Ear: Structure, Anatomy and Function

Ear is one of the significant sense organs that plays an important role in the human body. Apart from helping the human body hear sounds, ears also contribute towards maintaining the balance of the body. This article will discuss all the details related to ear which includes the structure, anatomy and the functions performed by ears. It is one of the important chapters in NCERT Biology books for Class 8th. Students need to focus on understanding this chapter thoroughly to be able to answer the questions in the exercises correctly.

Ear: Definition

Ears are one of the five sense organs of human body that mainly focuses on looking after the function of maintaining the body balance and on hearing.

Since, in humans, ears perform a dual function, i.e. perceiving sound waves and maintenance of body equilibrium, they are called the statoacoustic organ.

Ear: Position

The ears are located on the lateral sides of the head. In most mammals, the external ear is represented by a flap of tissue also known as the pinna. In humans, ear pinna has reduced mobility, while in animals like elephants, they are mobile.

Ear: Structure and Anatomy

The human ear can be anatomically divided into three major parts:

1. Outer or External ear
2. Middle ear
3. Inner ear

Ear: Diagrammatic Representation

Ear: Parts

The parts of the ear are discussed below:

Outer or External Ear

1. The external ear consists of a pinna and the auditory canal, which collect the sound waves and channel them to the tympanic membrane (or eardrum).
2. Eardrum is a biological membrane that separates the outer ear from the middle ear.
3. Eardrum is composed of connective tissues covered with skin outside and with the mucous membrane inside.
4. There are exceptionally fine hair and wax-secreting sebaceous glands in the skin of the pinna and the auditory canal, which form part of innate immunity.

Middle Ear

1. The middle ear contains three ear ossicles called malleus (hammer), incus (anvil), and stapes (stirr-up), which are attached to one another in a chain-like fashion.
2. The malleus is attached to the tympanic membrane and the stapes are attached to the oval window of the cochlea.
3. The ear ossicles increase the efficiency of transmission of sound waves to the inner ear by amplifying their magnitude.
4. The middle ear connects with the pharynx through the eustachian tube.
5. The Eustachian tube maintains the pressure on either side of the eardrum.
6. Stapes is the smallest bone of the skeletal system.

Short Trick: Worried about how to remember the sequence of bones in the middle ear? Here, is a short trick for you:

Don’t MISS this Trick!! M : Malleus; I : Incus; S : Stapes

Practice Class 11 Mock Tests

Inner Ear

1. The inner ear consists of a labyrinth of fluid-filled chambers within the cavity formed by the temporal bone of the skull.
2. The inner ear is also called labyrinth and is composed of two types of labyrinth, i.e. bony labyrinth and membranous labyrinth, which in turn are composed of canals and sacs.
3. Bony labyrinth has a series of channels, inside which a membranous labyrinth is present.
4. Bony labyrinth encloses a fluid called perilymph, which in turn surrounds membranous labyrinth.
5. The membranous labyrinth is filled with a fluid called endolymph.
6. The inner ear has \(3\) main parts, i.e. cochlea, semicircular canals, and vestibule.
7. Cochlea: It is the auditory area of the inner ear that changes sound waves into nerve signals.
8. Semicircular canals: They help in maintaining posture and equilibrium.
9. Vestibule: It lies between the cochlea and semicircular canals, also assisting in the maintenance of body equilibrium.

Cochlea

1. The coiled portion of the labyrinth or inner ear is called cochlea.
2. It receives sound waves from stapes (the ossicles of middle ear).
3. The membranes constituting cochlea (the Reissner’s and Basilar), divide the bony labyrinth into large canals, i.e., an upper vestibular canal (scala vestibuli), and a lower tympanic canal (scala tympani).
4. Scala vestibuli and scala tympani are separated by a small cochlear duct called scala media that is filled with endolymph.
5. The fluid filled in scala vestibuli and scala tympani is called perilymph.
6. At the base of the cochlea, the scala vestibuli ends at the oval window, while the scala tympani ends at the round window, which opens to the middle ear.
7. The part of cochlea, where scala vestibuli and scala tympani meet is called helicotrema.
8. Helicotrema is mainly associated with the identification of low-frequency sound waves.

Organ of Corti

1. Organ of Corti is the auditory organ of the cochlear duct, present on the basilar membrane, which separates scala tympani with scala media.
2. Organ of Corti contains the mechanoreceptors of the ear in the form of hair cells.
3. These hair cells are present in rows on the internal side of the organ of Corti that act as auditory receptors.
4. The hair cells are of two types, i.e. inner hair cells and outer hair cells.
5. Inner hair cells occur in one layer and are about \(3500\) in number, while the outer hair cells are arranged in \(3 – 4\) rows and are about \(20,000\) in number.
6. Inner hair cells respond to the velocity of movement of the basilar membrane.
7. Outer hair cells are primarily concerned with the displacement of the basilar membrane by the sound waves.
8. A large number of processes called stereocilia are projected from the apical part of each hair cell.
9. Above the rows of hair cells, a thin elastic membrane called tectorial membrane is present, that determines the patterns of vibration of sound waves.
10. The basal end of the hair cell is in close contact with the afferent nerve fibres.

Vestibular Apparatus

1. The inner ear also contains a complex system called vestibular apparatus located above the cochlea.
2. It is composed of three semicircular canals and the otolith organ consisting of saccule and utricle.
3. Each semicircular canal lies in a different plane at right angles to each other.
4. The membranous canals are suspended in the perilymph of the bony canals.

