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Bio Med > Craniofacial Development > Flashcards

Craniofacial Development Flashcards

1
Q

What two types of bone is the skull formed from

A

Endochondral bones and dermal (membrane) bone

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2
Q

Endochondral bones

A

-cartilaginous precursors
Turn into cartilage and then bone

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3
Q

Dermal (membrane) bone

A

Bones which ossify directly from mesenchyme

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4
Q

What is mesenchyme

A

Loosely organised embryonic connective tissue derived from either mesoderm or neural crest cells in the head

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5
Q

What are the 3 developmental parts that form the skull

A

Chodocranium
Splanchonocranium
Dermatocranium

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6
Q

What kind of bone is the Chodocranium made from

A

Endochondral
Cartilaginous precursors

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7
Q

What kind of bone is the splanchnocranium made from

A

Endochondral
Cartilaginous precursors

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8
Q

What kind of bone is the Dermatocranium made from

A

Dermal bones
Ossifys directly

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9
Q

What does the chondocranium develop from

A
  • 3 pairs of cartilaginous, hypophyseal and parchordal cartilages
  • the occipital cartilages
  • the capsules for sensory organs
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10
Q

Chondocranium- ethmoid

A

Derived from prechordal cartilage and olfactory capsule

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11
Q

Chondocranium- body of sphenoid (basisphenoid)

A

From hypophyseal cartilage

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12
Q

Chondocranium - lesser wings of sphenoid (orbitosphenoid)

A

From optic capsule

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13
Q

Chondrocranium- basioccipital

A

Derived from parachordal cartilage

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14
Q

chondocranium- petrous and mastoid parts of temporal bone (petromastoid bone)

A

Derived from optic capsule. Houses inner and middle ear

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15
Q

Dermatocranium

A
  • Flat bones of the cranial vault and face are dermal bones.
  • Ossify directly from mesenchyme (from either mesoderm or neural crest cells) in the dermis.
  • Bone of cranial vault complete their development after birth.
  • Fontanelles allow bones to move relative to one another.
  • Posterior and anterolateral fontanelles close by 3 months, anterior and posteolateral fontanelles close by 2 years.
  • Sutures close and in some cases fuse (eg metopic) later still.
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16
Q

Splanchocranium

A
  • Phrayngeal arches evolved from gill arches of jawless fishes (non-gnathostome vertebrates)
  • Five pairs in humans 1,2,3,4,6 (5 is either transient or doesn’t form at all)
  • Form in rostro-caudal succession (first around day 22)
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17
Q

What did pharyngeal arches evolve from

A

Gill arches of jawless fishes (non-gnathostome vertebrates)

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18
Q

How many pairs of pharyngeal arches is there

A

Five pairs in humans
1,2,3,4,6

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19
Q

What are phrayngeal arches lined with on the outside

A

Ectoderm

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20
Q

What kind of core do pharyngeal arches have

A

Mesenchymal core

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21
Q

What are pharyngeal arches lined with on the inside

A

Endoderm

22
Q

What kind of muscle are the pharyngeal arches

A

Striated muscle (from head mesoderm) innervated by arch specific cranial nerve

23
Q

Pharyngeal clefts and membranes

A
  • Phrayngeal clefts ie between each arch
  • Phrayngeal membranes separate the clefts from the pharyngeal pouches which lie deep to them.
24
Q

First arch

A
  • First arch has two swellings associated with it- the maxillary and mandibular prominences (from neural crest)
  • Maxillary prominence from mesenchyme rostral to first arch- becomes upper jaw.
  • First arch proper-Meckels cartilage
  • First arch forms lower jaw of jawed vertebrates (gnathostomes)
  • Gives rise to malleus, anterior ligament of the malleus and the sphenomandibular ligament.
  • Mandible, which is dermal bone, condenses around meckles cartilage.
25
Q

Maxillary cartilage

A
  • Maxillary cartilage- palatopterygoquadrate bar
  • Gives rise to incus and alisphenoid.
  • The following dermal bones condense around it: maxilla, zygomatic and squamous part of temporal bone.
26
Q

