Neurulation and Nervous System Development

Neurulation and nervous system development describe how the embryonic ectoderm gives rise to the brain, spinal cord, and peripheral nervous system. The process begins when signals from the underlying notochord induce a neural plate, which folds and fuses into a neural tube; this tube then regionalizes into the major brain divisions and spinal cord, while a migratory population called the neural crest disperses to build much of the peripheral and autonomic nervous system.

Definition

Neurulation is the embryonic process by which the neural plate is shaped, folded, and fused to form the neural tube, the primordium of the central nervous system; nervous system development extends this to the patterning of the brain and spinal cord and to the neural-crest-derived peripheral nervous system.

Scope

This area orients the reader to the sequence from neural induction through neural tube closure, brain regionalization, spinal cord patterning, neural crest migration, and peripheral and autonomic nerve formation. It is an educational reference to the developmental anatomy and core molecular mechanisms of the early nervous system, not a guide to diagnosis or management of congenital conditions.

Sub-topics

• Autonomic and Peripheral Nerve Development
• Brain Regionalization and Vesicle Formation
• Neural Crest Cell Migration and Derivatives
• Neural Tube Formation and Closure
• Spinal Cord Development

Key concepts

• Neural induction by the notochord and node
• Neural plate, neural folds, and neural groove
• Primary versus secondary neurulation
• Neural tube closure at discrete sites
• Anteroposterior and dorsoventral patterning
• Brain vesicles and spinal cord
• Neural crest and its derivatives
• Neural progenitors and neurogenesis

Mechanisms

After gastrulation, the notochord and node induce overlying ectoderm to become neuroectoderm, forming the neural plate. The plate elongates and its lateral edges elevate as neural folds that converge and fuse to create the neural tube, a process driven by coordinated changes in cell shape, apical constriction, and convergent extension. The tube closes in a regionally staggered manner, leaving transient openings (neuropores) at the cranial and caudal ends. Once closed, gradients of signalling molecules pattern the tube along its axes and it expands cranially into brain vesicles. Cells at the dorsal margin of the folds delaminate as neural crest and migrate widely to form peripheral and autonomic neurons, glia, and non-neural derivatives. Proliferating neuroepithelial and radial-glial progenitors then generate the neurons and glia of the central nervous system.

Clinical relevance

Failures of these developmental steps underlie a recognised group of congenital nervous system anomalies, including neural tube defects such as anencephaly and spina bifida. Understanding the normal sequence clarifies why and when such anomalies arise and provides the anatomical and embryological background for the health sciences; this entry describes developmental biology and is not a basis for individual diagnosis or treatment.

Epidemiology

Neural tube defects are among the most common structural birth defects of the central nervous system worldwide, with frequency varying by geography, genetic background, and nutritional factors; periconceptional folate status is a well-documented modifier of risk at the population level.

History

The study of neurulation grew out of classical experimental embryology, including the demonstration of neural induction by the dorsal organizer in the early twentieth century. Twentieth-century work mapped the morphogenetic movements of neural tube closure and the contributions of the neural crest, while molecular embryology later identified the signalling pathways and transcription factors that pattern the developing nervous system.

Key figures

• Thomas M. Jessell
• Andrew J. Copp
• Roberto Mayor
• Nicole Le Douarin

Seminal works

• jessell-2000
• nikolopoulou-2017
• mayor-2013

Frequently asked questions

What is the difference between neurulation and nervous system development?

Neurulation refers specifically to forming the neural tube from the neural plate; nervous system development is the broader sequence that also includes brain regionalization, spinal cord patterning, neural crest migration, and the building of peripheral and autonomic nerves.

Where does the peripheral nervous system come from?

Much of the peripheral and autonomic nervous system arises from the neural crest, a migratory cell population that delaminates from the dorsal neural folds, rather than from the neural tube itself.