Mechanism of Hearing

Introduction

Human physiology is a fantastic concept in the CBSE class 11th syllabus. Students who’ve just got into the biology line may find it challenging to understand all the dedicated concepts. The mechanism of hearing is one such topic that includes a detailed understanding of human physiology and functioning. So, let us discuss the mechanism and physiology of hearing.

Process

Ears are one of the sensory organs and are responsible for hearing and maintaining the body’s equilibrium. The mechanism of hearing is nothing less than a step-by-step process that can be understood with a detailed analysis of the different parts of the ears, including the outer ears, middle ear and inner ear.

Mechanism of hearing

Sound waves enter the outer ear, pass through the middle ear and get processed in the inner ear. Part of ear with function mentioned below:

    Outer and Middle ear

The outer ear consists of the pinna, external auditory canal and tympanic membrane. The functions of these parts are:

• Pinna: The outer ear has excellent ears and glands that secrete wax and protect dust and foreign materials from entering the ears
• External auditory canal or meatus: It has wax glands and connects to the pinna outside and the tympanic membrane in the inner ear
• Tympanic membrane or eardrum: The connective tissues make a majority of the eardrum, and the inner part is covered with mucous membrane while the outside is covered with skin

The middle ear amplifies the sound waves and consists of the malleus, incus, stapes, and the Eustachian tube. The functions of these parts are:

• Malleus is connected to the tympanic membrane and is a hammer-shaped bone
• Incus is located between the stapes and malleus and is an anvil-shaped bone
• Stapes: It is connected to the cochlea’s oval window and is stirrup-shaped. Further, it is the smallest bone in the body
• The Eustachian tube: It forms the link between the middle ear and pharynx and equalizes the pressure of the middle ear and the outside atmosphere.

Inner ear

The inner ear consists of a collection of interconnected canals and sacs and is called the labyrinth. The functions of these parts are:

• Cochlea looks like a snail and is the membranous labyrinth’s coiled part. It comprises the central cochlear duct or scala media, the upper vestibular canal or scala vestibuli, and the lower tympanic canal or scala tympani
• Reissner’s membrane: It separates scala vestibule and scala media
• The organ of Corti: It is the auditory organ present in the scala media
• The basilar membrane separates the scala media and tympani and contains hair cells
• Stereocilia: These start from the hair cells and reach the cochlear duct
• Vestibular apparatus: It has two chambers resembling sac called utricle and saccule and has three semicircular canals

What is the mechanism of hearing?

It can be understood with the following steps:

• The pinna receives the sound waves and these waves reach the tympanic membrane from the meatus
• The vibrations from the eardrum are transmitted to the three ossicles of the middle ear
• The sound waves amplification is ensured by the malleus, incus and stapes
• The amplified sound vibrations reach the scala vestibuli lymph by the oval window
• The pressure waves reach the basilar membrane by passing through the scala media’s endolymph and then to the scala tympani’s perilymph. This fluid movement is facilitated by the round window located at the end of the scala tympani
• The rubbing of stereocilia with the tectorial membrane is caused due to the basilar membrane movement
• The plasma membrane’s ion channels present in hair cells are opened with the bending of stereocilia. The movement inside the cells causes the release of a neurotransmitter i.e., glutamate
• The depolarization of neurons occurs as the neurotransmitters stick to the receptors of afferent neurons, which connect with hair cells. This generates a nerve impulse that is transmitted to the auditory nerve to reach the brain’s auditory cortex
• The vibrational impulse from the inner ear is converted into an electrical impulse. The brain analyzes these electrical impulses, coming from the inner ears. That’s how we hear sounds
•  It further gives an idea of the sound’s direction, pitch and loudness

The mechanism and physiology of hearing

When we discuss the mechanism and physiology of hearing, we know that ears are responsible for the additional role of equilibrium maintenance. The hearing function has been maintained by the organ of Corti, which is present inside the cochlea. Static equilibrium has been maintained by maculae and dynamic equilibrium has been maintained by cristae. The static equilibrium is managed by the utricle and macula of the saccule. The otoliths push against the stereocilia because of the gravitational pull and stimulate the nerve impulse initiation. The cristae of semicircular canals further detect the dynamic equilibrium.    

Conclusion:

We covered the mechanism of hearing in this article. Ears are one of the sensory organs and are responsible for hearing and maintaining the body’s equilibrium. In the hearing process, sound waves enter the outer ear, pass through the middle ear and get processed in the inner ear. The mechanism of hearing is nothing less than a step-by-step process that can be understood with a detailed analysis of the different parts of the ears, including the outer ears, middle ear and inner ear.