1 The Ear

2 What are we going to learn ? Sound waves Function of the ear Parts of the ear External ear Middle ear Internal ear Sound pollution

3 Sound waves Sound is generated when objects vibrate e.g Guitar string Vibration of objects results in surrounding air expanding and compressing This creates a longitudinal wave in the air Continuous expansion and compression of air results in transmission of the sound wave CompressionExpansion A: Air layers when sound waves are absent B: Changes in air layers because of sound waves

4 The function of the ear Before we can hear anything the related sound waves must reach our ear These waves need a medium to travel, which is usually air The function of the ear is to collect these sound waves and convey them to the auditory nerve for onward transmission to the brain The brain interprets these waves as appropriate sound

5 The three parts of the ear Outer ear Middle ear Inner ear

6 Outer ear Pinna Made of fleshy muscles Used as a funnel to collect sound waves External auditory canal Approx. 2.5 cms long Contains glands that produce a wax like substance which absorbs dust from the atmosphere, thus protecting the ear Pinna External auditory canal

7 Middle ear Ear drum A screen which vibrates when sound waves fall on it Ossicles : three small bones Malleus – attached to the ear drum Incus Stapedius These three bones carry sound waves to the inner ear Eustachian tube Connects the middle ear to the pharynx (throat) Helps maintain equal pressure on both sides of the ear drum MalleusIncusStapedius Eustachian tubeEar drum

8 Inner ear Cochlea Hollow tube filed with fluid Carries the sound waves received from middle ear to the auditory nerve Contains microscopic hairlike cells which vibrate due to sound waves These vibrations excite the auditory nerve Semicircular canals Filled with fluid, these tubes help maintain balance of the body Semicircular canals Cochlea

9 Sound intensity and sound pollution The intensity of sound is measured in decibels ( dB) Sound intensity greater than 80dB can cause permanent hearing loss Such sound pollution can also cause insomnia and hypertension Rustling of leaves, our respiration Upto 20 dB Quiet home or office 20 to 40 dB Ordinary conversation40 to 60 dB TV with volume turned up60 to 80 dB Sound of a truck, small crackers or machines in a factory 80 to 100 dB Drilling machine, car horn100 to 120 dB Sound of large crackers 120 to 140 dB Sound intensity

10 How do we hear (Video)

11 The End