2.1 Development of the Head & Neck

Question 1

The pharyngeal apparatus refers to the primitive pharynx and its associated paired structures developing on either side:
• Contributes significantly to the embryonic development of the face, jaw, ear, and neck
• Consists of pharyngeal arches, pharyngeal clefts (grooves) and pharyngeal pouches

• _________: Series of swellings making up the pharyngeal arches made of mesoderm
• _________: Depressions between the arches on the inner surface lined by endoderm
• _________: Depressions between the arches on the outer surface lined by ectoderm

Answer 1

Arch;

Pouch;

Cleft

Question 2

PHARYNGEAL ARCHES
The six pairs of pharyngeal arches appear during the 4th week of embryonic development on either side of the ventrolateral aspect of the neck:
• Develop in a _____________ sequence
• 5th pharyngeal arch usually never forms or forms as a short-lived rudiment and promptly regresses → arches are numbered as 1st, 2nd, 3rd, 4th, 6th

Each pharyngeal arch consists of a mesenchymal core (derived from the somatic mesoderm and neural crest cells) covered externally by ectoderm and internally by endoderm:

1. ___________________ element (derived from neural crest cells)
2. _______________ (derived from head mesoderm) → innervated by an arch-specific cranial nerve (each arch has a different nerve associated with it)
3. Aortic arch artery (numbered from 1 – 6)

Answer 2

rostral to caudal (anterior to posterior) ;

Central cartilaginous skeletal;

Skeletal muscle rudiments

Question 3

Cartilage forms in each arch, with _______ cartilage forming in the 1st arch and __________ cartilage forming in the 2nd arch (no name for other 3 cartilages):
• 1st arch splits into the maxillary process and mandibular process
- Maxillary: Maxilla (upper jaw), _______, _______________
- Mandibular: Mandible (lower jaw; from mesenchyme surrounding Meckel’s cartilage), Meckel’s cartilage (disappears except at its dorsal end with further development)

Answer 3

Meckel’s;

Reichert’s;

palate;

zygomatic bone

Question 4

What are the derivatives of Meckel’s Cartilage (4)?

Answer 4

1. Auditory ossicles (incus, malleus)
2. Spine of sphenoid bones
3. Anterior ligament of malleus (connects malleus to sphenoid bone)
4. Sphenomandibular ligament (connects spine of sphenoid to mandible)

Question 5

What are the derivatives of Reichert’s cartilage? (5)

Answer 5

1. Auditory ossicles (stapes)
2. Styloid process
3. Lesser cornu (horn) of hyoid bone
4. Upper portion of the body of the hyoid bone
5. Stylohyoid ligament (connects styloid process to hyoid bone)

Question 6

What are the derivatives of 3rd cartilage?

Answer 6

1. Greater cornu (horn) of hyoid bone

2. Lower portion of the body of the hyoid bone

Question 7

What are the derivatives of 4th & 6th cartilage?

Answer 7

1. Thyroid cartilage
2. Corniculate cartilage
3. Cuneiform cartilage
4. Cricoid cartilage
5. Arytenoid cartilage

Question 8

1st pharyngeal arch syndrome: due to abnormal development of the components of the 1st pharyngeal arch ( insufficient migration of _______________ into the 1st arch)

• Causes various congenital anomalies of the eyes, ears, mandible, and palate
• Treacher Collins syndrome (mandibulofacial dysostosis): caused by an autosomal dominant mutation (___________ gene) –> _______________ hypoplasia with down slanting palpebral fissures, defects of lower eyelids, deformed external ears
• Robin sequence : autosomal recessive condition –> extreme __________ (small mandible), cleft palate , posteriorly placed tongue , associated defects of ears

Answer 8

neural crest cells;

TCOF;

mandibular and zygomatic;

micrognathia

Question 9

What is the muscles derived from the 1st arch?

Answer 9

1. Muscles of mastication (temporalis, masseter, medial pterygoid, lateral pterygoid)
2. Tensor tympani
3. Tensor veli palatini
4. Mylohyoid
5. Anterior belly of digastric

Question 10

What cranial nerve and artery is derived from the 1st arch?

Answer 10

Mandibular division of trigeminal nerve (V3);

Maxillary artery (transitory)

Question 11

What is the muscles derived from the 2nd arch?

Answer 11

1. Facial muscles (including buccinator and platysma)
2. Stapedius
3. Stylohyoid
4. Posterior belly of digastric

Question 12

What artery and cranial nerve is derived from the 2nd arch?

Answer 12

CN VII (facial); Hyoid and stapedial arteries

Question 13

What is the muscles derived from the 3rd arch?

Answer 13

Stylopharyngeus

Question 14

What icranial nerve derived from the 3rd arch?

Answer 14

CN IX (glossopharyngeal)

Question 15

What is the muscles derived from the 4th & 6th arch?

Answer 15

1. Pharyngeal muscles

2. Laryngeal muscles

Question 16

What cranial nerve derived from the 4th & 6th arch?

Answer 16

CN X (vagus)

For 6th: recurrent laryngeal branch

Question 17

Each pharyngeal arch receives an artery, so there are 6 aortic arch arteries (but the 5th artery never forms or disappears after forming):
• All the aortic arch arteries arise from the _________________
• Embedded in the ______________ and terminate in the right and left dorsal aorta
• Right and left dorsal aorta remain paired in the region of the aortic arches, but fuse to form a single vessel below this region

Arch

• 1st: Disappears except for small portion (gives rise to _________ artery)
• 2nd: Disappears except for small portion (gives rise to __________ artery)
• 3rd: Common carotid artery and 1st part of internal carotid artery
• 4th: (Left side) arch of aorta between left common carotid and subclavian arteries, (Right side) proximal part of right subclavian artery
• 6th: (Left side) ______________________, (Right side) ________________

Answer 17

aortic sac of the primitive heart tube;

mesenchyme of the pharyngeal arches;

maxillary;

stapedial;

ductus arteriosus and left pulmonary artery;

right pulmonary artery

Question 18

Which arteries are derived from 3rd pharyngeal arch?

