Development of central nervous system in human
Nervous system begins developing early in third week of development from ectoderm.Nervous tissue also develop from ectoderm except microglial cell, develop from mesoderm.The central nervous system of vertebrates includes the brain and the spinal cord.These are derived from a longitudinal mid-dorsal ectodermal thickening of the embryo,called the medullary or neural plate.This neural plate or neural groove is converted by fusion into a closed mid-dorsal longitudinal neural tube lying above the notochord .Histologically,the embryonic neural tube exhibits three zones of cells
These are actively dividing cells lining the neural canal.They form the connective tissue lining of neural canal,called ependyma,and ventricles of brain.
It consists of embryonic neurons or nematoblasts,forming the grey matter.
It consists of nerve fibres,mostly surrounded by fatty myelin sheaths,and forms the white matter.Neurons and fibres are supported by a special connective tissue of ectodermal origin,the neuroglia,cells of which become increasingly abundant and diversified in higher vertebrates.
What is brain?
The human brain is the central information processing organ in our body .Brain lies in the cranium of skull. It receives input from the sensory organs and sends output to the muscles.It's weight is about 3.3 lbs or 1.5 kg.
Development of brain:
The anterior end of embryonic neural tube is already enlarged forming the embryonic brain,called encephalon.By differential growth and two constrictions, it is divided into a linear series of three primary cerebral vesicles,termed the forebrain,midbrain and hindbrain.These gives rise to the three major divisions of the adult brain.
These further become subdivided into 5 subdivisions.Prosencephalon divides into an anterior telencephalon and posterior diencephalon;the mesencephalon remain uncharged .The rhombencephalon divides into an anterior metencephalon and a posterior myelencephalon.Ultimately, telencephalon develops into cerebral hemisphere and basal ganglia and houses lateral ventricle.Diencephalon develops into thalamus,hypothalamus,and pineal gland and houses the third ventricle. Mesencephalon develops into midbrain and houses cerebral aqueduct.Metencephalon develops into pons and cerebellum;and myelencephalon develops into medulla oblongata,houses 4th ventricle.The area of neural tube inferior to myelencephalon gives rise to spinal cord.
Central nervous system(CNS):
In all the vertebrates including man,CNS is dorsal,hollow and non-ganglionated while in invertebrates when present,it is ventral,solid,double and ganglionated. CNS is formed of two parts:
Upper and broader part lying in the head.
Lower,long and narrow part running from beginning of neck to trunk.CNS is covered by 3 meninges and its wall has two type of matter.
Types of matter:
CNS of vertebrates is formed of two types of matter-
It is formed of cell-bodies,non-medullated nerve fibres,neuroglia,dendrites of association neurons and motor neurons.
It is formed of medullated nerve fibres or myelinated axon of motor and sensory neurons,which appear white due to the presence of medullary sheath.