Embryology 2: Development of Face to Prenatal
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Questions and Answers

Which cranial nerves are responsible for the sensory and special functions of the anterior two-thirds of the tongue?

  • CNV3 and CNXII
  • CNV3 and CNVII (correct)
  • CNVII and CNIX
  • CNX and CNV3

    • Which embryonic structure contributes to the formation of the secondary palate?

  • Oral cavity
  • First pharyngeal arch
  • Lingual swellings (correct)
  • Nasal cavity

    • Which of the following is NOT associated with the development of the mandible?

  • First pharyngeal arch
  • Condyle cartilage
  • Meckle's cartilage
  • Palatoglossus muscle (correct)

    • What is the primary ossification method for the cranial base?

    <p>Endochondral ossification</p> Signup and view all the answers

    What condition is primarily characterized by failure of the forebrain to divide into two hemispheres?

    <p>Holoprosencephaly</p> Signup and view all the answers

    What is the principal region of the neural tube that develops into the forebrain?

    <p>Prosencephalon</p> Signup and view all the answers

    Which of the following describes the role of somites in embryonic development?

    <p>Somites give rise to the vertebral column and skeletal muscle.</p> Signup and view all the answers

    Which of the following correctly identifies the component of the neural tube associated with motor neurons?

    <p>Anterior grey horn</p> Signup and view all the answers

    What type of mesodermal tissue does the cranial portion of paraxial mesoderm differentiate into?

    <p>Head mesoderm</p> Signup and view all the answers

    What is the main characteristic of the marginal zone in the neural tube?

    <p>It contains the neural epithelial cells.</p> Signup and view all the answers

    Which part of the neural tube is associated with the formation of the cerebellum?

    <p>Metencephalon</p> Signup and view all the answers

    During neurulation, which region of the neural tube is specifically associated with the development of the thalamus?

    <p>Diencephalon</p> Signup and view all the answers

    What embryological process is responsible for the creation of somites?

    <p>Somitogenesis</p> Signup and view all the answers

    In the context of embryonic development, what is the significance of rhombomeres?

    <p>They are structural divisions of the neural tube in the hindbrain.</p> Signup and view all the answers

    Which component of the neural tube is primarily responsible for sensory neuron development?

    <p>Alar plate</p> Signup and view all the answers

    Which nerve is associated with the first pharyngeal arch?

    <p>CNV3 + CNV2</p> Signup and view all the answers

    What is derived from the second pharyngeal arch?

    <p>Tonsil</p> Signup and view all the answers

    Which of these structures does NOT derive from the neural crest cells?

    <p>Epithelial tissues</p> Signup and view all the answers

    Which structure is NOT formed by the first pharyngeal arch?

    <p>Levator veli palatini</p> Signup and view all the answers

    What is one of the main roles of NCC (neural crest cells) during craniofacial development?

    <p>Contribute to bone and muscle of the head</p> Signup and view all the answers

    Which nerve is related to the third pharyngeal arch?

    <p>CNIX</p> Signup and view all the answers

    Which component is NOT associated with the signaling mechanisms in craniofacial development?

    <p>Neural plate</p> Signup and view all the answers

    During which weeks of intrauterine life does the development of the face occur?

    <p>4th - 10th weeks</p> Signup and view all the answers

    The maxilla arises from which embryonic structure?

    <p>First pharyngeal arch</p> Signup and view all the answers

    Which of the following is associated with the development of the larynx?

    <p>Third and fourth pharyngeal arches</p> Signup and view all the answers

    Which structure does NOT come from the first pharyngeal arch?

    <p>Cricothyroid muscle</p> Signup and view all the answers

    Which of these is an endodermal derivative associated with the first pharyngeal arch?

    <p>Tympanic membrane</p> Signup and view all the answers

    Which of the following is NOT a role of the neural crest cells?

