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Neurons during Numb feeling

Neurons during Numb feeling


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We become numb when there is short supply of blood to some parts, as mentioned here.

If that is the reason, why don't neurons and other cells die at that part if they don't receive oxygen and other things needed?


A lower supply of blood does not mean no supply of blood, so my guess is there's generally enough to keep stuff alive for some time. But if the supply is restricted for long periods (think frostbite), then stuff starts to die.

Also, the sensory neuron endings in the skin are normally just one long projection from a cell body, the major components of the neuron are protected by being located in e.g. The Dorsal Root Ganglion.


Simply put, the cells and "other stuff" WOULD die if the blood flow and/or oxygen were too severe, and would be cut off for too long.

It would probably take some time though.


The feeling of having a foot ⋺ll asleep" is a familiar one. This same combination of numbness and tingling can occur in any region of the body and may be caused by a wide variety of disorders. Sensations such as these, which occur without any associated stimulus, are called paresthesias. Other types of paresthesias include feelings of cold, warmth, burning, itching , and skin crawling.

People of all ages experience episodes of numbness and tingling. These generally become more common as people age. Episodes of numbness and tingling are more common among people with diabetes, hypothyroidism , alcoholism , malnutrition , or who experience mechanical trauma, especially to their limbs, neck or spine.


What makes us thirsty?

When your body starts to run low on water, a number of changes take place: for one, the volume of your blood decreases, causing a change in blood pressure. Because the amount of salt and other minerals in your body is staying constant as the volume of liquids decreases, their relative concentration increases (the same number of particles in a smaller volume means that the particles are more concentrated). This concentration of particles in bodily fluids relative to the total amount of liquid is known as osmolality, and it needs to be kept in a narrow range to keep the cells in your body functioning properly. Your body also needs a steady supply of fluids to transport nutrients, eliminate waste, and lubricate and cushion joints. To some extent, the body can compensate for water depletion by altering heart rate and blood pressure and by tweaking kidney function to retain more water. For you, though, the most noticeable indication that your body is running low on fluids is likely the feeling of thirst, as you increasingly feel like you need to drink some water.

So how does your body know that these responses are necessary, and how are they coordinated across so many different organ systems? Scientists are still trying to uncover how this process works, but research over the past several decades indicates that a highly specialized part of the brain called the lamina terminalis is responsible for guiding many of these thirst responses (Figure 1). Brain cells within the lamina terminalis can sense when the body is running low on water and whether you’ve had anything to drink recently. When researchers manipulate this brain region , they can also drive animals to seek out or avoid water, regardless of how hydrated that animal might be.

Figure 1: Brain regions controlling thirst. The lamina terminalis (yellow) is a series of interconnected brain structures that act as a central hub to control fluid levels in the body. Some cells in the lamina terminalis are adjacent to large, fluid-filled compartments in the brain, called ventricles (blue). When the body begins to run low on water, the composition of the body’s fluids (including the fluid in the brain’s ventricles) starts to change. The lamina terminalis neurons that border the ventricles can sense changes in the ventricular fluids, giving a snapshot of whether the body has enough water. These neurons also receive messages from other parts of the brain to give an even more complete picture of the body’s water needs.

The lamina terminalis is located towards the front of the brain and occupies a prime location just below a fluid reservoir called the third ventricle. Unlike much of the rest of the brain, many cells in the lamina terminalis aren’t guarded by a blood-brain barrier. This barrier prevents many circulating factors in the blood and other fluids from interacting with cells in the brain, offering the brain protection against potentially dangerous invaders like certain bacteria, viruses, and toxins. However, the blood-brain barrier also cuts the brain off from many circulating signals that might hold useful information about the body’s overall status. Because certain cells in the lamina terminalis lie outside the blood-brain barrier, these cells can also interact with the fluid in the third ventricle to keep tabs on factors that indicate whether the body needs more or less water. In particular, these cells can monitor the fluid in the ventricle to determine its osmolality and the amount of sodium present.

