20
(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", ...
13
Generally, cold suppresses sweetness. As an example, consider soft drinks that are usually served cold: they taste sweeter when warm (like you said with your examples of drinks).
Our taste receptors send a stronger signal to the brain when activated by warmer substances and so the perception of sweetness, in this case, is lessened when we consume cold food ...
10
Short answer
The mechanism of action of serotonin-specific reuptake inhibitors, a commonly-prescribed class of antidepressants, is a downregulation of 5HT1A receptors through negative feedback. This downregulation of receptors takes time.
Background
Serotonin-specific reuptake inhibitors (SSRIs) are a class of antidepressants commonly prescribed to treat ...
8
You've got a few things mixed up here:
A signal may travel down a pathway, passing through several neurons (e.g. around 4-8). However, this signal is not always in the same form: From one end of a neuron to the other, it is merely an electric potential which travels down the neuron's cell membrane (from the dendrite to the axon hillock, where the cell ...
7
One of the many advantage of an all-or-none system is that resources can be conserved for timing events that require synchronized collaboration between many cells (like locomotion). Binary behavior may also partially be a side effect of speed and efficient long-distance information transfer (which is one of the great advantages of neurons as cells in the ...
6
There are an estimated 100 billion neurons within the human brain. In general a minor variation in the number of neurons should not effect individuals too much, however when there is a more significant loss, such as brain injury or in some forms of dementia cognitive abilities do decline. So in this sense yes the number of neurons does relate to intelligence....
6
Short answer
Widening of the action potential increases neurotransmitter release;
Generally, an action potential results in the release of about one vesicle of neurotranmitters;
An action potential does not have to lead to neurotransmitter release - the chance being anywhere between 9 - 100%, depending on the synapse under investigation.
Background
...
6
how is one type of neurotransmitter secreted rather than another
Most neurons release a single major neurotransmitter. JM97 commented a link about cells releasing more than one, but that is talking about "extra" neurotransmitters are short peptides, different from the major neurotransmitters like glutamate, GABA, acetylcholine, dopamine, norepinephrine, etc ...
6
The enzyme responsible for the breakdown of acetylcholine (Ach), i.e., acetylcholinesterase, rapidly degrades, and inactivates Ach in the synaptic cleft after release. This process is particularly fast, as the synapse has to be cleared of neurotransmitter for a next action potential to occur (Čolović et al., 2013). So no, Ach does not leak away under ...
6
Receptors
Any drug or compound with specific effects has a receptor. You can read about this general concept in Goodman and Gillman's The Pharmacological Basis of Therapeutics. Chapter 1 introduces the concept, chapters 3 and 5 expand further. As far as the history of this concept is concerned, receptors mediating the specificity of action was first clearly ...
5
You are correct that cocaine "fills the tunnel" (the pharmacology terminology is that it "blocks the transporter"). But it is not an autoreceptor, so the reuptake transporter does not send a stop signal, it just removed neurotransmitter from the cleft. But once you've blocked it with cocaine, neurotransmitter is not being removed from the cleft so it has a ...
5
Mechanical force can compress neurons and cause action potentials as you probably experienced in the form of hitting the funny bone. Strong enough acceleration of the brain tissue may be causing massive excitation of neurons as indicated by animal EEG study. It suggests that the loss of consciousness is due to generalized epileptic seizure. However, it is ...
5
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 simulates a spike. If you were to model an organism such as C. elegans, whose neurons aren't spiking (but use "graded action potentials"), you would use ...
5
Dopamine (DA) secreted by neurons is selectively reuptaken by the dopamine transporter (DAT), present on nerve terminals.
(source: inist.fr)
Image source: Plasma membrane monoamine transporters: structure, regulation and function - Torres et al. - Nat Rev Neurosci., 2003
DAT acts as a symporter, using the Na+ and Cl- gradients to generate the energy ...
5
I know of no correlation between number of neurons in cortex and intelligence. This question is fraught with controversy because there has been very little work on it but much speculation. Some have suggested that the connectivity between neurons is what is important rather than the number which is logically possible but remains to be supported by definitive ...
