Excitation Contraction Coupling Flashcards Preview

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Flashcards in Excitation Contraction Coupling Deck (75):
1

innervation of skeletal muscle

somatic motor neurons

ventral horn of spinal cord
-except cranial nerves

2

motor unit

motor neuron and all muscle fibers it innervates

3

synapse vs NMJ?

-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)

4

active zone

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

5

postjunctional folds

where there are lots of receptors
-folds increase SURFACE AREA

6

type of receptor in skeletal muscle?

nicotinic acetylcholine receptors

high density expression at crests of postjunctional folds

7

acetylcholinesterase

high concentration associated with synaptic basal lamina (basement membrane)

terminates synaptic transmission**
hydrolyzes acetylcholine > choline + acetate

8

neurotransmitter at NMJ?

acetylcholine

9

acetylcholine

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

10

site of ACh synthesis and uptake?

nerve terminal

11

choline acetyltransferase

synthesizes ACh from choline and acetyl CoA

12

ACh-H+ exchanger

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

13

synaptobrevin

v-snare

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

14

synaptotagmin

Calcium receptor of vesicle
-detects rises in calcium and triggers exocytosis of docked vesicles

15

syntaxin and snap 25

t-snares

16

vesicle fusion?

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

17

exocytosis of neurotransmitter?

synaptotagmin is calcium sensor

calcium triggers vesicle fusion and exocytosis

18

tetanus toxin

endoproteinase that digests synaptobrevin

19

botulinum B, D, F, G

endoproteinase that digests synaptobrevin

20

botulinum A, E

cleave SNAP-25

21

botulinum toxin C1

cleave syntaxin

22

acetylcholine receptor?

ionotropic, nicotinic AcHR channel

non-selective cation channel at muscle endplate

23

what happens when ACh binds receptor?

allows influx of multiple cations (non-specific)
-to raise Vm above threshold

24

threshold at membrane with ACh receptor?

-50mV

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