The nervous system is a system that plays a leading role in the regulation of physiological functions in the body. It is mainly composed of neural tissues and is divided into two parts: the central nervous system and the peripheral nervous system. The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes the cerebral and spinal nerves.
Figure 1. Human nervous system.
Central Nervous System
The central nervous system is the main part of the nervous system, including the spinal cord located in the spinal canal and the brain located in the cranial cavity; its location is often on the central axis of the animal's body. Composed of connected components. A large number of nerve cells gather together in the central nervous system to form a network or circuit organically; its main function is to transmit, store, and process information, generate various psychological activities, and control and control all the behaviors of animals.
Figure 2. Human central nervous system.
Vertebrate Central Nervous System: The vertebrate brain is located in the cranial cavity and the spinal cord is located in the spinal canal. The central nervous system of vertebrates develops from the neural tube on the dorsal side of the body during the embryo. The head of the neural tube evolves into the brain, and the tail ends into the spinal cord. The part of the neural lumen in the brain evolved into the ventricle, and the part of the spinal cord into the central duct. The brain is initially three brains: the forebrain, midbrain, and rhizome, and later evolved into the telencephalon, mesencephalon, midbrain, cerebellum, pontine and medulla.
Central nervous system development
The development of a single human fertilized egg into an individual is still relatively mysterious. The reason lies in the complexity of the development process: from a single cell, it has developed into millions of cells with special functions to a few of mature individuals. Ten billion cells, and this complex apex is the development of the central nervous system. The central nervous system is formed by the development of the ectoderm of the embryo. At the stage of the neuroblast, the chordal cord runs through the central axis of the early embryo, and induces the undifferentiated ectoderm cells above it to transform into the primordium of the central nervous system. First, the dorsal ectodermal cells above the spinal cord are elongated and thickened to form a neural plate that is wide anteriorly and narrowly; the edge of the neural plate is thickened and pleated to form a neural fold; the central depression of the neural plate forms a neural groove. Then, the nerve fold moves toward the dorsal midline, and finally closes to form a neural tube, which develops into the brain at the front and spinal cord at the back. From this stage on, the general characteristics of the brain are determined by the growth and bending of the front part of the neural tube. With the gradual enlargement of the cerebral cortex and the generation of cortical folds, a mature brain is formed. In the early stages of human embryonic development, human fetuses and mammalian fetuses have striking similarities. This is the general neuroanatomical feature of central nervous system development.
Rakic, P.; et al. Evolution of the neocortex: a perspective from developmental biology. Nature Reviews. Neuroscience. 2009, 10 (10): 724–35