Introducing the brain: interpreting somatosensory input (Introduction)

by David Turell , Monday, October 04, 2021, 19:38 (1144 days ago) @ David Turell

Requires specialized receptors:

https://www.quantamagazine.org/medicine-nobel-prize-goes-for-temperature-and-touch-disc...

"We often talk about having five senses: sight, hearing, smell, taste and touch. But as a category of sensation, touch is so broad that it really should be treated as more than one. Tactile perception is just one component of the body and brain’s somatosensory system, which also includes the perception of temperature, pain, body position and self-movement.

"The ability to feel hot and cold, to recognize an object by touch alone, to respond to pain, to balance on a beam — all fall under the umbrella of somatosensation. The somatosensory system also helps to regulate many key internal physiological processes, including blood pressure, respiration, urination and bone remodeling.

***

"What makes the somatosensory system even more complex is that it needs to discriminate between sensations that are graded in intensity but sometimes sharply distinguished in their effect: Gentle warmth can build into searing heat, and what starts as a welcome embrace can become crushing pressure. Moreover, those thresholds can change depending on context: A light touch can feel uncomfortable or painful if one has a sunburn, and our experience of the same stimulus can similarly shift in different social settings. The somatosensory system has to integrate a wide range of different signals to correctly interpret what’s going on and how to respond.

"As Julius’ and Patapoutian’s work has shown, somatosensory receptors are ion channels. When stimulated — by some degree of temperature or physical force, or by a chemical compound — the channels open and allow charged particles to flow into a nerve cell, which in turn allows the cell to pass along somatosensory information in the form of electrical signals.

"Even within one category of somatosensation, different receptors respond to different sets of stimuli. There are distinct receptors for specific ranges of temperature; receptors for sharp pain versus a dull ache; for a gentle touch or a rapid vibration or a firm pressure. Still others are tuned to how muscles or tendons might be contracting or stretching.

***

"While the various types of somatosensory information are all vital for day-to-day activity and survival, their involvement in pain stands out in importance. It’s the job of pain to attract immediate attention and alert us to potential dangers, both external and internal. Free nerve endings respond to chemicals released by inflamed or damaged tissue, or to extreme levels of mechanical force that we perceive as painful. Different receptors distinguish between kinds of pain: sharp or pinching, dull or aching."

Comment: How does a very necessary system like this develop if evolution is just chance mutations? It must be designed as part of our sensory protection. In practice I told my patients pain was a waring friend. Of course chronic pain must be treated.