Menu:

 

My Neuropshysiology pages

The goal of these pages is to examine the link between neuron networks and neuroimaging data. An extensive review is, of course, not possible; also I focused on neuron properties and communication, metabolism and imaging devices.

 Brain in numbers:

The whole brain

The cerebral cortex is composed of 3 cortices with different phylogenetic origins:
- the paleocortex (1% of the cortical surface, mainly olfactif cortex)
- the archicortex (3-4% of the cortical surface, hippocampic region)
- the neocortex (95% of the cortical surface, 6 layers organization, 32% frontal cortex, 30% parietal cortex, 23% temporal cortex and 15% occipital cortex)

The whole cerebral cortex volume is around 300cm^3 for men and 270cm^3 for women. The cortical surface represents 2200cm^2 and the neocortex thickness varies from 1.5 to 4.5mm.

Blood flow and Metabolism

An average brain weights about 1400g, i.e. only 2 to 3% of the total body weight. The air entering our lungs contains 21% oxygen, and by the time the oxygen reaches our brain this value has fallen to 4%. Yet, an adult brain consumes about 20% of the whole blood oxygen and about 750mL of blood every minute, extracting 10% of the 90mg/dL of glucose contained in the blood.

Neurons

The estimated number of neuron varies between 2.6x10^9 and 16x10^9, with a density of 14-18 neurons in the agranular cortex to 40-100 neurons for 0.001mm^3 in the visual cortex. Despite this huge numbers, neurons make up only 10% of brain cells and about 90% of the cells are glial (microglia, astrocytes, oligodendrocytes).

One neuron may have hundreds or thousands of synapses on its dendrites and soma and the estimated number of synapses is 100x10^12 synapses for the human brain.

Neurons in fMRI

For an average 55mm cubic voxel, less than 3% of the volume is occupied by vessels and the rest by neural elements. This means that in an unfiltered (smoothed) voxel there is about 5.5 million neurons, 2.2^10 to 5.5^10 synapses, 22 km of dendrites and 220 km of axons (Logothetis, Nature 453, 2008)