Neural Development and Embryology

Neural Development: Anatomy

• Understanding neural development relies on knowing the anatomy of developing nervous systems.
• The focus is on model organisms.
• Nervous systems have both peripheral and central components.
• The periphery gathers information from within and around the body, sending signals to the central nervous system (CNS) to process and store information.
• Decisions made in the CNS are then sent back to the periphery to generate responses.
• Vertebrates have a complex CNS consisting of the brain and spinal cord, and a PNS made up of all neurons outside the CNS.

Embryonic Development

• Animal embryos develop into three germ layers: ectoderm, mesoderm, and endoderm.
• Ectoderm gives rise to the epidermis and nervous system (neuroectoderm).
• Neuroectoderm can also be called neuroepithelium.
• The process of rearranging cells to form germ layers is called gastrulation.
• This process varies greatly in different species.

Invertebrates: Development

• C. elegans development: Initial cleavage creates large (AB) and small (P1) cells. AB forms the ectoderm and nervous system. Gastrulation doesn't involve the same degree of spectacular migration as in other species.
• Drosophila development involves a nuclear syncytium where many nuclei share a common cytoplasm before differentiating. The embryo later becomes fully cellular.

Vertebrates: Neurulation

• Neurulation involves the development of the neural tube from the neural plate.
• This happens through rapid growth, cell movement, and shape changes in neuroectodermal cells.
• Primary neurulation: Neural plate rolls up to form the neural tube in a sheet of neuroectodermal cells.
• Secondary neurulation: Cells from the caudal neuroectoderm form a solid rod that then cavitates to form the neural tube. A variety of vertebrate animals utilize each of these two methods.

Vertebrates: Mouse Development

• Mouse development involves the blastocyst stage.
• Neural tube formation takes place in the epiblast.
• A primitive streak forms which eventually gives rise to Hensen's node, which is the equivalent of the dorsal lip of the blastopore in Xenopus. Cells in this structure contribute to components of the nervous system.
• Neural crest is generated and plays a significant role in developing aspects of the peripheral nervous system.

Peripheral Nervous System

• Peripheral nervous systems originate from cells located outside of the CNS.
• Key to extracting sensory information, transmitting it to the CNS, and controlling responses of the body.
• Vertebrates: arises from the neural crest and cranial placodes.
• Invertebrates: sensilla (like bristles) develop from sense organ precursors (SOPs).

Sense Organ Development

• Vertebrate sensory organs, like the eye and ear, develop from specialized regions of the embryo.
• The otic placode gives rise to parts of the inner ear for hearing.
• Optic vesicle and lens placode develop to support light-detecting capability in the eye.