Embryology Flashcards
What are the components of the pharyngeal apparatus?
1) 4 Pharyngeal pouches
2) 4 Pharyngeal arches
3) Pharyngeal cleft
1st Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery
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
2nd Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery
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
3rd Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery
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
What are the layers of the pharyngeal arches and what do they respectively form?
Each composed of mesoderm
External covering: ectoderm → pharyngeal clefts
Internal covering: endoderm → pharyngeal pouches
4th/6th Pharyngeal arch:
a) bones
b) muscles
c) nerve
d) artery
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
What does the 1st pharyngeal pouch form?
Eustachian tube
What does the 2nd pharyngeal pouch form?
Palatine tonsil
What does the 3rd pharyngeal pouch form?
1) Inferior parathyroid
2) Thymus
What does the 4th pharyngeal pouch form?
1) Superior parathyroid
2) Ultimobranchial body
What does the the 1st pharyngeal cleft form?
1) External auditory meatus
2) Outer tympanic membrane
What do the 2nd-4th pharyngeal cleft form?
1) Side of neck
2) Mesenchymal component
3) Cervical sinus (eventually obliterates)
What is Meckel’s cartilage and what is its function?
Part of mandibular prominence of 1st pharyngeal arch
- provides U shaped template/scaffold for mandible to form
What is an example of a congenital disorder associated with malformation of pharyngeal apparatus structures?
Treacher Collins Syndrome
What is laryngomalacia?
Congenitally Omega shaped epiglottis → stridor
What is Reichert’s cartilage and what is its function?
Part of 2nd pharyngeal arch
- forms:
i) Stapes
ii) Styloid process
iii) Stylohyoid ligament
iv) Lesser and upper part of hyoid bone
What are 2 classifications of skull bones?
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
True or false:
Unlike long and axial bones, the bones of the skull are all formed by intramembranous ossification.
False.
Both by intramembranous and endochondral
What is the stomodeum?
Rudimentary mouth
- forms opening between future oral cavity and foregut
- surrounded by 5 facial prominences
What lines the stomodeum?
Bucco(Oro)pharyngeal membrane
- stops developing during 4th week to form opening between future oral cavity and foregut.
Where are the nasal placodes located and what do they form?
Bilateral on frontonasal prominences
Form → Nasal pits → medial/lateral nasal prominences → (i) lip philtrum (ii) lateral sides of nostrils (iii) primary palate
What are the embryological structures that form the upper lip?
2 medial nasal prominences and 2 maxillary prominences
Facial development fml
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
What are the structures formed by the frontonasal prominences?
1) Forehead
2) Nose bridge
3) Frontal and nasal bones
What are the structures formed by the maxillary prominences?
1) Upper cheek
2) Lateral upper lip
3) Maxilla
4) Zygomatic bone
5) Secondary palate
What are the structures formed by the mandibular prominences?
1) Mandible
2) Chin
3) Lower lip
4) Lower cheek
What are the structures that are formed by the medial nasal prominces?
1) Midline of nose
2) Lip philtrum
What do the lateral nasal prominences form?
Nasal ala
How does the nasal and oral cavity become continuous during embryonic development?
Rupturing of oronasal membrane lining the stomodeum → continuous nasal and oral cavity via primitive choanae
Describe the process of neurulation.
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)
Where do neural tube defects tend to present and why?
Cranial and caudal ends (last to close)
What are 3 examples of neural tube defects?
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
Describe the formation of the cauda equina.
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
What are the 2 cell types that arise from the neurocoele/central canal of the neural tube and what do they form?
1) Neuroblasts
- neurons
(Marginal layer → white matter, mantle layer → grey matter)
2) Glioblasts
- neuroglial cells
The spinal cord forms from the (cranial/caudal) portion of the neural tube.
Caudal
Describe the formation of the primary, secondary and final brain vesicles.
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
Describe the formation of the ventricles.
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
How are the lateral and third ventricles connected?
Foramen of monro
What is the encephalocoele?
Congenital defect → herniation of intracranial contents
What is hydrocephalus?
Enlarged head due to ventricles filled with extra fluid (excess CSF)
