Head and neck Flashcards
When does head and neck development start and what with?
week 4- with the development of the pharyngeal (Ph) arches and frontonasal prominance
How many Ph arches are there?
5- arches 1,2,3,4 and 6
What are the ph arches?
Proliferations of mesenchyme in the neck region of the embryo, with an outer layer of ectoderm and innerlayer of endoderm.
What cranial nerves associate with each arch?
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)
What muscles derive from the Ph arch 1?
Muscles of mastication
What muscles dervice from Ph arch 2?
Muscles of facial expression
What muscles and bone derive from the 3rd Ph arch?
Stylopharyngeus muscle and most of hyoid bone
What muscles and structures derive from Ph 4?
All cartilages and extrinsic muscles below hyoid bone
What does the ph arch 6 derive?
Intrinsic muscles of larynx
From where to the bones of the middle ear derive from?
Malleus and incus- Ph arch 1
Stapes- Ph arch 2
Other than the melleus and stapes, what other cartilage does the 1st Ph arch derive?
the mandible
What happens to he aeortic arches which are within the pharyngeal arches?
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
What is the significance of the 1st ph pouch?
It is the largest and becomes the tympanic cavity.
What do the 2nd, 3rd, 4th and 5th Ph pouch become?
2nd= palatine tonsils
3rd= parathyroid gland
4th= thymus
5th= superior parathyroid gland
What are the pharyngeal clefts? What do they become?
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
What happens if you ph cleft not regressing?
A branchial cyst or branchial fistula
From what does the face develop?
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.
Describe the development of the nose
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
Describe the seperation of the oral and nasal cavities
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
What is the difference between a lateral cleft lip and a cleft palate?
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
Describe the movement of the ear as it develops
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.
Why does fetal alcohol syndrome occur?
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.
Describe the consequences/ characteristsics of fetal alcohol syndrome?
Slow development
Small head
Low nasal bridge
Short nose
Under developed jaw
Smooth philthrum
Flat midface
From where do the anterior and posterior lobes of the pituitary gland develop?
Anterior= endocrine= ectoderm= Rathke’s pouch
Posterior= neuroendocrine= neuroectoderm= Infundibulim
Describe the development of the pituitary gland
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
From where does the tongue develop?
from all of the Ph arches
Describe the origins of the lateral 2 lingual swellings, the 3 median lingual swellings, the cupola and the epiglottal swelling
Lateral 2 lingual= Ph arch 1
3 Median swellings= arch 1
Cupola swelling= arch2,3 and some of 4
Epiglottal swelling= Arch 4
Describe the development of the tongue
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.
How is the development of the tongue related to its general sensory innervation?
Anterior 2/3rds= derived from Ph arch 1= Facial nerve (CN V)
Posterior 1/3= arch 3= Glossopharyngeal (CN IX)
How does the tongue get its special sensory innervation?
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.
What is the motor innervation of the tongue? How is this related to its development?
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.
From where does the thyroid gland primordia start to appear?
In the floor of the pharynx, between the tuberculum impar and the cupola (at the formane caecum)
Describe the development of the thyroid gland
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.
What is a potential consequence of the thryoglossal duct not regressing?
thryoglossal duct cyst
What is a pyramidal lobe thyroid?
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.
