Other Senses

Sounds can easily be localized in space. This is because there are binaural and monaural cues to sound localization. Binaural cues require two ears. Monaural cues refer to the way the auricle can detect sounds that are coming from above, below, in front or behind the person. Binaural cues depend on differences in the way sounds are detected by the two tympanic membranes. Sounds from each ear are heard at slightly different times and at different intensities so as to be able to localize sound.

Hearing loss or deafness can be congenital, in which the person has it from birth, or conductive, which usually happens because of noise exposure, age, or exposure to certain toxins or diseases, such as measles or mumps. Hearing aids can help this. With sensorineural hearing loss, the problem is within the signaling of nerve cells from the inner ear to the brain. The only treatment for this is cochlear implants, which stimulate the auditory nerve.

OTHER SENSES

There are two chemical senses. These are taste or gustation and smell or olfaction. These senses work together in order to describe the properties of the food a person eats. There are probably six different basic tastes. These include the categories of salty, sour, bitter, and sweet, as well as the taste called umami, which detects the amount of monosodium glutamate in food. The taste sensation of fatty is also suggested as a probable separate taste category.

The taste of something is detected by taste buds, which stick out from the surface of the tongue. These taste buds detect chemical changes in the saliva and transport the information to the brain through different cranial nerves. The parts of the brain associated with taste are the thalamus, the limbic system, and the medulla. There is also a gustatory cortex found between the temporal and frontal lobe. Figure 17 shows the anatomy of these taste buds:

Figure 17.

The sense of smell is also chemical in nature. There are numerous olfactory receptor cells on top of the nasal cavity that pick up chemicals from the air that are dissolved in the nasal mucous membrane. The signal gets transmitted directly to the olfactory bulb in the frontal lobe. This information goes partially to the limbic system and onto the primary olfactory cortex, which is located near the gustatory cortex. Figure 18 shows the olfactory system in the nasal cavity:

Figure 18.

Olfaction is different among the different species. Dogs especially have a strong sense of smell compared to humans. Pheromones are chemical messengers that are sent from one gender in a species to another as part of sexual attraction.

There are several sensations associated with the skin, which contains a number of different receptors that detect different sensations. Meissner s corpuscles are those that respond to low-frequency vibrations and pressure. Pacinian corpuscles detect highfrequency vibrations and brief episodes of pressure. Merkel s disks detect light pressure and Ruffini corpuscles detect the sensation of stretch. Figure 19 shows the different receptors:

Figure 19.