Hot answers tagged human-anatomy
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Brain, indeed, cannot feel pain, as it lacks pain receptors (nociceptors). However, what you feel when you have a headache is not your brain hurting -- there are plenty of other areas in your head and neck that do have nociceptors which can perceive pain, and they literally cause the headaches.
In especially, many types of headaches are generally thought to ...
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Probably because it's easier to retain what the body wants than get rid of what the body doesn't want.
What does your body want to keep from your Urine? Pretty much water and selective ions (Cl-, K+, Na+, Ca+2, etc.). Maybe a few other things, depending on how healthy you are.
Now, what does your body want to get rid of in your Urine? Well, anything it ...
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Neither the nostrils nor the mouth originally evolved for breathing. Fish have (two pairs of) nostrils which they use to smell and mouths which they use to eat, but they breathe through their gills. Some lobe-finned fishes (the ancestors to tetrapods) evolved a connection between the posterior nostrils and the oral cavity called choanae. A fossil called ...
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There are two types of sweat glands: (1) eccrine sweat glands and (2) apocrine sweat glands.
Eccrine sweat glands are present from birth in humans and secrete sweat that is mostly water and functions in evaporative cooling.
Apocrine sweat glands are found in the armpits and groin regions and become active in humans at puberty (although the distribution ...
4
My foray into the literature suggests that mature adipocytes do not divide. See, for example:
Lefterova, MI et al. (2009) New developments in adipogenesis. Trends in Endocrinology and Metabolism 20:107-114
In the context of looking at the possibility of stimulating the conversion of white adipose tissue to brown adipose tissue, the authors outline the ...
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The cloaca, which is the common opening of the urinary, excretory, and reproductive systems, is present in birds as well as in non-avian reptiles (and thus presumably dinosaurs), amphibians, and monotremes (e.g., duck-billed platypus). To answer your first question, yes, this condition does seem to be universal for those groups mentioned above.
To answer ...
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The general belief is that these agents are irritants which do not have a very specific effect. That is to say that there is no specific cell or biological function that they set off, but that they irritate the cells, so the cells respond by putting up general defenses to insulate themselves from the noxious chemicals.
Mucous and tears wash away the ...
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The answer is probably No.
"Long" bones - like the tibia, fibula, femur, humerus, etc. grow at the ends during childhood via a special formation called the Epiphyseal plate (also known as "growth plates"). The plates are composed of a special cartilage that grows, and slowly calcifies as a person reaches adulthood.
When the growth plates completely stop ...
3
Its pretty well established that there are photoreceptors in cells besides the cones and rods in the retina of the eye. Humans and most animals have four light receptor genes known (so far). In addition to Rhodopsin - there are the short, med and long wavelength opsin genes.
While they are mostly expressed in the retina of the eye, they can be found in ...
3
I would argue from an evolutionary perspective: not all kidneys are created equal. The mammalian kidney has a long evolutionary history and potentially a lot of phylogenetic inertia. Mammals do what they can with what they inherited from their ancestors.
The metanephric kidney, which is what mammals have, is thought to have evolved with the first amniotes ...
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The situation you are describing where muscles are situated on opposites sides of a joint and produce opposing movements is called "antagonism." Most joints are set up where one or more muscles on either sides will produce such movements (e.g., flexors vs. extensors). Here's a question about muscles without antagonists.
When you contract all the muscles ...
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This is a very good question. Red light is routinely used by scientific laboratories to do low light dissections of retinas, and of course it is used in other low light contexts such as printing plate development.
In both of the above contexts, you have a clear subject: the retina being dissected or the printing plate being developed. In the case of the ...
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Yes, the blood from the hepatic artery (proper) and the portal vein mix in the sinusoids of the liver. The hepatic vein supplies about 75% of the blood to the liver, and the hepatic artery the remaining 25%. Because the portal vein provides such a large part of the blood supply to the liver, then any disease that causes the blood to build up can cause portal ...
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Here is a great diagram (from here) that outlines all of the different white matter tracts running up (blue) and down (red) the cord.
The portion in the center, as you have found in your research, is the gray matter. In there are the different interneurons (cells that exist in the network to integrate information from descending controls and do further ...
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The alternative articulation, called dentolabial, is more difficult to articulate, so it is very rarely used in human language. However, it apparently is common enough in disordered speech to be allocated an ExtIPA diacritic.
