Embryology

Question 1

What are the components of the pharyngeal apparatus?

Answer 1

1) 4 Pharyngeal pouches
2) 4 Pharyngeal arches
3) Pharyngeal cleft

Question 2

1st Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery

Answer 2

1st Pharyngeal arch:
a) bones
i) Maxilla
ii) Mandible
iii) Malleus
iv) Incus
v) Squamous part of temporal bone
vi) Zygomatic bone
vii) Palatine bones

b) muscles
i) Muscles of mastication
ii) Anterior belly of digastric
iii) Tensor veli palatini
iv) Tensor tympani

c) nerve
- trigeminal

d) artery
- maxillary

Question 3

2nd Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery

Answer 3

2nd Pharyngeal arch:
a) bones
i) Stapes
ii) Styloid process
iii) Lesser horn
iv) superior part of hyoid bone body

b) muscles
i) Muscles of facial expression
ii) Stapedius
iii) Mylohyoid
iv) Posterior belly of digastric

c) nerve
- facial

d) artery
i) Hyoid
ii) Stapedial

Question 4

3rd Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery

Answer 4

3rd Pharyngeal arch:
a) bones
- (i) greater horn and (ii) inferior part of hyoid bone

b) muscles
- stylopharyngeus

c) nerve
- glossopharyngeal

d) artery
i) common carotid
ii) 1st part of internal carotid artery

Question 5

What are the layers of the pharyngeal arches and what do they respectively form?

Answer 5

Each composed of mesoderm

External covering: ectoderm → pharyngeal clefts

Internal covering: endoderm → pharyngeal pouches

Question 6

4th/6th Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery

Answer 6

4th/6th Pharyngeal arch:
a) bones
i) Thyroid
ii) Cricoid
iii) Arytenoid
iv) Corniculate
v) cuneiform

b) muscles
4th:
i) cricothyroid
ii) levator veli palatini
iii) pharyngeal constrictors

6th:
- intrinsic muscles of larynx (except cricothyroid)

c) nerve
4th: superior laryngeal
6th: recurrent laryngeal

d) artery
4th: left aortic arch, right subclavian
6th: pulmonary arteries

Question 7

What does the 1st pharyngeal pouch form?

Answer 7

Eustachian tube

Question 8

What does the 2nd pharyngeal pouch form?

Answer 8

Palatine tonsil

Question 9

What does the 3rd pharyngeal pouch form?

Answer 9

1) Inferior parathyroid
2) Thymus

Question 10

What does the 4th pharyngeal pouch form?

Answer 10

1) Superior parathyroid
2) Ultimobranchial body

Question 11

What does the 1st pharyngeal cleft form?

Answer 11

1) External auditory meatus
2) Outer tympanic membrane

Question 12

What do the 2nd-4th pharyngeal cleft form?

Answer 12

1) Side of neck
2) Mesenchymal component
3) Cervical sinus (eventually obliterates)

Question 13

What is Meckel’s cartilage and what is its function?

Answer 13

Part of mandibular prominence of 1st pharyngeal arch
- provides U shaped template/scaffold for mandible to form

Question 14

What is an example of a congenital disorder associated with malformation of pharyngeal apparatus structures?

Answer 14

Treacher Collins Syndrome

Question 15

What is laryngomalacia?

Answer 15

Congenitally Omega shaped epiglottis → stridor

Question 16

What is Reichert’s cartilage and what is its function?

Answer 16

Part of 2nd pharyngeal arch
- forms:
i) Stapes
ii) Styloid process
iii) Stylohyoid ligament
iv) Lesser and upper part of hyoid bone

Question 17

What are 2 classifications of skull bones?

Answer 17

1) Neurocranium
- 2 temporal
- 2 parietal
- 1 frontal
- 1 occipital
- 1 sphenoid
- 1 ethmoid

2) Viscerocranium
- 2 nasal
- 2 lacrimal
- 2 zygomatic
- 2 palatine
- 2 maxillae
- 2 inferior nasal conchae
- 1 vomer
- 1 mandible

Question 18

True or false:
Unlike long and axial bones, the bones of the skull are all formed by intramembranous ossification.

Answer 18

False.
Both by intramembranous and endochondral

Question 19

What is the stomodeum?

Answer 19

Rudimentary mouth
- forms opening between future oral cavity and foregut
- surrounded by 5 facial prominences

Question 20

What lines the stomodeum?

Answer 20

Bucco(Oro)pharyngeal membrane
- stops developing during 4th week to form opening between future oral cavity and foregut.

Question 21

Where are the nasal placodes located and what do they form?

Answer 21

Bilateral on frontonasal prominences

Form → Nasal pits → medial/lateral nasal prominences → (i) lip philtrum (ii) lateral sides of nostrils (iii) primary palate

Question 22

What are the embryological structures that form the upper lip?

Answer 22

2 medial nasal prominences and 2 maxillary prominences

Question 23

Facial development fml

Answer 23

1) Maxillary prominences grow → compress medial nasal prominence towards midline → fuse (lose cleft)

2) Nasolacrimal groove (formed between maxillary and lateral nasal prominence) form epithelial cord → canalise → nasolacrimal (eventual tear) duct

3) Upper end of nasolacrimal duct widens → lacrimal sac

4) Epithelial cord detaches → maxillary and lateral nasal prominences merge

5) Maxillary prominence form cheek and maxilla

6) Lateral nasal prominences form ala of nose

7) Mandibular prominences cross midline and fuse → lower lip and mandible

8) Maxillary and mandibular prominences fuse → angles of mouth

9) Superior portion of frontonasal prominences → forehead

Question 24

What are the structures formed by the frontonasal prominences?

