894 Reading Notes: Neurobiology

Brief summary of video

The embedded video is an appealing feature of the content-rich online textbook (animations, unfortunately, did not work for me)

Research is revealing more about the mechanisms for neuron firing and in turn, adding to our knowledge of how memory functions.  New imaging techniques are playing a vital role in helping scientists visualize these processes.  One key finding is that new neurons do emerge even in adults.  Other research is showing how neurotransmitters work within reward pathways and how this mechanism relates to addictive behaviors.  

Interesting facts from the chapter

• I hadn’t thought about it before, but I found it interesting and useful to consider that the brain basically has three functions, namely, to take in sensory information, to process information (i.e. everything from reflexes to higher order cognition) and to “make outputs,” meaning primarily to control the muscles and allow movement.
• It is interesting that neurons use both electrical and chemical information, and that there are at least fifty neurotransmitters.  I also found it interesting that “most neurons release only one type of neurotransmitter.”
• I’ve always found myelination fascinating, particularly the fact that the myelination process around adolescence may be responsible, in part, for the critical window for language learning and also is implicated in some of the interesting aspects of teenage behavior.  Apparently the teenage years are also when t the fine tuning of the emotional controls in the brain is completed.  I once read a book about brain changes in adolescence and early adulthood.  These years and the toddler years are apparently some of the most important for brain development.
• I’d forgotten that, in fact, most of the brain is made up of other cells besides neurons.  “For every neuron there are about ten to fifty supporting cells, called glial cells, in the brain.... They perform many vital tasks, including removing dead neurons and debris, releasing critical growth factors to neurons, and acting as insulating material for the neurons.”   
• The chapter says that “a signal traveling through the brain often involves many neurons, each making so many connections… the activation of a single sensory neuron could quickly lead to the activation or inhibition of thousands of neurons.” Add to this the fact that for each moment of experience the brain is receiving a variety of sensory perceptions, making cognitive connections, and controlling movements.  Each of these activates different parts of the brain.  Impressive!
• I did not realize that long-term memory requires the synthesis of new proteins, though I did know that long-term memory involves plasticity which refers to physical changes in the brain.  I guess it makes sense that this would be accomplished through protein synthesis.  Incidentally, I had read about the cab driver studies before.  I also once read that illiterate adults who were taught to read showed differences in their brain scans.  Different experiences different brains!

Making new neural connections, Taiwan, 2004

• Finally, while I did know the difference between declarative and what the chapter is calling “reflexive” memory (also called procedural, I believe), I did not know that the two types of memory use different neuronal circuits.  I found this an intriguing fact.

Neurology and networking: Terms and commentary

(Quoted definitions from Annenberg Learner, Rediscovering Biology, Neurobiology unit glossary)

Action potential—“A nerve impulse; a traveling wave of positive voltage that is propagated along a neuron.”  We have been talking about what moves along networks.  In the brain, what moves is electrical impulses.  A lot of people believe that memories are stored somewhere in the brain when, in fact, memories involve the simultaneous firing of a multitude of neurons in different parts of the brain.
Hippocampus—“A region of the brain associated with both short-term and long-term memory formation. Also the site of long-term potentiation (LTP).”  It sounds like the hippocampus plays some role in directing and shaping how neurons fire together.  Perhaps we could in a very crude way think of it as something like a router?

Membrane potential—“The difference in voltage between that inside the cell and its surroundings.” It is the membrane potential that makes activation possible.  The chemical processes that cause neurons to fire are impressively complex.
Neurogenesis—“The formation of new neurons from precursor stem cells.” A particularly interesting finding in recent years has been the possibility of neurogenesis throughout the lifespan.  To put it in another way, the network is more capable of renewing itself than we had believed. 

Neurotransmitter—“A molecule that travels across the synapse and, by binding to the receptor on the postsynaptic neuron, influences its probability of firing.”  Put simply: essential brain chemicals.  It is amazing that the brain can work as rapidly as it does while being depending on the release and uptake of chemicals that cross the gaps between neurons.  Another fascinating point is that the brain uses a number of different neurotransmitters for different purposes.  I imagine dopamine is the best known, and of course the video mentions dopamine.  I once read a book about how alcohol and caffeine act on the brain and dopamine was a player.  If I remember correctly, caffeine doesn’t activate dopamine directly, but instead suppresses the suppressor of dopamine.  The book, incidentally, was Buzz:The Science and Lore of Alcohol and Caffeine by science writer Stephen R. Braun.   

Reuptake—“The recapture of neurotransmitters in the synapse by the presynaptic neuron.” This one impresses me, too.  Of course it is necessary to recapture and recycle the neurotransmitters to maintain the system.  A few years ago, I took a physiological psychology class (as a free class at my current institution, one of our employment benefits).  I don’t recall all of these details of the process, but I do remember that they were impressively complex, and it is interesting to refresh my memory of that. 

Image adapted from: https://en.wikipedia.org/wiki/Dendrite#/media/File:Complete_neuron_cell_diagram_en.svg (public domain image)

Synapse—“A functional connection between two neurons where information can be exchanged.”  There aren’t too many terms that connect very obviously to the networks that we have been discussing this semester.  When we conceptualize a computer network or a metaphorical network, we tend to think of things connecting directly.  Ignoring the fact that all materials—even solids—are mostly made up of spaces between molecules, we have, I think, imagined things touching.  It is interesting that in neural networks things do not touch; there are gaps between the synapses which the neurotransmitters cross to fire the neurons.  I wonder whether this idea might not be productive in our metaphorical conceptualizations of networks?
Voltage-gated channels—“Ion channels on the cell membrane that will open or close depending upon the voltage.” This is another essential feature of the system.  It is interesting to think of the vast network of neurons that makes up the brain.  To consider that each synapse has multiple channels through which neurotransmitters pass is a whole other layer of complexity within this system.      

References

Annenberg Learner. (2016). Neurobiology. Rediscovering Biology. Retrieved from
http://www.learner.org/courses/biology/textbook/neuro/index.html