As a normal hearing person, hearing is considered a simple matter of course with which nature has endowed us. But it represents a complicated process that comes about in a finely constructed and sensitive sensory organ.
Structure and function of hearing and ear.
Schematic diagram showing the anatomy of hearing and the ear. Click to enlarge. What we refer to in common parlance as the ear is just the outer pinna, which has no practical significance for hearing itself, at least in humans, other than to catch and focus sound and noise more directionally, much like a satellite dish. It attaches to the auditory canal, which leads with a slight bend into the interior of the skull and ends at a depth of about 3.5 cm at a thin membrane, the tympanic membrane. Behind the tympanic membrane lies the middle ear, which is normally filled with air and communicates with the nasopharynx through the tubular eustachian tube. In this middle ear space, which is about 1 cc in size, lie the ossicles, the smallest bones in our body in general. According to a finely constructed system of levers, these are articulated together and form the ossicular chain. The first, the malleus, is attached by its handle to the inside of the eardrum. With its head pointing inward, it rests in a trough-shaped depression in the second bone, the incus. This then touches with its other end the stirrup, the third bone of the chain, which is exactly like a real stirrup in its shape. The sounds of our environment, e.g. spoken words or music, physically represent air vibrations that strike the eardrum as sound waves from the outside world through the auditory canal and cause it to resonate. The absorbed vibrations are transmitted from the malleus via the ossicular chain to the footplate of the stapes. The actual hearing organ, the so-called inner ear, lies deep in the skull and is embedded in the hardest of our bones, in the labyrinth capsule of the temporal bone. The outer wall of this bone is also the inner wall of the middle ear. There are two small windows in it. In the larger oval window, the stapes footplate is vibrationally clamped, while the smaller round window is closed by an elastic membrane. The inner ear, surrounded by bone, is filled with lymphatic fluid and consists of two parts, the arcuate system as our organ of equilibrium and the cochlea, which contains the actual organ of hearing. Inside it, a spiral duct runs around a bony spindle-shaped axis, divided into three continuous channels by two thin membranes. Up to this point, the whole process is a purely physical one, by means of which the sound waves of the outside world are mechanically conducted first through the ossicles and then in the fluid of the inner ear to the sensory cells. This is called sound conduction, and any damage or disturbance in the course of this complicated system means an interruption or weakening of the sound supply to the nervous receiving apparatus. The stimulation of the sensory cells caused by the received vibrations is transmitted from here via the auditory nerve to the cerebral cortex, and only there does it reach the sensory perception as auditory sensation. The physical vibration processes of the environment then enter our consciousness as tones, sounds or noises.
Hearing tones, sounds and words
Schematic diagram showing the anatomy of the auditory pathway, Auditory System. Click to enlarge. The human auditory organ is capable of picking up both very low and very high-pitched sounds. Our so-called auditory field thus has a quite considerable frequency range of about 20 to 20,000 double oscillations per second (hertz). Only when hearing damage also occurs in the range of these speech frequencies is the person concerned hard of hearing in the narrower sense, as he now has difficulty conversing with his fellow human beings. It is different for hearing music. The tones of orchestral instruments are approximately between 64 and 10,000 hertz, so that sensory damage in this extended frequency range will impair the full enjoyment of, for example, a symphony concert. However, each individual tone is not only perceived, but is also perceived in a graded manner according to its loudness. One only gets a proper idea of this fact when one considers that the sensitivity of our hearing extends over an enormous volume range.For example, we are able to perceive the very soft buzzing of an insect and to hear the booming thunder of a waterfall.
Diseases and disorders of hearing
With such a complicated process, it is natural that very sensitive reactions to even small disturbances can set in and impair auditory function. Now, since intact hearing is the prerequisite for learning and understanding language, it represents the most important factor for the undisturbed relationship of human beings with their fellow human beings and their environment. Disturbed relationships in this respect can have far-reaching, often fate-deciding effects on a person’s environmental relationships in society, at work, and even in the smallest circle of the closest family. Therefore, it is a high social task and duty to help the hearing impaired as much as possible so that he can cope more easily with all the difficulties and hardships of his suffering, which life imposes on him anew every day. In particular, however, it must be an essential task of children’s and youth education to teach hearing-impaired children in special schools so well that they can take a full place in society as joyful and creative people, according to their abilities.