Hearing

HEARING IS NOT SIMPLE!!

Hearing is the process which the ear transforms sound vibrations in the external environment into nerve impulses that are conveyed to the brain, where they are interpreted as sounds.

Sounds are produced when vibrating objects, such as the plucked string of a guitar, produce pressure pulses of vibrating air molecules, better known as sound waves.

The ear can distinguish different subjective aspects of a sound, such as its loudness and pitch by detecting and analyzing different physical characteristics of the waves.

Sound waves (Photo credit: Wikipedia

Physiology of the ear

The basic function of the outer ear is to collect sound and direct it to
the middle ear. The outer ear consists of the ear flap and a 2 cm long
ear canal. The function of the ear flap is mostly to provide protection
for the middle ear and the ear drum. It is also shaped to channel sound
waves in the form of pressure waves into the middle ear. The ear canal
amplifies these sounds, and detects up to 3,000 Hz sounds. The pressure
waves must reach the middle ear before the mechanical energy is
converted into vibrations in the inner ear bone structure.

The basic function of the middle ear is to transform pressure wave vibrations into compressional waves for the inner ear. An air-filled cavity made up of an eardrum and three connected bones – the hammer, anvil, and stirrup – is the basic construction of the middle ear. The eardrum is a membrane stretched very tightly that vibrates as incoming pressure waves hit it. Compressions in the waves force the ear drum inward toward the ear, and rarefactions allow it to bounce back out. This is how the ear drum vibrates to detect sound and replicate it at the same frequency. Since the eardrum is connected to the hammer, its movement will influence that of the hammer, anvil, and stirrup, creating equal frequency vibrations within them, as the hammer is connected to the anvil, and the anvil to the stirrup, which is connected to the inner ear. These three bones merely amplify the sound as it passes through each of them by means of a mechanical advantage. The force of the small stirrup is approximately 15 times greater than the wide, small energy reception of the eardrum. This enhances our ability to hear sounds of little volume. The middle ear is connected to the mouth by the Eustachian tube, a cavity of air. This connection allows for the equalization of pressure in the ear, which is, of course, an air filled cavity. This tube, often during colds, has the potential to become clogged with mucus or other obstructions, leading to a buildup of pressure inequality.

The inner ear’s objective is to translate the energy of compressional waves within the inner ear fluid into nerve impulses that are sent to the brain and allow us to hear. The main structures of the inner ear, include the cochlea, semicircular canals, and the auditory nerve. Watery fluid fills the cochlea and canals. These semicircular canals actually provide no means of hearing themselves, but are “accelerometers,” assisting in maintaining balance in the ear’s tasks. The cochlea is perhaps the most important structure in the ear. Its surface is lined with 20,000 + diminutive hairs that differ in very small amounts and have different resiliency degrees to the fluid inside. These small hair/nerve cells are moved by compressional sound waves of their frequency. If a hair detects a match with a particular wave frequency, it will resonate with increased motion, and also match the amplitude of the frequency in the incoming sound. Through this vibration, the nerve cell transmits an electrical impulse to the brain through the auditory nerve. It has for long been a mystery to scientists just how the brain can interpret these sounds.

Related articles

• Modern living is too noisy for our ears (mirror.co.uk)