Fore brain comprises the following regions: Cerebrum and Diencephalon. Cerebrum is the ‘seat of intelligence’ and forms the major part of the brain. The cerebrum consists of an outer cortex, inner medulla and basal nuclei.
The superficial region of the cerebrum is.called cerebral cortex, which looks grey due to the presence of unmyelinated nerve cells. Cerebral cortex – consists of neuronal cell body, dendrites, associated glial and blood vessels.
The surface of the cerebrum’shows many convolutions (folds) and grooves. The folds are called gyri, the shallow grooves between the gyri are called sulci and deep grooves are called fissures. These sulci and gyri increase the surface area of the cerebral cortex. Several sulci divide the cerebrum into eight lobes; a pair of frontals, parietals, temporals and occipital lobes.
A median longitudinal fissure divides the cerebrum longitudinally into two cerebral hemispheres. A transverse fissure separates the cerebral hemispheres from the cerebellum.
The hemispheres are connected by a tract of nerve fibres called corpus callosum. Cerebral cortex has three functional areas namely sensory areas occur in the parietal, temporal and occipital lobes of the cortex. They receive and interpret the sensory impulses.
Motor area of the cortex which controls voluntary muscular movements lies in the posterior part of the frontal lobes. The areas other than sensory and motor areas are called Association areas that deal with integrative functions such as memory, communications, learning and reasoning. Inner to the cortex is medulla which is white in colour and acts as a nerve tract between the cortex and the diencephalon.
Diencephalon consists largely of following three paired structures. Epithalamus forms the roof of the diencephalon and it is a non-nervous tissue. The anterior part of epithalamus is vascular and folded to form the choroid plexus. Just behind the choroid plexus, the epithalamus forms a short stalk which ends in a rounded body called pineal body which secretes the hormone, melatonin which regulates sleep and wake cycle.
Thalamus is composed of grey mater which serves as a relay centre for impulses between the spinal cord, brain stem and cerebrum. Within the thalamus, information is sorted and edited and plays a key role in learning and memory. It is a major coordinating centre for sensory and motor signalling.
Hypothalamus forms the floor of the diencephalon. The downward extension of the hypothalamus, the infundibulum connects the hypothalamus with the pituitary gland. The hypothalamus contains a pair of small rounded body called mammillary bodies that are involved in olfactory reflexes and emotional responses to odour.
Hypothalamus maintains homeostasis and has many centres which control the body temperature, urge for eating and drinking. It also contains a group of neurosecretory cells which secrete the hypothalamic hormones. Hypothalamus also acts as the satiety centre.
Limbic system: The inner part of the cerebral hemisphere constitutes the limbic system. The main components of limbic system are olfactory bulbs, cingulate gyrus, mammillary body, amygdala, hippocampus and hypothalamus.
The limbic system is called ‘emotional brain’ because it plays a primary role in the regulation of pleasure, pain, anger, fear, sexual feeling and affection. The hippocampus and amygdala also play a role in memory. Brain stem is the part of the brain between the spinal cord and the diencephalon. It consists of mid brain, pons varolii and medulla oblongata.
