Vertebrate brain

A **vertebrate brain** is the main organ of the central nervous system. Here is a list of some of the most important areas, with a brief description of their functions as currently understood. These functions may still be disputed to some degree. Starting from the back (or, in humans, the underneath part) the regions are:
* The medulla (and the spinal cord) have many small nuclei, which deal with various autonomic functions. These include the heart beat and blood pressure, breathing, and vomiting.ch 44, 45
* The pons is a relay station, carrying messages between the cerebrum and the medulla and cerebellum.
* The hypothalamus is a small region at the base of the forebrain. It is the central control station for sleep/wake cycles, control of eating and drinking, control of hormone release, and many other functions. It sits immediately above the pituitary gland, and secretes hormones into the gland. These hormones inhibit or stimulate the pituitary gland. The gland, in turn, makes hormones which affect the rest of the body.
* The thalamus sits above the hypothalamus, and below the cerebral cortex. It is a collection of nuclei with various functions. It acts as a relay station, gathering sense information of all kinds (except olfactory) and passes it on to the cerebral cortex. Also, it has a role in consciousness and sleep. There are action systems for several types of behaviour, including eating, drinking, defecation, and copulation.
* The cerebellum adjusts the output of other brain systems to make them more precise. Removal of the cerebellum does not prevent an animal from doing anything in particular, but it makes actions hesitant and clumsy. This precision is not built-in, but learned by trial and error. Learning how to ride a bicycle is an example of a type of neural plasticity that may take place largely within the cerebellum.
* The hippocampus is, strictly speaking, only in mammals, but it has counterparts in all vertebrates. It is involved in spatial memory and navigation in fishes, birds, reptiles, and mammals.
* The basal ganglia are a group of structures in the forebrain, which are strongly connected to the cerebral cortex and the thalamus. The main function of the basal ganglia seems to be selecting . They send  signals to all parts of the brain that can generate actions. In the right circumstances they release the inhibition, so that the action-generating systems can execute their actions. Rewards and punishments exert most important neural effects on the basal ganglia.
* The cerebral cortex is a layer of grey cells that is on the surface of the forebrain. It is involved in multiple functions, including olfaction and spatial memory. In mammals, where it dominates the brain, it controls functions from many subcortical areas.
* The olfactory bulb is a special structure that processes olfactory sensory signals (smells), and sends its output to the olfactory part of the cerebral cortex. It is a major brain component in many vertebrates, but much reduced in primates. Dogs are the classic example of a mammal whose scent perception is in many ways the basis of their sensory life.

## Brain size 
The relationship between brain size, body size and other variables has been studied in a wide range of vertebrate species. Brain size increases with body size but not proportionally.

### Mammals 
Averaging across all mammals, it follows a power law, with an exponent of about 0.75. This formula applies to the average brain of mammals but each family departs from it, reflecting their sophistication of behavior. For example, primates have brains 5 to 10 times as large as the formula predicts. Predators tend to have larger brains. When the mammalian brain increases in size, not all parts increase at the same rate. The larger the brain of a species, the greater the fraction taken up by the neocortex.

## References