122 votes
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Are male and female brains physically different from birth?

Short answer Yes, men and women's brains are different before birth. Background First off, learning effects versus genetic differences is the familiar nature versus nurture issue. Several genes on ...
AliceD's user avatar
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82 votes

Are there organisms with fewer than 1000 neurons?

Short answer As far as I know, a complete neural map (a connectome) is only available for the roundworm C. elegens, a nematode with only 302 neurons (fig. 1). Fig. 1. C. elegans (left, size: ~1 mm) ...
AliceD's user avatar
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78 votes
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Is there an RGB equivalent for smells?

There are about 100 (Purves, 2001) to 400 (Zozulya et al., 2001) functional olfactory receptors in man. While the total tally of olfactory receptor genes exceeds 1000, more than half of them are ...
AliceD's user avatar
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74 votes
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What is the evolutionary advantage of red-green color blindness?

Short answer Color-blind subjects are better at detecting color-camouflaged objects. This may give color blinds an advantage in terms of spotting hidden dangers (predators) or finding camouflaged ...
AliceD's user avatar
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46 votes
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Why can't we see in low light if staring long enough?

For simplicity's sake, let's really reduce this to something like photography. A camera's aperture can stay open indefinitely, allowing the plate (or whatever is receiving and recording light) to "...
anongoodnurse's user avatar
40 votes

Can humans ever directly see a few photons at a time? Can a human see a single photon?

A single molecule of rhodopsin (actually the cis-retinal bound to it) can and actually does react to one photon (Purves et al. Chapter: Phototransduction in Neuroscience). It has been estimated ...
WYSIWYG's user avatar
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36 votes
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Why does my room suddenly look 'reddish'? My eyes seem to adapt to color

Short answer The phenomenon you describe can be explained by the negative afterimage effect, which indeed is elicited by adaptive processes in the retinae. Background In the retina there are three ...
AliceD's user avatar
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34 votes
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What are the advantages of forgetting?

Short answer It has been shown that loss of long-term memories may enhance the retrieval of others. Short-term working memory is explicitly designed to be volatile and non-lasting. However, there are ...
AliceD's user avatar
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28 votes

Can humans ever directly see a few photons at a time? Can a human see a single photon?

A recent study published in Nature by Tinsley et al. Direct detection of a single photon by humans found that it is possible for dark-adapted humans to respond to a single-photon stimulus, but only ...
llama's user avatar
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27 votes
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Why is saltatory conduction in myelinated axons faster than continuous conduction in unmyelinated axons?

Short Answer Myelination acts as an electrical insulator and allows saltatory propagation. By reducing membrane capacitance and increasing membrane resistance, myelination increases the velocity of ...
theforestecologist's user avatar
27 votes
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Why is loud music much louder after pausing and resuming it?

Hearing is capable of sensory adaptation such that prolonged constant stimulus is perceived as less intense. In hearing, the adaptation to loud sounds is called acoustic reflex and is mediated by two ...
Domen's user avatar
  • 1,923
25 votes

Are there organisms with fewer than 1000 neurons?

The organism you are looking for is the nematode C. elegans, which always has the same number of neurons, 302, and has been fully mapped, see WormWeb or you can chase original publications from there. ...
Jack Aidley's user avatar
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25 votes
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Is C. elegans always observed with precisely 302 neurons? Are there ever individual viable exceptions?

According to the highly respected WORMATLAS: A Database of Behavioral and Structural Anatomy of Caenorhabditis elegans, the number is invariable in this animal, one of the most studied in the world. ...
anongoodnurse's user avatar
21 votes
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Why do we go blind for a few seconds after switching off the light?

Short answer The eyes need to adapt to the low lighting condition after you switch off the lights, a process called dark adaptation. Background The process behind the reduced visual function when ...
AliceD's user avatar
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20 votes

What is the evolutionary advantage of red-green color blindness?

