Inner Ear Anatomy

Table of Contents

• Internal Ear Anatomy
• Parts of Inner Ear
• Inner Ear – Function
• Frequently Asked Questions

Internal Ear Anatomy

The exterior, middle and inner ears are the three components that make up the human ear. The interior of a vertebrate’s ear is called the inner ear or internal ear. The inner ear is primarily responsible for sound perception and balance in vertebrates.

The internal ear, also known as the labyrinth, is a membranous structure surrounded by a bony labyrinth in the hard portion of the temporal bone. It consists of the sense organs for hearing and balance. The vestibular apparatus is the sense organ for balance, while the cochlea is the sense organ for hearing.

Let’s explore more about the anatomy of the inner ear.

Parts of Inner Ear

The membranous labyrinth creates three parallel fluid-filled chambers, which run inside the bony labyrinth. The inner chamber is filled with endolymph and the two outer chambers are filled with perilymph. The vestibule of the ear, the cochlea and the semicircular canals are the three principal components of the bone labyrinth.

Inner Ear Structure – Diagram

Cochlea

The cochlea is a coiled structure like the shell of a snail. There are two structures in it:

1. The spongy bone called the modiolus, which forms the central conical axis.
2. Bony tube or canal that surrounds the modiolus.

The bony canal begins at the cochlea’s base and ends at its top (apex) by making two and a half rounds. Cupula is the name of the canal’s end. The central bony pillar, modiolus and the periotic or osseous canal, which coils around the modiolus, are visible when the cochlea is cut through at its axis.

A bony ridge known as the osseous spiral lamina extends from the modiolus and winds around it like a screw thread. After following the cochlea’s spiral turns, the spiral lamina terminates at the cupula in a hook-shaped structure known as the hamulus.

Compartments of Cochlea

The osseous spiral lamina and the spiral canal’s outer wall are divided by two membranes – the vestibular membrane and the basilar membrane. The cochlea’s spiral canal is divided into three compartments by both these membranes.

1. The scala vestibuli, also known as the vestibular duct, contains perilymph. It is located above the cochlear duct and borders the oval window.
2. The scala tympani, also known as the tympanic duct, contains perilymph. It is inferior to the cochlear duct and ends at the round window.
3. The scala media, also known as the cochlear duct, contains endolymph. It is an area of high potassium ion concentration where the hair cell’s stereocilia project into.

Explore: MCQs on Structure of Ear

Vestibule of the Ear

The vestibule is located medial to the tympanic membrane (eardrum), behind the cochlea and in front of the three semicircular canals. It is the centre portion of the bony labyrinth in the inner ear. It has an oval-shaped structure that is transversely flattened. The oval window is located in its tympanic or lateral wall, while the perforated recessus sphericus is a small circular depression on its medial wall.

Otolith organ and three semicircular canals make up the vestibular apparatus of the human ear. Each of the semicircular canals has two ends. One end is narrower than the other. Its enlarging end is known as an ampulla. Utricle and saccule combine to produce the otolith organ, or vestibule. Otoliths are frequently used to describe the utricle and saccule together. The macula is the otolith organ’s receptor organ. These structures of the vestibule aid in the maintenance of equilibrium.

Semicircular Canals

The inner ear contains three interconnected semicircular tubes called semicircular canals or semicircular ducts. The lateral, anterior and posterior semicircular canals are the three canals. Motion sensors are embedded into the endolymph that fills each canal. They offer sensory inputs for the experience of head rotatory movements.

• The lateral or horizontal semicircular canal is the shortest of the three canals. The rotation of the head around the neck (transverse plane rotation) correlates to fluid movement within this canal.
• The anterior or superior semicircular canal detects rotations of the head about the lateral axis (sagittal plane rotation). This happens when someone nods their head.
• The posterior semicircular canal detects rotation of the head about the anteroposterior axis (coronal plane rotation). This happens when someone moves their head to touch their shoulders.

The endolymph in the canals trails behind when the head moves because of inertia. This affects the cupula, which then causes the cilia of the hair cells to flex. The brain receives a signal that acceleration is occurring when the hair cells are stimulated.

Organ of Corti

The organ of Corti is a cellular layer of sensory epithelium on the basilar membrane. It is the receptor organ for hearing. It is composed of a variety of supporting cells as well as sensory cells known as hair cells. The cochlea’s organ of Corti cells is all arranged in a circular pattern, starting from the centre and moving outward.

Inner Ear – Function

The internal ear’s structures receive the sound waves from the external ear. The internal ear contains both balance and hearing-related organs. Hair cells in the cochlea detect sound pressure waves and provide messages to the brain.

In older adults, the ability to hear higher pitch sounds declines gradually. The two fundamental mechanisms the human ear has developed to encode sound waves are distinct in how they detect low and high frequency sounds. The basilar membrane moves in a manner similar to a travelling wave and this shape changes according to the frequency of the pitch. The apex or tip of the membrane moves most when subjected to low-frequency sounds and it moves most at its base when subjected to high-frequency sounds.

This was a brief note on the anatomy of the internal ear. For more NEET-related content, visit BYJU’S.

See more:

• Outer Ear Diagram
• What Is the Function of Eustachian Tube?
• What Is the Function of Cochlea?