When other parts of the brain detect information that’s relevant to understanding the body’s water needs, they frequently pass it along to the lamina terminalis, as well (Figure 2). In this way, the lamina terminalis also collects information about things like blood pressure, blood volume, and whether you’ve eaten recently (even before food can cause any change in circulating salt or water levels, your body tries to maintain a balance between these factors by encouraging you to drink water every time you eat). Information from the part of the brain that controls the circadian clock also gets forwarded to the lamina terminalis, encouraging animals to drink more water before sleeping to avoid becoming dehydrated during long periods of sleep. Collectively, this information gives the lamina terminalis the resources needed to make a call about whether the body needs more or less water. In turn, cells in the lamina terminalis project to many other areas of the brain, sending out their verdict about current water needs. Although scientists are still trying to figure out exactly how information from the lamina terminalis affects other brain regions, it’s clear that this output can influence an animal’s motivation to seek out water, as well as physiological factors like kidney function and heart rate (Figure 2).

Figure 2: Thirst signals and their effects. Neurons in the lamina terminalis receive many different messages about the body’s water needs. Thanks to their location next to ventricles in the brain, they can directly sense key indicators of water need like sodium levels and osmolality (the ratio of salt particles to a given amount of liquid). They also receive information about what time of day it is from another brain region, as well as cues from the mouth and kidneys. Neurons in the lamina terminalis can pool all of this information to determine whether the body needs more or less water. If it needs more, they can trigger feelings of thirst and appetite suppression. If it needs less, the brain will send signals telling you to stop drinking. The lamina terminalis also sends messages to a brain region called the hypothalamus. In turn, the hypothalamus can affect heart rate or urge the kidneys to retain more or less water.


Abstract

The concept that the gut and the brain are closely connected, and that this interaction plays an important part not only in gastrointestinal function but also in certain feeling states and in intuitive decision making, is deeply rooted in our language. Recent neurobiological insights into this gut–brain crosstalk have revealed a complex, bidirectional communication system that not only ensures the proper maintenance of gastrointestinal homeostasis and digestion but is likely to have multiple effects on affect, motivation and higher cognitive functions, including intuitive decision making. Moreover, disturbances of this system have been implicated in a wide range of disorders, including functional and inflammatory gastrointestinal disorders, obesity and eating disorders.


Numbness and Tingling: When to Worry

Numbness and tingling in the arms and legs are abnormal sensations that result from disorders of a nerve or nerves. There are many different possibilities as to the cause of these symptoms. Most of the time the cause is not serious, but certain associated signs and symptoms can signal the need to see your doctor.

A major cause of numbness and tingling is peripheral neuropathy. This refers to an abnormality of the nerves outside the spinal canal. Several causes of neuropathy exist, including, but not limited to diabetes, peripheral nerve entrapment, vitamin and mineral deficiencies, inflammatory or rheumatologic disorders, alcoholism, kidney failure, circulatory issues and damage from chemotherapy and radiation. In diabetics, the numbness and tingling is often accompanied by increased thirst, hunger, and urination. The most common nerve entrapment is carpal tunnel syndrome which affects the hand and wrist. Increased risk of carpal tunnel syndrome is noted in people who do repetitive wrist activity such as typing or cutting hair. Vitamin B-12 and folate are common vitamin deficiencies and can be associated with weakness from anemia, paleness, loss of appetite, and sore tongue and mouth. Long term excessive alcohol drinking can cause numbness and tingling and is usually associated with a wide-based gait. Certain rheumatologic or endocrine conditions that can cause neuropathy include rheumatoid arthritis, amyloidosis, fibromyalgia, thyroid problems, or Raynaud&rsquos phenomenon. Neurologic neuropathies (such as chronic inflammatory demyelinating polyneuropathy) are typically associated with weakness in the arms or legs. Sciatica is a condition where the sciatic nerve is affected after exiting the spinal cord as it passes through the hip or buttock area. This is commonly associated with leg pain and/or back pain.

Disorders of the brain and spinal cord also commonly cause numbness and tingling. Problems in the cervical spine can result in symmetrical arm and leg numbness and possible paralysis of the arms and legs. Thoracic (mid back) problems affect the trunk and legs. Lumbosacral (low back and tailbone) conditions affect the hips and legs. Multiple Sclerosis is an autoimmune disorder which can cause these symptoms, but these will rarely occur in a symmetrical pattern. Other spinal cord problems such as tumors or cysts can be associated with pain, weakness, clumsiness, or bowel or bladder problems.

