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A right human ear.
An ear is an organ used by an animal to detect sound. The term may refer to the entire system responsible for collection and early processing of sound (the beginning of the auditory system), or merely the externally-visible part. Not all animals have ears in the same part of the body.
Spiders have hairs on their legs which are used for detecting sound.
Reptilian ears only have one bone - the malleus (see below).
The outer ear is the external portion of the ear. The visible part is called the pinna, or auricle, and functions to collect and focus sound waves. Many mammals can move the pinna in order to focus their hearing in a certain direction, in much the same way that they can turn their eyes. Humans have generally lost this ability. From the pinna, the sound pressure waves move into the ear canal , a simple tube running to the middle ear. This tube amplifies frequencies in the range 3 kHz to 12 kHz.
The middle ear includes the eardrum ( tympanum or tympanic membrane) and the ossicles, three tiny bones of the middle ear. Their Latin names are the malleusThe malleus is hammer-shaped small bone or ossicle of the middle ear which connects with the incus and is attached to the inner surface of the eardrum. It transmits the sound vibrations from the eardrum to the incus''. The malleus is unique to mammals, an, incusThe incus is the anvil-shaped small bone or ossicle in the middle ear. It connects the malleus to the stapes. The incus only exists in mammals, and is derived from a reptilian upper jaw bone, the quadrate. See also Bone terminology Terms for anatomical lo, and stapesThe stapes or stirrup is the stirrup-shaped small bone or ossicle in the middle ear which attaches the incus to the fenestra ovalis, the " oval window" which is adjacent to the vestibule of the inner ear. It is the smallest bone in the human body. The sta, but they are also referred to by their English translations: the hammer, anvil, and stirrup respectively.
Mammals are unique in having three ear bones. The incus and stapes are derived from bones of the jaw, and allow finer detection of sound.
These bones form the linkage between the tympanic membrane and the oval window that leads to the inner ear. The tympanum turns vibrations of air in the ear canal into vibrations of the ossicles. The ossicles in turn transmit the vibrations through the membrane of the oval window into the fluid of the inner ear. The ratio in area between the tympanic membrane and the oval window results in an effective amplication of approximately 14 dBThe decibel is a "dimensionless unit" (like percent) that is a measure of ratios on a logarithmic scale. Usually, it is ten times the base-10 logarithm of the ratio. It's not an SI unit, although the International Committee for Weights and Measures (BIPM), peaking at a frequency of around 1 kHz. The combined transfer functionA transfer function is a mathematical representation of the relation between the input and output of a linear time-invariant system. It is mainly used in linear system theory, signal processing, communications theory, and control theory. Signal processing of the outer ear and middle ear gives humans a peak sensitivity to frequencies between 1 kHz and 3 kHz. The tensor tympani muscle and stapedius muscle of the inner ear contract in response to loud sounds, reducing the transmission of sound to the inner ear. This is called the acoustic reflexThe acoustic reflex is an involuntary muscle contraction that occurs in the middle ear of mammals in response to loud sound stimuli. When presented with a loud sound stimulus, the stapedius and tensor tympani muscles of the ossicles contract. The stapediu.
The middle ear is hollow. If the animal moves to a high-altitude environment, or dives into the water, there will be a pressure difference between the middle ear and the outside environment. This pressure will pose a risk of bursting or otherwise damaging the tympanum if it is not relieved. This is one of the functions of the Eustachian tubes - evolutionary descendants of the gills - which connect the middle ear to the nasopharynx. The Eustachian tubes are normally pinched off at the nose end, to prevent being clogged with phlegm, but they may be opened by lowering and protruding the jaw.
The inner ear comprises both the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule.
The cochlea is a hollow organ filled with endolymph, a fluid medium that receives the sound vibrations transmitted from the air to the oval window through the ear drum and ossicles of the middle ear (see above). The cochlea is wrapped in a spiral shape and also contains the coiled basilar membrane, which resonates preferentially in different locations along its length depending on the frequency of the impinging vibrations. Sitting on top of the basilar membrane is a cellular layer known as the Organ of Corti, which is lined with hair cells - sensory cells topped with hair-like structures called stereocilia . When a region of the basilar membrane resonates, the hair cells in that region send nerve impulses to the brain, which are perceived as a sound of whatever pitch the hair cell is associated with. A very strong movement of the endolymph due to very loud noise may cause hair cells to die. This is a common cause of partial hearing loss, and the reason why anyone near guns or heavy machinery should wear earmuff s or earplugs.
The vestibular apparatus is filled with the same endolymph as the cochlea, but instead of detecting sound, it detects rotation of the head. If a line is drawn through the middle of each of the three semicircular canals, perpendicular to the plane in which the canal lies, the three lines would be perpendicular. They would represent three axes of rotation. Any rotation could be represented as three simultaneous rotations about the three axes.
The human ear has ear lobes at the bottom which are vestigial, but serve the purpose in ear piercing, usually in the case of females. The earlobe is usually formed cleft from the side of the face and hangs from the rest of the ear, but occasionally will be found looking fused and "lobeless". The helix is the outer edge of the outer ear[1].
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