PHYSIOLOGY OF AUDITORY SYSTEM

Dr. Sudeep k.c.

AUDITORY SYSTEM ORGAN OF CORTI:-It is a sense organ of hearing situated in a

basilar membrane.COMPONENTS OF ORGAN OF CORTI: Tunnel of corti- Formed by inner and outer

rods, contains a fluid cortilymph. Hair Cells-Receptors cells of hearing and

transduce sound energy into electrical energy.Inner hair cells:-impt. in transmission of

auditory impulse.Outer hair cells:-impt. in modulating the

function of inner hair cells.

Supporting cells:-Situated between the outer hair cells and important for support.

Tectorial Membrane:-It overlies the organ of corti. It produces a stimulus to hair cells.

ORGAN OF CORTI

AUDITORY NEURAL PATHWAYS The receptors of hearing are linked by a chain

of neurons with the receiving centers for hearing in the temporal lobes of a cerebral cortex.

The main nuclei in the ascending auditory pathways are:

1. Superior olivary complex.2. Nucleus of lateral laminiscus.3. Inferior colliculus.4. Medial geniculate body.5. Auditory Cortex.(Area 41)FIGURE

AUDITORY PATHWAYS

Mechanism of Hearing

Broadly divided into:1. Mechanical conduction of

sound(Conductive apparatus).2. Transduction of mechanical energy

to electrical impulse (Sensory system of Cochlea).

3. Conduction of electrical impulse to the brain(Neural pathways).

VESTIBULAR SYSTEM

Divided into:Peripheral Vestibular System:--Made up of membranous Labyrinth and Vestibular

nerve.-Peripheral receptors- CRISTAE –Semicircular duct.

-MACULA- Utricle and Saccule

Central Vestibular System:--Made up of Nuclei and Fibers tract in CNS.-It integrates the vestibular impulses with other

systems to maintain body balance.

Crista (cupula and ampullary crest) When movement of the endolymph causes cupula to bend, sensory hair cells generate nerve impulses which the brain perceives as angular acceleration.

Semicircular Canals

They responds to angular acceleration and deceleration.

Three canals lies at right angle to each others so that any change in position of head can be detected.

Stimulation of this canals produce Nystagmus

Utricle and Saccule

Collectively called as OTOLITH ORGAN.

Stimulated by linear acceleration and deceleration and gravitational pull during the head tilts.

Maintenance of Body EquilibriumMaintain by Vestibular , Visual and

Somato-sensory components. If one of these components is

disturbed for longer period Vertigo and Ataxia will develop.

VERTIGO AND DIZZINESS

Disorientation in space causes vertigo or dizziness which arises due to disorder of Vestibular, Visual and Somato-sensory system.

Motion Sickness

Characterized by Nausea ,Vomiting , Pallor and Sweating during travel in sea, Bus, or car.

Arise from the mismatch of information reaching the vestibular nuclei and cerebellum from the visual, labyrinthine and somato-sensory system.