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How does the body know what to sense?

  1. Aug 10, 2018 #1
    Sense perception, weather it is smelling,hearing, tasting, etc, how does the body know what to sense? For example, hot and cold, how does the body know what is hot and what is cold? How does it know the difference bewteen hot and cold in order to activate those specific sensory receptors for hot and receptors for cold?

    Another example is how does the tongue sense hot of a chemical instead of sensing cold? What mechanism separates the sensation from hot and cold so the tongue knows that chilli peppers are hot and not cold? Is there some type of information present in chemicals that tells the tongue it is either hot or cold?

    I hope my question is clear, I am trying to understand how the body knows when to sense a specific sensation as opposed to another sensation. How can it tell the difference bewteen something hot and cold? (for example).

    We all know sensation occurs via sensory neurons, but how does sensation sense one sense instead of another like hot and cold?I

    I think there must be some sort of information or mechanism in sensed things that allow the body to read it and sense that instead of another sense , what is this information or ability?

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  3. Aug 10, 2018 #2


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  4. Aug 10, 2018 #3


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    The sensory elements in your body are available to pick up sensations all the time. You probably don't notice it usually.
    Different sensory organs/nerves are made so that they respond to certain conditions and transmit neural impulses to other parts of the nervous system where they can be pondered or acted upon.
    This is like a thermometer or a barometer. Always sensing, not always noticed.
    Signals from different sensory modalities (like sight, hearing, ...) are (normally) conveyed by different nerves to different areas or the brain, so the signals are not mixed up.

    There are different visual pigments for detecting different wavelengths of light.
    There are many different hair cells that detect sound in your ear. Their sensitivity to a particular frequency varies by where they sit in the cochlea of the ear. Their position in the cochlea determines which frequency they vibrate to, not the cells themselves.
    There are something like 5 or 6 different kinds of taste receptors that are specific kinds of chemicals.
    There are however many, many different kinds of olfactory (smell) receptors that are specific for different chemicals.
    Normally smell and taste sensations get combined in some way to give complex sensations that can be not so easy to describe.
    There are a lot of different skin receptors for different kinds of sensory input. You might want to look it up on wikipedia (I believe hot and cold have different receptors). The structure, functioning, and location of the receptors will determine what they respond to.

    There are also a lot of other sensory receptors you probably have never heard of for proprioceptive sensing of body position, tendon tension, muscle contraction, blood pressure, blood pH, etc.).
    Some animals sense electrical fields (with hair cells).
  5. Aug 10, 2018 #4
    Thanks! So basically each sensed object only excites a specific type of sensory receptor is what you are saying. But I don't think this answers my question. The tongue has 5 or 6 different receptors as you and modern sciences says, but that is not what I am asking. Let's use the tongue here to simplify my question, these taste receptors fire by chemicals as we all know, but what is it about these chemicals that allows them to excite ONLY a certain receptor and not another one? I know you are saying the different receptors RESPOND to these chemicals tastes, but I am asking how does the body DIFFERENTIATE these chemicals so it "KNOWS" a certain chemical triggers a certain taste receptor? Eating something sweet triggers a sweet receptor, hence we taste sweetness, how does the tounge know what chemicals are sweet and what ones are not? There are millions of chemicals yet we have 5 or 6 taste receptors that divides all of these millions of chemicals into a group of 5 or 6 and the combination of these 5 or 6 lead to complex flavors.

    But what is the process of the tongue selecting a taste for a chemical instead of another taste? How does it know that sugar is sweet and not salty? What information is in sugar that makes it so it fires a sweet receptor and not a salty one? And how does the tounge know that information is for sweet and not salty?
  6. Aug 10, 2018 #5


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    In the case of taste, the molecules being tasted are just whatever kind of molecule they are.
    Their presence is sensed when they active the receptor cells in a taste bud that is capable of tasting them.
    Molecularly, this is done when the molecules being tasted bind (stick) to a protein in at the surface of the taste receptor cell.
    The protein (also called a receptor, but not a cell, just a protein) acts as described below.

    From wikipedia:
    The specificity of reacting to a particular chemical by the receptor protein (and therefore by the receptor cell) depends upon the receptor and other systems associated with its functioning, which have been evolved for that function over millions of years.

    By this point in time (after much evolution) the various specifics of sensory sensitivities are an already established fact and passed on through genetics to each new generation.

    There are also other possible sensory inputs that are not sensed by people, but in theory could be (like UV light being described in a SciFi thread at this time). Bees can see UV, we can't. We do not have the proper receptor proteins to detect those wavelengths.
    The chemical or wavelength of light doesn't know or do anything to get detected or not detected.
    The tongue (and other sense organs) can achieve what it can because the species has evolved the proteins and associated sensory systems necessary to do that job.

    The actual taste of sweet or whatever is produced in the brain by brain mechanisms that are not understood to produce the psychological sensation of the taste. It is not in any way dependent upon the molecule being tasted.
    A fairly common visual example of this is color blindness, where someone with the proper mutation might see green instead of the red "normal" people see.

    There is a lot of complexity in there. You might want to do some googling and reading of the details.
  7. Aug 11, 2018 #6


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    For a way too simplified example, consider ordinary baking soda. Put a little baking soda in a dish and add a few drops of water, Not much will happen, maybe a few tiny bubbles. Now add some vinegar. It starts bubbling rather actively. The baking soda effectively 'senses' vinegar, where the sensing signal is the gas emitted.

    You body does essentially the same thing, the receptor protein on the sensory cells act like the baking soda above; when a substance reacts with the receptor protein it triggers another chemical reaction, etc which eventually triggers a nerve to send a signal to the brain.

    Different sensory cells have different receptor proteins to react with different substance.

    Hope this helps.
  8. Aug 16, 2018 #7
    Just for fun and maybe for some edifying food for thought (this is great with young kids) try this experiment:

    Using 3 mixing bowls (each large enough to hold a hand immersed; one large enough for 2 hands),
    fill one bowl halfway with hot (not scalding; just hot) water,
    one with cold (not freezing; just cold) water,
    and the third (large enough for both hands) with lukewarm water;
    put one hand in the cold water bowl, and the other hand in the hot water bowl,
    for about 30 seconds or so,
    then put both hands in the lukewarm bowl;
    observe that the cold-water hand will feel the lukewarm water as hot or warm,
    while the hot-water hand will feel the same lukewarm water as cold or cool --
    it can be amusing when the hands report two different temperature sensations,
    regarding what the eyes see to be the same water.

    This illustrates the idea that hot and cold,
    when both are within a reasonable range of lukewarm,
    are experienced more with reference to recent comparative bias,
    than with reference solely to an external temperature standard.
    Last edited: Aug 16, 2018
  9. Aug 20, 2018 #8
    Its also worth considering that we also combine sensory information, taste for instance often involves sight and smell. We can also get information about the intensity or strength of a stimulus by having a collection of sensory neurones set to detect different levels of stimulation or nerves firing at different rates.
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