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82 Cards in this Set

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List the 8 precursors of the head and neck:
1. Olfactory placodes
2. Frontal prominence
3. Pharyngeal arches
4. Pharyngeal clefts
5. Pharynx
6. Pharyngeal pouches
7. Oral membrane
8. Oral cavity
What do the olfactory placodes become?
Olfactory epithelium
What does the frontal prominence become?
-Mostly nose
-Primary palate
Where do the pharyngeal arches form?
At the foregut opening
What are the pharyngeal clefts?
External grooves between arches
How does the pharynx form? What kind of tissue is it?
As dilated foregut
-Endoderm
What are the pharyngeal pouches? What happens as they form?
-Internal grooves between arches
-Associate w/ pharyngeal clefts at the closing plate.
What is the oral membrane?
An opening in the gut that consists of Endoderm/Ectodermal fusion.
What is the oral cavity?
The space cranial to the oral membrane.
What type of tissue is the oral cavity; what does it become?
Ectoderm - becomes mouth.
What are the 2 sources of pharyngeal arch mesenchyme?
1. Mesoderm
2. Neural crest
There are 2 types of mesoderm contributing to mesenchyme; what are they, what do they become?
1. Paraxial - becomes skeletal muscle
2. Lateral Plate - nobody knows
What does Neural Crest mesenchyme become?
Everything except skeletal muscle (Bones, CT, smooth musc, nerves)
What are the 5 things in each arch? What do they become?
1-Condensed mesenchyme (cartilage)
2-Loose mesenchyme
3-Paraxial mesoderm (skeletal muscle)
4-Aortic arch (artery)
5-Cranial nerve (duh..)
Reminder: what do the EPIBRANCHIAL placodes contribute neurons to?
CN 7-10
What fills the Frontal Prominance and Pharyngeal Arches?
Condensed mesenchyme
How many pharyngeal arches develop?
How many are visible externally?
5
4 visible
What does arch#1 divide into?
-Maxillary Process
-Mandibular Process
What happens to arches 1 and 2 by Day 22?
They (and only these two) fuse ventrally at the midline
How many pharyngeal clefts are visible externally?
3
What 2 terms are used for the floor of the cleft?
Closing plate or Pharyngeal membrane
What does a closing plate include (3 things)? What tissue is each derived from?
1. Lateral wall of a pouch (endoderm)
2. Medial wall of a cleft (ectoderm)
3. Intervening mesenchyme
What does the Oral MEMBRANE consist of, and whats its purpose? What happens to it?
-Endoderm/ectoderm fusion
-Purpose is to separate the pharynx from oral cavity
-Ruptures by day 24-26
Where does the oral cavity develop in relation to the oral membrane?
Cranial to it
What is the stomadeum?
Another name for oral cavity
What causes the oral cavity to develop?
Simultaneous growth of arch 1 and the frontal prominence.
What are the boundaries of the oral cavity? (caudal, cranial, lateral, posterior)
Caudal = cardiac bulge
Cranial = frontal prominence
Lateral = 1st pharyng. arch
Posterior = oral membrane
So recap; 5 components of every arch/what they'll become:
1. Cond Mesenchyme - Cartilage
2. Loose Mesench. - fibrous CT
3. Parax Mesoderm - Sk. Muscle
4. Aortic arch - Artery
5. Cranial nerve - CN duh
What is the fate of Meckel's Cartilage (arch 1)?
-Sphenomandibular ligament (mandible)
-Incus
-Malleus
Fate of Reichart's cartilage (arch 2)
-Stapes
-Styloid process
-Stylohyoid ligament
-Upper 1/2 of hyoid bone
-Lower horns of hyoid
Fate of Arch 3 cartilage:
-Lower 1/2 of hyoid bone
-Greater horns of hyoid bone
Fate of Arch 4/6 cartilage:
Larynx cartilg - cricoid/thyroid
How do skeletal components form from the arch mesenchyme?
Via intramembranous ossification
What skeletal components form from Arch 1a and Arch 1b?
Maxillary = facial bones, squamous temporal, Sphenoid greater wing and pterygoids

