The cortical pyramidal neuron in all its 3 dimensional glory

Thanks to a technological tour de force (to be described in a later post) we now have complete images of all the cells, vessels and processes in 1 cubic millimeter of human cerebral cortex.  Here is what one cortical pyramidal neuron looks like

Note the pyramidal cell body.  The thick process going toward the top is the apical dendrite.  The multiple processes leaving the cell horizontally are the basal dendrites.  All the cobwebby stuff are processes of other neurons and glial cells.  The green blobs are synapses between other neuronal processes and the dendrites of the pyramidal neuron. Notice how many there are and how they vary in size.   The axon isn’t seen in this picture, but it might be one of the processes headed toward the bottom coming off a dendrite.  Unfortunately no size marker is given but the literature says the cell body of a pyramidal neuron is around 20 microns in diameter.  A micron is 1/1,000th of a milliMeter.  Chemists think in terms of atoms the smallest being hydrogen which is 1/10,000th of a micron or 1 Angstrom.

You can read much more about this work in Nature vol. 629 pp. 739 – 740 ’24 and Science vol. 384 p. 635, eadk4858 pp. 1 –> 12 ’24, but they may be behind a paywall.  Hopefully not.

The cubic milliMeter of cortex was obtained on the way into deeper in the brain  at surgery for epilepsy.  Presumably it is normal.  It contains 57,000 cells (not all of them neurons) and 150,000,000 synapses.  Since 1 cubic milliMeter of cortex is only 1 millionth of the amount of cortex in the human brain ,  this means that our cerebral cortex likely contains 57,000,000,000 (57 billion cells) and 150,000,000,000,000 synapses (150 trillion).

We do know that synapses vary in strength (e.g. how likely the post synaptic neuron is to respond to an impulse from the presynaptic neuron).  We also know (from animal work) that they change in size and strength depending on use.   So they are adjustable, just like the weights in CHAT GTP 4.0 which has 220,000,000,000 of them according to what I was able to find on the net.  This means that our brain has about 1,000 times more of them.

All this from a fertilized egg.

There is much more to say about this work in future posts.

xxx