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Neuro > Neuromuscular Junction > Flashcards

Neuromuscular Junction Flashcards

1
Q

What is synaptogenesis

A

Formation of the synapse

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2
Q

The neuromuscular junction (NMJ) comprises portions of what 3 cells

A
  1. Motor neuron
  2. Muscle fiber
  3. Schwann cell
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3
Q

True or False:

The motor nerve terminal is specialized for NT release

A

True

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4
Q

What are used for energy involved with synthesis and release of NT

A

Mitochondria

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5
Q

Where is there a high concentration of AChRs on the postsynaptic cell

A

Clustered at the top of the folds

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6
Q

Where are voltage gated Na+ channels located on the postsynaptic cell

A

In the depression of folds

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7
Q

What do the Schwann cells do for the NMJ

A

Provide insulation and nourishment

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8
Q

Where do myoblasts originate from

A

The somite

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9
Q

Where do motor axons arise from

A

Somata

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10
Q

Where do Schwann cells arise from

A

Neural crest cells

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11
Q

True or False:

Neural crest cells are the precursor to Schwann cells

A

True

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12
Q

What do myoblasts turn into

A

Muscle fibers

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13
Q

Do myoblasts, motor axons, and Schwann cells travel short or long distances to create the NMJ

A

Long distance

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14
Q

True or False:

Early connections are none specific and go through a period of differentiation

A

True

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15
Q

True or False:

At birth the NMJ is fully functional and multiply innervated

A

True

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16
Q

Where do motor axons originate from

A

Neural tube

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17
Q

What do myoblasts turn into before muscle fibers

A

Myotubes

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18
Q

What does nerve to muscle contact lead to (2)

A
  1. Early synaptic transmission

2. Postsynpatic membrane differentiation

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19
Q

When do vesicles start to form in the presynaptic cell

A

As soon as the presynaptic cell touches the motor end plate

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20
Q

True or False:

AChRs subunits are expressed at low levels in myoblasts

A

True

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21
Q

Are the AChRs subunits slowly or quickly upregulated on the nerve to muscle contact

A

Quickly

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22
Q

What are the 3 way AChRs subunits are quickly upregulated

A
  1. AChR clustering
  2. Transcriptional activation of AChR subunit genes by sub-synaptic nuclei
  3. Transcriptional repression of AChR subunit genes by non-synpatic myonuclei
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23
Q

What are the 3 pathways that are implicated in the process of postsynaptic differentiation

A
  1. Agrin interacts with MuSK
  2. Neuregulin interacts with erbB kinases
  3. Activation of AChRs which stimulates voltage gated channels allowing for Ca++ to enter the cell
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24
Q

What does agrin interacting with MuSK do

A

Organize rapsyn mediated clustering

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25
Q

What does neuregulin interacting with erbB kinases do

A

Induce expression of AChR subunit genes in subsynaptic nuclei and eventually upregulate AChR

26
Q

What does stimulation of voltage gated channels allowing more Ca++ to enter the cell do

A

Leads to repression of AChR expression in extrasynaptic nuclei

27
Q

What happens if you do not have agrin

A

AChRs fail to cluster in the forming NMJ

28
Q

True or False:

Agrin is a master organizer

A

True

29
Q

What does MuSK act like

A

A second messenger the joins and phosphorylates interacting with rapsin

30
Q

True or False:

Rapsin is an anchoring protein

A

True

31
Q

How does the Ca/CAM system effect AChRs formation

A

Causes repression

32
Q

What do the AChRs do in early embryogenesis and when does this occur

A

Cluster forming a plaque (17 days in embryo)

33
Q

What happens to the plaque as the AChR density increase and when does this occur

A

The borders sharpen and length decreases (0 days postnatal)

34
Q

What happens to the plaque postnataly and when does this occur

A

It perforates to form a pretzel like structure (5-30 days postnataly)

35
Q

How do the junctional folds run in relation to each other

A

Parallel

36
Q

How are the junctional folds spaced out in relation to one each other

A

Equally spaced

37
Q

How do the junctional folds run in relation to the muscle fibers

A

Orthogonal or at right angles

38
Q

True or False:

AChRs are densely positioned at the rest of the folds closely opposed by ACh active zones

A

True

39
Q

What do the voltage gated Na+ channels do in the valleys of the junctional folds

A

Amplify synaptic current

40
Q

How do the voltage gated Na+ channels amplify synaptic current

A

By lowering the threshold for an AP

41
Q

What is the function of the basal lamina

A

It is an anchoring structure

42
Q

Do junctional folds occur quickly or over weeks or months

A

Over weeks or months

43
Q

When does transmission start to occur

A

When the growth cone contacts the myotube

44
Q

What do the junctional folds help with

A

Stregnthening the connection and making the NMJ functional

45
Q

What is one function of MuSK

A

Initiate the process of rapsyn anchoring AChRs to the membrane

46
Q

What does rapsyn allow for

A

AChRs to be directly under an active zone

47
Q

How are muscle fibers innervated at birth

A

Multiply innervated

48
Q

How long does it take synaptic terminals to begin to segregate

A

Days

49
Q

At what point are most muscle fibers innervated by one input

A

2 weeks

50
Q

Is synaptic elimination a stereotyped response

A

Nope

51
Q

What synapses are subject to elimination

A

Only those that fire an action potential

52
Q

True or False:

Synapse elimination is competitive and depends on the activity of neighboring synapses

A

True

53
Q

What are the 3 ways synaptic elimination occurs

A
  1. Synaptomedian model
  2. Synaptotrophin model
  3. Synaptotoxin model
54
Q

What is the synaptomedian model

A

Retrograde signaling may differentially reward or punish competing axons

55
Q

What is the synaptotrophin model

A

Decrease in trophic factors necessary to maintain synapse

56
Q

What is the synaptotoxin model

A

Damaging toxins destabilize the nerve terminal thus leading to retraction of losing input

57
Q

What is BDNF important for

A

Maintenance of synapse

58
Q

What happens if there is less BDNF

A

The axon retracts

59
Q

What may agrin function as in the synaptotoxin model

A

Protease inhibitor

60
Q

What is agrin responsible for at the motor terminal

A

Forming and inhibiting axons

61
Q

What contacts the muscle fiber first Schwann cell, motor axon, or myoblasts

A

Motor axon

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