    <p>Development of skeletal muscles</p> Signup and view all the answers

    The structure primarily developed from the second pharyngeal arch includes:

    <p>Hyoid bone</p> Signup and view all the answers

    Study Notes

    Neurulation

    • Neural tube formation begins after gastrulation with the development of a neural plate
    • Folding of neural plate results in the formation of the neural groove and neural folds
    • Neural folds fuse to form the neural tube
    • The neural crest cells (NC) migrate away from the neural tube and differentiate
    • The neural tube further differentiates into three primary brain vesicles: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)
    • Prosencephalon is further subdivided into the telencephalon (cerebrum) and the diencephalon (thalamus)
    • Mesencephalon remains as the midbrain
    • Rhombencephalon is further subdivided into the metencephalon (pons and cerebellum) and the myelencephalon (medulla oblongata)

    Vesiculation

    • Vesiculation refers to the formation of cavities within the brain
    • The neural tube differentiates further to form the ventricles of the brain.
    • The telencephalon gives rise to the lateral ventricles
    • The diencephalon gives rise to the third ventricle
    • The mesencephalon gives rise to the cerebral aqueduct
    • The metencephalon gives rise to the fourth ventricle
    • The myelencephalon gives rise to the central canal of the spinal cord

    Rhombomeres formation and NC migration

    • The rhombencephalon becomes segmented into eight bulges called rhombomeres, which help to regulate the migration and differentiation of NCC
    • NCC migrate from the rhombomeres along defined pathways and differentiate into a variety of cell types

    Somite formation

    • The mesoderm differentiates into the paraxial mesoderm, intermediate mesoderm, and the lateral plate mesoderm which is then further subdivided into the somatic and splanchnic mesoderm
    • The paraxial mesoderm forms somites - segmented blocks of mesoderm that give rise to the vertebral column, skeletal muscle, and dermis
    • Each somite differentiates into three components:
      • Sclerotome: Gives rise to vertebrae
      • Myotome: Gives rise to skeletal muscles
      • Dermatome: Gives rise to dermis

    Neural Crest Cells

    • NCC are a multipotent cell population that originates from the neural tube during neurulation
    • NCC migrate to various locations in the body and differentiate into a variety of cell types including:
      • Chromaffin cells: part of the adrenal medulla
      • Cranial structures: bones, cartilage, muscles of the head and neck
      • Enteric nervous system: neurons and glial cells in the digestive system
      • Schwann cells: myelin-producing cells in the peripheral nervous system
      • Satellite cells: support cells in the peripheral nervous system
      • Spinal nerves
      • Carotid bodies
      • Endocardial cushions
      • Melanocytes: pigment-producing cells in the skin
      • Leptomeninges: delicate membranes that surround the brain and spinal cord

    NCC induction

    • NCC induction involves a complex interplay of signaling molecules, including:
      • BMPs (Bone Morphogenetic Proteins): induce NCC fate
      • Wnt: Wnt signaling promotes NCC migration and differentiation
      • FGFs (Fibroblast Growth Factors): involved in NCC proliferation and survival

    NCC fate decisions in the head region

    • The NCC in the head region give rise to various cell types, including the facial skeleton, the craniofacial muscles, and the sensory ganglia of the head
    • NCC fate decisions in the head region are influenced by:
      • Local signaling molecules
      • Position of the migrating NCC

    Signalling mechanisms

    • Craniofacial development is driven by complex signaling pathways, including:
      • FGFs (Fibroblast Growth Factors): regulate the expression of genes involved in craniofacial development
      • Retinoic acid: plays a role in the patterning of the face
      • Sonic hedgehog: involved in the development of the midface
      • Epithelial-mesenchymal interactions: essential for the proper development of the face and skull.

    Branchial arches

    • Six pharyngeal arches form during the 4th to 7th weeks of embryonic development
    • Each arch is composed of mesenchyme (derived from NCC) and is covered externally by ectoderm and internally by endoderm
    • Arches give rise to various facial structures, including the jaws, the tongue, the ear, and the neck
    • Each arch has its own:
      • Mesenchymal core (derived from NCC)
      • Ectodermally derived groove in between
      • Endodermally derived pouches in between
      • Specific cranial nerves

    Arch 1

    • Gives rise to the mandible, maxilla, zygomatic bone, temporal bone, and part of the sphenoid bone.
    • It also gives rise to the malleus, incus, and stapes of the middle ear, and to the Meckel's cartilage.
    • Muscles: muscles of mastication, anterior belly of the digastric, mylohyoid, tensor veli palatini, and tensor tympani.
    • Nerves: CN V (trigeminal nerve)

    Arch 2

    • Gives rise to the hyoid bone, the stapes, the styloid process of the temporal bone, and the lesser horn of the hyoid bone.
    • Muscles: muscles of facial expression, the posterior belly of the digastric, stylohyoid, and stapedius
    • Nerves: CN VII (facial nerve)

    Arch 3

    • Gives rise to the hyoid bone (greater horn), the stylopharyngeus muscle, and part of the carotid body.
    • Nerves: CN IX (glossopharyngeal nerve)

