by Simon Cohen

Created on: November 26, 2010   Last Updated: November 28, 2010

The cortex (surface area) of the brain consists of sulci (small groves), fissures (big groves) and gyri (large convolutions). These greatly enlarge the surface area of the brain, and because of the mass of cell bodies, gives the surface a grey appearance.

The brain can be broken down into three components: the forebrain; the midbrain; and the hindbrain. The forebrain consists of the telencephalon and the diencephalon. The telencephalon includes the two cerebral hemispheres that make up the cerebrum.  The cerebrum can be broken down into the four lobes: frontal; parietal; occipital; and temporal. The primary visual cortex is located on the side of the brain in the occipital lobe; the primary somatosensory cortex is located at the parietal lobe; and the primary motor cortex is located at the temporal lobe.  The diencephalon consists of the thalamus and hypothalamus. The thalamus is in the middle of the cerebral hemispheres and most neural input goes through it. The hypothalamus lies at the base of the brain and controls the autonomous nervous system and endocrine system.

The midbrain consists of the tectum and tegmentum. The most noticeable parts of the tectum are the superior and inferior colliculi. The inferior colliculi plays a role on the auditory system and the superior colliculi plays a role in the visual system. Notable areas of the tegmentum are the substantia nigra, the ventral tegmentum area and the lateral tegmentum field. The substantia nigra plays a role in reward, addiction and behaviour. Degeneration of the neurons in this area are responsible for the symptoms of Parkinson’s. The ventral tegmentum area is important for cognition, motivation, and several psychiatric conditions. The lateral tegmentum field is the source of several neurons of the noradrenalin system of the brain.

The hindbrain is made up of the metencephalon and myelencephalon. The metencephalon consists of the cerebellum and pons. The cerebellum (literally means ‘mini-brain’) is one of the oldest structures in the brain and resembles a mini cerebrum. It receives auditory, visual, somatosensory and vestibular information and is essential to movement and coordination. Damage to the cerebellum impairs  standing, walking and coordination. The pons (literally means t ‘the bridge’) contains portions of the reticular formation and is important in sleep and arousal. The myelencephalon  main feature is the medulla oblongata, which is essential for non-conscious functions, such as regulation of the cardiovascular system, respiration and skeletal muscle tonus.

The brain works on a primarily contralateral basis i.e. what happens on the left side of the body is controlled by the right side of the brain and vice versa. The structure responsible for this cross-over is called the corpus callosum and it is the largest fiber bundle in the brain.

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