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OCB02 > Temporomandibular Joint Development > Flashcards

Temporomandibular Joint Development Flashcards

1
Q

What type of joint is the TMJ?

A

Synovial hinge and gliding joint

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2
Q

Describe the TMJ when the jaw is closed.

A

Disc fits in socket, sandwiched between mandibular fossa and condyle

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3
Q

Describe the TMJ when the jaw is open.

A

Disc slides forward and condyle moves forward

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4
Q

Where does the TMJ form?

A

Between the mandibular (glenoid) fossa of temporal bone

And the condylar process of the dentary/mandible

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5
Q

What is the TMJ equivalent in some mammals which do not involve the temporal bone?

A

Squamosal-dentary joint

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6
Q

How many synovial cavities are in the TMJ?

A

2

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7
Q

Why is the human temporal bone described as composite?

A

Formed by the fusion of the petromastoid, squamosal, tympanic and styloid bones

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8
Q

What processes is the proximal part of the mandible divided into?

A

Condylar process

Coronoid process

Angle

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9
Q

The coronoid process acts as an attachment for which muscle?

A

Temporalis

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10
Q

The angle acts as an attachment for which muscle?

A

Internal pterygoid

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11
Q

The condylar process acts as an attachment for which muscle?

A

External pterygoid

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12
Q

What ligaments help stabilise the TMJ/jaw movement? (3)

A

TMJ ligament

Sphenomandibular ligament

Stylomandibular ligament

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13
Q

What is the jaw joint in non-mammalian jawed vertebrates formed between?

A

2 cartilaginous bones:

  • Quadrate
  • Articular
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14
Q

What are the quadrate and articular homologous to in mammals?

A

Incus and malleus in the inner ear

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15
Q

Give three ways in which the TMJ can be abnormal.

A

Ankylosis

Auriculo-condylar syndrome

Under/overgrowth of condyle affects size and symmetry

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16
Q

What four basic steps are required to form the TMJ?

A

Patterning (formation and shaping) of dentary

Capping of condyle with secondary cartilage

Disc formation

Endochondral ossification of cartilage

17
Q

Why might a mammal have a large coronoid process?

A

Large muscle attachment for large bite force

18
Q

What would a TGF-β2 knockout cause in a mouse and why?

A

Loss of angular process

No tendon is formed so no muscle pulling (loss of mechanical stimulation)

19
Q

What would a Pax9 mutant mouse lack and why?

A

Coronoid process due to intrinsic defects

Also hypodontia

20
Q

What happens to the secondary cartilage that forms along the anterior coronoid border?

A

Disappears before birth

21
Q

When is the condylar secondary cartilage mostly ossified in humans?

A

Half-way through gestation

22
Q

Which TMJ synovial cavity forms first?

A

Upper/superior

23
Q

Briefly describe the formation of the disc. (2)

A

Upper cavity forms first

High levels of lubricin help disc to lift off condylar process

24
Q

Why is fetal jaw movement important in disc formation?

A

Movement stimulates cells to change shape from rounded chondrocytes to fibroblast-like

So disc can lift off condylar process

25
Q

How does loss of Indian Hedgehog affect the TMJ?

A

Reduction in condylar cartilage and failure in disc formation

26
Q

What syndrome are Tcof1 mutant mice used to investigate?

A

Treacher-Collins syndrome

27
Q

What is different about the TMJ in Tcof1 mutant mice?

A

Hypoplastic condyle with ossified disc (painful articulation)

28
Q

Why do condyle defects affect the developing mandibular fossa?

A

As condyle and temporal/squamosal tissues form they communicate to coordinate growth

Condyle disruption results in failure of squamosal bones to fuse and hence no fossa

29
Q

In the condylar secondary cartilage, where is most of the proliferation?

A

In progenitor cells in polymorphic cell layer (beneath the articular layer)

30
Q

In secondary cartilage, where is Runx2 expressed?

A

Prehypertrophic cartilage

31
Q

If Runx2 is knocked out, what does that mean for the secondary cartilage?

A

No hypertrophic cartilage

No bone/ossification

32
Q

What happens if there is too much proliferation in the condylar secondary cartilage?

A

More growth and enlarged condyle

33
Q

What happens if there is too much differentiation in the condylar secondary cartilage?

A

Depleted pool of progenitor cells so shortened condyle (achondroplasia)

34
Q

What is thanatophoric dysplasia?

A

Asymmetrical growth of condyles

35
Q

What happens to the condylar process if there is insufficient mechanical stress?

A

Reduced/failed endochondral ossification

OCB02 (19 decks)

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