ANA 307 Neuroembryology, Pharyngeal Apparatus and Oral cavity Flashcards
The pharyngeal apparatus consists of
pharyngeal arches,
pharyngeal pouches, pharyngeal clefts (grooves), and pharyngeal membranes.
Number, function and location of pharyngeal arches
Five in number and present
in the lateral wall and floor of the primitive
pharynx.
The pharyngeal arches provide support to the wall of the primitive pharynx laterally as well as ventrally
Number and location of pharyngeal clefts
Pharyngeal clefts (grooves): Four in number and
present externally between the arches. They are
lined by ectoderm.
Number and location of pharyngeal pouches
Pharyngeal pouches: Four in number and located
internally between the two pharyngeal arches.
They are lined by endoderm.
Number and location of pharyngeal membranes
Pharyngeal membranes: Four in number and
located between the two adjacent arches where
pharyngeal cleft and pouches are opposed to each other
The fate of the first pharyngeal arch (bones, muscles, nerves and arteries) aka mandibular arch
- Maxillary prominence (dorsal portion): becomes future maxilla, zygomatic bone and squamous part of temporal bone
it is associated with the maxillary cartilage which gives rise to incus - Mandibular prominence (ventral portion): furute mandible
Associated with meckels cartilage, which gives rise to the malleus and sphenomandibular ligaments
Muscles: myohyloid, anterior belly of digastric, muscles of mastication, tensor veli palatini and tensor tympani
Innervation: mandibular and maxillary branches of the trigeminal nerve CNV
Chorda tympani nerve
Artery: maxillary artery
Its sensory field is that of the trigeminal nerve too, namely the skin of the face, the lining of the mouth and nose, and general sensation to the anterior 2/3 of the tongue.
the muscles of the first arch are innervated by which branch of which nerve?
mandibular branch of trigeminal nerve
The fate of the 2nd pharyngeal arch (bones, muscles, nerves and arteries) aka hyoid arch
Skeletal structures and ligaments:
lesser cornu of the hyoid bone
upper part of the body of the hyoid bone
stapes
styloid process
stylohyoid ligament
Muscles:
stylohyoid
Muscles of facial expression
stapedius
posterior belly of digastric
Innervation:
Facial nerve (CNVII)
Artery:
Stapedial artery
Hyoid artery
Describe the stapedial and hyoid artery
Stapedial artery – connects the embryonic precursors of the internal carotid, internal maxillary and middle meningeal arteries. It regresses before birth.
Hyoid artery – gives rise to the corticotympanic artery in the adult
The fate of the 3rd pharyngeal arch (bones, muscles, nerves and arteries)
Skeleton:
Greater cornu
lower part of body of
the hyoid bone
Muscles:
Stylopharyngeus
Innervation:
Glossopharyngeal nerve CNIX
Artery:
the common carotid artery
proximal portion of the internal carotid artery
The fate of the 6th pharyngeal arch (bones, muscles, nerves and arteries)
Muscles:
intrinsic muscles of the larynx
striated muscles of the esophagus
Artery:
ductus arteriosus
proximal portion of the pulmonary artery
Recurrent laryngeal branch of
the vagus nerve
The fate of the 4th pharyngeal arch (bones, muscles, nerves and arteries)
Skeletal structures and ligaments:
Muscle:
Cricothyroid
levator palati
intrinsic muscles of the larynx
constrictors of pharynx
Laryngeal cartilages
except epiglottis
Innervation:
Superior laryngeal branch of vagus
nerve
Derivatives of the first pharyngeal pouch
with little explanation
Auditory tube
Tympanic (middle ear) cavity
The first pharyngeal pouch expands into an elongate tubotympanic recess
➢The expanded distal part of this recess contacts the first pharyngeal groove, where it contributes to the formation of the tympanic membrane (eardrum)
➢The cavity of the tubotympanic recess gives rise to the tympanic cavity and mastoid antrum
Derivatives of the second pharyngeal pouch
Palatine tonsil
Intratonsillar cleft
The second pharyngeal pouch is largely obliterated as the palatine tonsils develop
➢Part of the cavity of this pouch remains as the tonsillar sinus or fossa
➢The endoderm of the pouch proliferates and grows into the underlying mesenchyme
➢The central parts of these buds form crypts
The pouch endoderm forms the surface epithelium and the lining of the tonsillar crypts
➢At about 20 weeks the mesenchyme around the crypts differentiates into lymphoid tissue
➢These tissues soon organize into the lymphatic nodules of the palatine tonsil
Derivatives of the third pharyngeal pouch
Inferior parathyroid gland
Thymus
Derivatives of the fourth pharyngeal pouch
Superior parathyroid gland
Caudal pharyngeal complex* (ultimopharyngeal body)
Derivatives of the fifth pharyngeal pouch
When this develops, this rudimentary pouch becomes part of the fourth pharyngeal pouch and helps to form the ultimopharyngeal body
When and how do the pharyngeal arches form?
Pharyngeal arches begin to develop early in the fourth week as neural crest cells migrate into the head and neck region
The first pair of pharyngeal arches (primordium of jaws) appears as a surface elevations lateral to the developing pharynx
Soon other arches appear as obliquely disposed, rounded ridges on each side of the future head and neck regions
Describe the layers of the pharyngeal arches
Each pharyngeal arch consists of a core of mesenchyme
➢Is covered externally by ectoderm and internally by endoderm
➢In the third week the original mesenchyme is derived from mesoderm
➢During the fourth week most of the mesenchyme is derived from neural crest cells that migrate into the pharyngeal arches
Discuss the derivative of the first pharyngeal groove
External auditory meatus
Outer ectodermal layer of tympanic membrane
Only first pharyngeal cleft gives rise to a definitive structure—the external auditory meatus—whereas all other clefts (2, 3, and 4) are obliterated.
