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The first list shows number of neurons in their entire nervous system. The second list shows the number of neurons in the structure that has been found to be representative of animal intelligence. [1] The human brain contains 86 billion neurons, with 16 billion neurons in the cerebral cortex. [2] [1]
Neurons are highly specialized for the processing and transmission of cellular signals. Given the diversity of functions performed in different parts of the nervous system, there is a wide variety in their shape, size, and electrochemical properties. For instance, the soma of a neuron can vary from 4 to 100 micrometers in diameter. [7]
There are more than 86 billion neurons in the brain, and a more or less equal number of other cells. Brain activity is made possible by the interconnections of neurons and their release of neurotransmitters in response to nerve impulses. Neurons connect to form neural pathways, neural circuits, and elaborate network systems.
There are many types of neuron, and several types of glial cell. Neurons are the excitable cells of the brain that function by communicating with other neurons and interneurons (via synapses), in neural circuits and larger brain networks.
There are about 200 million (2×10 8) cortical minicolumns in the human neocortex with up to about 110 neurons each, [16] and with estimates of 21–26 billion (2.1×10 10 –2.6×10 10) neurons in the neocortex.
The enteric nervous system in humans consists of some 500 million neurons [11] (including the various types of Dogiel cells), [1] [12] 0.5% of the number of neurons in the brain, five times as many as the one hundred million neurons in the human spinal cord, [13] and about 2 ⁄ 3 as many as in the whole nervous system of a cat.
There are between 14 and 16 billion neurons in the cortex. [2] These cortical neurons are organized radially in cortical columns, and minicolumns, in the horizontally organized layers of the cortex. [9] [10] The neocortex is separable into different regions of cortex known in the plural as cortices, and include the motor cortex and visual cortex.
The number of neurons in the cerebellum is related to the number of neurons in the neocortex. There are about 3.6 times as many neurons in the cerebellum as in the neocortex, a ratio that is conserved across many different mammalian species.