Head and neck

Question 1

When does head and neck development start and what with?

Answer 1

week 4- with the development of the pharyngeal (Ph) arches and frontonasal prominance

Question 2

How many Ph arches are there?

Answer 2

5- arches 1,2,3,4 and 6

Question 3

What are the ph arches?

Answer 3

Proliferations of mesenchyme in the neck region of the embryo, with an outer layer of ectoderm and innerlayer of endoderm.

Question 4

What cranial nerves associate with each arch?

Answer 4

Ph1= V (trigeminal)

Ph2= VII (facial) and a bit of IX (glossopharygneal)

Ph3= IX (glossopharyngeal) Ph4= X (vagus nerve)

Ph6= X (vagus nerve) and a bit of XII (hypoglossal)

Question 5

What muscles derive from the Ph arch 1?

Answer 5

Muscles of mastication

Question 6

What muscles dervice from Ph arch 2?

Answer 6

Muscles of facial expression

Question 7

What muscles and bone derive from the 3rd Ph arch?

Answer 7

Stylopharyngeus muscle and most of hyoid bone

Question 8

What muscles and structures derive from Ph 4?

Answer 8

All cartilages and extrinsic muscles below hyoid bone

Question 9

What does the ph arch 6 derive?

Answer 9

Intrinsic muscles of larynx

Question 10

From where to the bones of the middle ear derive from?

Answer 10

Malleus and incus- Ph arch 1

Stapes- Ph arch 2

Question 11

Other than the melleus and stapes, what other cartilage does the 1st Ph arch derive?

Answer 11

the mandible

Question 12

What happens to he aeortic arches which are within the pharyngeal arches?

Answer 12

1st and 2nd regress

3 rd arch becomes the internal cartotid artery

4th arch (on left) becomes the arch of the aorta and brachiocephalic thunk (on right)

6th arch becomes the pulmonary arch

Question 13

What is the significance of the 1st ph pouch?

Answer 13

It is the largest and becomes the tympanic cavity.

Question 14

What do the 2nd, 3rd, 4th and 5th Ph pouch become?

Answer 14

2nd= palatine tonsils

3rd= parathyroid gland

4th= thymus

5th= superior parathyroid gland

Question 15

What are the pharyngeal clefts? What do they become?

Answer 15

Theyre the ectoderm pouches formed on the outside of the Ph arches.

Most regress due to the 2nd arch growing down and obliterating the others except the 1st which becomes the external auditory meatus

Question 16

What happens if you ph cleft not regressing?

Answer 16

A branchial cyst or branchial fistula

Question 17

From what does the face develop?

Answer 17

The forehead and nose devlop from the frontonasal prominence.

The 1st arch splits into an upper portion (maxillary prominence) and a lower portion (mandibular prominence) which will become the cheeks and mandible respectivly.

There is a cavity between the FNP and 1st Ph arch, which is to become the oral cavity.

Question 18

Describe the development of the nose

Answer 18

It begins as nasal placodes on the frontonasal prominence.

These sink to become nasal pits

Medial and lateral nasal prominences develop on either side of the pits

The maxillary prominence grows medially, pushing the nasal pits together

Until the medial nasal prominences fuse

Question 19

Describe the seperation of the oral and nasal cavities

Answer 19

The philthrum (upper lip) develop from the medial nasal prominence.

The Primary palate also develops down from the MNP.

Two palatal shelves grow verticually downwards from the maxillary prominence into the oral cavity on either side of the developing tongue.

The mandible then grows large enough for the tongue to drop down and the palatal shelves to grow towards eachother and fuse in the midline.

The nasal septum then grows down and fuses with the superior- anterior aspect of the palate

Question 20

What is the difference between a lateral cleft lip and a cleft palate?

Answer 20

Cleft lip is failure of fusion of the medial nasal prominence/ philthrum or primary palate with the maxillary portions (secondary palate or other)

Cleft palate is failure of fusion of the secondary palate

Question 21

Describe the movement of the ear as it develops

Answer 21

It initially develops from the 1st Ph pouch and cleft, taking components from the 1st and 2nd arches.

It therefor develops in the neck but as the mandible grows it ascends to lie either side of the head in line with the eyes.

Question 22

Why does fetal alcohol syndrome occur?

Answer 22

alcohol is toxic to neural crest cells, so it impinges development of their brain. Neural crest cells also invade the arches and drive their development.

Question 23

Describe the consequences/ characteristsics of fetal alcohol syndrome?

Answer 23

Slow development

Small head

Low nasal bridge

Short nose

Under developed jaw

Smooth philthrum

Flat midface

Question 24

From where do the anterior and posterior lobes of the pituitary gland develop?

Answer 24

Anterior= endocrine= ectoderm= Rathke’s pouch

Posterior= neuroendocrine= neuroectoderm= Infundibulim

Question 25

Describe the development of the pituitary gland

Answer 25

The infundibulim grows down as an outpouching from the neural tube.

The Rathke’s pouch grows up from the roof of the pharynx.

They meet and the developing sphenoid bone grows beneath it, pinching rathke’s pouch off, creating the sell turcica

Question 26

From where does the tongue develop?

Answer 26

from all of the Ph arches

Question 27

Describe the origins of the lateral 2 lingual swellings, the 3 median lingual swellings, the cupola and the epiglottal swelling

Answer 27

Lateral 2 lingual= Ph arch 1

3 Median swellings= arch 1

Cupola swelling= arch2,3 and some of 4

Epiglottal swelling= Arch 4

Question 28

Describe the development of the tongue

Answer 28

The lateral lingual swellings overgrow the tuberculum impar and it extends forwards. The 3rd arch component of the cupola overgrows the 2nd arch component.

Degeneration/ apoptosis of the oral cavity floor occurs to free the tongue, leaving it connected only by the lingual frenulum.

Question 29

How is the development of the tongue related to its general sensory innervation?

Answer 29

Anterior 2/3rds= derived from Ph arch 1= Facial nerve (CN V)

Posterior 1/3= arch 3= Glossopharyngeal (CN IX)

Question 30

How does the tongue get its special sensory innervation?

Answer 30

Taste buds develop from the invasion of pupillae. These connect to the chordae tympanii branch of the facial nerve (CN VII)–> this means facial nerve must invade the 1st Ph arch, and explains why its route comes through the middle ear canal.

Question 31

What is the motor innervation of the tongue? How is this related to its development?

Answer 31

Hypoglossal nerve (CN XII)

Intrinsic and extrinsic muscles of the tongue develop from invasion of myogenic precursors that migrate into the tongue from occipital somites.

Question 32

From where does the thyroid gland primordia start to appear?

Answer 32

In the floor of the pharynx, between the tuberculum impar and the cupola (at the formane caecum)

Question 33

Describe the development of the thyroid gland

Answer 33

After appearing in the foramen cecum, it partially bifucates and descends anterior to the thyroid and cricoid, remaining connected to the tongue by the thryoglossal duct. This duct normally regresses.

Question 34

What is a potential consequence of the thryoglossal duct not regressing?

Answer 34

thryoglossal duct cyst

Question 35

What is a pyramidal lobe thyroid?

Answer 35

Where bits of thyroid tissue in the thryoglossal duct dont regress, leaving a 3rd, pyrmidal shaped lobe in the midline.

You can also get ectopic thyroid tissue in the neck where bits get left behind on descent.