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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
If cervical sinuses are not formed properly what can result?
Cysts and fistulae | - either pre-auriculr or anterior to sternocleidomastoid
26
What do the first 2 pharyngeal pouches become?
1st: Middle ear Tympanic membrane Eustachian tube 2nd: Palatine Tonsils
27
What does the 3rd pharyngeal pouch split into?
Upper part = inferior parathyroid gland | Lower part = thymus
28
What does the 4th pharyngeal arch divide into?
``` Superior parathyroid gland Ultimobranchial body (c-cells containing calcitonin in thyroid) ```
29
What is the otic placode and what does it give rise to?
- Collection of ectoderm which develops near the hindbrain - Pinches in to from pit and eventually vesicle - vesicle gives rise to inner ear
30
What are the 2 parts to the otic vesicle and what do they develop into?
Pars Superior (Utricular) = semicircular canals Pars inferior (Saccular) = cochlear
31
How do the semicircular canals develop?
- Flattened outpocketings of utricular part | - Central part of the walls appose each other and break down
32
What is the name given to the dilated end of the semicircular canal?
Crus ampullare
33
What is the name for the non-dilated end of the semicircular canals?
Crus Nonampullare
34
What is the crista ampullaris found inside the ampullae of the semi-circular canals?
Sensory cells for balance
35
Describe how the saccule forms the cochlear duct
tubular outgrowth spirals around 2.5 times to form duct remains joined to saccule by ductus reuniens
36
Where are the outer and inner hair cells found in the ear?
Organ of Corti
37
What mechanical stimuli is converted into the sound we hear?
Fluid moving over the outer and inner hair cells
38
Most sound is conducted in the inner hair cells. TRUE/FALSE?
FALSE | outer hair cells conduct most sound (and there's more of them)
39
How is the middle ear formed?
- Mesenchymal cells come together and condense to form ossicles - ossicles attached to bony wall by ligaments to allow vibration of sound
40
What is the meatal plug?
- Proliferated epithelium present during embryonic development - Regresses before birth to form ear drum
41
What can occur if the meatal plug does not regress?
Congenital deafness | Requires surgical thinning
42
What helps to develop the external ear?
6 mesenchymal proliferations 3 from Arch 1 3 from Arch 2
43
What causes the ears to ascend during development?
Development of the mandible
44
Why are the ears normally low set in genetic disorders?
Stunt in development has caused ascending of ears to halt.

ENT (20 decks)

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