Hearing is a sense that detects pressure waves travelling through the air and turns them into a feeling of sound. The ear is also responsible for keeping our body in a stable position, in other words, maintaining our balance. In order to perform both of these functions, the structure of the ear is split into three sections: outer ear, middle ear and inner ear.
Outer ear
The outer ear is in charge of gathering sound waves and sending them to the middle ear. It is made up by the pinna and the external auditory canal. The pinna is what is commonly known as the ear, an oval-shaped protuberance containing cartilaginous tissue covered in skin. The external auditory canal is a tubular structure that measures between 2 to 3 cm long and 7mm in diameter. Inside, it is covered in ceruminous glands and tiny hairs that protect us from foreign elements. This canal ends in the eardrum, which is similar to an air-tight cover made up of fibrous tissue. It is highly flexible, which allows it to perform vibratory motions when it receives sounds waves. It then sends said waves to the ossicles in the middle ear, which it is connected to.
Middle ear
The middle ear turns sound waves into mechanical vibrations. It is located in the temporal bone of the skull, measures nearly 3 mm deep and is full of air. It has three mobile bones (hammer, anvil and stirrup), which are connected to the cranium through interlaced muscles that transmit and amplify the vibrations from the eardrum to the inner ear. At the bottom of this part of the ear we have the auditory tube, a 4 cm long tube that is connected to the pharynx. Its function is to balance the differences in pressure that form between the outer and inner parts of the eardrum.
Inner ear
The inner ear is the placed where the vibrations of the sound waves are turned into nerve impulses, which then travel on to the brain. It is split into two parts: the cochlea or snail and the vestibule. The cochlea is formed by the scala media (which contains cilia and a liquid called endolymph), the scala vestibuli and the scala tympani. These last two contain a liquid known as perilymph.
The vestibule is a liquid-filled tube that has two chambers in its central part, the utricle and the saccule, as well as three prolongations called the semicircular canals.
