Lecture 3 Flashcards
Neurulation proceeds through the _____ week of development.
Third
In what two directions does the embryo elongate and fold?
Laterally (sideways) and cephalocaudally (head and tail)
Between what two weeks of development does the head and neck begin to form?
4th and 5th weeks
What is the layman term for the pharynx?
throat
The embryonic pharynx develops a series of external ____ and _____ and internal ______
arches, clefts, pouches
How many pharyngeal arches are there?
six
Which pharyngeal arch exists only transiently?
Fifth arch
Pharyngeal structures are also called ______ structures by some anatomists, since in fish and amphibians these structures turn into gills.
Branchial
Which germ layer produces mesenchymal tissue?
Mesoderm
Pharyngeal arches consist of bars of _______ tissue separated from each other by _____ pouches and _____ clefts.
Mesenchymal; internal; external
Pharyngeal clefts are composed of what germ layer?Pharyngeal pouches?
- Ectoderm
2. Endoderm
What does the endoderm of the pharyngeal pouches give rise to?
- Middle ear cavity
- Auditory (eustachican) tube
- Palatine tonsil
- Parathyroid glands
- Thymus
- Ultimobrachial bodies
Which pharyngeal cleft is the only one that persists to give rise to an adult structure (external auditory meatus)?
First pharyngeal cleft
Which arch has two prominences? What are the names of these two prominences?
First pharyngeal arch. Maxillary and Mandibular
Each pharyngeal arch contains an ______, ______, and a cranial ______.
artery; cartilage, nerve
What germ layer are nerves derived from?
Ectoderm
How does an ectoderm-derived nerve end up in the mesoderm-derived mesenchymal tissue of the pharyngeal arch?
The ectoderm invades the endoderm.
The development of pharyngeal arches is dependent on the migration of what cells?
Neural Crest Cells (NCC)
What do signaling molecules such as sonic hedge hog (Shh), bone morphogenic protein (Bmp), and fibroblast growth factor (Fgf) do?
Facilitate the communication of NCCs with surrounding cells for the purpose of guiding the migration of NCCs to the pharyngeal arches.
What are Hox genes?
Hox genes control the body plan of an embryo along the cephalocaudal axis.
Why are regional growth factor gradients established by the migrating NCCs?
To regulate the differentiation of the developing head and neck tissues.
Each of the first four pharyngeal arches contain cartilage that is associated with the development of ______ bones and _______ cartilages.
Facial; laryngeal
Where are the cartilages derived from in the first and second pharyngeal arches? Cartilages of the 3rd-6th arches?
Neural Crest Cells. Mesoderm.
Meckel’s cartilage is formed in what pharyngeal arch?Reichert’s cartilage?
First. Second.
The hyoid bone is derived from what two pharyngeal arches?
Second and Third
The temporal bone is derived from what pharyngeal arch?
First
What role does cartilage play in the formation of bone?
Cartilage serves as a growth center that stimulates bone formation
The formation of the malleus and incus bones is stimulated by what cartilage? The stapes?
Meckel’s. Reichert’s.
The condensation of what kind of mesenchyme does the maxilla develop from?
Mesenchyme that contains NCCs
What kind of ossification is involved in the development of the maxilla?
Intramembranous
What is the mechanism of intramembranous ossification?
Bone progressively replaces embryonic connective tissue
Bone growth moves the maxilla ______ and forward.
downwards
Growth in the maxilla occurs from apposition at sutures between the maxilla and the _____ base. It also undergoes surface _______.
cranial; remodeling
Where does the mandible initially form relative to Meckels cartilage?
Lateral to it
In the formation of the mandible, what must the condensation of the mesenchyme contain?
Neural Crest Cells
During what week of embryonic development does the mandible form from a condensation of mesenchyme that contains NCCs lateral to Meckel’s cartilage?
Sixth
What happens to the mandible during the seventh week of embryonic development?
The mesenchyme undergoes intramembranous ossification.
What is the initial site of ossification (osteogenesis) of the mandible?
Where the inferior alveolar (IA) nerve divides into the incisive and mental branches.
How far anteriorly does the does bone formation of the mandible spread before birth?
All the way to the midline but remains separate until shortly after birth
How far posteriorly does the mandibular bone grow from the initial site of ossification?
To the point of division of the mandibular nerve.
What kind of ossification does the ramus and condyle of the mandible undergo?
Endochondral ossification
The membranous bone of the developing mandible eventually grows completely around the _____ _____ nerve and forms what will become the mandibular _____.
inferior alveolar; canal
From what point on the mandible does the ramus develop when it undergoes a rapid spread of ossification away from Meckel’s cartilage?
The point is marked by the lingula in an adult mandible
During what week does the condylar cartilage develop?
12th week
What shape is the condylar cartilage initially when it is inserted into the ramus of the mandible?
Cone-shaped
What happens to most of the cone-shaped condylar cartilage after it integrates with the ramus of the madible?
Most of the cartilage is replaced by bone through endochondral ossification?
In Treacher Collins Syndrome, the disruption of what cells is the cause of craniofacial defects?
