The Sense of Touch

[Chesterton]

How did the sense of touch evolve?

 

[Chesterton]

What, nobody? I'll accept wild speculation.

 

[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.

 

[Sphinx777]

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]

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]

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

Chemoreception.

 

[Chesterton]

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]

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.

 

[Chesterton]

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

Nor nerves.

 

[Mallon]

Nor nerves.

Exactly.

 

[Chesterton]

On a related note: I got some plant seeds a month ago (Pride of Barbados). I put 4 seeds under dirt, and left 4 seeds sitting on a table. The seeds surrounded by dirt have changed into plants. The seeds surrounded by air remain what they are. I guess a chemical reaction took place between the husks of the seeds in contact with dirt, which didn't take place between the husks of the seeds in contact with air.

What I can't fathom is how matter could ever come to "know" that it is in contact with something, or what it is in contact with. Chemical processes such as chemoreception could take place from here to eternity without the matter involved ever being conscious of what was happening.

I think evolutionists claim that sensation is the foundation of consciousness, but I have a hard time imagining how sensation even arose.

 

[laconicstudent]

The sense of touch operates via mechanically gated ion channels.

When someone touches you, the pressure opens a mechanically gated ion (Na+) channel, allowing sodium ions to flood the cell membrane of the neuron. This drives the the charge to +30 mV. This is the charge will propagate down the axon, and trigger the opening of voltage gated channels on neighboring dendrites, propagating the signal.

On the original neuron

The Na+ channel closes, and the Potassium (K+) gate opens, the neuron re-polarizes back to its rest state.


That's a bit rough, but that's the basic gist of it. That's not how seeds work of course. I think that the concept is that the moisture in the soil dissolves the outer layer.

And, um, senses is a good proof of evolution. A sensory improvement is an overwhelming advantage over less proficient individuals.

 

[MrJDSmith]

On a related note: I got some plant seeds a month ago (Pride of Barbados). I put 4 seeds under dirt, and left 4 seeds sitting on a table. The seeds surrounded by dirt have changed into plants. The seeds surrounded by air remain what they are. I guess a chemical reaction took place between the husks of the seeds in contact with dirt, which didn't take place between the husks of the seeds in contact with air.

What I can't fathom is how matter could ever come to "know" that it is in contact with something, or what it is in contact with. Chemical processes such as chemoreception could take place from here to eternity without the matter involved ever being conscious of what was happening.

I think evolutionists claim that sensation is the foundation of consciousness, but I have a hard time imagining how sensation even arose.

Did you water the seeds on the table ?

 

[laconicstudent]

Did you water the seeds on the table ?

Of course, watering them would have been pointless, since sitting on the table they wouldn't have had anything to metabolize, not being planted.

 

[Chesterton]

I didn't water the seeds in the dirt either. I think there is usually moisture in air as well as in dirt.

I appreciate your explanation, but what you describe seems very chemical/physical in nature, and could be analogous to operating a gas combustion engine. What I wish I understood, is how these physical processes could lead to "knowing" that these physical processes were taking place. It seems one has nothing to do with the other.

 

[Mallon]

Have you tried asking a biologist that works in this area about your question, Chesterton? If you're genuinely interested in the question, I'm sure someone with the relevant knowledge would be happy to provide an answer.

 

[laconicstudent]

I didn't water the seeds in the dirt either. I think there is usually moisture in air as well as in dirt.

Yes, but there is vastly more moisture in the soil, along with necessary nutrients.

 

[Chesterton]

Have you tried asking a biologist that works in this area about your question, Chesterton? If you're genuinely interested in the question, I'm sure someone with the relevant knowledge would be happy to provide an answer.

Of course I am not genuinely interested in the question because I already know the answer; I'm just testing you guys here. And not answering equals "fail".