We all have certain instincts, reflexes and other innate behaviors. Some help us survive dangerous situations, others are a side-effect of our neural architecture... and some are just plain weird. Let's take a look at...
Contagious YawningHave you ever seen someone else yawn, only to be struck by an overwhelming urge to do the same? One study found that mere watching a videotape of people yawning caused nearly six times as many yawns than watching a videotape of people smiling.
This could be something to do with mirror neurons, specialist cells that activate not only when you perform an action, but when you observe someone else performing an action. If you see someone getting struck by a flying object and automatically wince in sympathy, it is the mirror neurons that are responsible. Seeing someone yawn could be activating these neurons and causing us to do the same.
One study found that yawns were more "contagious" between friends and family than between strangers. Interestingly males were more likely to be the origin of a chain of yawns, while females were more likely to yawn in response.
This capability is thanks to the mammalian dive response (or reflex) which can activate when in contact with cold water or holding your breath. It isn't limited to humans and it essentially put you in "power saving mode" to prolong the oxygen you have in your body.
The response starts with bradycardia or a slowed heart rate. At the same time, blood vessels in your extremities constrict (peripheral vasoconstriction) and keep blood near your vital organs. Blood vessels around the lungs expand, promoting blood flow around the vital organs and helping the lungs resist pressure.
The spleen also reacts, releasing additional red blood cells into the bloodstream and thus increasing the amount of oxygen it can carry. This part of the response takes longer to have any effect (usually it only occurs if the reflex is triggered several times.)
The mammalian diving response temporarily changes the way our body operates - and researchers speculate it may be the most powerful autonomic reflex ever encountered.
Scratching, Contagious Scratching and Avoiding ScratchersItches are one of life's little irritations, typically occurring when nerve endings in the skin are stimulated. They follow a very similar (but not identical) nerve pathway to pain signals and can be the result of dry skin, a foreign entity, damage or an underlying medical issue.
Scratching an itch is double-edged sword. It can provide a short period of relief from an itch, usually by interrupting (or outright damaging) the nerves responsible. The itch-and-scratch can also help us identify and deal with a crawling insect (or a parasite, or rash, etc.) when springing away (as if from burning yourself) wouldn't be any use.
Humans and rodents are vulnerable to social itch contagion - seeing someone else scratching can make you want to do so yourself. Humans and other animals also seem to instinctively avoid those who are scratching - one study found mice would approach a mouse who seemed to be in pain, but avoid a mouse that was scratching. These could both be instinctive ways of avoiding parasites, either by being prompted to check yourself or by keeping clear of infested people!
Post-micturition convulsion syndrome is an involuntary shiver that occurs during or after urination - and it is not widely understood. One theory is that the warm urine leaving the body (or even the removal of undergarments) causes a small but sudden drop in body temperature, leading to a normal shiver response.
Another possibility is conflicting signals in the nervous system. Many of your bodies responses are controlled by two opposing systems, the sympathetic nervous system (fight-or-flight) and the counterpart parasympathetic nervous system (rest and digest.) When the bladder is full, it signals the parasympathetic nervous system to allow urination. The process leads to a drop in blood pressure... which can cause the sympathetic nervous system to release blood-pressure increasing hormones. The conflicting signals between the two systems may be behind the shivering.
When hypothermia sets in, the body automatically contracts blood vessels in the extremities and outer surface, trapping blood near the core and keeping the vitals organs warm. This can only be maintained so long - and when hot blood returns to the extremities it can make you feel like you are burning up. This can cause someone deep in the grip of hypothermia to remove their clothing even as they freeze - something called paradoxical undressing.
The other response is known as terminal burrowing. Hypothermia victims have been found "dug in" under a bed, hidden behind furniture and so on. Researches speculate that this may be an autonomous response from the brain stem, a last ditch attempt to find a burrow for shelter.
Since terminal burrowing is often accompanied by paradoxical undressing and is typically followed by death, fatal cases of hypothermia can resemble a crime scene, with a partially-clad or naked body stashed out of sight!
- Contagious yawning
- The mammalian diving response
- Scratching, contagious scratching and avoiding scratchers
- Post-micturition convulsion syndrome
- Paradoxical undressing and terminal burrowing
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| Do you feel the urge to yawn in sympathy? (Vitaly Gariev) |
Contagious YawningHave you ever seen someone else yawn, only to be struck by an overwhelming urge to do the same? One study found that mere watching a videotape of people yawning caused nearly six times as many yawns than watching a videotape of people smiling.