Answer 24

1) Forehead
2) Nose bridge
3) Frontal and nasal bones

Question 25

What are the structures formed by the maxillary prominences?

Answer 25

1) Upper cheek 2) Lateral upper lip 3) Maxilla 4) Zygomatic bone 5) Secondary palate

Question 26

What are the structures formed by the mandibular prominences?

Answer 26

1) Mandible 2) Chin 3) Lower lip 4) Lower cheek

Question 27

What are the structures that are formed by the medial nasal prominces?

Answer 27

1) Midline of nose 2) Lip philtrum

Question 28

What do the lateral nasal prominences form?

Answer 28

Nasal ala

Question 29

How does the nasal and oral cavity become continuous during embryonic development?

Answer 29

Rupturing of oronasal membrane lining the stomodeum → continuous nasal and oral cavity via primitive choanae

Question 30

Describe the process of neurulation.

Answer 30

Formation of neural tube from ectoderm: 1) Formation of notochord - migrating mesenchymal cells collect in midline of embryo → notochordal process → fuse with endoderm → notochordal plate → detach from endoderm → notochord 2) Thickening of ectoderm → neural plate 3) Elevation of lateral edges of neural plate → neural groove 4) Further elevation → canalisation of neural groove → neural tube 5) Spinal crest cells (from lateral edges) migrate to form other structures (eg. PNS)

Question 31

Where do neural tube defects tend to present and why?

Answer 31

Cranial and caudal ends (last to close)

Question 32

What are 3 examples of neural tube defects?

Answer 32

Caudal: 1) Spinal bifida occulta - gap anywhere from L5-S1 → tufting of hair - asymptomatic Vertebral fusion failure: 2) Spinal bifida meningocoele - protrusion of meninges 3) Spinal bifida myelomeningocoele - protrusion of meninges + nerve endings Cranial: 4) Execephaly - brain outside of skull - can progress to anencephaly 5) Anencephaly - missing parts of brain/skull

Question 33

Describe the formation of the cauda equina.

Answer 33

During development vertebral column grows much faster than spinal cord → at birth, spinal cord stretches to L3 → during development pulled back to L2 but meninges still extend to S2 → nerves suppling lower than L2 extend from conus medullaris → cauda equina

Question 34

What are the 2 cell types that arise from the neurocoele/central canal of the neural tube and what do they form?

Answer 34

1) Neuroblasts - neurons (Marginal layer → white matter, mantle layer → grey matter) 2) Glioblasts - neuroglial cells

Question 35

The spinal cord forms from the (cranial/caudal) portion of the neural tube.

Answer 35

Caudal

Question 36

Describe the formation of the primary, secondary and final brain vesicles.

Answer 36

1) Prosencephalon a) Telencephalon → (i) Cerebral cortex (ii) Basal ganglia b) Diencephalon → (i) Optic cup (ii) Stalk (iii) Pituitary gland (iv) Thymus (v) Hypothalamus (vi) Pineal body 2) Mesencephalon → midbrain 3) Rhombencephalon a) Metencephalon → (i) pons (ii) cerebellum b) Myelencephalon → medulla oblongata

Question 37

Describe the formation of the ventricles.

Answer 37

Formed from cavtity of neural tubes: 1) Lateral ventricle - telencephalon 2) Third ventricle - telencephalon + diencephalon 3) Future cerebral aqueduct - mesencephalon 4) Fourth ventricle - metencephalon + myelencephalon

Question 38

How are the lateral and third ventricles connected?

Answer 38

Foramen of monro

Question 39

What is the encephalocoele?

Answer 39

Congenital defect → herniation of intracranial contents

Question 40

What is hydrocephalus?

Answer 40

Enlarged head due to ventricles filled with extra fluid (excess CSF)

Question 41

How does the tongue form?

Answer 41

Anterior 2/3: 1st pharyngeal arch 1) proliferation of mesoderm → lateral lingual swellings + tuberculum impar (5th wk) 2) Lateral lingual swellings grow larger than tuberculum impar → fuse at median sulcus Posterior 1/3: 3/4th pharyngeal arch 1) proliferation of mesoderm → Copula + Hypopharyngeal eminence 2) Hypopharyngeal eminence grower larger than copula → fuse to anterior 2/3 at terminal sulcus

Question 42

What are 2 malformations of the tongue?

Answer 42

1) Ankyloglossia - frenulum extends to tip of tongue 2) Bifid tongue - Inadequate fusion of lateral swellings - a/w cleft lower lip

Question 43

How does the primary palate form and what does it give rise to?

Answer 43

Medial growth of maxillary prominences → union of medial nasal prominences Forms: 1) Labial components (philtrum) 2) Upper jaw component (4 incisors) 3) palatal component

Question 44

How does the secondary palate form?

Answer 44

1) Outgrowths of maxillary process → Palatine shelves 2) Tongue moves downwards + mandible grows down and out 3) Palatine shelves fuse → secondary palate 4) Nasal septum fuse with secondary palate → hard palate

Question 45

What is the malformation of the palate formation called?

Answer 45

Cleft palate eg. cleft lip, uvula, palate, full palate