Second pharyngeal arch

A
  • Second- reicherts cartilage
  • Evolved from a bracing element for the jaws.
  • Gives rise to stapes, styloid process, styloid ligament, lesser horns of hyoid and upper part of the body of the hyoid.
    Muscles (facial expression0
    Posterior belly of digastric
    Stylohyoid
    Stapedius

Stapedial artery

27
Q

Third pharyngeal arch

A
  • Third arch becomes the greater horns, and the lower part of the body of the hyoid.
    Common carotid artery
    Glossopharyngeal nerve
    Muscles for swallowing
    Sylopharyngeus
28
Q

Fourth and sixth arch

A
  • Fourth and sixth arches give rise to the laryngeal cartilages.
29
Q

Pharyngeal arch arteries

A
  • Each pharyngeal arch is supplied by paired aortic arch arteries.
  • Largely degenerate but also give rise to the definitive arteries of the head, neck, upper thorax.
  • 1st becomes maxillary artery.
  • 2nd becomes stapedial artery.
  • 3rd common carotid artery.
30
Q

Pharyngeal arch nerves

A
  • Each arch is innervated by a different cranial nerve.
  • Consequently, the muscles associated with an arch are innervated by branches of its cranial nerve.
31
Q

First pharyngeal arch muscles

A

mesoderm gives rise to the masticatory muscles, mylohyoid, anterior belly of the digrastic, tensor tympani and tensor veil palatini- all innervated by the (mandibular division of the) trigeminal nerve.

32
Q

Second pharyngeal arch muscles

A

Second- mesoderm gives rise to the muscles of facial expression, posterior belly of the digrastic, stylohyoid and stapedius, all innervated by the facial nerve.

33
Q

Fourth and sixth pharyngeal arch muscles

A

Fourth and sixth- superior, middle and inferior constrictors of pharynx, cricothyroid and lavatory veli palatini, all innervated by the vagus nerve.

34
Q

Composite bones

A
  • Several cranial bones are formed from several different elements that fuse together eg occipital, sphenoid, temporal, maxilla.
35
Q

Composite bones: temporal

A
  • The temporal is composed of the tympanic and petromastoid which are chondrocranial, the squamous and tympanic which are dermatocranial, and the styloid process, which is splanchocranial.
  • The middle ear houses ossicles which are derived from the splanchocranium:
  • Incus (maxillary cartilage)
  • Malleus (meckels cartilage)
  • Stapes (reicherts cartilage)
36
Q

Facial swellings 4th and 5th weeks

A
  • Mouth formed by disintegration of buccopharygeal (orophayrngeal) membrane.
  • Connects primitive oral cavity to GI tract.
  • Broad mouth produced.
37
Q

Facial swellings early 6th week

A
  • Morphology of the face is derived from the development and fusion of five prominences that surround the primitive oral cavity:
  • Paired maxillary prominences
  • Paired mandibular prominences
  • Frontonasal prominences
  • All form by end of the 4th week
38
Q

Maxillary and mandibular prominences

A
  • Neural crest cells from the midbrain and hindbrain give rise to the mesenchyme of the maxillary and mandibular prominences.
  • Lateral parts of the maxillary and mandibular prominences fuse during 2nd month, creating cheeks.
  • Reduces width of mouth
  • Mesenchyme proliferates to fill the gape between the two mandibular prominences during the 4th and 5th weeks.
  • Cretes primordium of lower lip
39
Q

Frontonasal prominence 5th week

A
  • Frontonasl prominences superficial to forebrain
  • Neural crest cells from the forebrain and midbrain give rise to the mesenchyme of the frontonalsa prominence thickens to form nasal placodes.
40
Q

Frontonasal prominence 6th week

A
  • Nasal placodes invaginate in the 6th week to form nasal pits.
  • Nasal pits separate lateral and medial nasal processs.
41
Q

Frontonasal prominence 7th week

A
  • During 6th week medial nasal processes migrate towards the midline and fuse.
  • Intermaxillary process is formed when the medial nasal processes expand laterally and inferiority and then fuse (7th week)
  • Forms bridge and septum of nose and philtrum.
42
Q

