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An example of a material in which absorption can observed: sound absorbing foam, also known as acoustic foam. In acoustics, absorption refers to the process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy.
The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear.The adult human ear canal extends from the auricle to the eardrum and is about 2.5 centimetres (1 in) in length and 0.7 centimetres (0.3 in) in diameter.
Foam earplugs, mainly made from either polyvinyl chloride (PVC) or polyurethane (PU) (memory foam), which are compressed (rolled) and put into the ear canal, where they expand to plug it. Wax earplugs, which are rolled into a ball and carefully molded to fit over the external portion of the ear canal.
The auricular branch of the vagus nerve is often termed the Alderman's nerve ("a reference to the old Aldermen of the City of London and their practice of using rosewater bowls at ceremonial banquets, where attendees were encouraged to place a napkin moistened with rosewater behind their ears in the belief that this would aid digestion") or Arnold's nerve (an eponym for Friedrich Arnold).
The folds of cartilage surrounding the ear canal are called the auricle. Sound waves are reflected and attenuated when they hit the auricle, and these changes provide additional information that will help the brain determine the sound direction. The sound waves enter the auditory canal, a deceptively simple tube.
The inner ear has two parts: the bony labyrinth and the membranous labyrinth. The membranous labyrinth is contained within the bony labyrinth, and within the membranous labyrinth is a fluid called endolymph. Between the outer wall of the membranous labyrinth and the wall of the bony labyrinth is the location of perilymph.
The eardrum is an airtight membrane, and when sound waves arrive there, they cause it to vibrate following the waveform of the sound. Cerumen (ear wax) is produced by ceruminous and sebaceous glands in the skin of the human ear canal, protecting the ear canal and tympanic membrane from physical damage and microbial invasion. [5]
Perilymph and endolymph have unique ionic compositions suited to their functions in regulating electrochemical impulses of hair cells necessary for hearing. The electric potential of endolymph is ~80-90 mV more positive than perilymph due to a higher concentration of potassium cations (K +) in endolymph and higher sodium (Na +) in perilymph. [4]