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15. Neuro Test 1 > 15. Pharyngeal Arch Development (Dennis) > Flashcards

15. Pharyngeal Arch Development (Dennis) Flashcards

1
Q

What muscles come from the fourth arch?

What cranial nerve innervates them?

A

Cricothyroid, levator veli palatini and the constrictors of the pharynx.

CN X

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2
Q

What is a cervical cyst?

A

An opening behind the mandible created by the failure of the second pharyngeal groove (of the cervical sinus) to close completely.

They are typically asymptomatid until they get larger and fill with fluid and cellular debris.

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3
Q

What happens at weeks 7, 10, 11, 20, and 35 of thyroid gland development?

A

7 weeks:

  • Solid mass of endodermal cells → broken up into epithelial cords by vascular mesenchyme
  • Thyroglossal duct has normally degenerated & disappeared
  • Proximal opening of the duct persists as foramen cecum on dorsal tongue
  • Pyramidal lobe extends superiorly from the isthmus in approximately 50% of people

10th week:

  • Cords have divided into cellular groups & a lumen
  • Cells arranged in a single layer around thyroid follicles

11th week: colloid appears & synthesis of TH occurs

20 weeks: the levels of fetal TSH & thyroxine increase

35 weeks: fetal TSH & thyroxine reach adult levels

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4
Q

What general structures are found in each pharyngeal arch?

A
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5
Q

What forms the body of the hyoid bone?

A

Hypopharyngeal eminence (from PA 3 and PA 4)

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6
Q

What is responsible for the formation of the maxillary and mandibular components of pharyngeal arch 1?

A

Neural crest cell migration into the area.

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7
Q

What is the “cervical sinus?”

A

A depression in ectoderm caused by PA 2 overgrowing PA 3 and PA 4. This leads to a common pharyngeal groove “sinus” for pharyngeal grooves 2,3, and 4.

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8
Q

What muscles come from the second arch?

What cranial nerve innervates them?

A

Stapedius and the muscles of facial expression.

CN VII

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9
Q

What embryological structure gives rise to the distal internal carotid?

A

Extensions of the dorsal aortae.

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10
Q

From what does the thyroid gland develop?

A

A median thickening in the endoderm of the primordial pharynx.

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11
Q

What is Treacher-Collins syndrome?

What is the cause?

A

(Mandibulofacial dysostosis)

Treacher-Collins syndrome (mandibulofacial dysostosis)

• Malar hypoplasia w/ down-slanting palpebral fissures, defects
of lower eyelids, deformed external ears, & sometimes middle
& internal ears
• Autosomal dominant disorder; mutations in Treacher Collins–
Franceschetti syndrome 1 gene (TCOF1)
• Encodes for the protein TREACLE, involved in ribosome
biogenesis
• Truncated in TCS leading to ↑↑ apoptosis of cranial NCC

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12
Q

What is Meckel’s cartilage?

What is it’s function?

A

The cartilage of pharyngeal arch 1.

Used as a model for osteoblasts to form the mandible. After the mandible is created, Meckel’s cartilgae will degenerate.

Also, two nodules break off and serve as a precursor from the malleus and incus.

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13
Q

What is formed by the cartilage of the third pharyngeal arch?

A

Greater cornu of the hyoid bone.

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14
Q

What embryological layer gives rise to the thyroid parafollicular cells (C Cells)?

A

Neural crest cells

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15
Q

The majority of the developing pharyngeal arches are what type of tissue?

A

Neural crest cells.

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16
Q

What muscles come from the sixth arch?

What cranial nerve innervates them?

A

Intrinsic muscles of the larynx.

CN X

17
Q

What muscle comes from the third arch?

What cranial nerve innervates it?

A

Stylopharyngeus.

CN IX

18
Q

What are the first structures the first pharyngeal arch develops into?

A

The maxillary and mandibular prominences.

19
Q

Where does the ultimopharyngeal body come from?

What is its function?

A

The ultimopharyngeal body comes from the ventral part of the 4th pharyngeal pouch.

(Endoderm)

It fuses with the thyroid gland and disseminates, forming the parafollicular (C Cells) of the Thyroid (which produce calcitonin).

20
Q

What embryological structure do the external carotid arteries come from?

A

Common carotid.

21
Q

What is formed from the 1st pharyngeal membrane?

A

The tympanic membrane

22
Q

What all is derived from the first pharyngeal pouch?

