53
votes
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Why is the brain white?
The brain is indeed stacked with blood vessels, as shown in a 3D model in Fig. 1.
Fig. 1. 3D-printed model of blood vaculature. Source: Biobots.
The blood supply on the surface of a live brain is ...
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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.
...
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12
votes
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The human brain in numbers I: neurons
First of all, let me clear out that these numbers are calculated, not observed (obviously, nobody has counted the number of neurons in any part of brain). So, take these with a grain of salt.
I was ...
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 ...
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10
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 ...
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9
votes
What are the advantages and disadvantages of being ambidextrous?
I think that the advantages of using both hands with equal ease is quite evident whether it be sports, at your work or while you are doing your household chores.
An obvious advantage is using both ...
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9
votes
Accepted
Where is the aneurysm in this picture?
Your image comes from the wiki page Aneurysm. The figure legend on the wiki page identifies it as:
Angiography of an aneurysm in a cerebral artery
I am not an MD so I chose to first dig up a ...
- 51k
9
votes
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Why can't our eyes smoothly transition from side to side without focusing on a moving object?
Short answer
Smooth pursuit is driven by retinal slip, which is determined by external input registered peripherally in the retina.
Background
The smooth pursuit system is a system designed to ...
- 51k
8
votes
What exactly is Tinnitus?
Although tinnitus is usually described as a ringing in the ear, there's a whole range of tunes, buzzes, whooshing sounds, humming and hissing sounds that are described of as tinnitus. The sounds can ...
- 5,488
8
votes
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Neurons with thousands of connections: where are the extra connections coming from?
As you say, a neuron can have thousands of inputs via its thousands of dendrites. Each of those dendrites can have a synaptic connection to the (axonic) output of a different neuron. So the neuron ...
- 8,718
8
votes
Why is the pituitary gland located in the brain?
The evolutionary pressure on the location of the pituitary is likely not the reason why it resides at the basis of the brain. Instead, its (partly) neural origin makes it anatomically (and ...
- 51k
8
votes
Accepted
Would the human body react faster to touch or sight
A "touch" or "haptic" sensation will be much faster due to several reasons:
Haptic feedback can be processed without the presence of any higher-order cognitive processing, therefore meaning that the ...
- 2,568
8
votes
Can turkeys run around when their head is cut off like chickens do?
The brain does not control all bodily movements. Some movements are to a great extent controlled by neural networks in the spinal cord. The spine contains a network which is pre-programmed to control ...
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7
votes
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How are bones growing, if bones are not connected to the brain?
The developmental growth of bone tissue is hormonally controlled. It is, as far as I know, not under direct neuronal control. Before reaching adolescence, the long bones (mainly in the arms and legs) ...
- 51k
7
votes
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Are there nerves in the umbilical cord?
Short answer
There are no functional nociceptors present in the umbilical cord.
Background
Having had the opportunity to cut the umbilical cord of one of my kids, I can anecdotally confirm neither ...
- 51k
7
votes
What is synaptic bias?
Often artificial neurons are created with conventions that zero is "rest" and 1 is "threshold". The unit starts at 0, and when it reaches 1 it will send an input to all of its targets and be reset ...
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7
votes
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Are there any known rules that neurons always follow while transmitting/receiving signals?
Short Answer:
"Always" is always a dangerous term in biology.
Longer Answer:
What does a neuron do if it does not get stimulated/receives no signal for a long time. Will it die ... or try to find ...
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6
votes
Can the dendrites of sensory neurons be a meter long?
Short answer
Axons can be over a meter long, but dendrites are never that long. Distance in the body is covered by axons. The dendritic part of skin receptors is generally considered to be the ...
- 51k
6
votes
Accepted
Cortical projections from layers 2/3 back to 4?
Excitatory neurons in layer 4 are not all stellate in all cortical areas, for example see Smith and Populin, 2001 who show clearly that in auditory cortex most excitatory cells in layer 4 are ...
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6
votes
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What is this structure in human brain?
Short answer
Based on shape and approximate position, I think it is the corpus callosum.
Background
I think it is the corpus callosum (Fig. 1). The corpus callosum is approximately 10 cm in length ...
- 51k
6
votes
Neuron connectivity- how are they connected physically
Neurons are suspended, as you say, in an extracellular matrix. Brain tissues are a little bit more specific. Here I quote a few summaries from literature to answer and give your a perspective on your ...
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6
votes
Accepted
Functional unit
In biology, functional unit of a system refers to the smallest structural element that is capable of performing the tasks typical for that system (MP Hlastala, Physiology of Respiration).
In the ...
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5
votes
Why has evolution made neurons use spiking?
One thing I think you're missing: a perceptron model and a spiking model aren't mutually exclusive. In fact, in perceptrons, people usually use a sigmoid function. That's not a coincidence: it kind of ...
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5
votes
What exactly is Tinnitus?
+1 for giving a solid answer to @AP, but being older I've had friends who have had tinnitus and I'd like to add some notes to try to flesh this out a bit.
I don't think tinnitus is the result of ...
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5
votes
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Neuroscience of mathematicians
Short answer
People competent in mathematics have been shown to have higher activation of the left angular gyrus according to fMRI. EEG recordings have shown larger activity in the posterior parietal ...
- 51k
5
votes
What is the distance between the sciatic nerve and the colon at the closest point?
Short answer
Sciatic nerve pain cannot be caused by a full colon.
background
The sciatic nerve runs at the back of the pelvis down the the leg. The sciatic nerve exits the spine from the lumbar spine ...
- 51k
5
votes
Does learning increase the number of neurons in the brain?
Short answer
Training increases white and gray matter densities in the brain. This may reflect increases in neuronal cell counts especially in the hippocampus. In the cortex, however, such observed ...
- 51k
5
votes
Accepted
Is there a map of the individual motor axons in the limbs?
No it is not possible to map axons at that fine of a scale between individuals.
You mention a possible use for controlling bionic arms. There are a bunch of problems with that approach.
Like @kmm ...
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5
votes
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Why ambidextrous persons are so rare?
While not specifically answering why ambidextrous persons are rare, one potential explanation is that mixed-handedness and/or ambidexterity seems to be related to adverse effects. For instance, some ...
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5
votes
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Why are the posterior and anterior inferior temporal cortex called area TEO and area TE respectively?
These are very old names for primate cortical areas, originally from the anatomist Constantin von Economo and also used by von Bonin and Bailey (1947) (where the TEO region name seems to originate).
...
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Only top scored, non community-wiki answers of a minimum length are eligible