(a) Neural coordination: Coordination is a mechanism by which two or more organs increases its activity and helps in the functioning of other organs, for example, when we do physical exercise, energy is used to operate the muscles. The need for oxygen also increases. For more supply of oxygen, it becomes natural for the respiratory rate, heart beat rate and blood flow rate in the renal vessels to increase. When physical exercise is stopped, coordination is established in the functions of the nervous system, lungs, heart, blood vessels, kidneys and other organs. In our body, the nervous system and endocrine system jointly coordinate and integrate the activities of other organs, due to which all the activities continue to operate simultaneously. The nervous system forms such an organised network, which is connected point by point for quick coordination. The endocrine system creates chemical coordination through hormones.
(b) Forebrain: Forebrain is made up of the following parts:
(1) Cerebrum: It constitutes eighty percent of the entire brain. With the help of vertical fissure, it is divided into two parts which are called right and left cerebral hemispheres respectively. Both cerebral hemispheres are connected by the corpus callosum.
Olfactory brain (Rhinecephalon): This is the area related to smell. All those areas of the cerebral hemispheres that are related to olfactory response, together form the olfactory brain. One olfactory bulb and olfactory pathways are found buried in the anterior frontal lobe of each cerebral hemisphere.
(2) Diencephalon: It is situated between the cerebrum and the midbrain. This is called thalamencephalon. This is the small and posterior part of the anterior brain. It has two parts:
(i) Epithalamus: The posterior cavity (third cavity) of the forebrain is called epithalamus. It contains a rhombic lattice. There is a pineal gland in its midline which secretes the hormone melatonin. The thalamic nucleus is located, which is made of grey matter.
(ii) Thalamus: It forms the upper lateral walls of the diencephalon and forms 80% of the diencephalon. It is oval and in the form of two thick lobes.
(3) Hypothalamus: It forms the lower part of the lateral walls of the diencephalon and the floor of its cavity. It is visible from the ventral side of the brain.
(c) Midbrain: This is a small and narrow part of the brain. The midbrain is located between the thalamus/hypothalamus of the anterior brain and the pons of the hindbrain. A canal called the cerebral aqueduct passes through the midbrain. Four projections are found in the posterior part which are called optic lobe or colliculus. All four bulges together are called corpora quadrigemina.
(d) Hindbrain: It has three parts:
(i) Cerebellum: It is made up of three bodies (two lateral bodies and one vermis). Both the lateral bodies become very round, hence these lateral bodies are called cerebellar hemispheres. Vermis is the central part. A pair of flocculonodular lobes are found at its extreme end. Three cerebellar stems emerge from it. The upper cerebellar stalk connects to the midbrain, the middle cerebellar stalk connects to the pons and the lower cerebellar stalk connects to the medulla oblongata.
(ii) Pons: It is located below the midbrain and above the medulla oblongata, which connects both the lobes of the cerebellum.
(iii) Medulla oblongata: This is the posterior part of the brain which is tubular and cylindrical. The cavity found in it is called IVth ventricle or metacoel. The lower end of the medulla ends in the spinal cord. Midbrain, pons and medulla, all three are located on an axis which is called brain stem.
(e) Synapse: A nerve impulse is transmitied from one neuron to another through junctions called synapses.