The reason labiodentals are easier: Humans normally have a slight overbite.
When the jaw and lips are in a "neutral" position, the ...
2
As you've already mentioned, cells near the primate macula tend to make one to one connections. Due to this lack of convergence they can be somewhat smaller than normal cells (particularly in the size of their dendritic arbors) earning them the moniker "midget" ganglion and bipolar cells (also P cells). By reducing the magnitude of photoreceptor ...
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I also had this thought about the bilateral symmetry of the body and the weight distribution. I'm sure if we were to Q & A a kinesiologist about this particular query we would find that the arrangement of the organs left and right and the difference in weight muscular development left to right is off set by our arms which move in and out from our body to ...
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If you are talking about sound damaging the sound sensing organs in the ear, analogous to an ultrasonic heavy metal concert, I've found an interesting report just on this topic.
For ultrasonic components above 20 kHz, the limits were set to avoid hearing damage in the audible (lower) frequencies. One-third-octave band levels of 105-115 dB were observed ...
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The cecum is a visceral landmark that delineates the change from the small intestine to the large intestine. It's essentially a road sign letting you know where you're at, and is not a organ of itself.
The appendix is a small, previously thought "superfluous" fleshy worm-shaped organ at the junction between the small and large intestines. Recent research ...
2
http://www.turbosquid.com/3d-models/max-human-brain/580672
That one is only 30 which really isn't bad for a model. You will have trouble finding an anatomically correct model for free.
I am curious, is the male brain that much different from the female brain? And do you want just the brain or a whole head with the skeleton and other anatomical features? ...
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Large cells: adipocytes, the cells that store fat are possible the largest in humans, because after puberty they rarely divide and just enlarge if a person gains weight. A typical adipocyte is about 0.1mm in diameter, but may be a lot larger. Another good candidate is a megakaryocyte, which is a gigantic (up to 0.1mm), cell with multiple copies of its genome ...
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That's because your hair grows out from the roots, and as you age the pigments (melanin) that would normally keep your hair a certain colour are not produced anymore becuase the pigment producing cells (melanocytes) start to die.
They're likely differnt colours in the middle becauase that will be the result of a gradual dying off of the melanocytes at the ...
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In an abstract, Brainerd at al. (2004) report the presence of yawn-like behaviors in "cartilaginous and ray-finned fishes, a lungfish, salamanders, caecilians, mammals, turtles, lizards, an alligator and birds".
So clearly the motor patterns necessary for this behavior evolved before air breathing and apparently have been conserved for ~400 million years. ...
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Probably because the blood would be forced, physically, that is, by inertia to move upwards during free-fall, thus causing the genital's blood supply to become obstructed thus reducing their temperature and thus leading to the sensation of them being frozen as you described. Plus you might feel cooler all over your body due to the air flow against it and ...
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The hair doesn't keep growing!
It's important to notice that there isn't a set point for the actual hair length. The hair doesn't know that it's been cut for example. Rather, there's a set point for time. A single strand of hair, in humans, on the scalp, will be in the growth phase for several years. The growth cessation takes a few weeks, and then the ...
1
A hair follicle is a mammalian skin organ that produces hair. Hair production occurs in phases, including growth (anagen), cessation (catagen), and rest (telogen) phases. Stem cells are responsible for hair production.
Many people can grow extremely long head hair and facial hair. Are there evolutionary theories as to why this is the case?
Ans: Basic ...
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No, because growth only occurs at the epiphyseal plate or growth plate. In the picture here, the epiphyseal plates are the two horizontal lines in the tibia and fibula, and bone growth occurs in the upward direction, or toward the middle (shaft) of the bone. Once the epiphyseal plates close, the bones can no longer elongate.
It's possible to have a second ...
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That the brain doesn't have pain receptors has somewhat drifted into the corpus of general knowledge, perpetuated by pamphlets, books and documentaries.
Your question caused me to look up wikipedia. Citing:
A headache or cephalalgia is pain anywhere in the region of the head
or neck. It can be a symptom of a number of different conditions of
the head ...
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Probably not many side effects except in specific instances, but no benefits either. My guess is that there are potential side effects because these glasses reduce the amount of light that the eye receives and restrict the visual field. Therefore, the restricted visual field would be bad for activities such as driving, in which you need your peripheral ...
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