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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
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 ...
another 'Homo sapien''s user avatar
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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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 ...
John's user avatar
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8 votes
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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 ...
Ebbinghaus's user avatar
  • 2,603
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 ...
AliceD's user avatar
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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 ...
Bryan Krause's user avatar
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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 ...
Bryan Krause's user avatar
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7 votes
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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 ...
Jan's user avatar
  • 8,079
7 votes

Is there a quantitative report for cortical homunculus?

I think you'd appreciate reading an 80-year update (Catani, 2017)) of the original paper (Penfield & Boldrey, 1937). Four things come to mind (with commentary from Catani 2017 sprinkled throughout:...
theforestecologist's user avatar
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 ...
AliceD's user avatar
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6 votes
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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 ...
Bryan Krause's user avatar
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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 ...
S Pr's user avatar
  • 6,262
5 votes
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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 ...
Bryan Krause's user avatar
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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 ...
fileunderwater's user avatar
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). ...
Bryan Krause's user avatar
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5 votes
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What makes synapses stay "fixed"?

Synapses are held together by adhesion molecules, like cadherins and neuroligins/neurexins, so they aren't just loose adjacent membrane, they are securely anchored in place. The adhesion molecules ...
Bryan Krause's user avatar
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5 votes
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Why is gyrification advantageous?

Short answer The structural anatomy of the cerebral cortex is closely related to its functionality. The cortex is a thin sheet of only a few cell layers deep. Expansion of processing power requires ...
AliceD's user avatar
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5 votes
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Why is the chordate nerve cord described as hollow when it appears to be solid?

Your book is talking about an embryonic structure, the neural tube. This structure forms from an invagination of the neural plate, a collection of cells on the dorsal surface of the early embryo. The ...
Bryan Krause's user avatar
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5 votes
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Why does Sanjay Gupta's brain look so unusual? (brain model shown on CNN) The subdivisions don't look like the lobes I learned in school

I don't know exactly what brain model he has, but if you search for "brain model" you'll find lots that have the precentral gyrus and postcentral gyrus colored separately from the frontal ...
Bryan Krause's user avatar
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5 votes
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Does communication with new parts of body requires internal changes in brain?

I think you'd benefit from reading about the concept of "critical periods" - basically, at different times during development, the brain is learning specific tasks, associating sensory ...
Bryan Krause's user avatar
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4 votes
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What is the specific role of the cerebellum when it comes to 'coordinating movement'?

The principal function of the cerebellum, which was detected years ago, is to calibrate detailed movements rather than initiating movements or deciding which movements to execute (Ghez et al, 1985). ...
another 'Homo sapien''s user avatar
4 votes
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How do different sensory stimuli differ in nerve signal?

I think the short answer to your question is that the contents of different types of sensory stimulation are communicated to different populations of cells in the brain (note this transmission is ...
Bryan Krause's user avatar
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4 votes
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Why is the thalamic reticular nucleus called a nucleus?

The thalamic reticular nucleus (TRN) is a thin layer of GABAergic cells adjacent to the thalamus (Fig. 1). Because of its strategic location between the thalamus and cortex, the TRN is often ...
AliceD's user avatar
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4 votes
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Where does the initial action potential come from?

The very first evoked spike is most likely triggered by spontaneous activity, as even neurons with no synaptic connections are able to fire action potentials (Luhmann et al. 2016). Later in life ...
vkehayas's user avatar
  • 1,198
4 votes
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What parts of the visual system could be responsible for a fixed, monocular scotoma?

Yes. You're right. A scotoma only affecting one eye (i.e., one that is not perceived when one eye is closed) is diagnostic of a lesion upstream from the optic chiasm. See Brust's Practice of Neural ...
De Novo's user avatar
  • 8,791
4 votes

Why is the hippocampus considered to be a cortical structure but not the amygdala?

You can't distinguish cortical from deep structures from a picture like the one you reference in Gray's Clinical Neuroanatomy. The hippocampus is a cortical structure because its cell bodies are in ...
De Novo's user avatar
  • 8,791
4 votes

Neuron connectivity- how are they connected physically

It's true, neurons in the brain are really sparse within an extracellular matrix. But I would like to say that there exist several type of synapsis. The first one, to which you referred is the ...
Ad87F's user avatar
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