There are some animals that do not really concern themselves with gathering food, eating, drinking, sleeping, reproducing and defending themselves. Therefore, their brains reflect the major centres that control these functions. We as humans perform these functions as well, and have a "reptilian" brain built into us.

Underside of the brain, displaying the brainstem and cranial nerves

The basic lower brain consists of the spinal cord, brainstem, diencephalon, cerebellum and cortex. Each of the above structures contains centres of nuclei that are specialized for particular functions. This may include the regulation of our breathing and heart-rate while we sleep.

The following are a few important terms and structures that are associated with the Lower Brain:

• Medulla: Contains nuclei for regulating blood pressure and breathing, and for relaying information from the sense organs that come in from the cranial nerves.

• Pons: Contains nuclei that relay movement and position information from the cerebellum to the cortex. It also contains nuclei that are involved in breathing, taste and sleep.

• Midbrain: Contains nuclei that link the various sections of the brain involved in motor functions, eye movements and auditory control. One portion, called the substantia nigra, is involved in voluntary movements and when this portion does not function, an individual can develop tremored movements such as Parkinson's disease.

• Thalamus: Transmits incoming sensory pathways to appropriate areas of the cortex, determines which sensory information will actually reach the consciousness and participates in motor-information exchange between the cerebellum, basal ganglia and cortex.

• Hypothalamus: Contains nuclei that control hormonal secretions from the pituitary gland. These centres control sexual reproduction, eating, drinking, growth, and maternal behaviour. The hypothalamus is also involved in almost all aspects of behaviour, including your biological "clock".

The above diagram is of the major internal parts of the human brain, and the size and shape of each of the individual components.

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