72 Hours Slightly Less Wasted

As I mentioned in my analysis of brain speeds post, I spent about 72 hours reading and researching various articles and topics. In my quest for facts on the physiology of the brain related to a few specific statistics, I stumbled upon some other very interesting (to me) facts. I thought I should go ahead and share them if for no other reason than to help justify that 72 hours a bit more.

• Single sodium pump maximum transport rate = 200 Na ions/sec; 130 K ions/sec
  Typical number of sodium pumps = 1000 pumps/micron² of membrane surface (from Willis and Grossman, Medical Neurobiology, Mosby, St. Louis, 1981, p. 36)
  Total number of sodium pumps for a small neuron = 1 million^[1]
  -- That's a lot of ions being transferred. I wonder how that compares with the best methods we've been able to engineer.... I'll try to resist the urge to make this into another blog post.
• Seasonal oscillations in neuron number in the song nuclei of canaries correlates well with singing ability (Goldman & Nottebohm 1983).^[2]
  -- Canaries kill off parts of their brain and regrow it regularly. Awesome! Practically speaking, adult neurogenesis can probably be induced, possibly helping people recover from various brain injuries.
• Conversely, in some instances increased neuron number has been shown to result in improved performance. Exposure of immature frogs and rats to excess growth hormone can boost neuron number 20 to 60% according to Zamenhof and colleagues (1941, 1966), and in several instances the hyperplasia or hypertrophy is correlated with improved performance on single-trial avoidance conditioning tasks (Clendinnen & Eayrs 1961, Block & Essman 1965). Similarly, the number of visual cortical neurons excited by one eye has been experimentally increased two-fold in both cats and monkeys, and this increase is associated with smaller receptive fields in visual cortex (Shook et al 1984). Preliminary work supports the idea that such experimental animals are able to resolve smaller differences in the offset between two lines than normal monkeys (M.G. MacAvoy, P. Rakic and C. Bruce, personal communication).^[2]
  -- How long before we have growth hormone supplements for our kids to make them smarter? Is this more scary or awesome?
• [Regarding axon transmission speeds] The higher the temperature, the faster the speed. So homoeothermic (warm-blooded) animals have faster responses than poikilothermic (cold-blooded) ones.^[3]
  -- I've always wondered what the advantages to being warm-blooded are! This fact prompted me to read http://en.wikipedia.org/wiki/Warm-blooded#Warm-blooded_vs._cold-blooded, which was full of interesting facts (and the correct spelling of homeothermic).
• Neurons in layer IV receive all of the synaptic connections from outside the cortex (mostly from thalamus)^[4]
  -- The thalamus is the key to The Matrix. We must not teach the machines about the thalamus.
• The longest axons in the human body, for example, are those of the sciatic nerve, which run from the base of the spine to the big toe of each foot. These single-cell fibers of the sciatic nerve may extend a meter or even longer.^[5]
  -- Just pretty darn cool.

Now then, tell me an interesting fact. I don't mind reading more than one, if you have extra to share. I obviously have plenty of time to kill....

Sources:

1. http://faculty.washington.edu/chudler/facts.html
2. http://www.nervenet.org/papers/NUMBER_REV_1988.html
3. http://www.biologymad.com/NervousSystem/nerveimpulses.htm
4. http://en.wikipedia.org/wiki/Neocortex
5. http://en.wikipedia.org/wiki/Axons