122
votes
Accepted
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 ...
- 52.3k
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) ...
- 52.3k
78
votes
Accepted
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 ...
- 52.3k
74
votes
Accepted
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 ...
- 52.3k
46
votes
Accepted
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 "...
- 24.5k
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 ...
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36
votes
Accepted
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 ...
- 52.3k
34
votes
Accepted
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 ...
- 52.3k
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 ...
- 439
27
votes
Accepted
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 ...
- 29.6k
27
votes
Accepted
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 ...
- 1,921
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. ...
- 6,879
25
votes
Accepted
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.
...
- 24.5k
21
votes
Accepted
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 ...
- 52.3k
20
votes
Accepted
How to make a fake auditory signal?
Devices that bypass the hair cells in the inner ear and directly stimulate the auditory nerve are called cochlear implants. Cochlear implants are used to treat deafness caused by the loss of hair ...
- 52.3k
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 ...
- 51.3k
20
votes
Accepted
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 ...
- 42.4k
19
votes
Accepted
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. ...
- 52.3k
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 ...
- 10.4k
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 ...
- 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 ...
- 52.3k
16
votes
Accepted
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 ...
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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 ...
- 939
14
votes
Accepted
Why are potassium channels slower than sodium channels?
Short answer
The activation kinetics of Na+ channels are faster than K+ channels.
Background
Voltage-dependent channel gating basically occurs through three possible states of the channel: open, ...
- 52.3k
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 ...
- 42.4k
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 ...
- 1,364
12
votes
Accepted
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 ...
- 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 ...
- 52.3k
12
votes
Accepted
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 ...
- 42.4k
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