Facial swellings 10th week

A
  • Philtrum and primary palate are derived from the inferior tips of the intermaxilary process (medial nasal processes)
  • Primary palate (premaxillae) contrains the 4 maxillary incisors
  • Tips of maxillary prominences expand towards intermaxillary process and fuse with it.
  • Nasolacrimal groove between lateral nasal process and maxillary prominence
  • Becomes nasolacrimal duct and lacrimal
43
Q

Development of the nasal cavity

A
  • Nasal passages derived from nasal pits.
  • Medial nasal processes start to merge in 6th week.
  • Nasal pits expand to give a nasal sac in the ectoderm.
  • This is supero-posterior to the primary palate.
  • Floor and posterior wall grows to form nasal fin (6-7 weeks)
  • This separates the oral and nasal cavities.
  • Voids develop in the nasal fin.
  • These fuse with nasal sac and enlarge it.
  • Nasal fin thins to become oronasal membrane.
44
Q

Nasal and oral cavity development

A
  • Primitive choana is formed in 7th week when the oronsal membrane ruptures.
  • Primary palate (premaxillae) forms floor of nasal cavity.
  • No contribution from maxillae or palatines yet
  • Oral and nasal cavities ultimately separated by palatine shelves.
  • These are medial growths of the maxillary prominences.
  • Initially grow inferiority on either side of the tongue.
45
Q

The palate

A
  • Premaxillae (primary palate) contain the 4 maxillary incisors.
  • Secondary palate formed when palatine shelves meet at a suture (before birth)
  • Secondary palate fuses with the primary palate early in childhood- incisive foramen marks where premaxillae and maxillae meet.
46
Q

Functional significance of the palate

A
  • Secondary palate= palatine processes of maxillae and palatine bones.
  • Secondary palate separates first stage of respiratory tract from first stage of digestive tract.
47
Q

Development of the palate

A
  • Growth of mandibular primordium lowers tongue- helps palatine shelves to elevate.
  • After 7th week palatine shelves rotate dorsally so that they become horizontal.
  • Palatine shelves fuse with each other, primary palate and nasal septum.
  • Incisive foramen marks where primary and secondary palates meet.
  • Fusion occurs in the centre of the shelves and progresses anteriorly and posteriorly.
  • Hard palate (maxillae and palatines) forms from condensations of mesenchyme in the anterior part of the secondary palate.
  • Nasal septum grows down from Frontonasal prominence to fuse with primary and secondary palates.
48
Q

Cleft lips and palate: aetiology

A
  • Cleft lips and palates result from the failure of the facial swellings to fuse normally.
  • They often (but do not always) occur together.
  • Phenytoin (an anticonvulsant) and vitamin A and its analogs may lead to cleft lip or cleft palates.
  • Mutations in MSX1, PVR1 and other genes may be linked to these conditions.
  • Distribution varies with gender, race, genealogy and geography.
  • Therefore, their origin is probably multifactorial.
49
Q

Cleft lips

A
  • lateral cleft lips usually result from the failure of intermaxillary process to fuse with the maxillary prominences
    -may be bilateral or unilateral
  • Can range from a small notch in the lip to complete separation of the lateral lip from nasal cavity and philtrum.
  • May separate maxillae from premaxillae- associated with tooth pathologies (eg absent, supernumerary or deformed teeth)
  • Median cleft lips result when the medial nasal processes fail to fuse together.
  • Therefore may be associated with a bifid nose.
  • Undervelopemt of mesenchyme in maxillary prominence or medial nasal process leads to insufficient contact between them.
50
Q

Cleft palate

A
  • Cleft palates results from the failure of the palatine shelves to fuse with each other.
  • Oral and nasal cavities in communication.
  • More common in females (palatal shelves elevation occurs one week later than in females)
  • Inadequate growth of palatine shelves due to:
    Lack of migration of mesenchyme
    Lack of proliferation or mesenchyme
    Cell death
    Failure of shelves to elevate
    Rupture after fusion
    Mandibular dysplasias.
51
Q

Mandibular dysplasia

A
  • Errors in development of the first pharyngeal arch means the tongue does not descend.
  • This obstructs the elevation of the palatine shelves.
  • Can be associate with a small mandible (micrognathia) and posterior displacement of the tongue (glossoptosis)1

Bio Med (24 decks)

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