Mandible = mandible
What else forms from Arch 1?
Skeletal muscle
Teeth
What somite pair are the arch 1 muscles derived from? What nerve?
4th pair - Trigeminal; CN V
What muscles form from the Trigeminal pair of somites?
-Mastication
-Tensor veli palatini
-Tensor tympani
-Mylohyoid
-Ant. belly of digastric
What forms from the rest of the arches noncartilage mesenchyme?
Just skeletal muscle
What somite pair are the arch 2 muscles derived from? What nerve?
6th pair - Facial; CN VII
What muscles form from the Facial pair of somites?
-Facial expression
-Stapedius
-Stylohyoid
-Post. belly of digastric
What somite pair are the arch 3 muscles derived from? What nerve?
7th pair - Glossopharyngeal; CN IX
What muscles develop from the Glossopharyngeal somite pair?
Just one - Stylopharyngeus
What somite pair are the arch 4/6 muscles derived from? What nerve?
Occipital somites 1-4; Vagus CN X
What muscles develop from the Vagus somite pair?
-Laryng/Pharyngeal muscles
-Palatoglossus
-Palatopharygneus
-Levator veli palatini
-Upper 1/3 of esophagus
What CN and Axial level are associated with Arch 1?
CN: V
Axial level: 4
What CN and Axial level are associated with Arch 2?
CN: VII
Axial level: 6
What CN and Axial level are associated with Arch 3?
CN: IX
Axial level: 7
What CN and Axial level are associated with Arch 4?
CN: X - superior larygneal
Axial level: Occip somites 1&2
What CN and Axial level are associated with Arch 4?
CN: X - inferior larygneal
Axial level: Occip somites 3&4
What does CN V give sensory innervation to?
-Arch 1
-Frontal process
What does CN X (sup/inf) give sensory innervation to?
Larynx
What gives the neck sensory innervation?
Segmented (?)
What is the fate of pharyngeal CLEFTS?
They all disappear except #1
What does Cleft #1 become?
the External Auditory Meatus
What happens to Cleft #2?
It overgrows the 3rd cleft and fuses w/ tissue on the side of the embryo.
What is the Cervical Sinus?
Cavity formed by overgrowth of Cleft 2 - normally dissapears.
What 4 cerical cleft defects can occur in developm of head/neck?
1. Duplication of 1st cleft
2. Cervical cyst
3. Persistent cervical sinus
4. Cervical fistula
What is the visible result of a duplicated 1st cleft?
Blind pouch or fistula running from external meatus to cheek.
What is the visible result of a cervical cyst?
Nonthyroidal mass in the lateral neck - this is most common.
What is the visible result of a persistent cervical sinus?
OPENING in the lateral neck, anterior to the SternoCMastoid
What is the visible result of a Cervical fistula?
A passage that opens from the neck to the air
What 2 types of cervical fistulas can develop?
From 2nd cleft - opening will be in tonsillar fossa.

From 3rd cleft - opening will pierce the thyrohyoid membrane in the superior larynx.
How does the development of structures as complex as the head/neck work out?
By segmentation and patterning
What directs segmentation and patterning?
Differential Hox gene expression
What is the result of Hox gene expression?
transient segmentation - sets the basis of axial Head and neck structure locations
What tissue is mainly responsible for setting up the h/n midline?
Neural crest - like the foreman with the blueprints (signalling centers etc)
What carries that pattern laterally to the arches?
Fibrous CT precursors via cell migration - myoblasts and endothelium like construction workers.
What is the result of patterning?
Each arch gets
1. Distinct skeletal structures
2. Group of muscles
3. Specific cranial nerve
4. Vessels
What does the tongue develop from in general?
Swellings filled with mesenchyme -in floor of pharynx
What swellings are contributed by Arch 1? What will they become?
3:
-2 lateral lingual swellings
-1 Tuberculum Impar
Laterals -> distal tongue bud
Tub Impar -> median tongue bud
What swelling does Arch 3 contribute? What will it become?
The cranial 1/2 of the Hypopharyngeal swelling -> will become the Root of the tongue.
What does the other caudal 1/2 of the Hypopharyngeal swelling become? What arch is it from?
The Epiglottis; from arch 4
What are the precursors of the tongue's skeletal muscle?
Occipital somites
(except palatoglossus)
From what tissue is the tongue's epithelial covering derived?
-Oral ectoderm
-Pharyngeal endoderm
What gives the tongue somatic sensory innervation? What part?
CN V - body
CN IX - root
What gives the tongue motor innervation?
CN XII - except palatatoglossus
What gives the tongue taste sensation?
CN VII, IX, X
What are the 4 main types of tongue development abnormalities seen?
1. Ankyloglossia (1/300 births)
2. Hypertrophy
3. Microglossia
4. Bifid tongue
What is ankyloglossia?
Failure of apoptosis to free the tongue from its extensive attachment to the mouth floor.
What is the common name for Ankyloglossia?
Tongue-tied
What is hypertrophy?
Enlarged tongue - macroglossia
Hypertrophy, Microglossia, and Bifid tongue are often associated w/ what 2 diseases?
Down syndrome & Hypothyroidism