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ENT > Embryology > Flashcards

Embryology Flashcards

1
Q

Briefly explain how the mesoderm is formed?

A
  • Embryo begins as 2 layers
  • epiblast layer invaginates
  • brings new cells between the layers (mesoderm)
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2
Q

WHat layer comes together to form the neural tube?

A

Ectoderm (neural cells)

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3
Q

All neural crest cells go on to form nerves or neural structures such as the brain and spinal cord. TRUE/FALSE?

A

False

Some form skeletal structures in head and neck

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4
Q

How many pharyngeal arches develop in humans?

A

6 arches

but 5th usually disappears

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5
Q

On what day of development do each of the pharyngeal arches form?

A

Arch 1 – Day 22
Arch 2 + 3 – Day 24
Arch 4 + 6 – Day 29

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6
Q

What are the 3 components to the pharyngeal arches?

A
  • Core pharyngeal arch (Mesenchymal tissue)
  • External pharyngeal CLEFT (Ectoderm)
  • Internal pharyngeal POUCH (Endoderm)
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7
Q

What cranial nerve is associated with each pharyngeal pouch?

A

1 - CN V2 and V3
2 - CN VII
3 - CN IX
4 and 6 - CN X

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8
Q

What are the 2 sections of the 1st pharyngeal arch?

A

Maxillary portion

Mandibular portion

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9
Q

What does the maxillary portion of the 1st pharyngeal arch give rise to?

A

Maxilla
Zygomatic bone
Squamous portion of temporal bone

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10
Q

What does the mandibular portion of the 1st pharyngeal arch give rise to?

A

Forms Meckel’s cartilage
Incus and Malleus (ear ossicles)
Mandible

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11
Q

What is Meckel’s cartilage?

A

embryological structure which eventually splits to form various other structures in the head and neck

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12
Q

All musculature associated with the 1st pharyngeal arch is innervated by which cranial nerve?

A

CN V3

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13
Q

What muscles are associated with the 1st pharyngeal arch?

A 
Muscles of mastication
Anterior belly of digastric
Mylohyoid
Tensor Tympani
Tensor veli Palatini
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14
Q

What is the function of the tensor tympani and stapedius?

A

Dampen sound

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15
Q

What cartilage is developed in the 2nd pharyngeal arch?

A

Reichert’s Cartilage

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16
Q

What are the skeletal derivatives of Reichert’s Cartilage?

A
  • Stapes (ear ossicle)
  • Styloid process of temporal bone
  • Stylohyoid ligament
  • Lesser horn of Hyoid
  • Upper part of Hyoid body
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17
Q

What cranial nerve supplies the muscles associated with the 2nd pharyngeal arch?

A

CN VII

Muscles of facial expression

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18
Q

What are the muscles of facial expression associated with the 2nd pharyngeal arch?

A
  • Posterior belly of digastric
  • Stylohyoid
  • Stapedius
  • Auricular muscles
19
Q

What cranial nerve supplies the stylopharyngeus (associated with the 3rd pharyngeal arch)?

A

CN IX Glossopharyngeal

20
Q

What skeletal structures are developed from the third pharyngeal arch?

A

Greater horn

Lower part of hyoid bone

21
Q

What skeletal structures do the 4th and 6th pharyngeal arches give rise to?

A

Laryngeal cartilages

22
Q

What muscles are associated with the 4th pharyngeal arc and what cranial nerve supplies them?

A

Cricothyroid
Levator veli palatini

Supplied by Superior Laryngeal from CN X

23
Q

What muscles are associated with the 6th pharyngeal arc and what cranial nerve supplies them?

A

Intrinsic laryngeal muscle

Supplied by recurrent laryngeal from CN X

24
Q

What do each of the pharyngeal clefts become during development?

A

1st cleft becomes = acoustic meatus

2nd, 3rd and 4th come inwards and form cervical sinus

25
Q

If cervical sinuses are not formed properly what can result?

A

Cysts and fistulae

- either pre-auriculr or anterior to sternocleidomastoid

26
Q

What do the first 2 pharyngeal pouches become?

A

1st:
Middle ear
Tympanic membrane
Eustachian tube

2nd:
Palatine Tonsils

27
Q

What does the 3rd pharyngeal pouch split into?

A

Upper part = inferior parathyroid gland

Lower part = thymus

28
Q

What does the 4th pharyngeal arch divide into?

A 
Superior parathyroid gland
Ultimobranchial body (c-cells containing calcitonin in thyroid)
29
Q

What is the otic placode and what does it give rise to?

A
  • Collection of ectoderm which develops near the hindbrain
  • Pinches in to from pit and eventually vesicle
  • vesicle gives rise to inner ear
30
Q

What are the 2 parts to the otic vesicle and what do they develop into?

A

Pars Superior (Utricular) = semicircular canals

Pars inferior (Saccular) = cochlear

31
Q

How do the semicircular canals develop?

A
  • Flattened outpocketings of utricular part

- Central part of the walls appose each other and break down

32
Q

What is the name given to the dilated end of the semicircular canal?

A

Crus ampullare

33
Q

What is the name for the non-dilated end of the semicircular canals?

A

Crus Nonampullare

34
Q

What is the crista ampullaris found inside the ampullae of the semi-circular canals?

A

Sensory cells for balance

35
Q

Describe how the saccule forms the cochlear duct

A

tubular outgrowth spirals around 2.5 times to form duct

remains joined to saccule by ductus reuniens

36
Q

Where are the outer and inner hair cells found in the ear?

A

Organ of Corti

37
Q

What mechanical stimuli is converted into the sound we hear?

A

Fluid moving over the outer and inner hair cells

38
Q

Most sound is conducted in the inner hair cells. TRUE/FALSE?

A

FALSE

outer hair cells conduct most sound (and there’s more of them)

39
Q

How is the middle ear formed?

A
  • Mesenchymal cells come together and condense to form ossicles
  • ossicles attached to bony wall by ligaments to allow vibration of sound
40
Q

What is the meatal plug?

A
  • Proliferated epithelium present during embryonic development
  • Regresses before birth to form ear drum
41
Q

What can occur if the meatal plug does not regress?

A

Congenital deafness

Requires surgical thinning

42
Q

What helps to develop the external ear?

A

6 mesenchymal proliferations

3 from Arch 1
3 from Arch 2

43
Q

What causes the ears to ascend during development?

A

Development of the mandible

44
Q

Why are the ears normally low set in genetic disorders?

A

Stunt in development has caused ascending of ears to halt.

ENT (16 decks)

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