Neurogenesis - Anatomy & Physiology

BACK TO DEVELOPMENTAL BIOLOGY

Introduction

The nervous system develops from ectoderm. Some of the ectoderm will also develop into the epidermis. Signalling factors from elsewhere in the embryo determine which parts of the ectoderm become neural tissue or epidermis.

In the anterior part of the embryo the ectoderm forms the neural plate, a flat layer of ectodermal cells lying directly above the node. The morphogenic changes from this neural plate to the nervous system is split into two parts; primary and secondary neuralation.

Neural Plate Induction

• Cells of the ectoderm are directed to develop into either neural ectoderm or epidermis.
• How is this choice made?
• Formation of the neural ectoderm is the default pathway.
  • Therefore, in order to make epidermis, a signal from the environment must be diverting cells from going down this default pathway.
  • This signal comes from the lateral plate mesoderm (LPM) which directs ectoderm to become epidermis.
    • The notochord (lying along the midline) secretes an antagonist to the factor of the LPM so that neural ectoderm is formed above the notochord.
• Therefore, in lateral regions ectoderm becomes epidermis and along the midline ectoderm becomes neural ectoderm.

Primary Neuralation

1. Cells of the neural plate proliferate causing the neural plate to thicken. Cells then converge at the midline and become wedge shaped, which drives the neural plate to become long and narrow.
2. Cells along the midline descend ventrally and contact the notochord, forming a "hinge". This forms a depression which is called the neural groove.