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Olfactory system anosmia blunt force trauma to the

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Olfactory System: AnosmiaBlunt force trauma to the face, such as that common in many car accidents, can lead to the loss of the olfactorynerve, and subsequently, loss of the sense of smell. This condition is known asanosmia. When the frontal lobe ofthe brain moves relative to the ethmoid bone, the olfactory tract axons may be sheared apart. Professional fightersoften experience anosmia because of repeated trauma to face and head. In addition, certain pharmaceuticals, such asantibiotics, can cause anosmia by killing all the olfactory neurons at once. If no axons are in place within the olfactorynerve, then the axons from newly formed olfactory neurons have no guide to lead them to their connections withinthe olfactory bulb. There are temporary causes of anosmia, as well, such as those caused by inflammatory responsesrelated to respiratory infections or allergies.Loss of the sense of smell can result in food tasting bland. A person with an impaired sense of smell may requireadditional spice and seasoning levels for food to be tasted. Anosmia may also be related to some presentations of milddepression, because the loss of enjoyment of food may lead to a general sense of despair.The ability of olfactory neurons to replace themselves decreases with age, leading to age-related anosmia. This explainswhy some elderly people salt their food more than younger people do. However, this increased sodium intake canincrease blood volume and blood pressure, increasing the risk of cardiovascular diseases in the elderly.Audition (Hearing)Hearing, oraudition, is the transduction of sound waves into a neural signal that is made possible by the structures ofthe ear (Figure 14.5). The large, fleshy structure on the lateral aspect of the head is known as theauricle. Some sourceswill also refer to this structure as the pinna, though that term is more appropriate for a structure that can be moved, suchas the external ear of a cat. The C-shaped curves of the auricle direct sound waves toward the auditory canal. The canalenters the skull through the external auditory meatus of the temporal bone. At the end of the auditory canal is thetympanicmembrane, or ear drum, which vibrates after it is struck by sound waves. The auricle, ear canal, and tympanic membraneare often referred to as theexternal ear. Themiddle earconsists of a space spanned by three small bones called theossicles. The three ossicles are themalleus,incus, andstapes, which are Latin names that roughly translate to hammer,anvil, and stirrup. The malleus is attached to the tympanic membrane and articulates with the incus. The incus, in turn,articulates with the stapes. The stapes is then attached to theinner ear, where the sound waves will be transduced into aneural signal. The middle ear is connected to the pharynx through the Eustachian tube, which helps equilibrate air pressureacross the tympanic membrane. The tube is normally closed but will pop open when the muscles of the pharynx contractduring swallowing or yawning.

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