Ear
From ArticleWorld
The ear is an organ used by animals to detect soundwaves. The term denotes the whole system, responsible for collecting, transmitting and processing the soundwaves. However, it is commonly used to denote only the outer, visible part of the ear.
Contents |
The mammalian ear
Mamals have two ears, sittuated on either sides of the head. Their ears have three parts - the Outer Ear, the Medium Ear and the Inner Ear, responsible for collecting and amplifying soundwaves, converting vibrations into action potentials and delivering the action potential signals to the brain respectively.
Outer ear
The Outer Ear has two main components: the auricle and the ear canal. The auricle is the visible part, which some mammals can move using the auriclae muscles, an ability that humans do not have. The auricle's role is to aid in capturing the vibrations. The ear canal leads the air vibrations to the tympanic membrane (eardrum).
Medium ear
The Medium Ear has three tiny bones called ossicles, two muscle tendons and two nerve bundles. It is distinctive for mammals that they have three ear bones.
The tympanic membrane is attached to the malleus (hammer). The malleus is, in turn, attached to the incus (anvil), which is linked to the stapes (the stirrup). The stapes is attached to the oval window of the cochlea. When the tympanic membrane vibrates, vibrations are transmitted through the three ossicles to the oval window. Due to the way the ossicles are attached, the vibrations in the oval window are almost 20 times more powerfull than those in the eardrum. The amplification is of about 14 dB, with a peak at frequencies of 1 kHz, giving humans a peak sensitivity to frequencies of 1-3 kHz.
The medium ear is hollow, which means that it is sensitive to pressure changes in the outside environment. If the pressure is not balanced, there is a danger of a burst that would affect the eardrum. The task of balancing pressure is handles by the Eustachian tubes.
Inner ear
The Inner Ear includes the organ of hearing, the cochlea, and the organ of balance, and the organ of balance, the labyrinth (or vestibular apparatus), which consists of three semicircular canals and the vestibule. Running throught the centre of the cochlea is the Organ of Corti, which includes tiny hair cells. The cochlea has three parts - two bony parts, filled with a fluid called perilymph, and a membraneous part filled with endolimph.
The vibrations of the oval window cause the cochlear fluid to vibrate. This fluid's vibrations cause the basilar membrane to vibrate, which produces travelling waves. Depending on the pitch of the vibration, they are captured in different parts of the cochlea. These waves cause the hair cells to bend, producing a generator potential. If these potentials are large enough, they will stimulate the auditory nerves and produce action potentials.
The vestibular apparatus contains a similar fluid to the cochlea, but detects head rotation instead of sound.