I can Hear you!!!

The workings of the ear…

A human version of a Rube golberg machine

Anatomy of the ear

• The ear is the organ that interprets sounds

• It is divided into three different regions– The outer ear

• What you can see and easily get at

– The middle ear• Smallest part of the ear

– The inner ear• Where the vibrations are transformed into nervous impulses

The Outer Ear

• Overall function:– Captures the sounds and concentrates them

to the membrane

• Parts:– Auricle or Pinna– Auditory Canal

The outer ear

• Sub-functions– Auricle:

• captures sounds

– Auditory canal: • protects the membrane from small insects,

bacteria and dust that could reduce hearing. • This is also where the ceriminous glands excrete

cerumen (ear wax)

The middle ear

• Overall function:– Transforms wave energy into mechanical energy– Amplifies (or attenuates) the sound– Equilibrates pressure on either side of the eardrum

• Parts:– Eardrum– Ossicles (middle ear bones)– Eutaschian tube

The middle ear

• Sub functions:– Eardrum:

• Sensitive membrane that transfers the sound wave into vibrations.

• The eardrum transfers these vibrations to the ossicles

– Ossicles (3)• Malleus (hammer)• Incus (Anvil• Stappes (stirrup)

The middle ear

• Sub functions (continued)– Eustachian Tube

• 4cm long tube that connects to the pharynx• Equilibrates the air pressure on either side of the

eardrum

• On either sound of the eardrum there is air pressure. These 2 pressure must be balanced if they are not balanced the eardrum cannot vibrate and your ear is blocked. To get the ear balanced you must get the pressure on either side to be balanced. Chew, swallow will balance air pressure. Diving, altitude, wind will unbalance them

The inner ear

• Overall function:– Transform the mechanical energy into a

chemical energy (nervous impulse)

• Parts:– Vestibule– Semicircular canals– Choclea

The inner ear

• Sub functions:– Vestibule

• Contains nerve cells that detect the bodies movement and that are sensitive to the gravitational attraction

• These cells send impulses to the cerebellum that allows you stay balanced

• Sub functions– Semicircular canals

• 3 rings filled with liquid• They are oriented according to the three axes in

space• As a person moves through space, the liquid in

these tubes moves differently. This information is passed on to the cerebellum.

• *** There is a specific part in the brain that combines the information received from the eye and from the inner ear : hand eye coordination

• Sub functions (cont.)– Cochlea

• Round tube filled with liquid• Where we find nerve cells able to transform mechanical

energy into nervous impulses• Small hairs inside the cochlea react to their own frequency of

the movement of the liquid• The lower frequencies stimulate the hairs at the end of the

cochlea. High frequencies stimulate hairs at the start of the cochlea.

• The louder a noise, the more nerve cells will be stimulated

How do we hear?

• Sound waves will cause the eardrum to vibrate. The eardrum vibrating pass the sound waves to the ossicles. This motion continues to the cochlea, where tiny hairs will be stimulated based on the frequency and strength of an auditory signal. These hairs stimulate nervous cells that transfer the information to the brain.

From the speaker to your brain

• The path of sound:– Sound which causes the air to vibrate– These vibrations are caught by the auricle and are

concentrated in the auditory canal– The vibrations cause the ear drum to vibrate, which

then starts a chain reaction in the ossicles.– The vibrations make it all the way to the vestibule,

where they travel through liquid– The hairs of the cochlea pick up on these vibrations

and signal the nervous cells that then transfer to the brain the information via nervous impulse

The path of sound

• Auricle

• Auditory canal

• Eardrum

• Ossicles

• Cochlea

• Auditory nerve

• Brain

Waves

• Sound:– Mechanical longitudinal wave

• Sound requires a material medium to propagate itself (in space no one can hear you scream)

• The speed at which sound travels depends on the material medium

– In air 340 m/s (compared with light 300 000 km/s

Sound

• In order to be perceived by the human ear:– 1. the vibrations have to be fast enough

» Frequency between 16 – 20 000 Hz

– 2. the amplitude has to be above the hearing limit (0dB)

** dogs can hear sound going to 80 000 Hz, bats to 120 000 Hz

Decibels

• Definition:– Measures the intensity of a sound

– Humans can hear a sound with an intensity between 0dB to 150 dB. But after a prolonged 80 dB you can permanently damage your hearing.

Decibels

Whisper 30 dB

Conversation at 5 feet 60 dB

Telephone dial tone 80 dB

Truck traffic 90 dB 8 hour max

Motorcycle 100 dB 2 hour max

Power saw at 3 feet 110 dB 30 min max

Loud rock concert 115 dB 15 min max

Pain begins 125 dB

Jet engine at 100 feet 140 dB

Taking care of your ears

• Do not use Q-tips

• Do not stick objects in your ear

• Do not listen to loud music (including earphones)– Music at max – 100 decibels– Desensitizes the cochlea– Eardrum can overvibrate– Ossicles can desensitize