Illustrate the structure and functions of brain.

Explanation

A human brain is ofrmed of three main parts forebrain, mid brain and hind brain.
1. Fore brain: The fore brain is formed of Cerebrum and Diencephalon. The diencephalon consists of dorsal thalamus and ventral hypothalamus.
(a) Cerebrum: It is the largest portion and nearly forms two third of the brain. The cerebrum is longitudinally divided into two halves, as right and left cerebral hemispheres by a deep cleft called median cleft. The two cerebral hemispheres are interconnected by thick band of nerve fibres called corpus callosum. The outer portion of each cerebral hemisphere is formed of grey matter, and is called cerebral cortex. The inner or deeper part is formed of white matter and is called cerebral medulla. The cortex is extremely folded forming elevations called gyri, with depressions between them termed as sulci, that increase the surface area. Each cerebral hemisphere is divisibleinto a frontal lobe, a parietal lobe, a temporal lobe and an occipital lobe. These lobes are also known as cerebral lobes.
(b) Thalamus: Thalamus present in cerebral medulla is a major conducting centre for sensory and motor signalling. It acts as a relay centre.
(c ) Hypothalamus: It lies at the base of the thalamus. It controls the secretions of hormones from anterior pituitary gland.
2. Mid brain: It is located between thalamus and Hind brain. The dorsal portion of the mid brain consists of four rounded bodies called corpora quadrigemina, that control visual and auditory (hearing) reflexes.
3. Hind brain: It is formed of three parts Cerebellum, Pons and Medulla Oblongata.
(a) Cerebellum: It is second largest part of the brain formed of two large sized hemispheres and middle vermis.
(b) Pons: It is a bridge of nerve fibre that connects the lobes of cerebellum. It relay signals between the cerebellum, spinal cord, midbrain and cerebrum.
(c ) Medulla Oblongata: It is the posterior most part of the brain, that connects the spinal cord and virous parts of brain.
Funcitons of brain: