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MSS > Nueromuscular Junction and excitability > Flashcards

Nueromuscular Junction and excitability Flashcards

week 2

1
Q

What is nebulin?

A

cytoskeleton element that stabilizes thin filaments and anchors it to Z line

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2
Q

What is the role a triad?

A

AP on surface not effective to stmulate deeper organelles so T-tubules bring depolarization into interior.

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3
Q

What are the three complex proteins of Troponin and what are their functions?

A

Troponin I = binds actin

Troponin T = Binds tropomyosin

Troponin C = binds calcium

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4
Q

Dystropin

A

Dystropin is a cytoskeletal element which links thin filaments to integral proteins of the sarcolemma, through a complex cytoskeletal structure called a costamere

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4
Q

What is tropmyosin?

A

covers active site on actin. Stabilizes and strengthensActin.(bike chain)

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5
Q

Functions of skeletal muscle

A

Produces movement

Maintains posture and body position

Maintains body temperature

Protects and supports soft tissue

Forms valves at openings

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6
Q

Neuromuscular junction

A

Site of communication between a motor neuron and muscle fibre

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7
Q

What parts of a contraction is chemical communication required?

A

1- across synaptic cleft (ACh)

2- Within sarcoplasm (Ca2+)

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8
Q

Describe steps fo excitation- contraction coupling simply.

A

Na iniates AP along sarcolemma and T Tubules

Voltage Gated receptors triggered releasing Ca from SR into cytosol

Ca binds to Troponin

Troponin changes shape as it removes blocking action of tropomyosin and exposes active sites

Contraction: myosin heads alternatively attach to actin and then detach = actin filaments pulled towards center

ATP energy powers process

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9
Q

What are the key steps for muscle relaxation?

A

NMJ stimulation ends.

AChe rapidly degrades ACh which is recycled by nerve terminal

Repolarization de-activates DHP-Rs and RYRs

Ca re-sequestered into SR

Troponin – tropomyosin complex reorientates so it covers active site.

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9
Q

Describe the interactions of Ca in the troponin-tropomyosin complex.

A

Ca binds to TRC of troponin complex

4 calcium = alters troponin complex (pulls tropomyosin away)

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10
Q

What are the two types of smooth muscle? List their characteristics.

A

Multiunit

Discrete cells that operate independently

Innervated (supplied with nerves) by motor neurons

Slow contraction

Single Unit

Act as a single unit

Gap junctions allow for AP and ion transmission

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11
Q

What are some unique features of Smooth muscle?

A

Thin filaments attached to dense bodies

Intermediate filaments (desmin) anchor actin and tropomyosin in thin

Scattered myosin when muscle relaxed.

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12
Q

What are the steps in Smooth Muscle contraction?

A

Voltage gated L-type Ca allows influx

Ca binds to Calmodulin (CaM)

CaCaM activates Myosin light chain kinase (MLCK)

MLCK phosphorylates MLC on myosin head = increased ATPase

Phosphorylated myosin polymerize (form a polymer) into thick filaments = forms cross-bridges

Cross-bridge cycling = dense bodies pulled towards each other

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13
Q

What are the steps of Smooth muscle relaxation?

A

VG Ca closes

Re-sequestration of Ca by SERCA

Ca concentration decreases = inactivates CaM and MLCK

MLCP dephosphorylates MLC = Thick filaments depolymerize

Smooth muscle relaxed.

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14
Q

What does smooth muscle contraction depend on?

A

Activation of MLCK by increased [Ca] intracellular

15
Q

Why can smooth muscle contractions be maintained for prolonged periods without fatiguing?

A

Low energy demand (cross bridge last longer)

Slow onset of contraction and relaxation (Ca channel open for longer)

Slow Cross bridge cycling (little excitation to maintain contraction as cross-bridge detachments is slow)

16
Q

What are points of difference between Smooth muscle and Skeletal muscle contractions?

A

thin filament attachment (dense bodies vs z-line)

Active site availability (always vs when [Ca] high)

myosin formation (scattered as a single molecule when relaxed vs always polymerised as thick and bound to M line)

influence of increased intracellular Ca on myosin (myosin polymerises into thick vs myosin always thick as long as ATP is present)

17
Q

What are the 4-steps of cross bridge cycling

A

1- cross bridge formation
2- power-stroke
3- cross-bridge detachment
4-myosin heads rest

18
Q

cross bridge formation

A

ATP binding pocket with mysoin ATPase in each myosin head

ATP hydrolyzed to ADP Pi which bind to myosin head

Re-cock and primes myosin head

19
Q

power stroke

A

Contraction mechanism: when myosin to actin undergoes conformational change –> pulls actin towards center of sarcomere –> shortens sarcomere

20
Q

What gets pulled towards the M-line in the power stroke?

A

thin filament and z-disc

21
Q

What is released before and afetr the power stroke?

A

before = Pi
after = ADP

22
Q

cross-bridge detachment

A

Binding of ATP to myosin head breaks cross-bridge

Importance: no more energy so cannot move any further.

23
Q

mysoin heads rest

A

ATP hydrolysis recocks head in high energy conformation

Mysoin head primed until active site of actin exposed.

24
Q

what do we call the posysynaptic membrane of the neuromuscular junction

A

Motor end plate

25
Q

How is the neurotransmitter inactivated in synaptic cleft?

A

AChE
-breaks down ACh by terminated the action of ACh after released.

26
Q

How does AChE regulate NM transmissiom?

A

By breaking down acetylcholine quickly, AChE helps ensure that muscle contraction is precisely controlled and that the muscle fiber does not remain in a state of constant contraction.

27
Q

what happens to the I bind in skeletal muscle contraction?

A

shortens and reduces in width

28
Q

what bands shorten in muscle contactions?

A

I band and H zone

29
Q

What three events of NMJ require ATP?

A

Detachment of cross-bridges (binding of ATP)

Recocking myosin head (hydrolysis)

Reuptake of Ca into SR via SERCA (hydrolysis)

30
Q

How do active sites on smooth differ from skeletal muscle fibres?

A

Smooth: Always available (no troponin)

Skeletal: Only available if intracellular Ca is elevated and troponin complex moves tropomyosin.

31
Q

Describe myosin in Smooth vs skeletal muscle

A

Scattered as a single molecule when relaxed

Always polymerized, bound to M line

32
Q
A

MSS (18 decks)

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