DEVELOPMENT OF THE HEAD AND NECK

NEUROCRANIUM: The part of the skull that surrounds the brain.

1.CARTILAGINOUS NEUROCRANIUM (CHONDROCRANIUM): Neurocranium that develops by endochondral ossification (with a cartilaginous

intermediate)

2.MEMBRANOUS NEUROCRANIUM: That part of the skull that develops by membranous ossification.

1.The Frontal and Parietal bones are membranous.

2.Sutures are connections between bones. They allow for growth of the cranium.

3.Fontanelles occur at the intersection of two sutures.

1.There are six of them.

2.The Anterior Fontanelle stays open until the middle of the 2nd year. KNOW THAT!

4.Craniostenosis is the failure for the skull to expand due to malformed sutures.

VISCEROCRANIUM: The rest of the skull, not overlying the brain. The Maxilla, Mandible, and facial skeleton.

1.ENDOCHONDRAL VISCEROCRANIUM:

1.The middle ear bones are endochondral.

2.Styloid Process of Temporalis

3.Greater Cornu and Inferior body of the Hyoid

4.Laryngeal Cartilages

2.MEMBRANOUS VISCEROCRANIUM: Maxillary and Mandibular Prominences

SPECIAL VISCERAL EFFERENT (SVE) FIBERS:

1.They all innervate Branchial Muscles, derived from Branchial arches

2.They all originate from the Nucleus Ambiguus.

GENERAL EFFERENT (GSE, GVE) FIBERS: They innervate muscles that are derived from somites.

BRANCHIAL (PHARYNGEAL) ARCHES: They are primitive gills in the neck region of the embryo.

1.In humans, we form a primitive gill but then we don't break down the membranes to form mature gills.

2.This is an example of ontogeny recapitulating phylogeny, and so is the Mesonephric Duct of the Kidney, which develops and then disintegrates, being replaced

by metanephric duct.

3.Two different types of mesenchyme compose the Neural Arches:

1.Neural Crest: Forms the Arch Cartilages. The arch cartilages are made of neural crest! So this would be ectodermal (neural crest) mesenchyme.

2.Mesodermal: The rest of the neural arch is mesodermal mesenchyme.

BRANCHIAL POUCHES: The outpocketing of endoderm, or the endodermal component on the inside of each arch.

BRANCHIAL CLEFTS (GROOVES): The ectodermal ingrowths, found in between each set of arches.

1.All of the clefts disappear except the 1st Branchial Cleft, which becomes the External Auditory Meatus. and the outer epithelium of the tympanic membrane.

DEVELOPMENT OF THE MOUTH:

1.The Breakdown of the Buccopharyngeal Membrane marks the future mouth. It is very important to the embryo, as it allows for communication of

amniotic fluid between the inside (gut) of the embryo and the environment.

DEVELOPMENT OF PARATHYROID: Reiterated from above. There are four parathyroid glands on the thyroid, two superior and two inferior.

1.The two Inferior Parathyroids are formed from Pouch III. Pouch III forms the inferior ones because it also forms part of the Thymus which migrates down

to the Anterior Mediastinum, hence the third pouch is dragged down a bit with it.

2.The two Superior Parathyroids are then formed by Pouch IV.

DEVELOPMENT OF THE THYROID GLAND: Starts in the floor of the pharynx and then works its way down.

1.For a short time it remains connected to the pharynx by a thyroglossal duct which disintegrates in the adult, leaving behind the remnant of the foramen

cecum of the tongue.

DEVELOPMENT OF THE TONGUE:

1.All tongue muscles are somite-derived -- not branchial arches!

2.Anterior 2/3: Formed from lateral lingual swellings from arch 1 mesenchyme.

3.Posterior 1/3: From hypobranchial eminence from arch 3 mesenchyme.

DEVELOPMENT OF THE FACE:

1.It forms from five processes.

1.FRONTONASAL PROCESS: Forms Nasal Processes and Globular Processes

2.PAIRED MAXILLARY PROCESSES: Grows toward the midline to meet each other.

3.PAIRED MANDIBULAR PROCESSES: Grows toward the midline to meet each other.

2.Process:

1.First, Olfactory Pits form in the Frontal Process.

2.The Frontal Processes then grow around these pits, forming the following:

1.2 Lateral Nasal Processes -- Forms the lateral ala of nose.

2.1 Medial Nasal Process -- Forms philtrum.

3.2 Globular Processes, on the end of the Lateral Nasal Processes. They fuse together to form the premaxilla.

3.CLEFT LIP: Failure to join of the Maxillary Process and Globular Process. Could be on the same side or bilateral.

1.Hare Lip: A midline cleft. Very uncommon.

4.CLEFT PALATE: An opening between the nasal and oral cavities, caused by a failure of the maxillary shelves to come together and fuse.

1.This is a different etiology then cleft lip! Although they commonly occur together.

BRANCHIAL FISTULA: Failure of the Branchial clefts to disappear. The cleft stays completely open. They are located on the side of the neck.

BRANCHIAL SINUS: Incomplete breakdown of the branchial clefts. The cleft is partially open, either to the inside or outside. They are located on the side of the

neck.

FIRST ARCH SYNDROMES: Rare syndromes involving the first arch. Due to middle ear ossicles, these syndromes lead to deafness.