Topic Sense of hearing

Sajida Batool M.sc(III) Department of Biological science KIU

Importance of hearing Hearing may initially have been important to vertebrate as a mechanism to alert them to dangerous activities. It also important in search for food and mates and in communication.

Cont….. Range; Humans are not able to hear low pitched sounds, below 20 cycles per second . Young children can hear high pitched sounds up to 20,000 cycles per second, but this ability decrease with age.

Structure of human Ear The human ear has three divisions… The outer Ear The middle Ear (eardrum) The inner Ear

Structure of human Ear The outer Ear; The outer ear consist of the Auricle and external auditory canal. Sound waves enter the outer ear and create pressure waves that reached the tympanic membrane.

Structure of human Ear The middle Ear; The middle ear begin at the tympanic membrane and ends inside the skull. Where two small membranous opening, the oval and round windows , are located. Three small ossicles are between the tympanic membrane & the oval window.

Structure of human Ear The middle Ear; They include the Malleus; (hammer) Incus; (anvil) Stapes;(stirrup) So name for their shapes. The Malleus adheres to the tympanic membrane & connect to the incus. The incus connects to the stapes, which adheres to the oval window.

Structure of human Ear The inner Ear; The inner ear has three components. The vestibule semicircular canal Cochlea The first two, The vestibule & semicircular canals, are concerned with equilibrium. Continuous movement of the fluid in the semicircular canal may cause motion sickness or seasickness in human..

Structure of human Ear The inner Ear; Cochlea; In mammals the long coiled sensory structure of the inner ear that contain receptor for sound is the cochlea. this structure provide more surface area for receptor cells & allow mammals greater sensitivity to pitch & volume Then is present in other animals.

Process of hearing The process of hearing can be summarized as follows; Sound waves enter the outer ear and create pressure waves that reached the tympanic membrane. Air molecules under pressure vibrate the tympanic membrane. The vibration move the Malleus to the other side of the membrane. The handle of the Malleus strike the incus, vibrating it.

Process of hearing 5. The vibrating incus moves the stapes back & forth against the oval window. 6. The movement of the oval window set up pressure changes that vibrate the fluid in the inner ear. These vibrations are transmitted to the basilar membrane, causing it to ripple. 7. Receptor hair cells of the organ of corti that are in contact with the overlying tectorial membrane are bent, causing a generator potential , which leads to an action potential that travel along the vestibulocochlear nerve to the brain for interpretation .

Process of hearing 8. vibration in the cochlear fluid dissipate as a result of movement of the round window.

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