A

Forms the tubotympanic recess.

This recess becomes both the pharyngotympanic tube (proximally) as well as the tympanic cavity, the mastoid antrum, and a contribution to the tympanic membrane (distally).

23
Q

What is DiGeorge syndrome?

A

• Agenesis of thymus & parathyroid glands
• Congenital hypoparathyroidism
• Shortened philtrum of upper lip, low-set &
notched ears
• Nasal clefts, thyroid hypoplasia
• Cardiac abnormalities (defects of the
aortic arch & heart)

CATCH22: Cardiac abnormality, Abnormal face, Thymus hypoplasia, cleft palate, hypocalcemia, 22nd chromosome problem”

24
Q

What is the Pierre Robin sequence?

A

Pierre Robin sequence:

• Typically occurs de novo in most patients
• Associated with hypoplasia of the mandible, cleft
palate, & defects of the eyes & ears
• Initiating defect is a small mandible
(micrognathia) → results in posterior
displacement of the tongue → obstruction of full
closure of the palate → results bilateral cleft
palate

PRS = Palate (cleft), Retracted Tongue, Small mandible

25
Q

What forms the stylohyoid ligament?

A

Riechert’s cartilage from PA 2.

26
Q

Where does Riechert’s cartilage come from, and what does it make?

A

Riechert’s cartilage comes from pharyngeal arch 2, and makes the stapes and styloid process of the temporal bone. It also makes the lesser cornu of the hyoid, and the ligament in between its structures - the stylohyoid ligament.

27
Q

What do we call the adult remnant of the thyroglossal duct?

A

The foramen cecum.

28
Q

What all is derived from the fourth pharyngeal pouch?

A

This forms a dorsal bulbar part and a ventral hollow part (just like arch 3).

The dorsal part becomes the superior parathyroid gland (not to be confused by the more superior pouch number 3 forming the inferior parathyroid gland).

The hollow part becomes the ultimopharyngeal body, which fuses with the thyroid gland and disseminates to form the parafollicular cells.

29
Q

What important arteries do the 3rd pharyngeal arch arteries give rise to?

A

The root of the internal carotid and the common carotid.

30
Q

What is formed from the perichondrium of Meckel’s cartilage?

A

Anterior ligament of the malleus.

Sphenomandibular ligament.

31
Q

What muscles come from the first arch?

What cranial nerve innervates them?

A

Muscles of mastication.

CN V

32
Q

Where do the muscular components of the pharyngeal arches come from generally?

A

Prechordal and paraxial mesoderm.

33
Q

What is formed by the fourth and sixth arch cartilages?

A

Laryngeal cartilages.

34
Q

What forms the lesser cornu, greater cornu, and body of the hyoid?

A

Lesser cornu = Reichert’s cartilage (PA 2)

Greater Cornu = Third arch cartilage

Body of Hyoid = Hypopharyngeal eminence (PA 3 and PA 4)

35
Q

What all is derived from the second pharyngeal pouch?

A

Part of the cavity of the pouch forms the tonsillar sinus.

Endoderm of the pouch proliferates and breaks down, forming the tonsillar crypts in the center, and the epithelium of the tonsils and crypts on the outside.

Mesenchyme of the pouch forms lymphoid tissue and will organize into lymphatic nodules of the palantine tonsil.

36
Q

What are the general roles of the neural crest cells, the paraxial mesoderm, the lateral plate mesoderm, and the pharyngeal endoderm in the developing pharyngeal arches?

A

Neural crest cells: make the maxillary and mandibular prominences, as well as the connective tissue (bone, dermis) and smooth muscle.

Paraxial mesoderm is called the myogenic mesoderm, because it forms the muscle primordium in each arch.

Lateral plate mesoderm gives rise to angioblasts which form endothelium.

Pharyngeal endoderm plays a regulatory role.

37
Q

What all is derived from the third pharyngeal pouch?

A

There are two parts: the dorsal bulbar part and the ventral hollow part.

The dorsal bulbar part (more superior) forms the inferior parathyroid gland.

The hollow part (more ventral and inferior) forms the thymus.

38
Q

What can cause the presence of accessory thyroid lobes?

A

Broken off pieces along the thyroglossal duct as the thyroid descends into its final resting place in the neck.

39
Q

What forms the stapes and styloid process of the temporal bone?

A

Reichert’s cartilage from PA 2.

15. Neuro Test 1 (21 decks)

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