The front of the brain is called the forebrain. It consists of three parts. namely-
1. Cerebrum: The forebrain consists of two large, coiled and grooved cerebral hemispheres. The two cerebral hemispheres are collectively called the cerebrum. It is the largest part of the brain (80% of brain weight). The cerebrum has two layers. The outer one is called the cerebral cortex (3 cm thick) and the inner one is called the cerebral medulla. The cerebral cortex is composed of gray matter and the cerebral medulla is composed of white matter. The cerebral hemispheres are connected by a bundle of nerves called the corpus callosum. Its surface is folded to create high and low areas. The higher area is called the gyrus and the lower area is called the sulcus.
A few folds deepen to form 3 fissures (central, parieto-occipital, lateral). Each cerebral hemisphere is divided into 5 lobes (frontal lobe, parietal lobe, occipital lobe, temporal lobe and limbic lobe).
Functions of the cerebrum
(i) It receives and analyzes feelings.
(ii) It controls the power of speech.
(iii) It governs intellect, will power, inventive power, thinking etc.
(iv) It acts as a regulator of instincts.
(v) It controls the voluntary muscle activity of the body.
2. Thalamus: Two oval-shaped regions located in the cerebral medulla are called thalamus. It is made up of gray matter. Each thalamus is accompanied by a pinna basal ganglia. The two thalamus are connected by a junction. The length of the thalamus is 4 cm. Each thalamus contains 1 oval ganglion.
Function of the thalamus
(i) It acts as a center for sensation of pressure, touch, pain etc.
(ii) It reveals human personality and social behavior.
(iii) It wakes up the sleeping person suddenly and alerts them to the environment.
3. Hypothalamus: A dozen separate regions below the thalamus are collectively called the hypothalamus. It is made up of gray matter. The hypothalamus is connected to the pituitary gland by a narrow part.
Functions of the hypothalamus
(i) It acts as a center of the autonomic nervous system.
(ii) acts as the center of hunger, thirst, sweat, sleep, anger, suffering, hatred, love, anxiety etc.
(iii) It regulates body heat.
(iv) It secretes ADH.
(v) It secretes two types of neurohormones namely vasopressin and oxytocin.
(vi) It regulates tropic hormone secretion with the help of neurohormones.