Vascular or circulatory problems leading to lack of blood supply to an area can cause numbness and tingling. This will commonly accompany blue or red discoloration, paleness or cold and painful sensation in the area.

While the potential causes of these symptoms are quite varied, certain causes are obviously of greater concern than others. Numbness and tingling that is associated with weakness, paralysis, or loss of bladder or bowel control warrant emergent evaluation and treatment by a healthcare professional. Also, any symptoms of confusion, vision or speech changes, weakness, or loss of consciousness should prompt a visit to a local emergency department. Numbness and tingling associated with neck or back pain, arm or leg pain, muscle spasms, or rash require a call or visit to your physician but are less urgent in nature. Obtaining a proper history and physical from a physician, as well as diagnostic testing and procedures, are necessary to make a correct diagnosis and implement proper treatment. If any of these symptoms are experienced and persist despite change in position or activity, please consider evaluation with your doctor for appropriate care.

Spinal stenosis causes pain and stiffness in your neck or lower back. You probably won&rsquot know that you have it, though, until you experience symptoms. If you&rsquore at risk for spinal stenosis, however, you can take action now to reduce its impact.

If you have back pain or sciatica, you may have avoided surgery because of possible complications. However, when back pain and sciatica don&rsquot respond to other therapies, minimally invasive endoscopic surgery can provide long-term relief, safely.

If you have lower back pain, the last thing you probably want to do is move it, twist it, and do exercises to strengthen it. But that&rsquos exactly what you should do to help your back heal and to reduce or eliminate your pain. Here&rsquos how to start.

If you have sharp or radiating pain, you could have a pinched nerve. Pinched nerves can cause pain or numbness almost anywhere, from your neck to your buttocks. Treat a pinched nerve quickly to avoid permanent damage.

Steroids aren&rsquot just for athletes who want to optimize their game. Steroids are anti-inflammatory agents that can also calm down irritated nerves. When doctors inject steroids into the epidural space in your spine, your back pain goes away.

You never even knew you had facet joints until you developed back pain. What are the facet joints? Why do you have facet joints? And why do they hurt so much?


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5. Allodynia

Allodynia refers to central sensitization that leads to the triggering of pain response that normally does not provoke pain, such as a light touch [7,13]. The cells involved in the mechanical sensation and nociception are those responsible for allodynia. Upon peripheral nerve injury, the anatomical reorganization occurs whereby sprouting the A-fibers into lamina II in the DH of the spinal cord, which originally receives the nociceptor input from C-fibers. Both hyperalgesia and allodynia occur due to the increase of prostaglandin E2 (PGE2) in the inflamed tissue via the activation of COX signaling pathway in the DH of the spinal cord [14].


Conduction

Nociceptors express a wide variety of voltage-gated channels (e.g., Nav, Cav, Kv) that transduce the receptor potential into an action potential or, more commonly, a set of action potentials that encode the intensity of a noxious stimulus applied within their receptive fields. There are 9 known Nav, 10 Cav, and 40 Kv genes in mammals (http://www.iuphar-db.org/DATABASE/), many of which have multiple splice variants with different functional characteristics (99). Cell excitability and firing behavior (e.g., threshold for action potential generation, action potential and undershoot amplitude and duration, and maximal firing frequency) depend on the complement of these channels as well as those contributing to frequency modulation (e.g., hyperpolarization-activated cyclic nucleotide-gated cation channel [HCN] and A-type Kv4.3 and Kv3.4 channels) (54). For instance, nociceptors responsive to noxious cold require the expression of the tetrodotoxin-resistant (TTX-resistant) Nav1.8 channel at the peripheral terminal (100), and mice lacking Nav1.8 and Nav1.7 display deficits in mechanosensation (95, 101). Peripheral CGRP release by inflammatory mediators is unaffected by TTX, suggesting an important role of TTX-resistant Nav in regulated pain thresholds, consistent with their robust modulation by bradykinin (BK) and PGE2 (102) (see below). Since enhanced excitability of primary sensory neurons in inflammatory and pathologic pain states is a major contributor to the perception of pain, specific pharmacological agents that specifically dampen aberrant activity are desirable in the design of pain therapeutics. To this end, an understanding of species-specific differences is critical, as exemplified by the dramatically different phenotypes in mice and humans lacking Nav1.7: although mice lacking Nav1.7 show a mechanosensory (pinch) and formalin-induced (5%) pain phenotype (103), humans lacking Nav1.7 are insensitive to pain altogether (104).


