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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 the Y-chromosome, unique to males, are expressed in the pre-natal brain. In fact, about a third of the genes on the Y-chromosome are expressed in the male ...


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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) and connectome of C. elegans (right). sources: Utrecht University & Farber (2012) Background Looking at the least complex of animals will be your best bet ...


78

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 inactive pseudogenes. The combined activity of the expressed functional receptors accounts for the number of distinct odors that can be discriminated by the human ...


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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 foods. Background There are two types of red-green blindness: protanopia (red-blind) and deuteranopia (green-blind), i.e., these people miss one type of cone, ...


45

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 "collect and save the effect of photons" over time, if you want to phrase it that way. That allows a camera to make images that our eyes never can, for example, of ...


35

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 many other types of memories where memory loss may not be explicitly beneficial, or even outright debilitating such as in the case of Alzheimer's or stroke. ...


34

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 types of color photoreceptors, called cones. They are sensitive to red, green and blue, respectively. Colors are processed in the retina through a process ...


31

Hearing declines with age and, typically, high frequencies are affected first. Age-related hearing loss (or presbyacusis (Kujawa & Liberman, 2006)) is progressive and starts at the highest frequencies and as a person ages the lower frequencies are affected. The reduction in hearing sensitivity is caused by the loss of hair cells. Hair cells are sensory ...


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What about physical differences from birth? Are there differences in size, regions, chemical composition, etc. from birth? One significant, inherent difference between male and female human brains [from birth & throughout the rest of life] is that male brains are 10-20% larger than female brains. According to a study performed by the United Medical &...


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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. C. elegans is particularly suited for this kind of work because it has a constant number of cells which divide in an entirely predictable order and its neurons ...


24

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. There are 302 neurons in the nervous system of C. elegans; this number is invariant between animals. Each neuron has a unique combination of properties, such ...


21

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 going from bright ambient light to low-lighting conditions is caused by a process called dark adaptation. The visual system works on a huge intensity scale. The ...


20

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 cells in the cochlea. The hair cells are the sensory cells that convert sound vibrations into electric neural signals (Purves et al., 2001). With state-of-the-art ...


19

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 differentiate between much more shades of khaki than unaffected people. This might help detecting camouflaged food in a green environment. Reference 2 quotes an ...


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(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 gave to one of the receptors that normally binds glutamate. They could have called it something else, like the "slow glu receptor", or "Glutamate Receptor A", ...


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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 that a single light-activated rhodopsin molecule can activate 800 transducin molecules, roughly eight percent of the molecules on the disk surface. Although ...


18

Short answer Peripheral vision is more light-sensitive than central vision. Background When you look directly at an object the image is projected onto the fovea. The fovea has maximal visual acuity (high resolution) and a high density of cones, which are specialized photoreceptors to sense colors. However, cones are not very sensitive to light. Here is a ...


17

There are two factors that need to be taken into account here: 1. Myelination decreases membrance capacitance. The rate at which sodium influx through a node can depolarize the axon at the next node is related to both the current and capacitance across the membrane (in addition to a few other factors). So while adding a new node to the axon would indeed ...


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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 signal (i.e., Action Potential) propagation. If you want to see a really wonderfully simplified explanation, see this Quora post by Edward Claro Mader. Four ...


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Short answer Color vision is not based on a calibration to the sky, vegetation and blood. The current leading theory of the development of trichromatic vision in humans is based on the foraging of fruit in our primate ancestors. Background The places of red, green and blue wavelengths in the spectrum are physically defined and, therefore, not arbitrary; ...


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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 scanning the "area of vision" and the body and head are supposedly also moving (willingly or not - nobody can freeze totally) so longer accumulation of data ...


16

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 nerve roots angina pectoris, pain from myocardial ischaemia felt in the throat (Latin angina "infection of the throat"), arms, chest etc shoulder tip pain from a ...


16

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 dissecting microscope, so they were popular among early electrophysiologists. I guess there are probably more neurons around the snail, but it's certainly one of ...


15

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 opinion. First off, in darkness we cannot focus on an object and our eyes will move. And even when we focus on a specific point there is always movement of the ...


13

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, closed and inactivated (Fig. 1). Fig. 1. Gating of a voltage-activated sodium channel. Source: Balseiro Institute. Basically, ion channels are protein pores in ...


13

A recent study found that it is possible for dark-adapted humans to respond to a single-photon stimulus, but only rarely. They used a source which created pairs of photons, and used one of the pair to determine whether the subject may have been exposed to a single photon. The subjects were asked to respond whether they had seen a single photon after an event,...


12

While Luke's answer is perfectly correct, the answer can be given in a more intuitive manner. First, the main point is that it is increased positive voltage (inside the axon) that opens the sodium ion channels to propagate the action potential. The question is: how fast can this voltage get to the sodium channels? In an unmyelinated axon, the movement of ...


12

First recall that pink is white minus green, more or less. Now, your perception can be explained by adaptation: Neurons try to control their gain (amplification factor) to have roughly the same range of output. So if there's a lot of stimuli they like, they will reduce their gain, and vice versa. It can be thought of as a form of fast time-scale homeostasis ...


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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 fixate on the black lightbulb for thirty seconds or more and then immediately turn your gaze to the white region on the right. The illusionary glowing white bulb ...


12

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 background in artificial neural networks but that might be inaccurate). These don't directly impact your question of whether these connections exist, but I ...


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