Brain :
The human brain is well protected by the skull. Inside the skull, the brain is covered by cranial meninges consisting of three layers namely outer durometer, middle layer called arachnoid and inner layer pia mater.
The brain is divided into three major parts.
Forebrain
Mid brain
Hindbrain.
(i) Forebrain: The forebrain consists of cerebrum, thalamus and hypothalamus. Cerebrum is divided longitudinally into two halves, 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. It is referred to as grey matter due to greyish appearance. The cerebral cortex contains motor areas, sensory areas and association areas which 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. This layer is white in colour, hence called white matter. The cerebrum wraps around a structure called thalamus, which is a major co-ordinating centre for sensory and motor signalling. Hypothalamus lies at the base of the thalamus and contains several group of neurosecretory cells, which secrete hormones called hypothalamic hormones. The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, etc. form a complex structure called the limbic lobe or limbic system.
(ii) Mid brain:
The midbrain is located between the thalamus / hypothalamus of the forebrain and pons of the hind brain. A canal called the cerebral aqueduct passes through the mid brain. The dorsal portion of the midbrain consists of four round swellings (lobes) called Corpora quadrigemina. Midbrain and hindbrain form the brain stem.
(iii) Hindbrain:
Hindbrain comprises pons, cerebellum and medulla. Pons consists of fibre tracts that interconnect different regions of the brain. Cerebellum has very convoluted surface in order to provide the additional space for many more neurons. The medulla of the brain is connected to the spinal cord.