5. The base of the canals is swollen and is called the ampulla, which contains a projecting ridge called crista ampullaris.

6. Crista ampullaris contains sensory hair cells that are associated with the sensation of angular rotation.

7. The saccule and utricle contain a projecting ridge called macula.

8. The crista and macula are the specific receptors of the vestibular apparatus responsible for the maintenance of the balance of body and posture.

9. Otoliths help in sensing spatial orientation, as it presses stereocilia against gravity.

Mechanism of Hearing

1. The sound waves from a vibrating object are collected and transmitted inwards by the external ear to the tympanum.
2. The vibrations of tympanum are conducted to the oval window of cochlea by the ear ossicles.
3. The movement of the oval window generates pressure waves in the perilymph of the vestibular canal.
4. The pressure waves are later transmitted to the perilymph of the tympanic canal.
5. Finally sound waves are dissipated into the air of the middle ear cavity through the vibration of the round window.
6. During the transmission of pressure waves from vestibular canal, tympanic canal, the vestibular and basilar membranes are made to vibrate.
7. The vibrations of the basilar membrane push the sensory hair cells against the tectorial membrane.
8. The displacement of hair generates receptor potentials which induce the production of nerve impulses in the cochlear nerve fibres.
9. These impulses are transmitted to the auditory cortex of the temporal lobe of the cerebrum.
10. The audible range of the human ear is \(20\) to \(20000Hz\).

Mechanism of Body Balance

1. The balance system of our body works through a constant process of position detection, feedback, and adjustment using communication between the inner ear, eyes, muscles, joints, and the brain.
2. The inner ear mainly consists of two parts, i.e., cochlea which is responsible for the hearing process, and the vestibular system which is responsible for maintaining body balance and posture.
3. The vestibular system consists of three semicircular canals and two pockets called otolith organs (utriculus and sacculus) that together provide constant feedback to the cerebellum about head movement.
4. Each semicircular canal varies in orientation to detect a variety of head movements like nodding and rotating.
5. The movement of fluid inside the semicircular canal due to head movements stimulates the tiny hair to send messages to the cerebellum via the vestibular nerve.
6. The two otolith organs send messages to the brain regarding the body movements in a straight line and about the head movements in relation to gravity.
7. The otolith organs contain small crystals that get displaced during these movements which stimulate the tiny hair cells to transmit the messages to the cerebellum via the vestibular nerve.
8. The vestibular system works in coordination with the visual system to stop the objects from blurring when the head moves. It also helps in maintaining awareness of positioning like walking, running, riding, etc.

Functions of Ear

1. The outer part of the ear, i.e., pinna helps in the collection of sound vibrations and sends them to the eardrum.
2. The ear ossicles present in the middle ear help in the amplification of the sound waves.
3. The cochlea present in the inner ear is responsible for the hearing process.
4. The two otolith organs, i.e., sacculus and utriculus are responsible for maintaining the static equilibrium of our body.
5. The three semi-circular canals are responsible for maintaining the dynamic equilibrium of our body.

Common Diseases of Ear

The ear may be affected by the following diseases:

1. Meniere’s Syndrome: It is a hearing loss due to pathological distention of the membranous labyrinth of the cochlea.
2. Eustachitis: It occurs due to inflammation of the Eustachian tube.
3. Tympanitis (Myringitis): It is due to inflammation of the eardrum.
4. Otalgia: Pain occurs in the ear.
5. Otitis media: Acute infection in the middle ear.
6. Tinnitus: Perception of sound when there is no corresponding external sound present.
7. Vertigo: A condition where a person is having the sensation of being off-balance or spinning dizziness.

Summary

The ear is one of the five sense organs of our body. The ear is the organ of hearing, but in mammals, it also helps in providing equilibrium to the body. Only vertebrate animals have ears. But there are many invertebrates that can detect sound using other kinds of sense organs. We also understood the mechanism of hearing, functions of the ear, and the common diseases related to the sense organ, the ear.

PRACTICE QUESTIONS RELATED TO HUMAN EAR

Frequently Asked Questions (FAQs) on Ear

Frequently asked questions related to Ear is listed as follows:

Q.1. What is the front part of the ear called?
Ans: The front part of the ear is called pinna which helps in the collection of sound waves and sending them to the eardrum.

Q.2. Where does your ear canal lead to?
Ans: The ear canal also known as the auditory canal leads to the eardrum. 

Q.3. What are the common ear problems?
Ans: There are many common ear problems like Meniere’s Syndrome (hearing loss), Tympanitis (inflammation of eardrum), Tinnitus (perception of sound when no external sound is present), etc.

Q.4. Can earplugs touch eardrums?
Ans: No, earplugs cannot touch the eardrum because the opening of the ear canal to the eardrum is not straight. 

Q.5. What are the three parts of the ear and their functions?
Ans: The three parts of the ear and their functions are as follows:
Outer ear: It consists of a pinna and auditory canal that collects the sound waves and sends them to the eardrum.
Middle ear: It consists of three ossicles (i.e., malleus, incus, and stapes) that increase the efficiency of sound transmission by increasing their amplitude.
Inner ear: It consists of the cochlea which is responsible for hearing and the vestibular system which is responsible for maintaining body equilibrium.

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