February 12, 2016 | David F. Coppedge

Nerves Find Their Way in the Dark

Scientists are beginning to be able to watch nerve cells reaching out and forming connections.

A day in the life of a synapse reveals new facets of the adult brain,” a headline on Medical Xpress teases. Yes, even cells have a list of things to do today. Synapses are the gaps between nerves where the signal turns from electrical to chemical and back again. Why would nerves make that break instead of keeping things electrical, like humans do with their transmission lines? The answer may lie in a trait called “plasticity,” the ability to make rapid changes between connections.

Neuron-to-neuron communication that allows the brain to coordinate activity and store new information takes place at synapses. If an outside stimulus doesn’t enact a synaptic change, it doesn’t register—no learning or memory formation takes place. Synapses can be strengthened or weakened, or even added and eliminated in response to new information….

“The key to enabling plasticity in the adult brain is understanding which elements of a brain circuit are changeable and which aren’t, and under what circumstances,” says study author Elly Nedivi, Picower researcher and professor of neuroscience in the MIT Department of Brain and Cognitive Sciences. “The good news is that while parts of the circuit are hard-wired, others are not—they retain a capacity for remodeling.”

The amazing axon adventure” takes us on another journey of discovery in Medical Xpress. Axons are the long extensions of nerve cells that can reach out long distances from the nucleus. This article discusses the ways that growing axons read cues around them to get them to the right connection points in the dark. The complexity of “beacons” is beyond current understanding. Among the surprises recently found are protein manufacturing sites at the very tips of the axons.

Adding to the complexity was another puzzling discovery – that the growth cones of axons can make proteins. Previous knowledge held that new proteins could be synthesised only within the main cellular part of each neuron, the cell body (where the nucleus is located), and then transported into axons. However, Holt’s group found that the growth cones of axons are also capable of synthesising proteins ‘on demand’ when they encounter new guidance beacons, suggesting that messenger RNA (mRNA) molecules play a role in helping axons to navigate to their correct destinations. mRNAs are the molecules from which new proteins are synthesised, and further experiments found that axons contain hundreds or even thousands of different types of this nuclear material.

Neurobiologists characterize nerve cells that detect motion by light changes” reads a subtitle on Science Daily about how the visual cortex puts together the information coming in from the eyes. To figure out the direction a signal is coming from requires more than a retina of light receivers. The collected information has to be interpreted across numerous levels of nerve cells. Suffice it to say here is another adventure that is more complex than previously thought—and scientists were trying to understand this in fruit flies! Previous mathematical models only considered two inputs; Max Planck researchers doubled that figure. It’s undoubtedly even more complex in vertebrates and mammals like us.

Man-made objects get simpler the closer you look. Living things get more complex the closer you look. Scientists have learned a great deal about the senses and brain, but they have only begun to understand the complexity of the systems involved. At each level, from the overall organ to the tissue to the cell to the proteins and DNA, there’s enough to keep teams around the world publishing findings for probably centuries. That’s the kind of design we must consider when thinking about the origin of the organ that helps us think.



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