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ENT > Embryology > Flashcards

Embryology Flashcards

1
Q

What does the neural tube form from

A

Ectoderm forms a tube

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2
Q

Describe neural crest cells

A

They can break off from the neural crest and travel to different parts of the foetus
Some form nerves such as sympathetic ganglia
Form many other structures

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3
Q

How many pharyngeal arches are there

A

5
Numbered 1,2,3,4,6
5 is missing

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4
Q

What (in general) do the pharyngeal arches form

A

Most of the head and neck

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5
Q

In which week do the pharyngeal arches first develop

A

Week 4 and 5

Develop in numerical order = 1 to 6

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6
Q

What are the 3 components of the pharyngeal apparatus

A

Core pharyngeal arch - mesenchyme
External cleft - exoderm
Internal pouch - endoderm

Cleft and pouch separate arches

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7
Q

What does each pharyngeal arch consist of

A

Core of mesenchyme that forms musculature
Neural crest cells which from skeletal components
Cranial nerve for innervation
Artery - one of the aortic arch arteries

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8
Q

Which cranial nerves supply each pharyngeal arch

A

1 =Trigeminal (V2,3)
2 = facial
3 = glossopharyngeal
4&6 = vagus (superior and recurrent laryngeal)

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9
Q

What skeletal elements are formed by the first arch

A

Maxillary process - maxilla, zygomatic bone and squamous part of temporal bone
Mandibular process - Meckel’s cartilage which then forms incus, malleus and the mandible

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10
Q

Which muscles are formed in the first arch

A 
Muscles of mastication
Anterior belly of digastric
Mylohyoid 
Tensor tympani 
Tensor veli palatini

All innervated by V3

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11
Q

Which nerve supplies the 1st arch structures

A

CNV - trigeminal

All 3 branches of this nerve give sensory supply to skin of the face

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12
Q

What skeletal elements are formed by the 2nd arch

A 
Stapes 
Styloid process of temporal bone 
Stylohyoid ligament 
Lesser horn of the hyoid 
Upper part of hyoid body
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13
Q

Which cartilage is found in the 2nd arch

A

Reichert’s Cartilage

Starts as a bar then splits up and ossifies to form the skeletal elements

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14
Q

Which muscles are formed in the 2nd arch

A 
Muscles of facial expression
Posterior belly of digastric
Stylohyoid 
Stapedius
Auricular muscles
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15
Q

Which nerve supplies the structures of the 2nd arch

A

CNVII - facial nerve

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16
Q

What skeletal elements are formed by the 3rd arch

A

Greater horn of hyoid

Lower part of hyoid body

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17
Q

Which muscles are formed in the 3rd arch

A

Stylopharyngeus

Longitudinal pharyngeal muscle

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18
Q

Which nerve supplies the structures of the 3rd arch

A

CNIX - glossopharyngeal

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19
Q

What skeletal elements are formed by the 4th and 6th arches

A

Laryngeal cartilages

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20
Q

Which muscles are formed in the 4th arch

A

Cricothyroid
Levator veli palatini
Pharyngeal constrictors

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21
Q

Which muscles are formed in the 6th arch

A

Intrinsic laryngeal muscles

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22
Q

Which nerve supplies the structures of the 4th and 6th arches

A

CNX - vagus nerve
Arch 4 = superior laryngeal branch and pharyngeal plexus
Arch 6 - recurrent laryngeal branch

23
Q

What does the 1st pharyngeal cleft form

A

external acoustic meatus

24
Q

What is formed by pharyngeal clefts 2-4

A

The cervical sinus
Arch 2 falls down to cover these clefts
They lose contact with the outside and form the sinus

25
Q

What is formed from the 1st pharyngeal pouch

A

Middle ear
Tympanic membrane
Eustachian tube

26
Q

What is formed from the 2nd pharyngeal pouch

A

Palatine tonsils

Starts as 2 little buds that become invaded by lymphoid tissue

27
Q

What is formed from the 3rd pharyngeal pouch

A

Inferior parathyroid gland

Thymus

28
Q

What is formed from the 4th pharyngeal pouch

A

Superior parathyroid gland

Ultimobranchial body = thyroid and C cells

29
Q

Describe how the parathyroid glands reach their final position

A

Inferior set of glands actually develops above the superior ones
As the thymus tracks down to it’s position in the thorax, it drags the inferior glands down with it
They jump over the superior ones and bud off to imbed in the thyroid
This occurs around week 7

