List of animals by number of neurons

This is a list of representative animals by the number of neurons in their whole nervous system and the number of neurons in their brain (for those with a brain). These numbers are estimates derived by multiplying the density of neurons in a particular animal by the average volume of the animal's brain.

The whole human brain contains 86 billion neurons and either 19 or 23 (respectively female and male) billion neurons in the cerebral cortex.

Neurons are the cells that transmit information in an animal's nervous system so that it can sense stimuli from its environment and behave accordingly. Not all animals have neurons; Trichoplax and sponges lack nerve cells altogether.

Neurons may be packed to form structures such as the brain of vertebrates or the neural ganglions of insects.

The number of neurons and their relative abundance in different parts of the brain is a determinant of neural function and, consequently, of behavior.

All numbers for neurons but Caenorhabditis and all numbers for synapses are estimations.

Only mammals appear in this list, because only mammals have a cerebral cortex (although the pallium of reptiles and birds is also frequently referred to as "cortex".)

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