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38 Cards in this Set

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What induces the sclerotome cells to differentiate into vertebral bodies?
Sonic Hedgehog pathway. They are also induced by notochord and neural tube.
What structure forms the vertebral bodies?
Sclerotome (which differentiates from paraxial mesoderm).
Which somites give rise to the 7 cervical vertebrae? Explain.
The first 8 somites give rise to the 7 cervical vertebrae because the upper half of the first somite contributes to the formation of the occupital bone.

Remember, the sclerotome from the somites split up so each vertebrae is formed by two somites fusing together!
In the intervertebral disc, what forms the outer annulus fibrosus? What forms the central nucleus pulposus?
Annulus fibrosus is formed by sclerotome.

Nucleus pulposus is formed by notochord.
How many primary ossification centers are in each vertebrae?
3 (one in the center where the notochord was, and two for the the vertebral arches)
What parts of the trilaminar embryo forms the skull?
Paraxial mesoderm
Neural crest cells of ectoderm (face region)
Which parts of the trilaminar embryoblast form the limbs?
Somites of the lateral mesoderm.
Limb bud.

What part of the trilaminar embryo is it from? What are the regions of the limb bud?
From somites of lateral mesoderm.

Regions:
Apical Ectodermal Ridge (secretes fibroblast growth factor)
Zone of Polarizing Activity (A-P organization). This is influenced by Sonic Hedgehog, and retinoic acid.
Progress Zone
What gives rise to epaxial and hypaxial muscles?
Epaxial: myotome.
Hypaxial: lateral somites.
What is the name of the gene which plays a critical role in formation of limbs?
HOX genes.
Expression is induced by retinoic acid which is secreted by mesenchyme cells.

HOX genes is also important for the pharyngeal arches.
What is the direction of the limb rotation in the seventh and eighth week?
Upper limb: lateral rotation.
Lower limb: medial rotation.
How many pharyngeal arches are there?
1 through 6 (with no 5)
What are the components of a pharyngeal arch?
Blood vessel
Muscle (from somites from paraxial mesoderm)
Skeletal (from mesenchyme from neural crest)
Nerve
Connective tissue from neural crest.
What is the innervation for each pharyngeal arch from 1 through 4?
Pharyngeal arches 1-4 are innervated by cranial nerves V, VII, IX, X, respectively.

CN X innervates both arch 4 and 6, which are hard to see or distinguish.
What are clefts and pouches in the the pharyngeal apparatus?
Cleft: indentations in ectodermal surface.

Pouches: outward bulges in pharynx endoderm.
What is Arch 1 called? What prominences does it have? (pharyngeal apparatus)
Arch 1 is mandibular arch.

It has maxillary and mandibular prominences.

The frontonasal prominence is not part of it, but all these (five prominences) surround the stomodeum (primitive mouth)
What is pharyngeal arch 2 called?
Arch 2 is hyoid arch.

MM of facial expression!!
Which pharyngeal arches give rise to the anterior and posterior bellies of digastric?
Anterior belly: Arch 1 (mandibular)
Posterior belly: Arch 2 (hyoid)
What is the pharyngeal arch 3 called?
Glossopharyngeal.
Which pharyngeal arches give rise to the hyoid bone?
Arches 2 (hyoid arch- lesser horn)
and 3 (glossopharyngeal arch- greater horn).
What does pharyngeal pouch 1 form?
Auditory tube, middle ear epithelium, and inner surface of tympanic membrane.

Compare to Cleft 1, which forms external auditory meatus, and outer lining of tympanic membrane.
What does pharyngeal pouch 2 form?
Primordium of palatine tonsil.
What does pharyngeal pouch 3 form? what about pouch 4?

EXAM
Pouch 3:
Dorsal portion: inferior parathyroid gland.
Ventral portion: thymus.

Pouch 4:
Ventral: superior parathyroid
Ventral: thyroid parafollicular cells.

Explanation: pouch 3 travels below pouch 4.
What does pharyngeal cleft 1 form?
External auditory meatus, and outer lining of tympanic membrane.

Compare to pouch 1, which forms auditory tube, middle ear epithelium, and inner surface of tympanic membrane.
What does pharyngeal cleft 2-4 form?
Cervical sinuses, which are transient structures.

They can form cysts if they don't completely obliterate, and may form fistulas in rare cases.
What pharyngeal arches form external ear?
Auricular hillocks derived from arches 1 and 2.
What arches form the tongue? Be specific.
Arch 1 (lateral lingual swellings form ant. 2/3, and tuberculum impar)
Arch 3 (hypobrachial eminence)
Arch 4 (epiglottal swelling)
What nerves innervate the tongue? What are their function?
Ant. 2/3
CN V: general sensory.
CN VII: taste.

Post. 1/3:
General sensory and taste: CN IX (glossopharyngeal)

Extrinsic muscles of tongue: CN XII (hypoglossus)

Remember: epiglottis is innervated by CN X for general sensory and taste!
Thyroid gland.

What pharyngeal arches form it? What's unique about it?
Thyroid starts as endodermal invagination of tongue.

Thyroid is formed from proliferation of cells on floor of pharynx between arches 1 and 2, which form diverticulum.

Diverticulum elongates caudally along midline until it reaches trachea.

Clinical correlation: thyroglossal cyst.
Midline remnants of the thyroglossal duct that do not regenerate and form cysts.
What happens to the buccopharyngeal membrane?
It breaks down in week 4 to produce continuity between mouth and pharynx.
What prominences form the face? (pharyngeal apparatus)
Five prominenses:
Frontonasal prominence (midline)
2 maxillary prominences.
2 mandibular prominences.

PLUS 2 nasal placodes.
Placode
Ball of ectoderm.
What forms the philtrum?
Medial nasal prominenses (from nasal placodes) fuse together to form intermaxillary segment.
They also form the crest and tip of nose.

Intermaxillary segment has three components!
What are the three parts of the intermaxillary segment?
Upper jaw/gum component w/4 incisor teeth.
Palatine component.
Temporary clef between med. nasal prominence, and maxillary prominence.
What is the junction where the primary and secondary palates fuse at the midline?
Incisive foramen.
What is the origin of the primary palate?
Frontonasal prominence.
What is the origin of the secondary palate?
Palatine shelves (from maxillary prominence).

The nasal septum grows downwards and fuses with the secondary palate along the midline.
When do paranasal air sinuses develop?
They develop postnatally through puberty.