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Sp. Phys 1 > 4a. Skeletal Muscle and Neuromuscular Junction (NMJ) > Flashcards

4a. Skeletal Muscle and Neuromuscular Junction (NMJ) Flashcards

1
Q

motor unit

A

motor neuron and all the fibers that it innervates

direct innervation (no ganglia)

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2
Q

motor end plates

A

located at skeletal muscle membrane
synapse with motor nerve terminal

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3
Q

motor neuron site of action potential

A

axon hillock

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4
Q

tetrodotoxin

A

blocks Na+ channel

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5
Q

botulinum toxiun

A

cleaves SNARE proteins
decrease NT release

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6
Q

physostigmine/neostigmine

A

blocks AChE
increases ACh at NMJ

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7
Q

curare
(d-tubocurarine)

A

competitive antagonist for ACh to bind to the AChR
less ACh able to bind
=muscle relaxant

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8
Q

end plate potential

A

graded potential (20mV)
generated by stimulation causing a change in membrane potential

almost always triggers AP

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9
Q

dihydropyridine receptor (DHPR)

A

functions as a voltage sensor in skeletal muscle
triggers intracellular Ca++ release from SR

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10
Q

T- tubules inside charge

A

+

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11
Q

T-tubules outside charge

A

-

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12
Q

t tubules function

A

conduct AP into interior muscle fibers

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13
Q

DHPRs activated by AP

A

results in physical contact w/RyR to release Ca++

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14
Q

Calcium-Induced Calcium Release
(CICR)

A

Ca++ release by the action of Ca++ alone without simultaneous action of other activating processes

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15
Q

Primary mechanism of Ca++ release

A
  • direct protein-protein interaction between the DHPR and RyR
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16
Q

Ryanodine Receptor

A

responsible for Ca++ release from SR

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17
Q

when DHPR connects w/RyR

A

Ca++ is released

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18
Q

Excitation-Contraction Coupling

A

DHPR connecting w/RyR to facilitate Ca++ release
increase intracellular Ca++

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19
Q

myosin head

A

attaches to actin
power stroke (hydrolysis products released)
binds to new ATP
detaches from actin

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20
Q

myosin chains

A

heavy chain
light chain (regulatory)

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21
Q

Actin filaments

A

provide cells w/mechanical support and driving forces for movment

22
Q

Troponin C (TnC)

A

Ca++ binding subunit

(during excitation)

23
Q

Troponin

A

works w/tropomyosin to unblock active sites between myosin and actin
allows cross-bridge cycling
contraction of myofibrils for systole

24
Q

Tropomyosin

A

binds w/troponin to help position it on the actin molecule

prevents myosin from forming cross-bridges while in a resting state

25
Q

actin

A

protein that interacts with myosin filaments to generate tension

26
Q

Hydrolysis of ATP/Power Stroke

A
  1. ATP binds to myosin head (Attached)
    - dissociation of actin-myosin complex for myosin to bind to ATP (RELEASED)
  2. ATP is hydrolyzed
    - myosin heads return to resting conformation
  3. cross-bridge forms
    - myosin head binds to new action position
  4. Phosphate release
    - power stroke: filaments slide past each other
  5. ADP released
27
Q

During muscle contraction, what happens to the H zones and I/A bands

A

H zones shrink/narrow
I band shrink/narrow
A band does not change

28
Q

sarcomere optimal overlap

A

produces optimal force

29
Q

too much overlap

A

lower force

30
Q

not enough overlap

A

lower force

31
Q

AChE breaks down ACh into

A

Choline + Acetic Acid

32
Q

choline acetyltransferase (ChAT)

A

converts choline and acetyl CoA into ACh

33
Q

3 ways to terminate contraction-reuptake of Calcium

A
  1. NCX (Na/Ca exchanger)
  2. SERCA
  3. Calsequestrin
34
Q

Na+/Ca++ exchanger

A

secondary active transporter
requires ATP
pumps one ion down gradient and the other up gradient

35
Q

Sarcoendoplasmic Reticulum Calcium ATPase (SERCA)

A

pump transports Ca++ from cytosol back into SR against concentration gradient after muscle contraction

primary active transport
requires ATP

36
Q

Calsequestrin

A

major Ca++ binding protein in SR
main Ca++ storage
regulator of Ca++ release channels in skeletal/cardiac muscle

37
Q

fiber summation

A

recruit additional motor units

38
Q

frequency summation

A

of individual fibers

39
Q

unfused tetanus

A

muscle fibers do not completely relax before next stimulus b/c they are being stimulated at at fast rate

Ca++ not at highest level (can trigger more Ca++ release from SR)

partial relaxation between twitches

(partial summation)

40
Q

fused tetanus

A

complete tetanus
no relaxation period between muscle contractions

Ca++ reached highest level (cannot trigger more Ca++ release from SR)

(full summation)

41
Q

muscle relaxants

A

depolarizing
non depolarizing

42
Q

depolarizing agent

A

succinylcholine
(partial agonist)

43
Q

succinylcholine mechanism

A

activates NAChR
maintains depolarization (keep open)
causes paralysis
- muscle fatigue
- ion conc gradient?
stops breathing

44
Q

non-depolarizing agent

A

d-tubocurarine
(antagonist)

45
Q

d-tubocurarine mechanism

A

blocks binding of receptor
ACh cannot bind
No conformational change of receptor
No EPP
No AP

46
Q

Rhabdomyolysis

A

damaged muscle tissue releases its proteins and electrolytes into the blood

47
Q

Rhabdo symptoms

A

reddish/brown urine
muscle pain/weakness/fatigue

48
Q

Rhabdo blood serum

A

high creatine kinase
high potassium
high myoglobin
low Ca++

49
Q

Rhabdo kidney damage

A

myoglobin is filtered out by the kidneys which causes damage to the kidneys

50
Q

Myasthenia Gravis

A

autoimmune diease
antibodies bind to nAChR
weakening skeletal muscles

Sp. Phys 1 (6 decks)

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