Answer 18

Common carotid artery & 1st part of internal carotid artery

Question 19

Which arteries are derived from 4th pharyngeal arch?

Answer 19

• Right side: proximal part of subclavian artery

- Left side: arch of aorta between origins of left common carotid and left subclavian arteries

Question 20

Which arteries are derived from 6th pharyngeal arch?

Answer 20

• Right side: right pulmonary artery

- Left side: ductus arteriosus, left pulmonary artery

Question 21

What are the derivatives of the 1st pharyngeal pouch?

Answer 21

Forms a diverticulum (with proximal and distal parts):
• Distal end: widens into the middle ear cavity
• Proximal end: auditory tube (communicates pharynx to the middle ear)
• Internal part of tympanic membrane (eardrum)

Question 22

What are the derivatives of the 2nd pharyngeal pouch?

Answer 22

Palatine tonsil (found in the lateral walls of the oropharynx)

Question 23

What are the derivatives of the 3rd pharyngeal pouch?

Answer 23

• Inferior parathyroid glands

- Thymus (migrates downwards to the thoracic region)

Question 24

What are the derivatives of the 4th pharyngeal pouch?

Answer 24

• Superior parathyroid glands

- Ultimobranchial body (parafollicular cells/C cells of the thyroid gland)

Question 25

DiGeorge syndrome: failure of development of the 3rd and 4th pharyngeal pouches into the parathyroid glands and thymus • Presents with ______________ (due to thymic hypoplasia failure of T cell development and maturation) • Also presents with _____________ (due to missing/hypoplastic parathyroid glands (secrete PTH) • May be combined with cardiovascular defects

Answer 25

immunological problems; hypocalcaemia

Question 26

What are the derivatives of the 1st pharyngeal cleft?

Answer 26

External acoustic meatus and external part of the tympanic membrane (between the external ear and middle ear): 1. Internal portion: derived from 1st pharyngeal pouch 2. Intermediate portion: derived from mesoderm of 1st pharyngeal arch 3. External portion: derived from 1st pharyngeal cleft

Question 27

What are the derivatives of the 2nd, 3rd, 4th pharyngeal cleft?

Answer 27

Normally obliterated during development as the 2nd pharyngeal arch grows rapidly and overlaps the 2nd to 4th clefts in a transient, ectoderm-lined cervical sinus (normally disappears rapidly and completely)

Question 28

Cervical cyst & fistulae: occurs due to the occasional persistence of the _____________ on one or both sides just anterior to the sternocleidomastoid muscle • Creates a fistula if the cyst opens (external fistula communicates with the ________; internal fistula communicates with the ___________) • Prone to infections

Answer 28

lateral cervical sinus; skin; pharynx

Question 29

[Body (anterior 2/3rd)} Two lateral swellings (lateral lingual swellings) and one midline swelling (tuberculum impar) develop from the floor of the 1st pharyngeal arch: • Grow rostrally and fuse together Sensory: _____________ Taste: ______________________(except for circumvallate papillae innervated by CN IX)

Answer 29

lingual branch of CN V; chorda tympani branch of CN VII

Question 30

[Root (posterior third)] - Develops from the hypobranchial eminence (from 2nd to 4th arches) Sensory: ______ Taste: ____________

Answer 30

CN IX; CN IX and CN X

Question 31

The thyroid gland begins to develop 24 days after fertilisation from the endodermal cells in the floor of the primitive pharynx: • Proliferate to form the _______________ which gives rise to the thyroid gland (initially located between the 1st and 2nd pharyngeal arches) • Thyroid gland migrates caudally into the neck as the embryo and the tongue grows, passing ventrally to the hyoid bone and laryngeal cartilages At first, the thyroid diverticulum is a hollow structure, but becomes a solid mass of cells: • Divides into right and left lobes that are connected in the midline by the isthmus (lies ventral to the 2nd and 3rd tracheal rings): o In about 50% of the cases, the __________________ forms a pyramidal lobe, which is connected to the isthmus • By the 7th week, the thyroid gland assumes its definitive shape and is usually located in the adult site in the neck • For a short time during development, the thyroid diverticulum is connected to the developing tongue by the thyroglossal duct (at the foramen cecum → junction between the ______________________), which usually disappears and degenerates completely with further development. As the thyroid gland descends through the neck, the parathyroid glands detach from the pharyngeal pouches and migrate caudally then join the thyroid gland in the posterior aspect.

Answer 31

thyroid diverticulum; lower end of the thyroglossal duct; anterior ⅔ and posterior ⅓ of the tongue

Question 32

Aberrant (ectopic) thyroid tissue: may be found anywhere along the path of descent • Commonly found in the _________________

Answer 32

base of the tongue behind the foramen caecum (lingual thyroid)

Question 33

Thyroglossal cyst: cystic remnant of the thyroglossal duct commonly found at the hyoid bone • May occur anywhere along the path of descent • Diagnostic characteristics: _____________________

Answer 33

midline swelling which moves with swallowing