30
Q

What structures make up the middle ear

A

Tympanic cavity and ossicles

31
Q

What structures make up the external ear

A

External auditory meatus

Auricle

32
Q

What structures make up the internal ear

A

Semi-circular canals - for balance

Organ of corti - hearing

33
Q

Describe how the otic vesicles form and what they give rise to

A

Starts as otic placode which pinches inwards to form the otic pit
This further closes off to form the hole that is the otic vesicles
This gives rise to the inner ear

34
Q

Describe how the shape of the vesicles develop

A

Vesicle stretches out and becomes tear shaped
Further shape changes form a small sac at the very top with a long thin duct that connects it to two other circular (ish) areas
These are the pars superior and inferior
These develop into the utricular portion and saccular portion of the otic vesicle

35
Q

What does the utricular portion of the otic vesicle give rise to

A

The semi-circular canals
The structure regresses in sections to change the sac into a series of canals
Responsible for balance

36
Q

What does the saccular portion of the otic vesicle give rise to

A

The cochlear

Main part for hearing

37
Q

Name the semi-circular canals

A

Superior
Lateral
Posterior
S and P connected by crus commune nonampullare

38
Q

What is found within the crus ampullae of the semi-circular canal

A

Crista ampullaris

This contains the sensory cells needed for balance and the fibres of CNVIII

39
Q

In which weeks does the cochlear duct begin to form its spiral shape

A

between weeks 6 and 8

40
Q

Describe the development of the external ear

A

6 mesenchymal proliferations form around the 1st cleft
3 come from arch 1 and 3 from arch 2 (3 above and below)
They then fuse to form the auricle

41
Q

How does the postion of the external ear change with development

A

Initally form in the lower neck
Ascend due to development of the mandible
If development is stunted it often leads to low set ears (feature of some congenital diseases)

42
Q

An abnormality in the shape of the external ear suggests what

A

Error with the neural crest cells elsewhere in the body

e.g. heart or gut

43
Q

How many facial swelling are present in week 4 of development

A

5
The frontonasal prominence
2 maxillary and 2 mandibular prominences

44
Q

What is the name for the primitive oral cavity

A

Stomodeum

Surrounded by the facial swellings

45
Q

How many facial swelling are present by week 5

A

The 5 initial ones and then 4 additional nasal swellings (2 medial and 2 lateral)

46
Q

What is the nasolacrimal groove and what will it form

A

Groove between the maxillary prominence and lateral nasal prominence
Connect the corner of nose to eye
Will form the lacrimal system

47
Q

Which facial prominences form the upper lip

A

2 medial nasal prominences

2 maxillary prominences

48
Q

Which facial prominences form the lower lip

A

Mandibular prominence

49
Q

Which facial prominences form the nose

A

Frontonasal prominence - bridge and septum
Medial prominences - crest and tip
Lateral - alae

50
Q

What forms the intermaxillary segment

A

Fusion of the medial nasal prominences

51
Q

What does the intermaxillary segment contain

A

Portion of the upper jaw - 4 incisors
Has a labial portion that forms the philtrum of upper lip
Palatal component forms part of the primary palate

52
Q

What forms the primary palate

A

Intermaxillary segment and two sides of the maxillary process
U shaped
Eventually fuse to form the secondary palate

53
Q

How do the nasal cavities form

A

Nasal pits deepen (move into the face) and frontal nasal prominence moves forward
Intermaxillary process moves forward and connecting nasal fin will eventually thins and disappears, leading to one big connected sac
Communicates with oral cavity initially
As the palate develops, this connection shifts back until the nasal cavity meets the pharynx

54
Q

Error of palate fusion can lead to what pathology

A

Cleft palate and lip

ENT (9 decks)

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