5)Anatomy and physiology of the Inner Ear(Cochlea,Vestibule and,Semi-Circular Canals)

The inner ear has a rather complex structure running through the temporal bone of the skull and contains two main compartments. The cochlea is involved in hearing while balance is controlled in the vestibular system, which includes the semi-circular canals, utricle, and saccule. Learn more about the basic structures, purposes, and locations of the different structures of the inner ear.

The vestibular system contains the:

• vestibule

• semi-circular canals

The central portion of the inner ear is called the vestibule. It is found beside the stapes and is sandwiched between the cochlea and the semicircular canals. This structure contains the utricle and the saccule. These pouches are membranous and help the body to maintain balance.

The semi-circular canals are looped fluid-filled spaces that also help to control balance. The bony tubes, or bony labyrinth, are filled with a fluid called perilymph. Within the bony labyrinth lies the membranous labyrinth. A fluid called endolymph is contained within the membranous labyrinth. No natural ducts or open connections exist between the endolymph and perilymph.

The cochlea is perhaps the most striking structure of the inner ear with its distinctive snail-like shape as it typically makes two and a half coiled turns. The name cochlea is derived from the Greek word “kokhlias,” which means “snail.”

The three fluid-filled chambers that extend along the coiled length of the cochlea are the:

• scala tympani

• scala media

• scala vestibuli

The scala vestibuli, or vestibular duct, forms the upper chamber of the cochlea and coils into the innermost aspect of the cochlea. The scala vestibule connects with the paralymphatic chamber of the vestibular system.

The apex of the cochlea contains an opening called the helicotrema, where the perilymphatic chamber of the vestibular system connects with the scala tympani. The scala tympani encompasses the outer aspect of the cochlea and connects to cerebrospinal fluid of the subarachnoid space by means of the cochlear aqueaduct.

The scala media, also known as the cochlear duct, is the endolymphatic system of the cochlea. It lies between the scala tympani and scala vestibule, is triangular in shape, and connects to the saccule by the ductus reuniens which eventually leads to the endolymphatic sac.

The scala media contains the Organ of Corti, the true organ of hearing. The Organ of Corti uses stereocilia and receptor hair cells with nerve endings that are deflected with movement of the fluid.

Mechanical energy is converted to electrical energy in the Organ of Corti through a process called transduction. High pitches are processed at the base of the cochlea, while low pitches are processed at the apex of the cochlea. The auditory nerve can then convert the electrical sound signals into nerve impulses that are carried to the primary auditory cortex in the temporal area of the brain called Wernicke’s Area.

The inner ear contains the vestibular system, which is responsible for balance, and the cochlea, which controls the body’s ability to hear. With looped semi-circular canals and a snail-like coiled cochlea, the structures of the inner ear contain two different fluids, perilymph and endolymph, which are controlled by ion transport rather than secretion and resorption.