The root of the problem

Akerman and Goadsby studied the effects of VIP and PACAP on a set of neurons that innervate the head and face, which are known to trigger a headache. The pair measured the electrical activity of these neurons in anaesthetised rats and studied blood vessels in the rodents’ brain to identify when they dilated or constricted.

Some rats were then given PACAP, while others were treated with VIP. Only PACAP caused the neurons to increase their activity – about an hour and a half after it was administered. This suggests that the peptide is responsible for kick-starting a migraine, says Akerman.

To block the effect, Akerman and Goadsby used molecules that block the receptors that PACAP binds to. The drugs made no difference when they were given to the rats intravenously, but when they were injected directly into the brain, the neurons responsible for a headache no longer surged with activity. “These receptors could genuinely represent a new therapeutic target for migraine,” says Akerman.

“It appears that these receptors are indeed important, and this is definitely vital to helping us understand migraine and for developing new treatments,” says Hay, who wasn’t involved with the work. “The receptors are a new and exciting target for migraine.”


Researchers discover the brain cells that make pain unpleasant

Pain sensation and the emotional experience of pain are not the same, and now, in mice, scientists at Stanford have found the neurons responsible for the latter.

Gregory Scherrer and his collaborators have identified in mice an ensemble of cells that seems to specifically function as an on-off switch for pain aversion.
Paul Sakuma

If you step on a tack, neurons in your brain will register two things: that there’s a piercing physical sensation in your foot, and that it’s not pleasant. Now, a team of scientists at Stanford University has identified a bundle of brain cells in mice responsible for the latter — that is, the negative emotions of pain.

Pain research has traditionally focused on the neurons and molecules at the frontline of pain perception — the cells in nerves that process stings, cuts, burns and the like — and ultimately convey a physical threat message. What Grégory Scherrer, PhD, assistant professor of anesthesiology and of neurosurgery, and Mark Schnitzer, PhD, associate professor of biology and of applied physics, are studying goes one step further. “We’re looking at what the brain makes of that information,” Scherrer said. “While painful stimuli are detected by nerves, this information doesn't mean anything emotionally until it reaches the brain, so we set out to find the cells in the brain that are behind the unpleasantness of pain.”

Backed by animal-brain imaging and molecular testing, the researchers have found an ensemble of cells in the amygdala, a region of the brain classically associated with emotion and fear, that seems to specifically function as an on-off switch for pain aversion. And although the finding was made in mice, there’s reason to think it could one day serve as a therapeutic target for human pain, since the mouse and human amygdala aren’t so different in function. Researching this group of cells could reveal a potential treatment for chronic pain, the scientists hope.

The idea is that patients suffer from the emotional unpleasantness of pain, rather than pain sensation itself. If there’s a way to dull the emotional hurt, rather than the physical sensation of pain, that could be big for chronic pain patients.

A paper describing the results of the study was published Jan. 18 in Science. Scherrer and Mark Schnitzer, PhD, who is also a Howard Hughes Medical Institute investigator, share senior authorship. Postdoctoral scholar Gregory Corder, PhD and former graduate student Biafra Ahanonu, PhD, are the co-lead authors.

Peeping at pain neurons

The amygdala seemed to the researchers a logical place to start, since it’s a well-established hub for emotion in the brain. Within the amygdala, they narrowed their search by looking for neurons in mice that were active during brief pain stimulation — such as a drop of hot, but not scalding, water applied to a paw. Neurons that are active express more of a specific gene called c-Fos, and indeed, a sea of c-Fos-expressing neurons flared after this stimulus.

“But that really only tells you that those neurons were active at some point, and it’s not specific enough,” Scherrer said. “What we wanted was to look at the neurons of freely moving animals.”

