The lecture examined sensory perception in the nervous system. The sensory systems that were examined were the chemical senses, which include both taste and smell. The sense of taste is produced on the tongue. The surface of the tongue has papillae, which consists of taste buds, and the taste buds consist of taste cells. There are different types of taste cells for the different types of basic tastes (salt, sour, bitter, sweet, umami). While there are a quite small amount of taste receptor, there are thousands of different olfactory receptors, and what one usually experiences as a taste is the combination of taste and smell. 

Retina is a multilayer structure with different cell types, such  as photoreceptors, bipolar cells and ganglion cells. Photoreceptors are the cells that react to light by changing the configuration of a retinal molecule. Photoreceptors then signal to bipolar cells, which convey information to ganglion cells. Ganglion cells form receptive fields of the visual space. Receptive fields are center-surround structures, where the center portion reacts either to a spot of light or darkness and the surrounding region reacts to darkness if the center reacts to light and to light if the center reacts to darkness. 

In the exercise session we discussed how senses are adapted to different situations. For example, what is the difference between the human eye and octopus eye. It is clear that both structures are developed to sense electromagnetic stimuli but how relevant is a good sight and colour separation in the depths of the sea.  All mammals have the same set of senses but their sensitivity is based on the habitat. For example, hawks have a very good vision because they have to spot their prey from far above and wolves have a good sense of smell for recognizing their pack and avoiding possible threats.

In some cases a sensory organs do not operate well or an organ has damaged so bad that it can not transfer stimuli to the brain. For ill-working organs we have found different solutions like eyeglasses to fix bad sight or hearing aid to allow us to hear clearly again, but if the sensory organ has failed completely it is very hard or impossible to repair.

Posted by Timo Tommila

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