Central nervous system
The central nervous system consists of brain and spinal cord which are covered by membranes called meninges. The brain is divided into three parts; (i) fore-brain (ii) mid-brain and (iii) the hind-brain.
It is a large and complex, five lobed structures; it has a central lobe (vermis), two lateral lobes and two outer lobes. The surface of cerebellum is much folded to form numerous grooves (sulci) and elevations (gyri). The two sides of cerebellum are joined by transverse nerve fibres forming pons varolii. The cerebellum is concerned with equilibrium and co-ordination of muscles.
The medulla oblongata constitutes the lowest part of the brain. It has centres which control respiration, heart beat and blood vessels. It also has conduction pathways for impulses passing from the cerebral hemispheres to the spinal cord and again in the opposite direction.
It has a thick roof called neopallium in mammals. Cerebrum is the largest part of the human brain and lies above the cerebellum. It is made up of two halves called cerebral hemispheres. Cerebrum is made up of an outer layer of millions of nerve cells called grey matter (cortex) and a thick inner layer of medullated nerve fibres (medulla).
The cortex and medulla constitute the neopallium. The cerebral hemispheres receive impulses from sense organs all over the body, i.e., visual, auditory, olfactory, tactile and peripheral receptors and are thus concerned with all forms of activities such as vision, hearing, touch, taste and smell.
The Spinal Cord:
The spinal cord runs from the medulla downward towards the vertebral column. It has an outer layer of white matter made up of medullated nerye fibres, an inner mass of grey matter and a central canal lined with ciliated ependymal cells. The fibres of the spinal cord are both sensory and motor in nature and thus conduct impulses to and from the brain and act as a reflect centre.