Background: Neurons and synapses
The human brain is, as one science writer put it, “truly awesome”:
A typical, healthy one houses some 200 billion nerve cells, which are connected to one another via hundreds of trillions of synapses. Each synapse functions like a microprocessor, and tens of thousands of them can connect a single neuron to other nerve cells. In the cerebral cortex alone, there are roughly 125 trillion synapses, which is about how many stars fill 1,500 Milky Way galaxies.
And as one researcher explains:
One synapse, by itself, is more like a microprocessor—with both memory-storage and information-processing elements—than a mere on/off switch. In fact, one synapse may contain on the order of 1,000 molecular-scale switches. A single human brain has more switches than all the computers and routers and Internet connections on Earth.
Neurons are the body’s wiring. They carry electrical signals called action potentials. When an action potential reaches the end of a neuron it is passed on to another neuron or to tissue, via the synapse. First, the action potential causes voltage-controlled calcium channels, located at the end of the neuron, to open. Positive calcium ions on the outside stream into the neuron throught the open channels. The calcium ions influence special proteins just inside the neuron, which in turn cause small bubbles to dock with the cell membrane. The bubbles contain a neurotransmitter chemical which is released to the outside of the cell.
The neurotransmitter chemical floats across the synaptic gap between the cells, and attaches to the other cell, setting off the desired action. It is here where thousands of different proteins work in tight coordination to handle the incoming signals. These proteins form visible blobs called post synaptic densities (PSDs).
New findings: PSD protein designs
New research now emphasizes PSD complexity and the tight tolerances of the PSD protein designs. In fact, a wide range of mutations in these proteins are known to cause a variety of neurological and psychiatric diseases. And the new research finds that these proteins are highly conserved across species, suggesting they are highly sensitive to mutations. Here is how the New York Times described the findings:
The work should help in understanding how the synapse works in laying down memories, as well as the basis of the many diseases that turn out to be caused by defects in the synapse’s delicate machinery.
The research team, led by Seth Grant of the Sanger Institute near Cambridge, England, compiled the first exact inventory of all the protein components of the synaptic information-processing machinery. No fewer than 1,461 proteins are involved in this biological machinery, they report in the current issue of Nature Neuroscience.
Each neuron in the human brain makes an average 1,000 or so connections with other neurons. There are 100 billion neurons, so the brain probably contains 100 trillion synapses, its most critical working part.
These receptors feed the signals they receive to a delicate complex of protein-based machines that process and store the information.
The complex of proteins involved in this information processing is known to neuroanatomists as the post-synaptic density, because the proteins stick together as a visible blob, but the name does scant justice to its critical function.
The 1,461 genes that specify these synaptic proteins constitute more than 7 percent of the human genome’s 20,000 protein-coding genes, an indication of the synapse’s complexity and importance.
Dr. Grant believes that the proteins are probably linked together to form several biological machines that process the information and change the physical properties of the neuron as a way of laying down a memory.
The tolerances of these machines seem to be very fine because almost any mutation in the underlying genes leads to a misshapen protein and, consequently, to disease. Looking through a standard list of Mendelian diseases, which are those caused by alterations in a single gene, the Sanger team found that mutations in 169 of the synaptic genes led to 269 different human diseases.
So the brain and its circuitry is phenomenally detailed and complex, the different parts are tightly integrated, and they have a low threshold to change. This adds yet more problems to the evolutionary narrative. The PSD proteins are even more sensitive to change than typical proteins (see here and here). Evolutionists must believe that these proteins underwent huge changes in their evolution. Not only is there scant evidence of intermediate designs leading to the known proteins, but the evidence we do have is that these proteins do not tolerate change.
So the evolutionary narrative, as usual, must believe that the biological world underwent radical, unheard of levels of change, though mysteriously today such change is not tolerated. All the while luckily creating an astonishing world of biological wonders.