Lecture Tuesday October 2: embryology face, eye and palate

A. Development of the Face

- Frontonasal prominence > forehead, bridge of nose, medial and lateral nasal prominences
- Medial nasal prominence > tip of nose and philtrum of lip
- Lateral nasal prominence > algae of nose
- Maxillary process > cheeks and lateral portion of upper lip
- Mandibular process > lower lip




Clinical correlation:
Cleft lip is the failure of the maxillary process and medial nasal process to fuse correctly. Can be unilateral or bilateral and involve the palate or not.








B. Development of the Eye

Early in the 4th week optic vesicles extend from the wall of the forebrain. As the vesicle reaches the surface ectoderm it flattens and invaginates to form the optic cup, which remains attached to the forebrain by the optic stalk (precursor of the optic nerve). Its presence induces the formation of the lens placode from the surface ectoderm.








The lens placode invaginates and (eventually) separates from the ectoderm to form the lens vesicle.




The primary optic vesicle becomes a double walled optic cup. With continued invagination the original lumen of the optic vesicle is reduced to a slit between the inner neural layer (future retina) and outer pigmented layer (future pigmented epithelium) of the optic cup.




Mesenchyme around the optic cup will contribute to the cornea and sclera and the extraocular muscles.

C. Development of the Palate

1. The medial nasal processes merge with the maxillary processes to form the upper lip and primary palate by the end of the sixth week.
2. The secondary palate develops as bilateral outgrowths from the maxillary processes, which grow vertically down the side of the tongue. Subsequently, the palatal shelves elevate to a horizontal position above the tongue, contact one another and fuse. Fusion of the palatal shelves ultimately divides the oronasal space into separate oral and nasal cavities.




Clinical Correlation:
Cleft palate- An orofacial cleft occurs when parts of the lip or palate do not completely fuse together during the first 3 months of pregnancy. A cleft lip may appear as a small notch in the edge of the lip only or extend into the nose. It may also extend into the gums.
A cleft palate may also vary in size, from a defect of the soft palate only to a complete cleft that extends through the hard palate. Because the lips and the palate develop separately, it is possible for a child to be born with a cleft lip only, cleft palate only, or both.




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Lecture Monday October 1: Deep Face, Orbit, Nasal and Oral Cavities

A. Eye and Orbit
**See handout on clinical testing of eye muscles. This handout includes all of the information you will need on the muscles, movements and innervation (III, IV and VI)

B. Muscles of Mastication
- Temporalis (close mouth)
- Masseter (close mouth)
- Medial pterygoid (close mouth)
- Lateral pterygoid (opens mouth)
*All innervated by branches of V3

C. Major branches of V3 in the infratemporal fossa:
1. Deep temporal (motor to Temporalis)

2. Buccal (sensory to the inside of the cheek)

3. Auriculotemporal (sensory to the side of the head posterior to the ear, carries postganglionic parasympathetic fibers from otic ganglion to parotid)

4. Lingual (sensory to anterior 2/3 of the tongue, associated with chorda tympani branch of VII that carries taste from anterior 2/3 of tongue and parasympathetics to submandibular ganglion)

5. Inferior alveolar (sensory to mandibular teeth, ends as mental nerve)

D. Oropharynx
- palatoglossal arch anterior and continuous with uvula
- palatopharyngeal arch posterior
- palatine tonsil in between the two arches




E. Tongue
- Extrinsic muscles:
Genioglossus (primary muscle that protrudes the tongue)
Hyoglossus
Styloglossus
Palatoglossus
*All innervated by cranial nerve XII except palatoglossus (X)

F. Nasal Cavities and Sinuses
- Lateral wall structures: Superior, middle and inferior choncha.
- Lateral wall spaces: superior, middle and inferior meatus. Sphenoethmoidal recess.

Blood Supply via the sphenopalatine A. (continuation of maxillary A.) and branches of the facial artery.

Sensory Innervation via the Ophthalmic (V1) to the nasal vestibule and the Maxillary (V2) to the posterior nasal cavity and nasopharynx.

Paranasal Sinuses:
- Frontal (drains to middle meatus via the infundibulum in hiatus semilunaris)
- Ethmoidal (anterior/middle drain to middle meatus; posterior drains to superior meatus)
- Maxillary (drains to middle meatus via hiatus semilunaris)
- Sphenoid (drains to sphenoethmoidal recess)




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