There seems to be some evolutionary advantages to red-green colorblindness. The paper in reference 1 (a summary can be found in reference 2) shows that people with red-green color blindness can ...
Chris's user avatar
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20 votes
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Is NMDA produced in the body?

(my comment reiterating the answer seemed useful, so I've reproduced it here) There are "NMDA receptors" in our body. There is not NMDA naturally in our body*. "NMDA receptor" is just a name people ...
Bryan Krause's user avatar
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19 votes
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If tinnitus is, in many cases, caused by damaged ear hair cells, couldn't it be solved by a mini cochlear implant that sends a constant signal?

Short answer You are right, with a few caveats. Background Most tinnitus cases are caused by sensorineural hearing loss, as you rightfully indicate, namely due to a loss of hair cells in the cochlea. ...
AliceD's user avatar
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18 votes

Have elephants (or any species other than humans) been known to cover their dead?

Yes. I was able to find a book1 (see p. 237-239) and a paper2 (I couldn't access this one) suggesting elephants bury their dead and other animals in African elephants (Loxodonta africana). I also ...
bob1's user avatar
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16 votes

Why can't we see in low light if staring long enough?

The simple answer is, that eye is not constructed such way. The eye have much more "pixels" than "links" to the brain and sends in "preprocessed" image. Moreover the the eye is constantly moving and ...
gilhad's user avatar
  • 261
16 votes

Why can't we see in low light if staring long enough?

The differences at the photoreceptor level have been addressed by others. The mechanical restrictions of the visual system were shortly hinted at by @gilhad et al., but deserve more attention in my ...
AliceD's user avatar
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16 votes
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Is it possible to feel pain in some part of a body, but the pain "feeling" is introduced somewhere else?

Yes, this is pretty common. Examples include sciatica, pain felt down the back of a leg to the foot, from irritation to components of the sciatic nerve but commonly at the level of the sciatic ...
Graham Chiu's user avatar
16 votes

Are there organisms with fewer than 1000 neurons?

I believe there are types of water snail with 8 distinct neurons in a ganglia, there's a bit of information here: molluscs.at. The cell bodies of the neurons are massive, visible under a standard ...
Oliver Houston's user avatar
13 votes
Accepted

Purpose of K+ channels in action potential

Great question! However, your question is based on some misconceptions about what polarization means and how ion movement is involved, as well as the difference between equilibrium and the time it ...
Bryan Krause's user avatar
  • 44.1k
12 votes

Why can't we see in low light if staring long enough?

There's probably a theoretical capacity to do so. The brain is amazingly good at signal processing, and could probably pull off such a summation. However, there is a limit. You have to hold very ...
Cort Ammon's user avatar
  • 1,364
12 votes
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How can a tongue-biting parasitic arthropod become a fully functional tongue?

Short answer There is no evidence whatsoever that the parasitic arthropod Cymothoa exigua develops itself into a functional tongue. Instead, it consumes the fish's tongue and occupies the freed buccal ...
AliceD's user avatar
  • 52.3k
12 votes

Why do I still see a bright light after looking directly at it?

Short answer The effect you describe is called a negative after image. It can be explained by adaptation effects of the photoreceptors in the eye. Background source: Dresden University Steadily ...
AliceD's user avatar
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12 votes
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Do self-exciting neurons exist?

Short Answer Yes, autapses exist, though the role of excitatory autapses in particular is unclear. Long Answer A lot of your assumptions are wrong for biological neurons (I'm suspecting you have a ...
Bryan Krause's user avatar
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12 votes
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How does pressure travel through the cochlea exactly?

Short answer The pressure wave through the scala vestibuli drives the basilar membrane response (BM). Your option (1) is correct, (2) is not. The pressure not really permeates or penetrates Reissner's ...
AliceD's user avatar
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11 votes
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Can acetylcholine leak away from the synapse and cause spasms?

The enzyme responsible for the breakdown of acetylcholine (Ach), i.e., acetylcholinesterase, rapidly degrades, and inactivates Ach in the synaptic cleft after release. This process is particularly ...
AliceD's user avatar
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