Yay! Awesome thread, I can be a smart-ass here as one of my lectures was about our senses.
First of all, whether we have more than 5 senses or not depends mostly on the definition of
sense. Usually, all receptors that are near to each other spatially are seen to belong to one certain sense (e.g. all receptors in the eyes belong to the sense
sight).
This approach seems to be logical but is disputable when taking into account neuroscience's findings.
Feeling pain (
nociception) is believed to belong to the touch sense (
somatosensation). That makes sense because the relevant receptors for feeling pain (Aδ fibers and C fibers) are located near to the receptors that are responsible for what we experience as touch sense (Ruffini's end organs, Meissner's corpuscles, Pacinian corpuscles, Merkel's discs).
However, one can argue that nociception and somatosensation are distinct senses as they involve different receptor cells and, more importantly, their processing involves different brain areas (
nociception is mostly processed in the periaquaductal grey matter, the nucleus raphe magnus and the nociception inhibitory neurons within the dorsal horns of the spinal cord whereas
somatosensation involves the dorsal column nuclei, the thalamus the ventrobasal complex).
Analogously, our ability to feel or at least estimate the temperature of external objects (
thermoception) is believed to be distinct from our touch sense.
So, what about balance and acceleration which allow an organism to sense body movement, direction, and acceleration, and to attain and maintain postural equilibrium and balance (
vestibular sense)? Is it a distinct sense?
Well, the relevant receptors are located in the inner ear. But it wouldn't be a good idea to assume that it belongs to the hearing sense, would it?
So... There might be more than 5 senses. It just depends on how you define
sense.
Ok, enough of that freak stuff for today.
)
(PS: I'm not quite sure whether my English was understandable... I hope you got the point
)
