Nervous System
Central nervous system
The brain and spinal cord comprise the central nervous system. The vertebrate brain is divided into three main sections: the fore-, mid- and hind-brains. Invertebrate brains are different, and in segmented animals, large ganglia may be largely responsible for the actions of the segment in which they reside, the brain being merely the large ganglion at the head end of the animal.
The hind-brain is evolutionarily the oldest of the vertebrate brain structures, and consists (from the back forwards) of the medulla oblongata (the site of cardiac control), the pons (breathing control), and the cerebellum, two paired hemispheres controlling proprioception, balance and coordination. The midbrain (mostly consisting of the tectum) was originally responsible for sight, but this has been subverted in vertebrates. The hind and mid-brains are collectively termed the brainstem.
The forebrain consists of the thalamus (principally wiring), the pineal gland (involved in sleep responses and circadian rhythms), the hypothalamus (involved in homoeostasis, via its effects on psychological drives, neurosecretion and releasing factors aimed at the pituitary and control of autonomic nerves) and the pituitary, the 'master' endocrine gland. The hypothalamus, pituitary, and other parts (e.g. the hippocampus) are collectively termed the limbic system and are the seat of drives such as thirst, hunger, libido and aggression.


The front most section of the brain is the cortex, primitively an olfactory centre, but in vertebrates, subverted to receive other sensory inputs (sight, hearing), generate motor outputs (including speech) and is responsible for 'thought' in general. The cortex consists of two hemispheres, which in humans are massively expanded, deeply furrowed with sulci, and hide most of the underlying structures. Many areas have been identified with particular functions, such as Warnicke's and Broca's areas, involved in speech. There is heavy bias bet