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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]
The human brain has some 8.6 x 10 10 (eighty six billion) neurons. [31] [32] Each neuron has on average 7,000 synaptic connections to other neurons. It has been estimated that the brain of a three-year-old child has about 10 15 synapses (1 quadrillion). This number declines with age, stabilizing by adulthood.
The challenge of doing this becomes obvious: the number of neurons comprising the brain easily ranges into the billions in more complex organisms. The human cerebral cortex alone contains on the order of 10 10 neurons linked by 10 14 synaptic connections. [16] By comparison, the number of base-pairs in a human genome is 3×10 9.
Estimates of the number of neurons in cortex or in neocortex are on the order of 2×10 10. [9] [10] Most [11] (perhaps 90% [citation needed]) of cortical neurons are neocortical neurons. Johansson and Lansner [4] use an estimate of 2×10 10 neurons in the neocortex and an estimate of 100 neurons per minicolumn, yielding an estimate of 2×10 8 ...
The rest of the brain tissue is the structural stroma that includes connective tissue such as the meninges, blood vessels, and ducts. The two main types of cells in the brain are neurons, also known as nerve cells, and glial cells, also known as neuroglia. [1] There are many types of neuron, and several types of glial cell.
In the human brain, it is between 2 and 3-4 mm. thick, [8] and makes up 40% of the brain's mass. [2] 90% of the cerebral cortex is the six-layered neocortex whilst the other 10% is made up of the three/four-layered allocortex. [2] There are between 14 and 16 billion neurons in the cortex. [2]
The adult human brain is estimated to contain 86±8 billion neurons, with a roughly equal number (85±10 billion) of non-neuronal cells. [41] Out of these neurons, 16 billion (19%) are located in the cerebral cortex, and 69 billion (80%) are in the cerebellum.
In the human brain alone, there are over eighty billion neurons. [1] Neurons are diverse with respect to morphology and function. Thus, not all neurons correspond to the stereotypical motor neuron with dendrites and myelinated axons that conduct action potentials.