Physiology of Hearing and Auditory Mechanism

Hearing is 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 EarOuter EarPinna 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 the pinna at the outer side and extends to the eardrum or eardrum. They even have wax glands.Tympanic membranes or eardrums are 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 EarIt 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 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 EarThe 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 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 the canals is swollen and referred to as the ampulla.Crista ampullaris 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 macula of saccule and utricle and stereocilia of hair cells are stimulated by the movement of endolymph within the canals.Physiology of EarEars 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 HearingThe pinna receives the sound waves and it reaches the eardrum through the meatus.The eardrum vibrates and these vibrations get transmitted to the three ossicles present within the tympanic cavity.These vibrations then reach the perilymph (scala vestibuli) through the fenestra ovalis.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.The membrane movement causes the rubbing of stereocilia against the tectorial membrane.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.An impulse is generated and transmitted to the auditory area of the brain through the acoustic nerve (cranial nerve VIII).The brain analyses the impulses and that we hear the sound.Mechanism of Maintaining EquilibriumWe 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 the 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.

The human ear is considered an organ of hearing and equilibrium. In technical terms, it is a conscious appreciation of the vibrations that are perceived as sound. Hearing is a major sense organ, like the vision which is important for communication and distant warning. The ear can be referred to as a biological microphone as the sound perceived by the ear is then sent as a signal in the higher parts of the brain. The main function of the ear is to convert this physical vibration into an encoded nervous impulse. The ear is stimulated by vibration. The sound perceived is converted into a nervous impulse which is then processed by the central auditory pathways present in the brain. It is an extremely complex mechanism. The study notes provided by Vedantu are based on a single topic and it deals with the structure and functions of the ear, the mechanism and various other minute details that are important in the study of the physiology of hearing.

The physiology of hearing is briefly discussed in chapter 21 called neural control and coordination. This chapter is studied by students of class 11 biology. It is the chapter of the NCERT Book which is prescribed by the Central Board of secondary education, students who are preparing to give the NEET exam should also go through the notes provided by Vedantu on class 11 and 12th physics chemistry and biology.

The outer ear and the middle ear are the sound conducting mechanisms of an ear and the inner ear is the sound transducing mechanism of an ear.

Parts of an ear include an external or outer ear that consists of a pinna or auricle and an external auditory canal or tube.

It also includes a tympanic membrane called an eardrum, a middle ear called the Tympanic cavity, ossicles, an eustachian tube, The inner ear consists of the cochlea, vestibule, and semicircular canal.

Hearing is processed in an extremely systematic manner, sound is first perceived by the outer ear, the sound waves or vibrations travel to the external auditory canal and strike the tympanic membrane, also called the eardrum. The vibration of the eardrum passes to the oscillations that are three tiny bones in the middle ear called malleus, incus, stapes. The sound is amplified by the ossicles and sound waves travel to the inner ear into the cochlea which is the fluid-filled hearing organ. After reaching the inner ear, sound waves are converted into electrical impulses. The auditory nerves then send these impulses to the brain and then the brain translates these electrical impulses as sound.

Important topics related to the physiology of hearing which is discussed in neural control and coordination-

21.1 Neural System

21.2 Human Neural System

21.3 Neuron as Structural and Functional Unit of Neural System

21.4 Central Neural System

21.5 Reflex Action and Reflex Arc

21.6 Sensory Reception and Processing

21.6.2 The Ear

20.6.2.1 Mechanism of Hearing