neural tube

Neural tube
Transverse section of half of a chick embryo of forty-five hours' incubation. The dorsal (back) surface of the embryo is towards the top of this page, while the ventral (front) surface is towards the bottom. (Neural tube is in green.)
Chick embryo of thirty-three hours' incubation, viewed from the dorsal aspect (30x magnification).
Gray's	subject #7 50
Carnegie stage	10
Precursor	Neural groove
Gives rise to	Central nervous system (brain and spinal cord)

Antibody stain against Neurofilament (green) and Ki 67 (red) in a Mouse embryo 12.5 days after fertilization. The cells expressing neurofilaments are in the dorsal root ganglions shown in green while proliferating cells are in the ventricular zone in the neural tube and colored red.

In the developing vertebrate, the neural tube is the embryo's precursor to the central nervous system, which comprises the brain and spinal cord. The neural groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into a closed tube, the neural tube or neural canal (which strictly speaking is the center of the neural tube), the ectodermal wall of which forms the rudiment of the nervous system.

Development

There are 2 ways in which the neural tube develops: Primary neurulation and Secondary neurulation.

1. In primary neurulation, the cells of the neural plate invaginate and pinch off to form the tube.
2. In secondary neurulation, the cells of the neural plate form a cord-like structure that migrates inside the embryo and hollows to form the tube.

Each organism uses primary and secondary neurulation to varying degrees.

• Neurulation in fish proceeds only via the secondary form.

• In avian species the posterior regions of the tube develop using secondary neurulation and the anterior regions develop by primary neurulation.

• In mammals, a similar pattern is observed where secondary neurulation begins around the 35th somite.

The manner in which the neural tube closes in mammals in the head is inverted in respect to the manner of closure in the trunk:

• In the head:

1. Neural crest cells migrate
2. Neural tube closes
3. Overlying ectoderm closes

• In the trunk:

1. Overlying ectoderm closes
2. Neural tube closes
3. Neural crest cells migrate

Structure

There are four subdivisions of the neural tube that will each eventually develop into distinct regions of the central nervous system: The prosencephalon, the mesencephalon, the rhombencephalon and the spinal cord.

• The prosencephalon further goes on to develop into the telencephalon (the forebrain or cerebrum) and the diencephalon (the optic vesicles and hypothalamus).
• The mesencephalon develops into the midbrain.
• The rhombencephalon develops into the metencephalon (the pons and cerebellum) and the myelencephalon (the medulla oblongata).

For a short time, the neural tube is open both cranially and caudally. These openings, called neuropores, close during the fourth week in the human. Improper closure of the neuropores can result in neural tube defects such as anencephaly or spina bifida.

The dorsal part of the neural tube contains the alar plate, which is primarily associated with sensation. The ventral part of the neural tube contains the basal plate, which is primarily associated with motor (ie, muscle) control.

References

• Schoenwolf, G. C. et Smith, J. L. Mechanisms of neurulation: traditional viewpoint and recent advances. Development 109, 243–270, 1990
• Meyer, B. I. & Gruss, P. Mouse Cdx1 expression during gastrulation. Developpment 117, 191–203, 1993
• Gamer, L. W. & Wright, C. V. Murine Cdx4 bears striking similarities to the Drosophila caudal gene in its homeodomain sequence and early espression pattern. Mech Dev 43, 71–81, 1993

See also

• Neural tube defects

External links

• Swiss embryology (from UL, UB, and UF) iperiodembry/carnegie03
• Embryology at UNSW Notes/week3_5
• Diagram at embryology.med.unsw.edu.au
• Diagram at brainviews.com

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.