ANA 307 Neuroembryology, Pharyngeal Apparatus and Oral cavity

Question 1

The pharyngeal apparatus consists of

Answer 1

pharyngeal arches,
pharyngeal pouches, pharyngeal clefts (grooves), and pharyngeal membranes.

Question 2

Number, function and location of pharyngeal arches

Answer 2

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

Question 3

Number and location of pharyngeal clefts

Answer 3

Pharyngeal clefts (grooves): Four in number and
present externally between the arches. They are
lined by ectoderm.

Question 4

Number and location of pharyngeal pouches

Answer 4

Pharyngeal pouches: Four in number and located
internally between the two pharyngeal arches.
They are lined by endoderm.

Question 4

Number and location of pharyngeal membranes

Answer 4

Pharyngeal membranes: Four in number and
located between the two adjacent arches where
pharyngeal cleft and pouches are opposed to each other

Question 5

The fate of the first pharyngeal arch (bones, muscles, nerves and arteries) aka mandibular arch

Answer 5

1. 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
2. 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.

Question 6

the muscles of the first arch are innervated by which branch of which nerve?

Answer 6

mandibular branch of trigeminal nerve

Question 7

The fate of the 2nd pharyngeal arch (bones, muscles, nerves and arteries) aka hyoid arch

Answer 7

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

Question 8

Describe the stapedial and hyoid artery

Answer 8

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

Question 8

The fate of the 3rd pharyngeal arch (bones, muscles, nerves and arteries)

Answer 8

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

Question 9

The fate of the 6th pharyngeal arch (bones, muscles, nerves and arteries)

Answer 9

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

Question 10

The fate of the 4th pharyngeal arch (bones, muscles, nerves and arteries)

Answer 10

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

Question 11

Derivatives of the first pharyngeal pouch

with little explanation

Answer 11

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

Question 12

Derivatives of the second pharyngeal pouch

Answer 12

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

Question 13

Derivatives of the third pharyngeal pouch

Answer 13

Inferior parathyroid gland
Thymus

Question 14

Derivatives of the fourth pharyngeal pouch

Answer 14

Superior parathyroid gland
Caudal pharyngeal complex* (ultimopharyngeal body)

Question 15

Derivatives of the fifth pharyngeal pouch

Answer 15

When this develops, this rudimentary pouch becomes part of the fourth pharyngeal pouch and helps to form the ultimopharyngeal body

Question 16

When and how do the pharyngeal arches form?

Answer 16

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

Question 17

Describe the layers of the pharyngeal arches

Answer 17

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

Question 18

Discuss the derivative of the first pharyngeal groove

Answer 18

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.

Question 19

Discuss the derivative of the first pharyngeal membrane

Answer 19

Tympanic membrane

Question 20

What are they layers of the pharyngeal membrane and how are they formed?

Answer 20

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

Question 21

When does oral cavity development begin?

Answer 21

4 weeks IUL

Question 22

What occurs in week 4 of oral cavity development?

Answer 22

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

Question 23

What occurs in week 5 of oral cavity development?

Answer 23

The frontonasal process produces the medial and lateral process
Failure of fusion is the maxillary and medial nasal processes produces a cleft lip

Question 24

What occurs in week 6 of oral cavity development?

Answer 24

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.

Question 25

What occurs in week 7 of oral cavity development?

Answer 25

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.

Question 26

What occurs in week 8 of oral cavity development?

Answer 26

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.

Question 27

The oral cavity develops from where

Answer 27

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.

Question 28

What are the stages of tooth development

Answer 28

1. Bud
2. Cap
3. Bell
4. Apposition

Question 29

The first sign of tooth develop occurs when?

Answer 29

6th week IUL

Question 30

Development of the primary epithelial band

Answer 30

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

Question 31

Development of the vestibular band and dental lamina

Answer 31

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

Question 32

Discuss the bud stage of tooth development

Answer 32

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

Question 33

Discuss the cap stage of tooth development

Answer 33

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

Question 34

Failure of midline fusion during embryogenesis results in

Answer 34

The spectrum of cleft lip, cleft palate, both cleft lip and cleft palate and mucus cleft palate

Question 35

Failure of midline fusion during embryogenesis results in

Answer 35

The spectrum of cleft lip, cleft palate, both cleft lip and cleft palate and mucus cleft palate

Question 36

When and how does the lip form during embryonic development?

Answer 36

The medial nasal tissue fuse to form the lip during weeks 5 to 6 of embryonic development

Question 37

Which aspects of the oral cavity form during week 6 to 10

Answer 37

The anterior hard palate alveolus and philtrum

Question 38

Types of cleft palate

Answer 38

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

Question 39

What are some causes of oral anomalies

Answer 39

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