Head And Neck

Question 1

What are the pharyngeal arches?

Answer 1

A system of mesenchymal proliferation a in the neck region of the embryo
1,2,3,4,6 (5 doesn’t form/regresses)
Each arch has an associated nerve, artery and cartilage bar

Question 2

Describe some differences between the frontonasal prominence and the pharyngeal arches

Answer 2

FNP - unpaired, developing brain

PA - paired, development of face

Question 3

Describe the nerve, artery and cartilage bar for Ph Arch 1

Answer 3

Nerve - muscles of mastication –> CN V3
Artery - disappears
Cartilage bar - Meckel’s, maxillary, mandibular prominences, malleus, incus, mandible

Question 4

Describe the nerve, artery and cartilage bar for Ph Arch 2

Answer 4

Nerve - muscles of facial expression –> CN VII
Artery - disappears
Cartilage bar - Reichert’s, stapes, styloid process, hyoid bone (lesser cornu and upper body)

Question 5

Describe the nerve, artery and cartilage bar for Ph Arch 3

Answer 5

Nerve - stylopharyngeus muscle –> CN IX
Artery - internal carotid
Cartilage bar - rest of hyoid bone

Question 6

Describe the nerve, artery and cartilage bar for Ph Arch 4

Answer 6

Nerve - cricothyroid, levator palatini, pharynx constrictors –> CN X, superior laryngeal nerve
Artery - arch of aorta (R), brachicephalic (L)
Cartilage bar - epiglottis, thyroid, arytenoid, cricoid

Question 7

Describe the nerve, artery and cartilage bar for Ph Arch 6

Answer 7

Nerve - intrinsic larynx muscles –> CN X, recurrent laryngeal nerve
Artery - pulmonary arch
Cartilage bar - epiglottis, thyroid, arytenoid, cricoid

Question 8

Differentiate between pharyngeal pouches and clefts

Answer 8

Pouch - endoderm

Cleft - ectoderm

Question 9

Describe the derivatives of the pharyngeal pouches and clefts

Answer 9

Ph pouch 1 - tympanic cavity, auditory tube
Ph pouch 2 - palatine tonsil
Ph pouch 3 + 4 - parathyroid
Ph pouch 6 - thymus
Ph cleft 1 - external acoustic meatus
Ph cleft 2 - grown down and obliterates others

Question 10

Describe conditions that may occur during branchial development

Answer 10

Branchial cysts - enclosed palpable remnants of pouches
Branchial fistulae - remnant maintains open to external environment
These can occur anywhere along anterior border of SCM

Question 11

Describe the development of the nose

Answer 11

Nasal placodes appear on FNP then sink –> nasal pits
Medial and lateral prominences form on either side of pits
Maxillary prominences grow medially,mouthing nasal prominences together in midline
Maxillary prominences fuse with medial nasal prominences
Medial nasal prominences fuse in midline –> creates intermaxillary segment (labial component philtrum, upper jaw 4 incisors, palate, primary palate)
Secondary palate derived from palatal shelves

Question 12

Describe the development of the lip and palate

Answer 12

Maxillary prominence –> two palatal shelves
Mandible grows large enough to allow tongue to drop
Palatal shelves fuse, nasal septum fuses with palatal shelves

Question 13

Describe the development of the face

Answer 13

FNP
1st Ph arch - maxillary prominence, mandibular prominence
Stomatodeum - buccopharyngeal mrmbrabe ruptures

Question 14

Describe the development of the eyes

Answer 14

4th week
Outpocketings of forebrain
Grow out to make contact with overlying ectoderm
Optic placodes –> lens (special sense)
Retina is derived from diencephalon
As facial prominences grow –> eyes move to front of face –> binocular vision

Question 15

Describe the development of the external and internal ear

Answer 15

External:
From 1st Ph cleft
Auricles develop from proliferation within 1st and 2nd Ph arches
Develop initially in neck
As mandible grows –> ears ascend to side of head (in line with eyes)
Internal:
Optic placodes appear towards back of head
Invaginate auditory vesicles –> membranous labyrinth of cochlea and semilunar canal system

Question 16

Describe how lateral cleft lips and cleft palates occur

Answer 16

Lateral cleft lip - failure of fusion of medial nasal prominence with maxillary prominence
Cleft lip + palate - combined with failure of palatal shelves to meet in midline

Question 17

Describe the development of the pituitary gland

Answer 17

Posterior pituitary:
Infundibulum
Downward outgrowth of forebrain grows towards roof of pharynx
Anterior pituitary:
Rathke’s pouch
Outpocketing of ectoderm of the stomatodeum
Evagination of roof of pharynx
Grows dorsally (upwards) towards the developing forebrain

Question 18

Describe the development of the thyroid

Answer 18

Between tuberculum impar and cupola
Originates from foramen cecum
Bifurcates and descends bilobed, connected by isthmus
Remains connected to tongue by thyroglossal duct
Myogenic precursors in occipital somites migrate (CN XII)

Question 19

Describe the development of the tongue

Answer 19

Lies partly on oral cavity and partly in pharynx
Highly mobile due to lingual frenulum
Receives a component from each Ph arch - 2 lateral lingual swellings (Ph 1), 3 median lingual swellings (Ph 1 - tuberculum impar, Ph 2,3,4 - cupola, Ph 4 - epiglottal swelling)
Lateral lingual swellings overgrow tuberculum impar
2 Ph arch obliterated
Degeneration frees tongue from floor of oral canal

Question 20

Describe conditions that may occur during development of the midline structures

Answer 20

Thyroglossal cysts/fistulae
Ectopic thyroid tissue - anywhere along descent
1st arch syndrome - failure of colonisation with neural crest cells e.g. Treacher Collins
‘Tongue tied’ - frenulum too short

Question 21

Describe the area of the pharynx

Answer 21

From the base of the skull to the inferior border of the cricoid cartilage of the larynx
Nasal - superior to soft palate
Oral - between soft palate and larynx
Laryngeal - posterior to larynx