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: Superior olivary complex. Nucleus of lateral laminiscus. Inferior colliculus. Medial geniculate body. Auditory Cortex.(Area 41) FIGURE

AUDITORY PATHWAYS

Mechanism of Hearing Broadly divided into: Mechanical conduction of sound(Conductive apparatus). Transduction of mechanical energy to electrical impulse (Sensory system of Cochlea). 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 Equilibrium Maintain 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.