Physiology of Hearing

Hearing - An Introduction

Hearing is that the process by which the ear transforms sound vibrations within the external environment into nerve impulses that are conveyed to the brain, where they're interpreted as sounds. Sounds in-ears are produced when vibrating objects, like the plucked string of a guitar, produce pressure pulses of vibrating air molecules, better referred to as sound waves. The ear can distinguish different subjective aspects of a sound, like its loudness and pitch, by detecting and analyzing different physical characteristics of the waves.

Structure of the ear is a crucial concept to find out intimately from an exam perspective. Ears are one of the five sensory organs of our body. Aside from hearing, the best function is to take care of the balance of the body. The hair cells present within the internal ear of mammals help in sensing the position of the body, in accordance with gravity and maintain the equilibrium.

The structure of the ear comprises three main sections: the external ear, tympanic cavity and internal ear. Let’s learn intimately about the structure and functions of every of those sections.

Anatomy and Physiology of Ear

Outer Ear

  • Pinna is the outermost part, it's very fine hairs and glands. The glands secrete wax. It protects foreign organisms and mud from entering.

  • External auditory meatus or meatus is connected to pinna at the outer side and extends till eardrum or eardrum. They even have wax glands.

  • Tympanic membrane or eardrum is formed from animal tissue. Skin covers the outer portion and from inside, it's covered by mucosa.

  • Pinna receives the sound within the sort of vibration. The sound waves reach and vibrate the eardrum through the external auditory meatus.

Middle Ear

  • It contains a sequence of three tiny bones malleus, incus, and stapes, present within the same order.

  • Malleus may be a hammer-shaped bone, attached to the eardrum.

  • Stapes is the smallest bone of the body. It's stirrup-shaped and attached to the fenestra ovalis of the cochlea.

  • The Eustachian tube is that the connection between the centre ear and therefore the pharynx. It equalises pressure between the centre ear and therefore the outer atmosphere.

The middle ear amplifies the sound waves and transmits to the internal ear.

Inner Ear

  • The internal ear is named the labyrinth. it's composed of a gaggle of interconnected canals and sacs.

  • The structure is present inside the osseous labyrinth and surrounded by a fluid referred to as perilymph.

  • The endolymph is filled within the structure.

  • Auditory receptors are located within the cochlea and vestibular system maintains the body balance.

Cochlea (Auditory Organ)

  • The Cochlea may be a coiled portion of the structure, which seems like a snail.

  • The cochlea is formed from three canals, upper vestibular canal or scala vestibuli, middle cochlear duct or scala media and therefore the lower tympanic canal or scala tympani, which are separated by thin membranes.

  • The scala vestibuli is crammed with the perilymph and terminates at the fenestra ovalis 

  • The scala tympani is additionally crammed with the perilymph and ends at the opening within the tympanic cavity , i.e. fenestra rotunda.

  • The scala media is crammed with endolymph and contains the auditory organ, the organ of Corti.

  • Each organ of Corti contains ~18000 hair cells. Hair cells are present within the membrane, which separates scala media from scala tympani.

  • There's another membrane called the tectorial membrane present above hair cells.

  • Hair cells present within the cochlea detect pressure waves, there are sensory receptors (afferent nerves) present at the bottom of hair cells that send signals to the brain.

Vestibular Apparatus (Equilibrium Organ)

  • Vestibular apparatus maintains the equilibrium and is present above the cochlea. it's present within the structure. it's two sac-like chambers called saccule and utricle and three semicircular canals.

  • Saccule and utricle have macula, which may be a projecting ridge.

  • Macula has sensory hair cells. Stereocilia protrude out from the hair cells.

  • Otoliths are calcium ear stones, which press stereocilia against gravity and play a crucial role in spatial orientation.

  • Each sense organ is crammed with endolymph and present at the proper angle to every other and connects to the utricle. the bottom of canals is swollen and referred to as the ampulla.

  • Crista ampullary is present in each of the ampulla and liable for sensing angular rotation. it's hair cells.

  • There are not any otoliths present in cristae like maculae of saccule and utricle and stereocilia of hair cells are stimulated by the movement of endolymph within the canals.

Physiology of Ear

Ears perform two main functions, hearing and equilibrium maintenance.

  • The organ of Corti (Cochlea) is liable for hearing function.

  • Maculae (Saccule and Utricle) are liable for static equilibrium.

  • Cristae (semicircular canals) are liable for dynamic equilibrium.

Mechanism of Hearing

  1. The pinna receives the sound waves and it reaches the eardrum through the meatus.

  2. The eardrum vibrates and these vibrations get transmitted to the three ossicles present within the tympanic cavity.

  3. These vibrations then reach the perilymph (scala vestibuli) through the fenestra ovalis.

  4. Then the pressure waves get transferred to the endolymph of scala media and reach the membrane then to the perilymph of scala tympani. This movement of fluid is facilitated by the fenestra rotunda present at the top of the scala tympani.

  5. The membrane movement causes the rubbing of stereocilia against the tectorial membrane.

  6. Stereocilia are bent leading to the opening of ion channels within the cell wall of hair cells. Glutamate, a neurotransmitter, is released thanks to Ca++ ion movement inside the cell.

  7. An impulse is generated and transmitted to the auditory area of the brain through the acoustic nerve (cranial nerve VIII).

  8. The brain analyses the impulses and that we hear the sound.

Mechanism of Maintaining Equilibrium

We all know that hearing ability is thanks to ears. aside from hearing, ears also are liable for maintaining equilibrium. The vestibular system is the main organ for maintaining equilibrium. Otoliths press against stereocilia thanks to gravitational pull and stimulate the initiation of an impulse. When the top is tilted or moves during a line with increasing speed, otoliths continue stereocilia of various cells. The brain interprets the nerve impulses leading to the notice of body position with reference to ground, regardless of the top position.

Utricle responds to the vertical movement and Saccule responds to the sideways movement of the top.

FAQs (Frequently Asked Questions)

Q1. What are the Three Structures of the Ear?

Answer: The three main structures of the ear are the external ear, tympanic cavity and internal ear.

Outer Ear – The external ear comprises the ear pinna, the external auditory meatus and the eardrum or eardrum. the most function of the external ear is to receive the sound vibrations and pass them on to the eardrum through the auditory meatus.

Middle Ear – The centre ear comprises the three ear ossicles, malleus, incus and stapes. Its main function is to amplify and transmit the sound waves to the interior ear. The Eustachian tube is additionally present within the tympanic cavity and it connects the centre ear to the nasopharynx. It equalises pressure between the centre ear and therefore the outer atmosphere.

Inner Ear – The internal ear is named the labyrinth. it's composed of a gaggle of interconnected canals and sacs. The internal ear comprises the cochlea, the auditory organ and the vestibular system, which is that the equilibrium organ.

Q2. Which Structure of the Ear is Liable for the Balance?

Answer: The vestibular system present above the cochlea within the structure is the main organ for maintaining equilibrium and body balance. it's two sac-like chambers called saccule and utricle and three semicircular canals. The static equilibrium is maintained by the macula of saccule and utricle and therefore the dynamic equilibrium is detected by the cristae of semicircular canals.

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