The cilia are  sensory receptors able to detect the chemicals floating in the air. Located in the olfactory epithelium,  the cilia are the extensions of the receptor neurons in the olfactory bulb (there are over 10 per neuron). The nerve signal created by these receptors is then widely distributed among other brain areas via the olfactory nerve (olfactory tract).
Because of direct connections between the primary olfactory cortex and the limbic system (a primitive part of the brain that includes the amygdala and the hippocampus), olfaction has a strong role in instantaneously recalling memory in comparison with the other senses. The theory has also been forwarded that these connections result in the sense of smell having a powerful role in emotion.

To see, enough light must go into the eye.
In general, light propagates from the source to the object and then from the object to the eye. The objects that are seen in this way are secondary sources. In contrast, the light bulb that illuminates the scene is a primary source.

Sound waves travel through the air as pressure vibrations of varying intensity.
Your ear senses those fluctuations and translates them into electrical impulses that your brain can interpret.

The parts of the eye and the accommodation principle.

Eye anatomy.