Forebrain: Cerebrum
- The cerebral hemispheres or cerebrum is the largest part of the brain occupying about two-thirds of the entire brain.
- It consists of left and right hemispheres connected by a large bundle of myelinated fibres, the corpus callosum and other smaller fibre bundles.
- The outer portion of the cerebrum is called the cerebral cortex that makes up the grey matter of the cerebrum.
- The surface of the cortex is highly folded.
- The upward folds are called gyri (sing. gyrus).
- They alternate with the downward grooves called or sulci (sing. sulcus).
- Below the grey matter millions of myelinated nerve fibres are present that connect the neurons of the cerebral cortex with those located elsewhere in the brain.
- The large concentration of myelinated nerve fibres gives this tissue an opaque white appearance. Hence they are collectively called White matter.
- In each cerebral hemisphere, three types of functional areas can be seen as:
Sensory areas: They receive impulses from the receptors.
Association areas: They interpret the input, store the input and initiate a response in light of similar past experience. Thus the associated areas are involved in memory, learning and reasoning.
Motor areas: They transmit impulses to the effectors.
- Each cerebral hemisphere of the cerebrum is divided into four lobes: frontal, parietal, temporal and occipital lobes.
- The central sulcus separates the frontal lobe from the parietal lobe.
- The lateral sulcus separates the frontal lobe from the temporal lobe.
- The parieto-occipital sulcus separates the parietal lobe from the occipital lobe