C ENTRAL N EURAL S YSTEM The brain is the central information processing organ of our body, and acts as the ‘command and control system’. It controls the voluntary movements, balance of the body, functioning of vital involuntary organs (e.g., lungs, heart, kidneys, etc.), thermoregulation, hunger and thirst, circadian ( -hour) rhythms of our body, activities of several endocrine glands and human behaviour. It is also the site for processing of vision, hearing, speech, memory, intelligence, emotions and thoughts. The human brain is well protected by the skull.
Inside the skull, the brain is covered by cranial meninges consisting of an outer layer called dura mater , a very thin middle layer called arachnoid and an inner layer (which is in contact with the brain tissue) called pia mater . The brain can be divided into three major parts: (i) forebrain , (ii) midbrain , and (iii) hindbrain (Figure . ). Figure .
Diagram showing sagital section of the human brain Forebrain . . Forebrain The forebrain consists of cerebrum , thalamus and hypothalamus (Figure . ).
Cerebrum forms the major part of the human brain. A deep cleft divides the cerebrum longitudinally into two halves, which are termed as the left and right cerebral hemispheres . The hemispheres are connected by a tract of nerve fibres called corpus callosum . The layer of cells which covers the cerebral hemisphere is called cerebral cortex and is thrown into prominent folds.
The cerebral cortex is referred to as the grey matter due to its greyish appearance. The neuron cell bodies are concentrated here giving the colour. The cerebral cortex contains motor areas, sensory areas and large regions that are neither clearly sensory nor motor in function. These regions called as the association areas are responsible for complex functions like intersensory associations, memory and communication.
Fibres of the tracts are covered with the myelin sheath, which constitute the inner part of cerebral hemisphere. They give an opaque white appearance to the layer and, hence, is called the white matter. The cerebrum wraps around a structure called thalamus, which is a major coordinating centre for sensory