NCCs
T/F. The majority of births with Treacher Collins Syndrome arise from new mutations.
True
Epibranchial placodes come from the surface of what germ layer?
Ectoderm
What do epibranchial placodes contribute to the first four pharyngeal aches? Which four cranial nerves are associated with arches 1-4?
They contribute to the formation of sensory ganglia. Cranial nerves V, VII, IX, X
The muscles of mastication are derived from which arch?What cranial nerve will innervate these muscles?
First. Trigeminal (V)
The VII cranial nerve will supply muscles derived from the ______ arch. These muscles control _____ ______.
Second. Facial Expression
The middle ear bones malleus and incus are derived from which arch? The stapes?
First. Second
Cranial nerves IX and X will innervate muscles involved in what pharyngeal activity?
swallowing
The lesser horn and superior part of the hyoid is derived from the _____ arch. The greater horn and inferior part of the hyoid is derived from the _____ arch.
second; third
The strap muscles of the neck are derived from what two arches?
Arches 3 and 4
What becomes of the four pharyngeal pouches?
Pouch 1: Tympanic cavity and Auditory tube
Pouch 2: Palatine tonsils and Tonsillar fossa
Pouch 3: Inferior Parathyroid gland and Thymus
Pouch 4: Superior Parathyroid gland, Ultimobrachial body, C-cells of thyroid gland
Why is the the parathyroid gland produced in Pouch 3 inferior to the one produced in Pouch 4?
This gland from Pouch 3 migrates down more inferior than Pouch 4
Where does the thyroid come from?
From the midsagittal invagination of the tongue (pharyngeal epithelium) at the foramen cecum.
How does thyroid tissue make it from the foramen cecum of the tongue to the trachea below the larynx?
The thyroid tissue migrates via a temporary thyroglossal duct.
What do parafollicular cells (C cells) produce? Where are they derived from?
Calcitonin. The Ultimobranchial bodies of Pouch 4.
How are thyroglossal cysts formed?
They are formed when ectoderm tissue that migrates down to become the thyroid gland does not make it all the way down. Any remnants in the thyroglossal duct will become thyroglossal cysts.
How are cervical cysts formed?
Form when the cervical sinus from Clefts 2, 3, and 4 does not become completely obliterated
Thyroglossal cysts form at the midline, whereas cervical cysts form ______
(Bi-)laterally
From how many prominences does the human face develop?
Five
All the facial prominences are paired except one. Which one is unpaired?
Frontonasal
What structures are formed from the frontonasal prominence?
Forehead, bridge of nose, medial and lateral nasal prominences (the later two become prominences of their own)
What structures does the Maxillary prominence form?
Cheeks, lateral portion of upper lip
What structures come from the medial nasal prominence? Lateral nasal prominence?
Philtrum of upper lip, crest and tip of nose. Alae of nose (or singular Ala)
What structure arises from the mandibular prominence? l
Lower lip
Why are maxillary defects more common than mandibular?
Maxillary prominences are further apart and therefore have more space to traverse before joining at the intermaxillary suture
What do nasal placodes become?
They become nasal pits and eventually the nasal passageway
What surrounds the nasal pits?
Elevated ridges that become medial and lateral nasal prominences
Which of the nasal prominences forms part of the upper lip?
Medial
As maxillary prominences grow towards the midline, what effect do they have on the medial nasal prominence?
The medial prominences are compressed towards the midline until they fuse together to form the tip of nose
The upper lip is formed by which two facial prominences?
Medial nasal and maxillary prominences.
T/F. The two maxillary prominences eventually fuse directly to one another.
False. The philtrum formed from the medial nasal prominence prevents the two from fusing directly.
Where does the nasolacrimal groove develop?
Between the Maxillary prominence and lateral nasal prominence.
The nasolacrimal duct develops from the ectoderm of the _________ groove
nasolacrimal
The premaxilla (primary palate), part of maxilla that holds 4 upper incisors, and the philtrum are all formed by the fusion of what facial prominence
Medial nasal prominence
The tongue is initially up and between what bilateral structures?
Palatine shelves from the maxillary prominence
When the two palatine shelves fuse, what is this structure called?
Secondary palate.
If the secondary palate is the greater part of the palate, what is the primary palate?
The primary palate is a smaller anterior part of the palate derived from the medial nasal prominence. It is also know as a premaxilla
What sex is more likely to have a cleft lip? Cleft palate?
Male (4/5). Female (2/3)
The tongue is derived from what three arches?
1st, 3rd, and 4th.
The body of the tongue is derived from which arch? What are two specific structures from which the body is formed?
First. Lateral lingual swelling and the tuberculum impar
The root of the tongue is developed from the copula of the _____ arch.
Third.
Where does the epiglottis develop from? From which arch?
The epiglottal swelling of the 4th arch
What would happen to a tongue in which the lateral lingual swellings and the tuberculum impar do not fuse together?
A bifid tongue would develop
Ankyloglossia (tongue-tied) results from the lack of what programed cellular activity?
Apoptosis
