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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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77 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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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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35 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
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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
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 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
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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
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
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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
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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
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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

Is C. elegans always observed with precisely 302 neurons? Are there ever individual viable exceptions?

Many Nematodes do not use traditional hox genes instead the have a strange set up which controls cell placement directly. This means individual adults of many nematode species have the exact same ...
John'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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11 votes

Why are nerves blocked even though potassium channels are not blocked?

In general, action potentials are initiated by an inflow of Na+ that depolarizes the neuron. Only after that, K+ channels open up that re-polarize the membrane potential to get the neuron back in ...
AliceD's user avatar
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10 votes
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Why are fearful stimuli more powerful at night?

Short answer The increased fear responses during the night are believed to be mediated by elevated corticotropin-releasing hormone (CRH) levels in the brain that drive the fear responses in the ...
AliceD's user avatar
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10 votes

How are neurons / synapses "biased"?

The term that most scientists use to describe a synapse's "bias" is synaptic strength. The strengths of synapses depend on their "history". The change of synaptic strength is called synaptic ...
a tiger's user avatar
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10 votes
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Why is Heart Rate Recovery after exercise reasonably well described by a mono-exponential decay?

I think most people would take exponential decay in a circumstance like this to be the null hypothesis. That is, if you had something not exponential decay, that would be curious and interesting and ...
Bryan Krause's user avatar
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9 votes
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Why is the human ear most sensitive to 4000 Hz tones?

The frequency-selectivity of loudness perception was first shown in the 1930s, when Fletcher and Munson published a set of curves showing the ear's sensitivity to loudness compared to frequency. These ...
AliceD's user avatar
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9 votes

Is there an RGB equivalent for smells?

There are many, many more parameters than 200! As an example, look at the nomenclature system for olfactory receptors (ORnXm). "OR" is the root name (Olfactory Receptor superfamily) n = an integer ...
Drunken Code Monkey's user avatar
9 votes
Accepted

Why is it possible to calculate the equilibrium potential of an ion using the Nernst equation from empirical measurements in the cell at rest?

Excellent question! The answer is actually a really cool and crucially important detail about membrane potentials and the movement of ions. Basically, the electric force is very strong. You don't ...
Bryan Krause's user avatar
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