ear

Description

Sound is a form of energy that moves through air, water, and other matter, in waves of  pressure. Sound is the means of auditory communication. The ear changes sound pressure waves from the outside world into a signal of nerve impulses sent to the brain.

Although the ear is the vertebrate sense organ that recognizes sound, it is the brain and central nervous system that "hears".

The ear consists of three basic parts

-    The outer ear.

-    The middle ear .

-    The inner ear.

Each part of the ear serves a specific purpose in the task of detecting and interpreting sound.
The outer ear serves to collect and channel sound to the middle ear. That sound pressure is amplified through the middle portion which serves to transform these vibrations into a compressed wave in the inner ear. The inner ear serves to transform the energy of a compressed wave within the inner ear fluid into nerve impulses that can be transmitted to the brain.

The outer ear consists of an earflap and an approximately 2-cm long ear canal. The earflap provides protection for the middle ear in order to prevent damage to the eardrum. Because of the length of the ear canal, it is capable of amplifying sounds with frequencies of approximately 3000 Hz. the sound is still in the form of a pressure wave, with an alternating pattern of high and low pressure regions.

The middle ear is an air-filled cavity that consists of an eardrum and three tiny, interconnected bones - the hammer, anvil, and stirrup. The eardrum is a very durable and tightly stretched membrane that vibrates as the incoming pressure waves reach it. ( the energy of the mechanical wave becomes converted into vibrations of the inner bone structure of the ear).

The inner ear is hollow, embedded in the temporal bone, the densest bone of the body. It consists of a cochlea, the semicircular canals, and the auditory nerve. The cochlea and the semicircular canals are filled with a water-like fluid. The cochlea is a snail-shaped organ that would stretch to approximately 3 cm. In addition to being filled with fluid, the inner surface of the cochlea is lined with over 20 000 hair-like nerve cells that perform one of the most critical roles in our ability to hear.  The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are mechanoreceptors that release a chemical neurotransmitter when stimulated. Sound waves moving through fluid push the filaments; if the filaments bend over enough it causes the hair cells to fire. In this way sound waves are transformed into nerve impulses.
Each hair cell has a natural sensitivity to a particular frequency of vibration. When the frequency of the compressional wave matches the natural frequency of the nerve cell, that nerve cell will resonate with a larger amplitude of vibration. This increased vibrational amplitude induces the cell to release an electrical impulse that passes along the auditory nerve towards the brain.