It is the anterior region of the brain. It has following parts:
i. Cerebrum (seat of intelligence, memory, consciousness and voluntary action)
ii. Diencephalon (thalamus, hypothalamus, pineal gland)
Cerebrum (Cerebrum: Brain):
The Cerebrum is the Main Part of Forebrain.
i. Cerebrum is the largest and the most prominent part of the brain. It is divided into right and left cerebral hemispheres.
i. The two hemispheres are connected by a thick band of nerve fibres called corpus callosum. Corpus callosum helps in the transfer of information from one hemisphere to another.
iii. Each hemisphere is hollow internally and its walls have two regions—an outer cortex and an inner region. The outer layer of the cerebrum is the cerebral cortex. It contains cell bodies of neurons and being greyish in colour, is called grey matter.
iv. It is highly convoluted in appearance with ridges and grooves. The ridges of these convolutions are called gyri (singular, gyrus) and depressions between them are called sulci (singular, sulcus). The ridges and grooves increase surface area for more nerve cells.
v. The number and pattern of convolutions in the cerebrum are associated with the degree of intelligence.
vi. The inner region of cerebrum consists of white matter that has axons of nerve cells.
The cerebrum (because of highly developed grey matter) governs mental abilities like thinking, reasoning, learning, memory and intelligence.
It also controls all voluntary functions; will power, emotions and speech. It enables us to observe things around us through sense organs. This part of the brain also controls feelings of love, admiration and hatred. Centres for subconscious mind are also located in the cerebrum.
The diencephalon mainly consists of the pineal gland, pituitary gland, thalamus and hypothalamus. It encloses a cavity called the third ventricle. The thalamus consists of two large ovoid masses. It is a relay station for sensory impulses going to the cerebrum. The hypothalamus is situated at the floor of the brain and helps in thermoregulation.
The diencephalon contains reflex centres for muscular and glandular activities. It also has centres of emotions, hunger and thirst. It also helps in controlling the body temperature (thermoregulation) and water-salt balance in the body (osmoregulation).
It is a thick-walled structure and constitutes a comparatively smaller portion of the brain. The midbrain or mesencephalon connects the anterior region of the brain to the posterior region and therefore all nerve fibres pass through this region. On the dorsal side of the midbrain lie optic lobes which control vision.
The hindbrain has three main parts.
iii. Medulla oblongata
Cerebellum (little brain):
i. The cerebellum is situated in the dorsal region of the hindbrain. Cerebellum is a much smaller area and is located at the base under the large cerebrum.
ii. There are no convolutions, but many furrows.
iii. It has an outer cortex made of grey matter and an inner section consisting of white matter.
It maintains body balance and controls muscular activities. It makes the body movements smooth, steady and coordinated. It regulates and coordinates contraction of skeletal muscles.
Pons forms the part of the brain stem at the floor of hindbrain. It is a bridge of transverse nerve tracts extending from the cerebrum to the cerebellum. It also connects the forebrain to the spinal cord.
The medulla oblongata is the third main part of the hindbrain. It is the lowermost part of the brain located at the base of the skull. It is continued as spinal cord in posterior region.
It contains vital reflex centres, such as cardiac centre, respiratory centre and centres for swallowing, sneezing, coughing and vomiting. Thus, it controls involuntary functions of the body like heart beat, swallowing and breathing.
Cerebrum, cerebellum and medulla oblongata are the parts of brain visible externally. While corpus callosum, thalamus and hypothalamus are parts that are not visible externally.