March 29, 2022
Written by: Lindsay Ejoh
Imagine you are in the emergency room for the worst abdominal pain you’ve ever felt- but you can’t tell where exactly it’s coming from or what is causing it. Have you ever wondered why it is so easy to tell what exact part of your skin is being touched, but so difficult to tell which abdominal organ is swollen or inflamed?
Sensory neurons, nerve cells that communicate information about the environment to the central nervous system, have specialized receptors at their endings1. For example, some sensory neurons have receptors in the skin that are selectively activated by touch, stretch, vibrations, temperature, pain, or itch. When activated, the sensory neurons send electrical signals to other neurons in the spinal cord, which then transmit the information about the external world to the brain. This process is detailed further in this Penn NeuroKnow article.
Similarly, sensory neurons have receptor endings at blood vessels and internal organs like the heart, lungs, pancreas, intestines, etc to relay similar information about our internal environment to the brain for processing and action2. The sensory neurons in areas like the fingertips and palms have much denser nerve endings, and therefore many more receptors, in the skin than those in the abdomen. This leads to us having extreme specificity to detect where exactly the hands are being touched, but difficulty specifying the exact location of signals from within the abdomen3.
Though in some cases it could be useful to be able to specify exactly where our abdominal discomfort is coming from, it may be a good thing that we are not too acutely aware of our internal state. The brain receives a lot of information from the environment, especially while we are awake, and must choose what it pays attention to and acts on4. Receiving detailed information about the state of our internal organs might be more distracting than helpful. Imagine you are on a first date in a crowded restaurant. While you and your date chat, your brain must filter out all the other sensory cues in the room and in your body, including the smell of the food, the feel of your clothes on your skin, or maybe even your sweaty palms, for you to be able to focus and carry on the conversation. A similar principle holds for how we might not need to be acutely aware of all our organs, their placement, and every time they shift or swell. That might make for a rather uncomfortable state of being!
Though inner sensations are not always part of our conscious awareness, the brain still senses changes in our inner environment, and produces whatever hormonal or behavioral changes are necessary for us to maintain a balanced and healthy internal state. These may result in other physiological changes or even changes in our mood or behavior5. As we live out our daily lives, our brains are doing a lot of work to keep our bodies stable and healthy, whether we are aware of it all or not.
If you would like to learn more, check out Lindsay Ejoh’s TikTok video on the topic!
- Abraira, V. E., & Ginty, D. D. (2013). The sensory neurons of touch. Neuron, 79(4), 618–639. https://doi.org/10.1016/j.neuron.2013.07.051
- Kirkup, A. J., Brunsden, A. M., & Grundy, D. (2001). I. Receptors on visceral afferents. American Journal of Physiology-Gastrointestinal and Liver Physiology, 280(5). https://doi.org/10.1152/ajpgi.2001.280.5.g787
- Sengupta J. N. (2009). Visceral pain: the neurophysiological mechanism. Handbook of experimental pharmacology, (194), 31–74. https://doi.org/10.1007/978-3-540-79090-7_2
- Kepelewicz, J. (n.d.). To pay attention, the brain uses filters, not a spotlight. Sentiers. Retrieved March 21, 2022, from https://sentiers.media/notes/to-pay-attention-the-brain-uses-filters-not-a-spotlight/
- Critchley, H. D., & Garfinkel, S. N. (2017). Interoception and emotion. Current opinion in psychology, 17, 7–14. https://doi.org/10.1016/j.copsyc.2017.04.020