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Apr
11
comment Why are amino acids in biology homochiral?
@TomD ha, fair enough. Oversimplifications aside, though, I still like the piece because my memory is that they do a good job giving an intuitive feel for what chirality is and its effects. Of course, its likely that they make more frustrating oversimplifications and I missed them or forgave them in my rapture that a popular show was willing to dig pretty deeply into an idea like chirality for entertainment purposes. Sometimes Radiolab makes major missteps, but in general, I think their stuff is pretty solid as far as popular accounts of tricky scientific concepts go.
Nov
2
comment Distribution of synaptic connections
I don't have time for a full answer, but here is a study on the hippocampal CA1 pyramidal neuron that makes an exhaustive catalog of all synapse types and locations: Megías, M., Z. Emri, T. F. Freund, and A. I. Gulyás. “Total Number and Distribution of Inhibitory and Excitatory Synapses on Hippocampal CA1 Pyramidal Cells.” Neuroscience 102, no. 3 (2001): 527–40. I know such papers exist for a few other cell types. This paper might provide a lead for finding those too.
Nov
1
comment Differences between synaptic connections
@Jean-Paul Yes, location matters. In general, the spatial and temporal pattern of synaptic activation matters a lot. Two synapses activated at the same time on different dendritic branches will have a different effect from two synapses on the same branch. Two synapses on the same branch will have a different effect depending on the order of activation. Good rule of thumb for thinking about neural computation: if something can vary, it probably matters (and if it doesn't matter, there is probably a very interesting story about how the neuron ignores the variation).
Nov
1
comment How do neurons inverse an action potential?
@Jean-Paul Close, but with one major misunderstanding. In this reflex, the flexor muscle is not flexed (contracted). It is being relaxed by the reflex. How does this work? In the diagram, activating the E neuron contracts the extensor muscle, activating the F neuron contracts the flexor muscle. No activity in these neurons means the corresponding muscle is relaxed. By inhibiting activity in the F neuron, the interneuron indirectly causes the flexor to relax. All the connections in the diagram are excitatory, except for the interneuron to F neuron connection which is inhibitory.
Nov
1
comment Differences between synaptic connections
I wrote that linked answer. I did not mean to imply that synaptic location is always compensated by local potential change.
Nov
1
comment How do neurons inverse an action potential?
@Jean-Paul Yes, a neuron will release the same set of transmitters at all of its synapses--often it will release just one neurotransmitter, but sometimes two or more at the same time. An inhibitory interneuron will not, for instance, release an inhibitory transmitter onto one cell and an excitatory transmitter onto a different cell. This is known as Dale's principle (en.wikipedia.org/wiki/Dale%27s_principle).
Sep
2
comment How do the brain and nerves create electrical pulses?
@Probably I'm building a simplified model of a neuron in the answer. When I say "we add" I mean "add this to your mental model of the parts of the system".
Feb
5
comment Extraretinal photoreception in mammals?
Possible duplicate: biology.stackexchange.com/q/700/72
Feb
5
comment Extraretinal photoreception in mammals?
-1. It is well-established that opsins are expressed widely, but their functions are not known. It hasn't been convincingly shown anywhere that human opsins confer light sensitivity to any cells other than those in the retina. The knee study you mentioned has been refuted (see my comment here: biology.stackexchange.com/a/704/72). Also, a point of nomenclature, photoreceptors are cells that are sensitive to light, and opsins are called photopigments when they are bound to a chromophore and are sensitive to light.
Feb
2
comment What is the point of being selection-free?
I agree that they are trying to demonstrate a method that will be applicable for in vivo gene therapy. The results are suggestive of some rate of efficacy for in vivo repair. However, an 18% fraction of repaired cells in a dish does not point to, or even imply, an 18% fraction of repaired cells in a body.
Feb
1
comment What is the point of being selection-free?
-1. "This implies that if their treatment were applied to living tissue, 18% of the cells would be repaired in situ." Not at all. If only it were true that findings in a dish could draw such a straight line to results in the body!
Jan
25
comment Why have humans evolved conciousness?
-1. The substantive part of this answer assumes the common misconception that only humans are intelligent and conscious, and that we somehow know this for a fact.
Jan
25
comment Why have humans evolved conciousness?
-1. Your question and comments are philosophical, not biological, and therefore not appropriate for this site. You seem to believe that evolution can't possibly explain it, and therefore there is really no science to be discussed. Read up on the philosopher David Chalmers, who agrees with you. Then read up on his main rival, Daniel Dennett. Note that when you get into these sorts of questions, your intuition about whether you "know" that you are "self-aware" and how to "prove" it are destined to fail.
Nov
28
comment Action Potential Distribution On Synapses
@Armatus, the ions that flow in through ion channels during the action potential are almost certainly not the same ions that carry current axially to depolarize adjacent sites. The charge travels (that's what current is) but the ion fluxes are local.
Nov
28
comment Action Potential Distribution On Synapses
Threshold is not fixed, even within a single neuron over short periods of time. Fundamentally, threshold is reached when enough voltage-gated sodium channels open so that a rapid depolarization occurs--that is, when inward current is much greater than outward current. When this occurs is a complicated function of membrane resistance, leak currents, the recent history of the membrane, other inward currents present, the kinetics and voltage-dependence of outward currents, etc., etc.
Nov
28
comment How do neurons form new connections in brain plasticity?
Like @nico says, there is a lot of literature on dendritic "reshaping" (see, for instance, biology.stackexchange.com/q/8/72). I'd say that dendritic reshaping is discussed with about as much frequency as axonal reshaping.
Nov
28
comment Action Potential Distribution On Synapses
Can you revise your question? I am not sure what you mean when you say the "whole 40 mV is distributed" versus "a total 40 mV" which is "not there."
Nov
28
comment How and where, in the human brain, are memories stored?
For a little more on ways in which the nervous system is plastic, see my answer here biology.stackexchange.com/a/1359/72
Jun
7
comment Understanding Membrane / Resting Potential from the perspective of ions?
The resting potential is only validly called an equilibrium potential in a system containing only one ion species. Of course, cell environments are composed of several ions so the resting potential is not described by any equilibrium potential, because (as you say) the system is at steady-state rather than equilibrium. A more general term is "reversal potential" which describes the potential at which net current switches sign (e.g., inward to outward). The concept of reversal potential simplifies to a Nernst/equilibrium potential in single ion cases, but also covers multiple ion cases.
May
9
comment Why do neurons die so quickly (relative to other cells) when deprived of oxygen?
+1. Neurons use a lot of active transport pumps that consume ATP to maintain ion gradients and to shuttle neurotransmitters.