The ear is an organ that is able to detect and recognize sound and also plays a role in balance, equilibrium and body position. All vertebrate animals, from fish to humans, have ears that are similar with some variation according to the function and species. In this article, we’ll discuss the human ear in particular.
Anatomy of the human ear
The human ear has three main parts, called the outer ear, middle ear and inner ear. The outer ear consists of the ear you can see out on outside of your head, the outer ear canal and the ear canal. The part of the ear you can see is called the pinna, and the ear canal is called the exterior auditory meatus, which ends at the tympanic membrane or eardrum. The design of the outer ear is very complex in order to catch and amplify sounds and send them into the ear canal, which is made up of bone and cartilage covered with a thin layer of skin. Inside the ear canal, there are many glands that produce a waxy substance called cerumen, better known as earwax. At the end, the eardrum transmits sound waves to the middle and inner ear.
The middle and inner ear
The middle ear is an air cavity surrounding the eardrum which includes three tiny bones called ossicles: the malleus (hammer), incus (anvil) and stapes (stirrup). The tip of the Eustachian tube is also found in the middle ear. Sound vibrations received by the eardrum are transmitted to these hearing bones, and each ossicle delivers the vibrations it receives to the next bone. The stapes is the smallest bone in the human body and its function is to transfer sound vibrations to the cochlea.
In humans and other land animals, the middle ear and auditory canal are filled with air under normal circumstances, although unlike the outer ear, the air in the middle ear is not associated with the air outside the body. Instead, the Eustachian tube connects the middle ear to the back of the pharynx.
The anatomy of the human inner ear consists of the bony labyrinth, a series of cavities in the temporal bone that are filled with perilymph fluid, and the membranous labyrinth, which lies deeper and contains endolymph fluid. In front of the labyrinth is the cochlea, whose cross-section contains three parts: the scala vestibuli, scala tympani and scala media. The base of the scala vestibuli is connected to the stapes through the webbed oval window, which the scala tympani is associated with the middle ear through the round window.
The top of the scala media is restricted by the vestibular membrane or Reissner membrane and the bottom is bound by the basilar membrane. At the top of the basilar membrane is the organ of Corti, which turns sound vibrations into impulses that can be sent to the brain along the vestibulocochlear nerve. The organ of Corti is composed of hair cells, three rows of outer hair cells and one row of inner hair cells. The inner hair cells send impulses from the ear to the brain, while the outer hair cells primarily receive information from the brain.