Discuss the derivative of the first pharyngeal membrane
Tympanic membrane
What are they layers of the pharyngeal membrane and how are they formed?
formed of two layers: (a) an inner layer formed by the endodermal lining of the pouch and (b) an outer layer formed by the ectodermal lining of the pharyngeal cleft.
Later these two layers become separated by thin layer of mesoderm. Now it consists of three layers: outer layer of ectoderm, middle layer of mesoderm, and inner layer of endoderm
When does oral cavity development begin?
4 weeks IUL
What occurs in week 4 of oral cavity development?
The primitive oral cavity (stomodeum) develops 5 facial swellings
One frontonasal process, 2 maxillary and 2 mandibular processes
The frontonasal process eventually develops to fiel the forehead, nose and philtrum
The 2 maxillary process form the middle face and the upper lip
The 2 mandibular processes form the mandible and lower lip
What occurs in week 5 of oral cavity development?
The frontonasal process produces the medial and lateral process
Failure of fusion is the maxillary and medial nasal processes produces a cleft lip
What occurs in week 6 of oral cavity development?
The primary nasal septum and the primary palate are formed, both derived from the frontonasal process.
2 lateral palatal shelves develop behind the primary palate from the maxillary process
A secondary nasal septum grows behind the primary nasal septum from the roof of the primitive oral cavity dividing the nasal cavity into 2
The mandible appears as a band of dense fibrous tissue known as meckels cartilage, the is cartilage provides a framework around which the fine will form.
What occurs in week 7 of oral cavity development?
Bone formation commenced at the mental foramen area and begins to spread backwards, forwards and upwards outlining the future body of the mandible.
As the bone grows backwards, 2 small secondary cartilages develop which eventually form the condyle and coronoid processes
Anteriorly the left and right mandibular palate of bone is separated by the mandibular symphysis; these 2 plates eventually unite to form a single bone approx. 2 years after birth
The upward growth of bone increases the height of the mandible joining the alveolar process which will surround the developing tooth.
What occurs in week 8 of oral cavity development?
Ossification on the maxilla commences at the area of the developing primary (deciduous) canines; from this area, bone formation spreads, developing the maxillary processes, palatal, zygomatic, frontal and alveolar
Growth of the maxilla occurs by the remodelling of bone and by sutural growth
the stimulus for sutural bone growth is thought to be related to to the tension produced by the displacement of bone.
The oral cavity develops from where
The oral cavity consists of two parts: (or) primitive oral cavity and (b) definitive oral cavity.
The primitive oral cavity develops from ectoder- mal stomodeum whereas the definitive oral cavity develops from cephalic part of endodermal foregut. At first the two parts are separated from each other by buccopharyngeal membrane.
The two parts communicate with each other when buccopharyngeal membrane ruptures during the third week of intrauterine life (IUL)
After rupture of buccopharyngeal membrane the line of junction of ectodermal and endodermal parts cannot be defined.
What are the stages of tooth development
- Bud
- Cap
- Bell
- Apposition
The first sign of tooth develop occurs when?
6th week IUL
Development of the primary epithelial band
Underneath the oral ectodermal epithelium there is a condensation of mesenchymal cells in areas where teeth will eventually form
The ectodermal epithelium thickens in those areas and protrudes into the mesenchymal cells forming the primary epithelial band
Development of the vestibular band and dental lamina
At 7 weeks of IUL the epithelial band develops 2 processes: vestibular band and dental lamina
The vestibular band forms buccally and will eventual form the vestibule, separating the lips and cheeks from yeh teeth and gingivae
The dentally lamina forms lingual my and develops into an arch shaped band
Discuss the bud stage of tooth development
At 8 weeks of intrauterine life, clumps of mesenchymal cells induce the dental lamina to form swellings known as enamel organs
Each enamel organ will be responsible for the development of each tooth
Discuss the cap stage of tooth development
As the enamel organs grow and increase in size, the inner aspect becomes concave, resembling skull caps
By the late cap stage, at 12 weeks IUL, cells on the inner aspect of the enamel organ change from cuboidal to columnar forming the inner enamel epithelium
Failure of midline fusion during embryogenesis results in
The spectrum of cleft lip, cleft palate, both cleft lip and cleft palate and mucus cleft palate
Failure of midline fusion during embryogenesis results in
The spectrum of cleft lip, cleft palate, both cleft lip and cleft palate and mucus cleft palate
When and how does the lip form during embryonic development?
The medial nasal tissue fuse to form the lip during weeks 5 to 6 of embryonic development
Which aspects of the oral cavity form during week 6 to 10
The anterior hard palate alveolus and philtrum
Types of cleft palate
Unilateral
bilateral
median
soft palate (mucous cleft)
midline (rare)
isolated (More common in females with no racial predilection)
cleft lip with palate (Twice as common as isolated cleft palate with an incidence great in males and those of Asian and Caucasian descent)
Cleft lip without palate is more likely to be associated with the syndrome
Complete: Extends all the way into the nostril
Incomplete: does not extend up into the nostril
What are some causes of oral anomalies
Tetragen exposures income indicated in class developments in clued organic solvents and agricultural chemicals e.g. pesticides, viral infections metabolic derangements and illicit drugs
Antiepileptic medications associated with oral facial defects include diazepam, phenytoin, phenobarabital, topiramate and vamotrigine 
