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) ...
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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. ...
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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 ...
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16 votes
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Why does biomagnification of mercury occur more in large fish?

Bioaccumulation occurs when organisms aren't able to excrete/eliminate/metabolize something as fast as they take it in. The specific circumstance of predators higher on the food chain accumulating ...
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10 votes
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How long can the brain survive during ongoing cardiac arrest?

From Boron and Boulpaep textbook of Medical Physiology, second edition, p.289: Because of falling ATP levels in the brain, consciousness is lost within 10 seconds of a blockade in cerebral blood ...
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9 votes
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How do our eyes detect light at different frequencies?

Short answer Action potentials generated to different colors are indeed similar throughout the nervous system and do not encode color as such. Instead, the different color- sensitive cells in the ...
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8 votes
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How are reflexes suppressed?

Short answer The pain withdrawal reflex can only be suppressed when touching something painful on purpose. Deliberate, conscious contraction of the extensor muscle before reflex initiation can prevent ...
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8 votes

Are there organisms with fewer than 1000 neurons?

Re: insect brain size Following article has a good summary — in short insects' nervous systems range from 7400 to 850000 neurons: http://blogs.discovermagazine.com/notrocketscience/2011/11/30/how-...
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5 votes

How is information sent from the skin to the brain?

The accuracy of sensation is actually quite variable depending on the region of our body. Highly innervated areas such as our fingers have a higher degree of accuracy than sparsely innervated areas ...
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5 votes
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Why is bacterial meningitis worse than viral meningitis?

One needs to be careful making broad generalizations about meningitis. The term simply refers to inflammation of the meninges (the outer layer surrounding the brain and spinal cord). Meningitis can ...
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5 votes
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Is the bipolar neuron of the retina considered a sensory neuron?

In short, yes. Any neuron that is involved in conveying sensory information from the periphery to the CNS is a sensory neuron. So I would consider all of those neurons in the retina sensory. Arguably ...
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5 votes

Do lobsters possess a nervous system to feel pain?

Yes they feel pain, at least in certain areas of their body without a doubt. Research has been done to test whether they feel pain consciously (a signal to the brain that is perceived allows for ...
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  • 13.2k
5 votes

Do lobsters possess a nervous system to feel pain?

To answer if lobsters have a nervous system: YES References: Mapping of serotonin-like immunoreactivity in the lobster nervous system BS Beltz, EA Kravitz Journal of Neuroscience 1 March 1983, 3 (3)...
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5 votes
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Are all cone cells connected directly to the brain?

Are all cone cells connected directly to the brain? No. Cones connect to ganglial cells. Let's explore the numbers. Our eyes contain about 6 million cone cells, 90 million rods, and comparative ...
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  • 166
4 votes
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Why are our muscles limited to 7 Hertz?

Our muscles are not limited to 7 hertz. You provide two examples yourself. I can provide a third: world's fastest clapper: 804 claps in 1 minute (video here), which is an average of 13.4 claps/sec --...
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4 votes

Why are our muscles limited to 7 Hertz?

According to the book, Principles of Animal Locomotion by R. McNeil Alexander, oscillatory movements in animals are limited by an organism's nature in general to minimize metabolic energy costs. The ...
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4 votes

Why we shiver/tremble/shake while performing some work which requires high accuracy?

If you thread needles often - like a dozen times a day for many days - you will eventually be steady as a rock, because practice improves the process (you will also unconsciously maneuver to steady ...
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4 votes
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How is information sent from the skin to the brain?

In addition to what Spinoral has said, and in response to your comment above, I will add a bit more about the mechanisms. Essentially, in some form or another it's receptive fields all the way up. A ...
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4 votes

Can low temperatures induce a withdrawal reflex?

The withdrawal reflex is a nociceptive flexor reflex and is a spinal reflex intended to protect the body from damaging stimuli. In other words, activation of heat receptors is not the trigger of the ...
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4 votes
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At what stage is the nervous system developed enough to interpret neuronal signals as 'pain'?

First, there is some confusion on your part about heart cells and pain perception. Heart cells generate an action potential intrinsically; they do not need the central nervous system to beat (your ...
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4 votes
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Do lobsters possess a nervous system to feel pain?

Before answer, What intuitively seems: Lobsters structurally contains sense-organs like eye and antennae, and output organs like muscles through which they move. So plausibly these organs should ...
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4 votes

Seizures and blood pressure

Yes, seizures can affect autonomic function including blood pressure. Such symptoms can even result in death. Note though that not all seizures are the same: there are many different types with many ...
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4 votes
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Alcohol consumption and central nervous system

After alcohol intake, the cerebrum related functions like vision and speech is affected first and later on there's problem with the cerebellar functions like balancing and hand-eye coordination. My ...
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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 ...
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4 votes

Does the nature of nervous impulses give us a finite number of things we can perceive?

I know we have sensors in the form of hairs that trigger a nervous impulse to the brain when they are stimulated. But as I understand it, each one can only send that on/off binary signal when they ...
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4 votes
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What are these two nerves running parallel to the spine called?

From this closeup image, you can see there is more than one nerve on each side that is parallel to the spine. Source: imgur.com First, they are the right and left sympathetic trunk that run from the ...
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4 votes
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Does ingestion of alcohol with methylphenidate make it act more like dexmethylphenidate?

Does the ingestion of alcohol, when taking (racemic) methylphenidate can actually make it more potent? It is the 2011 study you've mentioned that answers most of the question. In the study, ethanol ...
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  • 7,969
3 votes

Why we shiver/tremble/shake while performing some work which requires high accuracy?

Norepinephrine (noradrenalin) is a neurotransmitter and hormone released by the body in situations which, among other things, require focus. This may (partially) explain the shaking hands when ...
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3 votes

Is the autonomic nervous system only activated by internal stimuli?

Short answer External stimuli can drive autonomic responses. Background The autonomic nervous system is a visceral sensory and motor system. The viscera are the internal organs. Virtually all ...
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3 votes
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How pain can stimulate the vagus nerve

Short answer Given your comments you are referring to the cause of fainting after being triggered by certain stressors. The reason is a sudden drop in blood pressure due to parasympathetic nervous ...
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