The ear is the organ responsible for hearing, divided into three main sections as per textbooks: the outer ear, middle ear, and inner ear. However, functionally, the ear comprises four components: these three plus the brain. Hearing requires the involvement of all ear parts and the brain's auditory cortex. The outer ear, which is the visible part along the sides of our head, focuses sound vibrations onto the eardrum, causing it to vibrate. These vibrations are passed through a chain of small bones in the middle ear to the inner ear, where they activate auditory nerve fibers that send signals to the brain.The outer ear, while appearing intricate, is the simplest part, consisting of the pinna or auricle (the visible part), the ear opening, and the canal leading to the eardrum. Essentially, it includes the pinna, meatus, and canal, all working to focus air vibrations on the eardrum to make it vibrate.The middle ear features the eardrum and a cavity behind it, connected by a canal to the Eustachian tube. This tube helps balance the gas pressure in the middle ear with the external air pressure, like when your ears "pop" on a descending plane. The cavity also houses three small bones (ossicles) that link the eardrum to the inner ear: the malleus, incus, and stapes. In summary, the middle ear connects with the pharynx, balances pressure, and transmits vibrations to the inner ear.The inner ear is quite complex and includes the membranous labyrinth, where auditory nerve fibers end. This labyrinth, comprised of sacs and ducts filled with endolymph fluid, is located within the bony labyrinth. It is sometimes attached to, and sometimes suspended in perilymph fluid within, the bony labyrinth, which contains a central cavity, semicircular canals, and the cochlea. The membranous labyrinth's vestibule contains two sacs, the utriculus and sacculus, connected by a narrow tube. The utriculus is the main part of the vestibular system, aiding in head position and movement awareness, while the sacculus links to the cochlea's membranous tube containing the organ of Corti. The organ of Corti houses hair cells, the specialized sensory receptors for hearing.
