The Sense of Touch

Chesterton · #1 18th August 2009, 12:00 PM

How did the sense of touch evolve?

Chesterton · #2 19th August 2009, 12:00 PM

What, nobody? I'll accept wild speculation.

Mallon · #3 20th August 2009, 11:16 AM

The evolution of mechanoreceptors isn't something I'm particularly familiar with. It certainly doesn't garner the attention that the evolution of sight does. Have you tried searching for 'mechanoreceptor evolution' on Google Scholar? I get a number of results, many of which focus on the hydra, which is a commonly used model for the evolution of the nervous system. For example:

http://www.unige.ch/~galliot/pdf/2004-Miljkovic-Biosystems.pdf

I'm not as interested in the subject as you are and I don't have the time to devote to researching it, but I'd be interested in reading any concensus you can come up with from your readings.

Sphinx777 · #4 20th August 2009, 05:17 PM

The somatosensory system is a diverse sensory system comprising the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception (body position), and nociception (pain). The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal organs, and the cardiovascular system. While touch is considered one of the five traditional senses, the impression of touch is formed from several modalities; in medicine, the colloquial term touch is usually replaced with somatic senses to better reflect the variety of mechanisms involved.

The system reacts to diverse stimuli using different receptors: thermoreceptors, mechanoreceptors and chemoreceptors. Transmission of information from the receptors passes via sensory nerves through tracts in the spinal cord and into the brain. Processing primarily occurs in the primary somatosensory area in the parietal lobe of the cerebral cortex.

At its simplest, the system works when a sensory neuron is triggered by a specific stimulus such as heat; this neuron passes to an area in the brain uniquely attributed to that area on the body—this allows the processed stimulus to be felt at the correct location. The mapping of the body surfaces in the brain is called a homunculus and is essential in the creation of a body image.

Chesterton · #5 21st August 2009, 05:29 PM

Originally Posted by Mallon

The evolution of mechanoreceptors isn't something I'm particularly familiar with. It certainly doesn't garner the attention that the evolution of sight does. Have you tried searching for 'mechanoreceptor evolution' on Google Scholar? I get a number of results, many of which focus on the hydra, which is a commonly used model for the evolution of the nervous system. For example:

http://www.unige.ch/~galliot/pdf/2004-Miljkovic-Biosystems.pdf

I'm not as interested in the subject as you are and I don't have the time to devote to researching it, but I'd be interested in reading any concensus you can come up with from your readings.

Thanks but that article is a bit too technical for me. Anyway I'm wondering about earlier life than hydra. Does anyone think bacteria have some kind of sense of touch? It seems as if they'd have to in order to live. How could a bacterium cell grab a molecule of glucose without being able to sense that it had grabbed it? And when food passes inside the cell wall something must register the food's presence. I mean I guess it's done in a chemical mode, but our touch is also, so would you say that kind of perception is tactile perception in bacteria? Do you think touch would have been the first of our senses to evolve?

Mallon · #6 24th August 2009, 10:15 AM

Originally Posted by Chesterton

How could a bacterium cell grab a molecule of glucose without being able to sense that it had grabbed it?

Chemoreception.

Chesterton · #7 25th August 2009, 05:03 PM

Originally Posted by Mallon

Chemoreception.

Chemoreception involves taste and smell though, right?. That's how it would detect food. I've smelled and tasted sulphur driving certain highways in Texas and New Jersey and the source was at least a half mile away. But I wouldn't know I had food in my mouth or in my stomach without the sense of touch.

Mallon · #8 25th August 2009, 07:01 PM

Originally Posted by Chesterton

Chemoreception involves taste and smell though, right?. That's how it would detect food. I've smelled and tasted sulphur driving certain highways in Texas and New Jersey and the source was at least a half mile away. But I wouldn't know I had food in my mouth or in my stomach without the sense of touch.

But the bacteria you asked about have neither mouths nor stomachs.