    Arch 4 and 6

    • Gives rise to muscles of the larynx and the intrinsic muscles of the larynx.
    • Nerves: CN X (vagus nerve)

    Development of the face

    • The development of the face occurs between the 4th and 10th weeks of intrauterine life, with a visible face forming by the 6th week.
    • Facial development begins with the merging of five processes (frontonasal process, maxillary processes, and mandibular processes) around the stomodeum (primitive mouth)

    Formation of the secondary palate

    • The secondary palate divides the nasal and oral cavities, allowing the development of the hard and soft palates
    • The median nasal process forms the premaxilla, which contains the upper incisor teeth
    • The maxillary processes form the palatine shelves, which grow medially and fuse to create the secondary palate, joining with the premaxilla.

    Formation of the tongue

    • The tongue develops from the first four pharyngeal arches (1st arch: anterior 2/3rds of the tongue, 3rd arch: posterior 1/3rd of the tongue, 4th arch: base of the tongue) and the occipital myotomes (muscles of the tongue)
    • The tuberculum impar is a midline eminence that forms on the first arch
    • The lingual swellings develop on either side of the tuberculum impar, eventually fusing with it and with each other to form the anterior 2/3rds of the tongue

    Development of the skull

    • The skull develops in two parts:
      • Cranial vault, which is formed by intramembranous ossification
      • Cranial base, which is formed by endochondral ossification

    Development of the mandible

    • The mandible develops from the first pharyngeal arch
    • Its growth is independent of Meckel's cartilage.
    • After birth, the mandible's growth is influenced by the condylar cartilage and the surrounding soft tissues.

    Development of the maxilla

    • The maxilla develops from the maxillary processes of the first pharyngeal arch.
    • It develops independently of cartilage.
    • Important for formation of hard palate.

    Development of the maxilla sinus

    • The maxillary sinus is a large air-filled cavity within the maxilla.
    • It develops as an outpouching of the nasal cavity during fetal development.
    • Expands into the maxilla in a process dependent on the development of the teeth.

    Development of the TMJ

    • The temporomandibular joint (TMJ) develops from the interaction of the mandibular condyle and the temporal bone.
    • The development of the TMJ is influenced by the growth of the surrounding tissues.

    Conditions

    Holoprosencephaly

    • A developmental disorder characterized by a failure of the prosencephalon (forebrain) to properly divide into the two hemispheres
    • The severity of holoprosencephaly varies depending on the extent of incomplete brain division
    • Causes include genetic mutations and environmental factors such as exposure to alcohol or drugs during pregnancy.

    Clefts

    • Clefts are congenital defects that occur when tissues in the face and mouth do not fuse properly during fetal development.
    • They are a common birth defect and can occur in a range of severities
    • Cleft lip and cleft palate are the two most common types of clefts. They can occur together or separately.
    • Cleft lip: incomplete closure of the lip
    • Cleft palate: incomplete closure of the palate.

    First Arch Syndromes

    • These syndromes result from defects in the first pharyngeal arch development.
    • They commonly involve facial features, ear abnormalities and heart defects.

    Treacher Collins Syndrome

    • A rare genetic disorder that affects the development of the bones and tissues of the face, including the ears, eyes, and jaw.
    • Features:
      • Underdeveloped cheekbones
      • Down-slanting eyes
      • Small or absent ears
      • Hearing loss
      • Cleft palate
      • Malformations of the jaw

    Pierre Robin Sequence

    • A syndrome that affects three specific features:
      • Small lower jaw (micrognathia)
      • Cleft palate
      • Glossoptosis (tongue that is positioned abnormally posteriorly).
    • Features:
      • Facial features
      • Respiratory difficulties due to the tongue obstructing the airway
      • Issues with feeding

    Foetal alcohol spectrum disorder (FASD)

    • A group of birth defects that happen because a pregnant woman drinks alcohol.
    • The amount of alcohol consumed during pregnancy as well as when the alcohol was drank influences the severity of the disorder.
    • Features:
      • Characteristic facial features
      • Delayed growth
      • Neurological problems
      • Behavioral problems

    Environmental Factors Causing Congenital Defects

    • Environmental factors are important contributors to congenital defects in cranial facial development:
      • Maternal health: maternal diabetes, smoking, folate deficiency
      • Infections: rubella virus infection
      • Drug exposure: retinoic acid, alcohol, thalidomide
      • Radiation exposure
    • These factors can interfere with the complex signaling pathways and cellular processes that drive craniofacial development, leading to a variety of defects.

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