Earth Science: Human – Sensory Organs – The Ear
Animals often require good hearing for hunting or defense behavior. Humans mostly use hearing for communication among each other.
The human ear can be divided into three sections: the outer, middle, and inner ear. The outer ear consists of the auricle, the auditory canal lined with fine hairs and the tympanic membrane, or eardrum, which separates the outer ear from the middle ear. Specialized glands in the auditory canal produce earwax to protect the ear from dirt and dust.
The auditory ossicles-the malleus (hammer), incus (anvil), and stapes (stirrup) are located inside the middle ear and are the smallest bones in the hu- man body. They connect to each other and to the tympanic membrane. The eustachian tube runs between the middle ear and the throat. Here, pressure differences between the middle ear and the atmosphere are equalized.
The inner ear is filled with lymph and contains the cochlea, the actual hearing organ, which contains auditory sensory cells and semicircular canals. These form the vestibular apparatus, or balance system. When sound waves reach the ear, they cause the tympanic membrane to vibrate.
The auditory ossicles amplify the sound waves and transfer them to the inner ear via the elliptical window, a membrane between the middle and inner ear. The vibrations are transferred to the liquid in-side and are then registered by the tiny sensory hairs of the cochlea.
Sense of balance
The vestibular organs responsible for balance are filled with liquid and are located in the inner ear. The three semicircular canals, and the utricle and saccule of the vestibule, together respond to movement and position.
The semicircular canals and vestibule have sensory hair cells embedded into a gelatinous layer with tiny calcareous ear crystals (otoconia). During movement, the gelatinous mass shifts, bending the hair cells.
The semicircular canals simultaneously register the rotational movement of the head in three dimensions. The saccule and utricle register linear changes in position within space. The combined sense of rotation and position results in the sense of balance.
HEARING LOSS DUE TO NOISE
The human ear is very sensitive to excessive noise. Loss of hearing may already occur through a continuous noise impact of 85 decibels (dB). Traffic creates a noise level of about 80 dB and a jackhammer creates a noise level of about 110 dB.
Some music concerts subject visitors to a sound level of up to 120 dB Both short-term high noise impacts and long-term impacts result in loss of hearing.
BASICS
PERFECT PITCH or absolute pitch is the ability to recognize tones solely by their sound. Statistics show that only one in 10,000 people have this ability.