Pharyngeal Arches Flashcards
How are pharyngeal arches made?
• At beginning of the 4th week neural crest cells migrate into the developing head and neck region
– Neural crest differentiate into mesenchyme
– Stimulates the migration of myogenic mesoderm from the paraxial mesoderm (occipital
somites)
– Endothelial cells and invasive angiogenic cells give rise to vessels
– Pharyngeal endoderm plays an essential role in regulating
– Heavily under the influence of shh
• By the end of the 4th week 4 pairs of arches are visible in the cervical region
– 6 in total are formed but the last two are rudimentary and not visible on the surface
What are the contents of each pharyngeal arch?
- Each arch consists of a core of mesoderm covered by ectoderm externally and endoderm internally
- They work similar to the somites in that each give rise to areas of dermis, bone/cartilage, vessels and nerves
- Interruption or failure at any point leads to a sequence of mishaps
What are the components of pharyngeal apparatus components?
PHARYNGEAL ARCHES
Develop from mesoderm and migrating neural crest cells
PHARYNGEAL GROOVES/CLEFTS
Separate the arches externally Lined by ectoderm
PHARYNGEAL POUCHES
Separate the arches internally Lined by endoderm
PHARYNGEAL MEMBRANES
Areas between arches where the ectoderm and endoderm meet.
What passes through the pharyngeal arches?
An artery that arises from the truncus arteriosus and courses around the primordial pharynx to enter the dorsal aorta
A cartilaginous rod that forms the skeleton of the arch
A muscular component that will give rise to muscles of the head and neck A nerve that supplies the mucosa and muscles of the arch
What is the significance of the stomodeum?
• Stomodeum (primitive oral cavity)
– A surface ectodermal depression forms as the head fold overshoots the 1 arch
– The ectoderm of the 1st arch forms the oral epithelium
– Separated from the primordial pharynx by the oropharyngeal membrane
- The lateral walls of the pharynx is supported by the surface endoderm of the arches
- The oropharyngeal membrane ruptures to connect the developing oral cavity with the rest of the developing foregut and amniotic cavity
What’s the significance of 1st pharyngeal arch?
Divides into maxillary and mandibular prominences
Maxillary – maxilla, zygoma, portion of vomer
Mandibular – mandible, squamous temporal bone, sphenomandibular ligament, part of middle ear, part of external ear
What’s the significance of Meckels cartilage?
Meckel’s cartilage provides the framework for the development of the mandible but degenerates creating the mandibular canal and its remnants the sphenomandibular ligament
What muscles are developed from the pharyngeal arch?
Muscles of mastication, tensor tympani, tensor veli palatini, mylohyoid and anterior belly of digastric form from 1st arch
Myoblasts for the 2nd arch migrate from the neck region and form the muscles of facial expression, stapedius, stylohyoid and posterior belly of digastric
Third arch forms stylopharyngeus muscles
4th & 6th combined forms the pharynx and larynx muscles
What nerves come from the pharyngeal nerves?
Special visceral efferents (branchial motor) – arch derived muscles Special visceral afferents – dermis and mucous membranes
Sensory supply to the face, nasal cavity and hard palate, teeth and tongue is derived from the 1st arch (CNV2&V3) 2nd -6th arches supply the mucous membranes of tongue, pharynx and larynx
Superior laryngeal branch and recurrent laryngeal branches of CN X supplies the 4th arch
What are the derivatives of the 1st arch?
Nerve: Trigeminal (V2 / V3)
Skeleton: malleus, incus sphenomandibular lig., maxilla, mandible
Muscles: mastication, tensor veli palatini, tensor tympani, ant. digastric, mylohyoid
Artery: Maxillary
What are the derivatives of the 2nd arch?
Nerve: Facial (VII)
Skeleton: stapes, styloid process, stylohyoid lig., hyoid (lesser horn & upper body)
Muscles: stapedius, stylohyoid, post. digastric
What are the derivatives of the 3rd pharyngeal arch?
3RD
Nerve: Glosso- pharyngeal (IX)
Skeleton: Hyoid(greater horn and lower body)
Muscles: Stylopharyngeus
Artery: Common & internal carotid
What are the derivatives of the 4th arch?
4TH
Nerve: Vagus(X) superior laryngeal
Skeleton: Laryngeal cartilages
Muscle: Pharyngeal constrictors levator veli palatini, cricothyroid
Artery: aortic arch, R. subclavian
What are the derivatives of the 6th arch?
6TH
Nerve: Vagus(X) recurrent laryngeal
Skeleton: Laryngeal cartilages
Muscles: Intrinsic muscle of the larynx, striated muscles of the esophagus
Artery: Ductus arteriosus, pulmonary aa
