact with contractile proteins

-only interacts with the binding of regulatory proteins

62
Q

power stroke

A

with calcium
-troponin removes tropomyosin from myosin binding sites on actin

also need ATP hydrolysis on myosin heads (cocked)

63
Q

mATPase

A

hydrolyzes to cock the myosin

64
Q

what causes power stroke?

A

interaction between myosin and actin uses the stored potential energy

P is released from cross bridge to trigger power stroke
-ADP is released with power stroke completion

65
Q

what detaches myosin head?

A

binding new ATP

66
Q

what is needed for contraction cycle?

A

ATP and calcium

67
Q

cross bridge cycle

A

1) ATP binds myosin head - disocciation
2) ATP hydrolyzes - puts myosin in cocked state
3) cross bridge formed with actin
4) P release - myosin head changes conformation
- this is power stroke!
5) ADP released

REPEAT

68
Q

rigor mortis

A

can’t unbind the myosin from actin (no ATP)

69
Q

relaxation

A

need ATP!

requires reuptake from sarcoplasm back into SR

70
Q

what helps to remove calcium?

A

Na+ Ca2+ exchanger and Ca2+ pump
calcium to extracellular space
-minor mechanisms for calcium removal

SERCA
-sarcoplasmic and endoplasmic reticulum Ca2+ ATPase
calcium reuptake into SR
-MAJOR mechanism

71
Q

Ca2+ binding proteins

A

in SR lumen can delay inhibition of Ca2+ pump activity

buffers calcium

can increased the calcium capacity of the SR

72
Q

inhibition of SERCA?

A

high concentrations of calcium

73
Q

calsequestrin

A

primary Ca2+ binding protein in skeletal muscle
-localized in SR beneath triad junction

forms complex with RyR
-facilitates muscle relaxation by buffering Ca2+

unloads its Ca2+ in vicinity of Ca2+ release channel to facilitate EC coupling

74
Q

calreticulin

A

Ca2+ binding protein in smooth muscle

75
Q

terminal button

A

indentation of muscle cell where the nerve end plate is located

MSS - MSK Exam 3 (16 decks)

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