transduction , AUDITORY PATHOLOGY , AND AUDITORY PERCEPTION Mechanism of sound transduction , AUDITORY PATHOLOGY , AND AUDITORY PERCEPTION BY : NUR AZMINA MOHD ZAILAN NUR FARHANA OTHMAN NUR ZULAIKHA MAT ZAWAWI NUR NABILA ROZAINI NUR ATHIRAH MOHD AZHAR

BY : NUR AZMINA MOHD ZAILAN NUR FARHANA OTHMAN Mechanism of sound transduction BY : NUR AZMINA MOHD ZAILAN NUR FARHANA OTHMAN

HOW THE EAR HEARS ? SOUND BRAIN AURICLE AUDITORY OSSICLES (M, I, S ) TYMPANIC MEMBRANE VESTIBULAR WINDOW (OVAL WINDOW) PERILYMPH AUDITORY OSSICLES (M, I, S ) SCALA VESTIBULI COCHLEA (ORGAN OF CORTI ) BRAIN

COCHLEA Long coiled tube Three channels The top tube is the scala vestibuli, which is connected to the oval window. The bottom tube is the scala tympani, which is connected to the round window. The middle tube is the scala media, which contains the Organ of Corti. The Organ of Corti sits on the basilar membrane, which forms the division between the scalae media and tympani.

high frequency sounds stimulate the base of the cochlea, whereas low frequency sounds stimulate the apex. Sound waves cause the oval and round windows at the base of the cochlea to move in opposite directions   causes the basilar membrane to be displaced and starts a traveling wave that sweeps from the base toward the apex of the cochlea 

Organ of corti The traveling wave causes the Organ of Corti to move up and down. The tectorial membrane to move laterally over the hair cells. This motion bends the cilia and opens the trap-door channels . The influx of potassium and then calcium causes neurotransmitter release. Most of the afferent dendrites make synaptic contacts with the inner hair cells.

Most of the afferent dendrites synapse on inner hair cells. Most of efferent axons synapse on the outer hair cells. The outer hair cells are active. They move in response to sound and amplify the traveling wave. 

Auditory Pathology

Definition Auditory Pathology:- The cause and effect of diseases relating to the sense of hearing.

There are several major categories that can affect the auditory system:- Developmental defects Infections Trauma Vascular Disorders Aging Disorders Tumor

Developmental defect Potential development defects are numerous, and many of them are inherited. Many inherited disorders result in congenital hearing loss; others result in progressive hearing loss later in life. Infections Common cause of outer and middle ear disorder. Caused by bacteria, virus or fungus. Can result in significant sensorineural hearing loss. Trauma Physical and acoustic Physical- Ossicular disruption, fracture of temporal bone. Acoustic- Due to excessive noise.

Vascular disorder Interruption of blood supply to the cochlea can cause a loss of hair cell function which result in permanent hearing loss. Causes of blood supply interruption- stroke, diabetes mellitus. Aging disorder Presbyacusis- a decline in hearing as a part of aging process.

Types of Hearing Loss Critical Fact types: CONDUCTIVE: processes that prevent sound from reaching the cochlea. It caused by problems in the external ear (often when the ear canal is blocked, by wax for example), or the middle ear (otitis, glue ear, damaged ossicles,…). SENSORINEURAL: processes that damage hair cells, spiral ganglion cells (and/or the auditory nerve) or cochlear nucleus neurons.

MIXED: both conductive and sensorineural OTHER CONDITIONS Central auditory processing disorders (CAPD) -primarily CNS problems, but may involve sensorineural hearing loss Presbycusis

Conductive

Otitis Externa Infections of the ear canal Caused by bacteria, virus or fungus cultivated in the external ear canal.

Otitis Media Inflammation of middle ear. Caused primarily by Eustachian tube dysfunction.

Sensorineural

Damaged Hair Cells

Tumor in Vestibulocochlear nerve

Auditory Perception The ability to perceive and understand sounds with a specific organ; ears No auditory perception is inability to hear = deafness Different species have different range of hearing – dogs can hear high pitched sound that human can’t hear

Approximate Range (Hz) Species Approximate Range (Hz)  Human 20-20,000 Dog 67-45,000  Cat 45-64,000  Cow 23-35,000  Horse 55-33,500  Sheep 100-30,000  Rabbit 360-42,000  Rat 200-76,000  Mouse 1,000-91,000  Gerbil 100-60,000  Guinea pig 54-50,000  Hedgehog 250-45,000  Raccoon 100-40,000 Ferret 16-44,000  Opossum 500-64,000  Chinchilla 90-22,800  Bat 2,000-110,000  Whale 1,000-123,000 Elephant 16-12,000  Example of the range of hearing in different species