5
When discussing the control of gut motility there is more to mention than the use of serotonergics and opioids - a number of peptide and nonpeptide neurotransmitters are important. Somatostatin and nitric oxide are two examples which each happen be inhibitory of intestinal motor function, but by two completely different mechanisms. A bit of understanding in ...
5
Neurons encode the "largness" of the stimulus in firing frequency. Neurotransmitters are stored in vesicules near the end of the axon. It has been shown that neurotransmitter release follows Poisson-distribution and that usually a single "packet" (quantum) is released - this is known as quantal release. Although the actual number of molecules in a single ...
5
First there was opium. Then the active components of opium (morphine etc.) were defined and called opiates. Then the receptors for opiates were discovered, along with their endogenous ligands (enkephalins etc.), and since those endogenous ligands were not derived from opium and indeed (being peptides) were not chemically related to opiates, a new term was ...
5
Short answer
Withdrawal effects are generally associated with drugs that induce feelings of euphoria by stimulating the reward center of the brain, either directly (cocaine, morphine) or indirectly (alcohol, nicotine). The classic hallucinogens have little effect on the dopaminergic pathways and hence do not cause serious withdrawal effects as observed with ...
5
is every neurotransmitter receptor also an ion channel?
No.
There are two general types of receptors for neurotransmitters, ligand gated ion channels and receptors that activate second messenger systems, for example, G protein coupled receptors. They are sometimes referred to as ionotropic and metabotropic receptors. This figure from Principles of Neural ...
4
The half life of dopamine in the extracellular space is of the order of 200 milliseconds.
Yavich,L. (2007) Site-Specific Role of Catechol-O-Methyltransferase in Dopamine Overflow within Prefrontal Cortex and Dorsal Striatum. J. Neurosci. 27:10196-10202
In Figure 1 of this paper the authors present values for the half-life (τ) of dopamine elimination ...
4
The use of spikes is a mixture of their computational advantages and the limitations of the biological substrate in which they are implemented:
They can travel long distances at high speeds because they can profit from the saltatory conduction which is much faster than diffusion and it can be maintained over long distances. A digital signal is less prone to ...
4
Dr. Helen Fisher's conclusions are plain bunkum. What does it even mean when she says associated with a particular neurotransmitter? The sheer work required to even get at this question is vast and difficult so it is unsurprising that she is venturing as much as a guess.There is scientific evidence to support different neurotransmitters systems can go awry ...
4
$H_2S$ is the end product of sulfur related respirations (like sulfate respiration, sulfur respiration, etc...).
By aerob (oxygen) respiration the oxygen in $O_2$ has 0 oxidation number, by $CO_2$ the oxygen has -2 oxidation number, so it was reduced while the carbon was oxidized.
By the thiosulfate respiration of Salmonella enterica the following reaction ...
4
Strictly stated, Hebb's rule applies only to existing synapses, and not to the formation of new synapses. (This answer applies to biological neurons, not to ANNs).
Synapse formation is a topic of active research. During development (and in fact continuously even during adulthood), many synapses are created and destroyed. It is not unreasonable to suspect ...
4
Unlike a computer, the speed at which any brain can perform a computation is related to the number of synapses it goes through. This means fewer synapses in series correlate with decreased reaction time.
An example of fewer neurons correlating with a decrease in reaction time is exemplified in sensory neurons. All sensory nerve cell bodies are all located ...
4
They are two different mechanisms.
Opium is arguably one of the oldest herbal medicines, being used as analgesic, sedative and antidiarrheal drug for thousands of years. These effects mirror the actions of the endogenous opioid system and are mediated by the principal μ-, κ- and δ-opioid receptors. In the gut, met-enkephalin, leu-enkephalin, β-endorphin ...
4
Short answer
A single pacemaker neuron can generate oscillatory behavior.
Background
Given our exchange in the comments, I will focus on single neurons with intrinsic oscillatory behavior. For example, thalamocortical relay neurons and inferior olive neurons have intrinsic oscillatory properties, mainly through the interaction of a hyperpolarization-...
4
Excellent question.
Different neurotransmitters operate at different temporal scales (and even the same transmitter can operate at different temporal scales). Examples of the fastest-acting neurotransmitters are glutamate, GABA, and acetylcholine (with the caveat that they can also act more slowly). These neurotransmitters (usually) open ion channels in the ...
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