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MSS - MSK Exam 3 > Excitation Contraction Coupling > Flashcards

Excitation Contraction Coupling Flashcards

(75 cards)

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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
opening of AChR channel?
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
26
end-plate potential
for action potential -due to increased sodium permeability relative to potassium type of graded potential is an EPSP
27
will you run out of ACh?
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
28
termination of neurotransmitter action
enzymatic destruction removes ACh from NMJ synaptic cleft ACETYLCHOLINESTERASE -two step reaction
29
MEPP
??
30
myofibril
contractile element | contain thick and thin filaments
31
striations
ordered arrangements of thick and thin filaments
32
sarcomere
z line to z line
33
what changes during contraction of sarcomere?
A band no change H zone gets smaller I band decreases in width sarcomere shortening
34
thick filament
2 myosin heavy chain regions: rod (tail) hinge (arm) head 2 alkali light chains 2 regulator light chains
35
rod of thick filament
alpha helices
36
heads of thick filaments
form cross-bridges binding actin on thin filament
37
binding sites on heavy chain?
2 important sites** actin site myosin ATPase site both on heads of heavy chains
38
actin site
for cross-bridge formation
39
myosin ATPase site
for binding and hydrolyzing ATP
40
myosin light chain
alkali and regulatory stabilizing and rate of ATP hydrolysis regulation
41
thin filaments
F-actin | -globular actin polymerizes to alpha helix of F-actin
42
how many actin monomers in one turn?
13
43
regulatory proteins of thin filament
tropomyosin and troponin
44
tropomyosin function?
blocks the myosin binding site at rest on actin
45
troponin
interacts with one tropomyosin molecule
46
tropomyosin
interacts with 7 actin monomers
47
what allows regulated actin-myosin interaction?
troponin, tropomyosin, and actin interactions
48
structure of tropomyosin?
2 alpha helices coiled around each other | regulate binding of myosin heads to myosin binding site on actin
49
components of troponin
troponin T troponin C troponin I
50
troponin T
TnT, TNNT bind to single tropomyosin molecule
51
troponin C
TnC, TNNC bind calcium
52
troponin I
TnI, TNNI bind to actin and inhibit contraction
53
when calcium binds troponin?
tropomyosin slips away from its blocking position between actin and myosin allows cross bridge to form and muscle contraction can occur
54
titin
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
T-tubule?
action potential originating at sarcolemma propagate to the cell interior via these specialized membrane invaginations
56
location of T-tubules
extend into muscle fiber and surround myofibrils at junction of A and I bands
57
sarcoplasmic reticulum
stores calcium
58
triad
t-tubule with 2 cisternae of sarcoplasmic reticulum
59
dihydropyridine receptor?
L-type Ca2+ channel responds to change in voltage -causes conformation in ryanodine receptor
60
ryanodine receptor
located in SR membrane -cluster at portion of SR membrane that faces T tubules release stored Ca2+ from SR
61
calcium role?
does not directly interact with contractile proteins -only interacts with the binding of regulatory proteins
62
power stroke
with calcium -troponin removes tropomyosin from myosin binding sites on actin also need ATP hydrolysis on myosin heads (cocked)
63
mATPase
hydrolyzes to cock the myosin
64
what causes power stroke?
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
what detaches myosin head?
binding new ATP
66
what is needed for contraction cycle?
ATP and calcium
67
cross bridge cycle
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
rigor mortis
can't unbind the myosin from actin (no ATP)
69
relaxation
need ATP! requires reuptake from sarcoplasm back into SR
70
what helps to remove calcium?
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
Ca2+ binding proteins
in SR lumen can delay inhibition of Ca2+ pump activity buffers calcium can increased the calcium capacity of the SR
72
inhibition of SERCA?
high concentrations of calcium
73
calsequestrin
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
calreticulin
Ca2+ binding protein in smooth muscle
75
terminal button
indentation of muscle cell where the nerve end plate is located

MSS - MSK Exam 3 (16 decks)

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