Introduction l outer ear l the middle ear

Introduction l outer ear (外耳) l the middle ear (中耳) l inner ear (內耳) l Ear Photo l

The mammalian ear serves both for hearing and balance. It is divided into three parts: the outer ear (外耳), the middle ear (中耳) and inner ear (內耳).

It have two parts: the ear flap (pinna) and the ear canal or passage (external auditory meatus).

Ear flap (pinna) (耳殼) It is a flap of funnel-shaped skin supported by cartilage(軟骨). It is movable in some mammals such as cats and dogs. Functions: It collects the sound waves (air vibrations) into the ear. It locates the direction of a sound.

It is a passage directing the sound waves to the tympanum (ear drum). This canal is lined with hairs and wax which is secreted from wax glands. They trap the dust particles and germ to prevent them from getting into the middle ear.

Otoliths embedded in the gelatinous mass of sacculus

Middle Ear: The middle ear have 3 parts: It is ear drum/Tympanic membrane (耳鼓/膜) Ear bones and Round Window Niche: (正圓窗)

Photomicorgraphof organ of Corti on Section

Tympanum is a tough membrane present at the end of the external auditory meatus (canal). Function: It changes the sound waves into vibrations (震動). Then it transmits (傳遞) the vibrations to the ear bones in the middle ear.

The incus is attached to the malleus, and so vibrates as the malleus vibrates. The long process of the incus is also attached to the head of the stapes. Because the long process of the incus is slightly shorter than the long process (manubrium) of the malleus, incoming sound is given a slight (2. 5 d. B) boost in energy. This is referred to as the lever advantage.

The malleus is the most lateral (toward the side of the head) of the three ear bones (ossicles) in the middle ear. The long process of the malleus is attached to the inner layer of tympanic membrane. When the TM vibrates in response to sound, the malleus vibrates in concert

The stapes has a footplate and a superstructure. Its footplate is seated in the oval window, which separates the middle ear from perilymph of the inner ear. As the long process of the incus vibrates, so does the footplate of the stapes. Because the vibrating area of the tympanic membrane is larger than the area of the stapes, incoming sound is given a significant boost in energy of over 20 d. B. This is referred to as the hydraulic advantage.

The round window is located within the round window niche. The round window is the most basal end of the scala tympani, and allows release of hydraulic pressure of perilymph that is caused by vibration of the stapes within the oval window

The last energy transformation occurs here. Mechanical energy is transformed into the traveling wave pattern of the basilar membrane

Arranged in 3 planes at right angles to one another. At one end of each is a swelling known as ampulla containing sensory hairs. The canals are filled with endolymph. It is responsible for the balance of the body.

This tube "opens" with swallowing or coughing to equalize pressure between the middle ear and ambient pressure that is found in the throat. Because the eustachian tube is shorter and has a more horizontal orientation in young children, it is less likely to open. Therefore, fluid collect more often within the middle ear space of young children. See our link on Serous Otitis Media for more detail on this

The mechanism of hearing

A snail shaped structure that is the sensory organ of hearing. The vibration patterns that are initiated by vibration of the stapes footplate set up a traveling wave pattern within the cochlea. This wavelike pattern causes a shearing of the cilia of the outer and inner hair cells. This shearing causes hair cell depolarization resulting in all or none neural impulses that the brain interprets as sound

Cochlea: ( 耳蝸)

l It is leads from the inner ear to the brain. It is the transmission line from the sense organs to the central processor of the brain

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