Ocular Embryology

• What is the head end of an embryo called?

  Rostral or cranial
• What is the tail end of an embryo called?

  Caudal
• What are the three planes of motion in embryology?

  • Transverse
  • Frontal
  • Sagittal
• What is the process of Neurulation?

  • Folding of a flat disc into a hollow cylinder
  • Involves three germ layers: ectoderm, mesoderm, endoderm
• At what day do mesodermal cells migrate towards the embryo's head end?

  Day 16
• What structure is formed by mesodermal cells migrating towards the head end?

  The notochord
• What is the function of the notochord during embryonic development?

  It induces neural plate formation
• What does the neural plate include?

  Neural crest cells and neural tube
• What does the neural tube develop into?

  The central nervous system (CNS)
• What is the future mouth end of the embryo called?

  Head end
• What is the future anus end of the embryo called?

  Tail end
• What happens to the neural plate by the end of week 3?

  Its edges rise up to form neural folds
• What is formed when the neural folds fuse?

  The neural tube
• What do specialized neuroectodermal cells form during neurulation?

  Neural crest
• What types of cells can neural crest cells become?

  Various cell types including sensory neurons
• What structures does the neural tube develop into?

  • Brain
  • Spinal cord
  • Oculomotor nerves
  • Retina
  • Iris muscles
  • Eye's internal epithelial layers
• What is the origin of the neural tube?

  Ectodermal origin
• When does complete closure of the neural tube occur?

  At the end of week 4
• What are the steps of primary neurulation?

  1. Formation & folding of neural plate
  2. Growth of neural plate cells
  3. Convergence of neural plate edges
  4. Fusion of neural folds to complete neural tube
• What is spina bifida?

  Incomplete closure of the neural tube at the caudal end
• What happens to the notochord during neurulation?

  It degenerates
• What do somites differentiate into?

  Dermis, skeletal muscle, cartilage, tendons, ribs, and vertebrae
• How many pairs of somites are present by the end of week 5?

  42-44 pairs
• What are the primary brain vesicles formed from the neural tube?

  • Prosencephalon (forebrain)
  • Mesencephalon (midbrain)
  • Rhombencephalon (hindbrain)
• What are the secondary brain vesicles developed from the primary brain vesicles?

  • Prosencephalon: telencephalon & diencephalon
  • Rhombencephalon: metencephalon & myelencephalon
• What fills the neural tube by the 8th week?

  Cerebrospinal fluid (CSF)
• What are the distinct regions of the CNS by the end of the 8th week?

  • Forebrain: cerebrum
  • Diencephalon: thalamus, hypothalamus, pituitary & pineal glands
  • Midbrain: corpora quadrigemina
  • Hindbrain: pons, medulla & cerebellum
  • Spinal cord
• What is the anterior-most aspect of the brain called?

  Forebrain (prosencephalon)
• What is the major development period for the eye?

  • Takes place at 3-10 weeks
  • Involves ectoderm, neural crest cells, and mesenchyme
• What does the neural ectoderm develop into?

  Retina, optic nerve fibers, and iris
• What does the surface ectoderm develop into?

  Lens, conjunctival & corneal epithelia, eyelids, and lacrimal apparatus
• What does mesenchyme become in eye development?

  Corneal stroma, sclera, choroid, ciliary muscle, parts of vitreous, muscles lining anterior chamber
• What forms on day 22 during eye development?

  Optic grooves
• What do optic vesicles grow towards during development?

  The surface ectoderm
• What happens to the lens placode during development?

  It invaginates to become a lens pit
• What does the lens pit form during eye development?

  A lens vesicle
• What happens to the distal end of the hyaloid artery during lens maturation?

  It disintegrates
• What are the key structures involved in the development of the eye?

  • Neural ectoderm: retina, optic nerve fibers, iris
  • Surface ectoderm: lens, conjunctival & corneal epithelia, eyelids, lacrimal apparatus
  • Mesenchyme: corneal stroma, sclera, choroid, ciliary muscle, parts of vitreous, muscles lining anterior chamber
• At what weeks does the development of the eye take place?

  1. 10 weeks
• Which three components are involved in the development of the eye?

  Ectoderm, neural crest cells, and mesenchyme