To observe the deep-seated wiring of a mouse’s brain, Scherrer partnered with Schnitzer, who had developed a “miniscope” — a microscope about the length of a small paper clip, which could be affixed to a mouse’s head to record activity in its brain. They positioned the device strategically to visualize the amygdala. The mouse, alive and well, could stroll as it pleased, while the miniscope recorded calcium flux in the neurons, a proxy for cell activity.

The scientists monitored the mouse brains with the microscope, watched the mice detect something uncomfortable, observed the aversive reactions and then checked which neurons were active. “With this setup, we identified a set of neurons in the amygdala that selectively encodes signals related to the emotional aspects of a painful experience,” Schnitzer said.

When the mice touched a drop of uncomfortably hot or cold water (neither of which were severe enough to injure the mice), they withdrew, signaling to the scientists that the rodents were not pleased. Upon this withdrawal, the microscope’s recording showed a bundle of neurons firing in the amygdala — specifically in the basolateral region — suggesting that these neurons were specifically responsible for the emotion of pain.

It was, however, still possible that this basolateral ensemble was simply firing to relay general emotion, rather than the unpleasantness of pain specifically. So, the researchers fed the mice sugar water — a sweet treat known to bring joy to any mouse — and kept an eye on the collection of neurons suspected to relay displeasure. As expected, those neurons stayed silent.

“There’s also a difference between experiencing pain and experiencing something annoying, so we further wanted to test if the amygdala neurons active during pain were also associated with overall negative emotion, rather than pain particularly,” Scherrer said.

What miffs a mouse? The same things that might bother a sibling: tiny puffs of air to the face, an unappetizingly bitter taste or a very bad smell. While bothering the mice, the researchers again monitored the basolateral amygdala pain ensemble, and here, too, the neurons remained subdued.

Tracking the perception of pain

“After all of that, we concluded that this ensemble of neurons selectively responds during pain,” Scherrer said. “But it still didn’t fully demonstrate that they underpinned the emotional response.”

To investigate that question more deeply, the researchers set up a walking track with three invisible lanes: On the far left was a cold strip on the right, a hot one and in between the two was a temperate middle ground. (For context, walking in the two outer lanes was comparable to walking barefoot on pavement during winter or summer, respectively — uncomfortable, but not permanently damaging.)

Normal mice that walked on the track gradually learned that the middle lane was tolerable, while the outer two were unpleasant. But in a select group of mice, the researchers temporarily disabled the bundle of amygdala pain neurons thought to relay feelings of physical discomfort. These mice — free of pain-incited unpleasantness — skittered around the outer regions, undeterred by the extreme temperatures.

What’s intriguing about this, Scherrer said, was that these mice weren’t bereft of physical feeling. “Pain was just no longer unpleasant for them,” he said. The rodents could still feel and respond to physical sensations, but the stimuli they once perceived as unpleasant (hot or cold drops of water) were no longer bothersome. When exposed to a drop of hot water, for example, the mice with a muted basolateral neural ensemble would move their paw away from the dropper, signaling that they felt the stimulus — but they would move their paw back to its original position, something that normal mice did not do. This is a crucial part of harnessing the ensemble as a tool in pain therapy, Scherrer said, as an animal, or human, without the ability to physically feel anything at all leaves them vulnerable to injury.

Long term, Scherrer aims to confirm that the function of the basolateral ensemble in mice is the same as it is in people, and then down the line, find a safe and effective way to silence the ensemble’s function without interfering with other neurons.

“There’s really no good treatment for chronic pain in humans, and that’s a major driver of the opioid epidemic,” Scherrer said. “But you’ll notice, patients who take opioids for pain report that they can still feel the sensation of pain but say it’s less bothersome — the emotions of pain are different. Our big future hope is that the cells in the basolateral ensemble could be a tactic to curb the ailment of pain without causing addiction and thus, ideally, act as a possible substitute for opioid treatment.”

Other Stanford co-authors of the study are former Stanford postdoctoral scholar Benjamin Grewe, PhD, and research scientist Dong Wang, PhD.

The study was funded by the National Institutes of Health (grants R00DA031777, R01NS106301, K99DA043609, F32DA041029 and T32DA35165), the New York Stem Cell Foundation, the Rita Allen Foundation, the American Pain Society, the National Science Foundation, the Howard Hughes Medical Institute, the Bill and Melinda Gates Foundation and the Swiss National Science Foundation.