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Head and Neck > Head and Neck embryology > Flashcards

Head and Neck embryology Flashcards

1
Q

How many somites are in human embryos?

A

33

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2
Q

How many pharyngeal/branchial arches are there in human development?

A

In humans 5 branchial arches develop. (6 arches start to develop but arch number 5 disappears so we are left with arches 1,2,3,4 and 6. )

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3
Q

What are the pharyngeal/branchial arches?

A

Series of arches which develop around the future mouth (stomatodeum) and pharynx.

Called “branchial” because in lower animals (fish) it forms the gills (branchium).

Support the primitive pharynx (this is why the term ‘pharyngeal arches’ can be used instead) and the face and neck develop from them.

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4
Q

Describe the 3 layers that make up the pharyngeal/branchial arteries?

A

Ectoderm lines the outside – also forms clefts inbetween arches

Mesoderm in the middle ( + neural crest cells) – forms cartilage and muscles

Endoderm on the inside – also forms pouches in between arches

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5
Q

What are the nerves of the pharyngeal arches?

A

1st arch - mandibular branch of trigeminal nerve (CN V3)
2nd arch - facial nerve (CN VII)
3rd arch - glossopharyngeal n. (CN IX)
4th arch - superior laryngeal branch of vagus (CN X)
(no 5th arch)
6th arch - recurrent laryngeal branch of vagus (CN X)

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6
Q

What is the nerve of the 1st branchial arch?

A

1st arch - mandibular branch of trigeminal nerve (CN V3)

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7
Q

What is the nerve of the 2nd branchial arch?

A

2nd arch - facial nerve (CN VII)

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8
Q

What is the nerve of the 3rd branchial arch?

A

3rd arch - glossopharyngeal n. (CN IX)

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9
Q

What is the nerve of the 4th branchial arch?

A

4th arch - superior laryngeal branch of vagus (CN X)

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10
Q

What is the nerve of the 6th branchial arch?

A

6th arch - recurrent laryngeal branch of vagus (CN X)

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11
Q

What nerve innervates all the muscles of facial expression?

A

CN VII (facial nerve)

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12
Q

Why are all muscles of facial expression innervated by the same nerve (facial nerve)?

A

All these muscles developed from the 2nd branchial arch, and its nerve supply is the facial nerve

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13
Q

From which pharyngeal/branchial arch do the muscles of facial expression develop?

A

2nd arch

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14
Q

Which muscle of the face and neck is spit between two arches and therefore has split nerve supply?

A

Digastric muscle:
• Anterior belly innervated by mandibular division of trigeminal nerve (CN V3) – anterior belly originates from first arch
• Posterior belly innervated by facial nerve – originates from 2nd arch

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15
Q

What muscles are derived from the 1st pharyngeal arch?

A

temporalis, masseter, anterior digastric, muscles of chewing etc

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16
Q

From which arch does the temporals, master, anterior digastric and muscles of chewing arise from?

A

1st arch

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17
Q

What muscles are derived from the 2nd pharyngeal arch?

A

muscles of face e.g. occipitofrontalis, posterior digastric, orbicularis oris etc

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18
Q

From which arch does the muscles of face e.g. occipitofrontalis, posterior digastric, orbicularis oris etc arise from?

A

2nd arch

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19
Q

What muscles are derived from the 3rd pharyngeal arch?

A

3rd arch – only one muscle, stylopharyngeus

20
Q

From which arch does the stylopharyngeus arise from?

A

3rd arch

21
Q

What muscles are derived from the 4th and 6th pharyngeal arches?

A

All the pharyngeal muscles, muscles of larynx and muscles of the palate

22
Q

What is the fate of the 1st arch cartilage?

A

1st arch cartilage – mandible, malleus and incus of ear

23
Q

The cartilage of which arch creates the mandible, malleus and incus?

A

1st arch cartilage

24
Q

What is the fate of the 2nd arch cartilage?

A

2nd arch cartilage - near external auditory meatus e.g. hyoid + styloid process of temporal bone + stapes

25
Q

The cartilage of which arch creates the hyoid, the stapes and the styloid process on the temporal bone?

A

2nd arch cartilage

26
Q

What is the fate of the 3rd arch cartilage?

A

3rd arch cartlage – greater horn of hyoid bone

27
Q

The cartilage of which arch creates the greater horn of the hyoid bone?

A

3rd arch

28
Q

What is the fate of the 4th arch cartilage?

A

4th arch cartilage – thyoid cartilage

29
Q

The cartilage of which arch creates the thyroid cartilage?

A

4th arch

30
Q

What is the fate of the 6th arch cartilage?

A

6th arch cartilage – cricoid cartilage

31
Q

The cartilage of which arch creates the cricoid cartilage?

A

6th arch

32
Q

From what processes does the face develop from?

A

One frontonasal process (from mesenchyme superior to future mouth)

Two maxillary processes (from maxillary part of 1st branchial arch mesoderm)

Two mandibular processes (also 1st arch mesoderm)

33
Q

Describe the development of the palate

A
  • Stage 1: Medial nasal process grows downwards and forms philtrum. This forms the primary palate
  • Stage 2:From the maxillary processes, two palatine shelves grow inwards
  • Stage 3: The palatine shelves meet in the midline to form the secondary palate. Now the oral cavity and nasal cavity are separate.
34
Q

List some issues associated with a cleft lip and palate

A

These disorders can result in feeding problems, speech problems, hearing problem and frequent ear infections

35
Q

What fails in facial development leading to a cleft lip?

A

It is due to the failure of fusion of the maxillary and medial nasal processes to form the philtrum (formation of the primary palate).

36
Q

What are some risk factors for developing a cleft lip and palate?

A

Risk factors include smoking during pregnancy, diabetes, obesity, an older mother, and certain medications (such as some used to treat seizures).

37
Q

Describe the formation of the cranial vault

A
  1. Cranial vault – flat bones: Membranous bones; formed by membranous ossification calvaria
38
Q

Describe the formation of the base of the skull

A
  1. Base of skull – irregular bones: Bones formed by endochondral ossification
39
Q

Describe the formation of the viscerocranium

A
  1. Viscerocranium – skeleton of face: Partly from branchial arches, and partly from sensory (special sense) capsules
40
Q

What are the 3 components of the skull?

A

Cranial vault
Base of skull
Viscerocranium

41
Q

When does the anterior fontanelle close?

A

1.5 years old

42
Q

Describe craniosynostosis

A

Craniosynostosis - a condition in which one or more of the fibrous sutures in an infant (very young) skull prematurely fuses by turning into bone (ossification), thereby changing the growth pattern of the skull.

43
Q

What are sensory capsules?

A

Sensory capsules are derived from mesoderm of ‘somites’ in head and neck region.

These preform in cartilage and ossify to form bones around the sense organs – ie nose, eye and ear

They form partly base of skull, partly viscerocranium

44
Q

Describe a condition linked to a 1st pharyngeal arch abnormality

A

Treacher Collins syndrome (TCS) is a autosomal dominant genetic disorder characterized by deformities of the ears, eyes, cheekbones, and chin

45
Q

From what embryological abnormality does Treacher Collins syndrome arise from?

A

1st pharyngeal arch abnormality

Head and Neck (20 decks)

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