What does it mean to have pain receptors? How do we feel pain - do insects feel the same?

This is a short article about animal and human pain, basic neurobiology and ethical implications of the possession of pain receptors.

Humans are inherently compassionate. A lot of humans choose not to eat meat for ethical reasons, and a lot more actively choose to ignore the ethical issues which come along with eating meat.

To avoid sounding like a PETA activist we will not go into the details of the suffering we humans inflict on other species. Whether you personally eat meat or not, we can agree that the human race actively enslaves, imprisons and kills millions of feeling, thinking animals. We all heard somewhere that pigs are actually very intelligent animals, that is not just talk but a lot of academic research suggests that pigs possess complex ethological traits similar, but not identical, to dogs and chimpanzees. So all the vegetarians and vegans do have a academically backed and valid point.

The question here is, if we eat insects, are we causing the same suffering to even more individual creatures? We need to eat a lot more single insects to reach our nutritional goals than individual chickens.

But first, how do we humans feel pain?
Let us take the example of burning your hand on a hot plate. First, there is the tissue damage on your hand (noxious stimuli = actual or potential tissue damaging event). This is registered by microscopic small pain receptors in your skin called nociceptors. The nociceptors are part of nerves which are connected to your spinal cord by long nerve fibres. When you burn your hand and the pain receptor is activated, it sends an electrical signal up the nerve. This is not “pain” yet, it is just an electrical signal which goes trough your nerves, spinal cord and up to your brain. In to the Thalamus to be exact, which acts like a relay station for different nerve signals. From there the message gets passed along to the somatosensory cortex (responsible for physical sensation – oh this is hot and painful), the frontal cortex (in charge of thinking - I need to pull my hand away), and the limbic system (linked to emotions – that was stupid, I do not want to feel this again).

Keep in mind, I am not a neurobiologist, so this is only a very rough explanation.
We can already see that there are different components to pain. The noxious stimuli is perceived in various regions in the brain. Human pain is physical and emotional, affects our thinking and our movements. So pain is not = pain. A hot plate can hurt, but so can a heartbreak or a tough work out in the gym. It is certainly more than just physical stimulus.
So is human pain discomfort on various levels?

The international Association for the study of pain defines it as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage”

Now to the original question, do insects feel “unpleasant sensory and emotional experiences”?
Insects have a nervous system than differs from humans, research suggests although they have nociceptors, they lack the neurological pathways to transform physical pain into emotional pain. They hurt but are not suffering?

We humans learn from pain, (I should not touch a hot plate again, I will hurt my hand), insects do not seem to change their behaviours. (ever seen a fly flying into the window countless times, a moth almost, and eventually, burning on a hot lamp).

Insects also do not show pain responses, just because they have lost a leg does not mean they stop crawling around.

This would suggest insects do have pain receptors, but not a capacity to react or learn from pain. So do insects feel pain? Do they feel pain but do not “know” it? Is it more ethical to kill (and eat) an insect because it feels but does not react to pain? Is it different from killing and eating a chicken or cow?