Neural crest cells

• The neural crest cells develop into numerous and varied cell types and migrate to regions far anterior (ventral) from their site of origin

NEURAL CREST CELL DERIVATIVES

Basic derivatives

• Peripheral nervous system (PNS) cells: glial cells & Schwann cells.
• Meninges: Specifically, the inner layers: the pia and arachnoid
• Melanocytes
• The Enteric Nervous System

Cranial neural crest cell derivatives

• Pharyngeal Arch Components
  • Musculoskeletal structures
  • Pharyngeal arch cranial nerves

Trunk and lumbosacral neural crest cell derivatives include:

• Dorsal root ganglia
• Sympathetic chain ganglia
• Adrenal medullary cells
• Prevertebral ganglia

NEURAL TUBE: PRIMARY BRAIN VESICLES

Primary brain vesicles

From anterior to posterior:

• Prosencephalon
• Mesencephalon
• Rhombencephalon
• Caudal neural tube

Neural crest cell organization

• Neural crest cells originate along the midline of the dorsal aspect of the neural tube.
• Somites lie lateral to them.

Placodes

• The placodes are areas of thickened surface ectoderm that play an integral role in development of key cranial nerves (CNs 1, 2, and 8 – the solely sensory set) and also contribute to the development of merge the pharyngeal arch cranial nerves along with the neural crest cells.
• Examples of placodes:
  • The olfactory placode forms the olfactory nerves and epithelium.
  • The lens placode forms the optic nerve.
  • The geniculate placode contributes to the development of cranial nerve 7 (along with the neural crest cells of the 2nd pharyngeal arch).
  • The otic placode forms the vestibulocochlear nerve.

NEURAL CREST CELL DEVELOPMENT

Superior view

• Folding of the neural plate into the neural tube is key to the development of the neural crest cells.

Day 18

• The neural folds form the neural crests.
• The neural groove forms the base of the neural tube.

Trilaminar germ disc

• From top to bottom, the trilaminar germ disc comprises ectoderm, intraembryonic mesoderm, and endoderm.
• Mesoderm comprises somites and notochord (which induces the overlying ectoderm to form the neural plate).
  Then, draw the underlying endoderm.
• Along the floor of the ectoderm lies the neural folds (again the neural crests are the neural fold tips).
• The neural groove is the floor of the neural tube.

Day 21

• The neural folds abut centrally, first, and remain open at their ends anteriorly and posteriorly.
• The neural crest lies along the dorsal neural tube.
  • Elsewhere we see that this is the roof plate of the neural tube and is biologically influenced by the neural crest cells.

Day 23

• The neural tube is folded a long distance along its center but remains open at the anterior (cranial) and posterior (caudal) neuropores.
• The somites are visible, centrally, where the neural folds abut.
• The somites generate bumps that appear on the surface of the overlying neural tube.
• The neural crest cells make their migrations ventrally.

NEURAL CREST CELL MIGRATION

• Migrate to form the peripheral nervous system derivatives

Relevant structures:

• Ectoderm
• Mesoderm
• Neural tube
• Notochord
• Dorsal aorta
• A portion of the Gut Tube
• Somites (the paraxial mesoderm), which forms axial musculoskeletal elements, from lateral to medial:
  • Dermatome (dermis)
  • Myotome (muscle)
  • Sclerotome (skeleton): it migrates to form around the neural tube as the spine and posterior basal occipital bone.

Peripheral nervous system derivatives

• Portions of Cranial Nerves: 5, 7, 9, and 10 (the Pharyngeal Arch cranial nerves) and portions of CNs 3 and 8, as well.
• Dorsal root ganglia
• Sympathetic chain ganglia
• Adrenal medulla (the chromaffin cells)
• Prevertebral ganglia
• Enteric nervous system

Additional neural crest cell derivativs

• Don’t forget, however, that the neural crest cells are responsible for much more than the aforementioned peripheral nervous system derivatives.

Other elements include:

• Additional peripheral nervous system cellular structures:, for instance – glial cells and Schwann cells.
• Melanocytes
• [Inner meningeal layers (pia and arachnoid – the leptomeninges)
• Musculoskeletal elements of the head and neck, such as the key cartilages and ear bones (learned elsewhere).