It happens quite a lot in neuroscience that something can be described without really knowing why it’s doing something. Bear with me a bit, as what I’m about to describe is probably unfamiliar to most people and also very much concerns the nitty-gritty of how the cells (neurons) of the brain and nervous system work.
Neuroscientists have known for some time that nerve endings near the critical junction points between nerve cells, the synapses, are filled with tiny sacs (like microscopic bubbles) containing chemicals called neurotransmitters. Neurons work by sending a pulse of electro-chemical energy along the length of the cell (through nerve fibers of the axons) until it reaches a synapse – a gap between the end of one neuron and the beginning of another. For the pulse to cross this gap it must trigger the release of neurotransmitters stored in vesicles (those tiny sacs) that cross the gap. Depending on how much and what kinds of neurotransmitters are released, they may fire triggers in the next neuron and so the nerve impulse passes on, from toe to brain in some cases. This is not, as you can tell, the convenient metaphor of an electrical charge travelling down a wire. We are not ‘wired,’ actually; it’s more like tenuously and conditionally connected, something like your computer connected to Wi-Fi.
This is not the most efficient or high speed way of transmitting an electrical signal (parenthetically, some types of neuron actually do act like an efficient ‘wire’); so why are most neurons set up this way? That’s one of the big questions in neuroscience. I mention this because it’s also been clear for some time that the function of the synaptic vesicles and their neurotransmitters is to ‘filter’ or ‘weigh’ the meaning or importance of a pulse coming across the synapse. More
Plasmonic nanostructures make graphene viable for super-fast communications
On the one hand graphene, a single layer of carbon atoms in a honeycomb pattern, can move electrons (electricity) very fast and efficiently. On the other hand graphene is lousy at absorbing energy, specifically from sunlight; only about 3% is absorbed. Sounds like graphene, a wonder material in many accounts, isn’t cut out for solar cells or photonics (such as communication by light). Well by itself it’s not, but graphene is such a tempting material that clever minds are set upon making it do all kinds of things it doesn’t appear to do. In this case, among the clever minds are the two fellows who won the Nobel Prize for their work with graphene, Andre Geim and Kostya Novoselov plus their team at the University of Manchester, and Cambridge University (UK). Their newest work, published in the journal Nature Communications [30 August 2011, paywalled, Strong plasmonic enhancement of photovoltage in graphene] advances the use of graphene.
Their approach to making graphene part of a photonics system, where it contributes higher speed transmission, is to put closely-spaced nanoscale metallic wires (nanowire) on top of the graphene layer. The wires, called a plasmonic nanostructure, can take on a large variety of shapes with exotic names such as nanoshells, nanomatryushkas, and nanorice. The shapes (structures) of wire are significant because of what they do to incoming light energy – they, in effect, bend, reflect and transform it so that, in this case, far more energy is absorbed by the graphene layer. In fact, it boosts the absorption efficiency by about twenty times, a rather remarkable figure. More »