This could be something to do with mirror neurons, specialist cells that activate not only when you perform an action, but when you observe someone else performing an action. If you see someone getting struck by a flying object and automatically wince in sympathy, it is the mirror neurons that are responsible. Seeing someone yawn could be activating these neurons and causing us to do the same.
One study found that yawns were more "contagious" between friends and family than between strangers. Interestingly males were more likely to be the origin of a chain of yawns, while females were more likely to yawn in response.
The Mammalian Diving Response
Humans are land based creatures - being cut off from an air supply rapidly leads to unconsciousness or death. Despite this, people can go freediving (diving without an oxygen tank) for prolonged periods of time - Budimir Šobat managed a mind-boggling 24 minutes and 37.36 seconds without taking a breath.This capability is thanks to the mammalian dive response (or reflex) which can activate when in contact with cold water or holding your breath. It isn't limited to humans and it essentially put you in "power saving mode" to prolong the oxygen you have in your body.
The response starts with bradycardia or a slowed heart rate. At the same time, blood vessels in your extremities constrict (peripheral vasoconstriction) and keep blood near your vital organs. Blood vessels around the lungs expand, promoting blood flow around the vital organs and helping the lungs resist pressure.
The spleen also reacts, releasing additional red blood cells into the bloodstream and thus increasing the amount of oxygen it can carry. This part of the response takes longer to have any effect (usually it only occurs if the reflex is triggered several times.)
The mammalian diving response temporarily changes the way our body operates - and researchers speculate it may be the most powerful autonomic reflex ever encountered.
 |
| It's not just humans... (Arjun MJ) |
Scratching an itch is double-edged sword. It can provide a short period of relief from an itch, usually by interrupting (or outright damaging) the nerves responsible. The itch-and-scratch can also help us identify and deal with a crawling insect (or a parasite, or rash, etc.) when springing away (as if from burning yourself) wouldn't be any use.
Humans and rodents are vulnerable to social itch contagion - seeing someone else scratching can make you want to do so yourself. Humans and other animals also seem to instinctively avoid those who are scratching - one study found mice would approach a mouse who seemed to be in pain, but avoid a mouse that was scratching. These could both be instinctive ways of avoiding parasites, either by being prompted to check yourself or by keeping clear of infested people!
Post-Micturition Convulsion Syndrome
Shivering is a human response to being cold. By rapidly contracting and relaxing muscles, the body generates heat - the actual "shiver" is a by-product of flexing those muscles. Shivering can occur at other times though - when you're excited, afraid... or even after urinating.Post-micturition convulsion syndrome is an involuntary shiver that occurs during or after urination - and it is not widely understood. One theory is that the warm urine leaving the body (or even the removal of undergarments) causes a small but sudden drop in body temperature, leading to a normal shiver response.
Another possibility is conflicting signals in the nervous system. Many of your bodies responses are controlled by two opposing systems, the sympathetic nervous system (fight-or-flight) and the counterpart parasympathetic nervous system (rest and digest.) When the bladder is full, it signals the parasympathetic nervous system to allow urination. The process leads to a drop in blood pressure... which can cause the sympathetic nervous system to release blood-pressure increasing hormones. The conflicting signals between the two systems may be behind the shivering.
Paradoxical Undressing and Terminal Burrowing
Hypothermia occurs when the core of the human body drops below safe operating temperatures - around 95°F or 35°C. Typical symptoms can include shivering, poor coordination and confusion... eventually leading to unconsciousness and death. There are a couple of other responses to hypothermia than can creep out in that window between shivering and mortality - namely, casting away clothing and trying to burrow.When hypothermia sets in, the body automatically contracts blood vessels in the extremities and outer surface, trapping blood near the core and keeping the vitals organs warm. This can only be maintained so long - and when hot blood returns to the extremities it can make you feel like you are burning up. This can cause someone deep in the grip of hypothermia to remove their clothing even as they freeze - something called paradoxical undressing.
The other response is known as terminal burrowing. Hypothermia victims have been found "dug in" under a bed, hidden behind furniture and so on. Researches speculate that this may be an autonomous response from the brain stem, a last ditch attempt to find a burrow for shelter.
Since terminal burrowing is often accompanied by paradoxical undressing and is typically followed by death, fatal cases of hypothermia can resemble a crime scene, with a partially-clad or naked body stashed out of sight!
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