1. Auditory System…What??? It plays an important role in language development and social interactions… Plus…it alerts us to dangerous situations! The auditory system transforms sound waves into neural messages that the brain then processes into what we consciously hear.

2. The Ear….Part 1 (The Outer Ear)..The Sound Comes In… The outer ear “collects” the sound waves. Its made up of… – The Pinna The flap of skin and cartilage attached to each side of our head. The Pinna catches sound waves and channels them into the auditory canal. – The Auditory Canal Sound waves travel down the auditory canal and bounce into the ear drum.

3. The Outer Ear, Con’t. The Eardrum or tympanic membrane – A tightly stretched membrane located at the end of the auditory canal. – The eardrum vibrates when hit by sound waves. The vibrations of the eardrum match the intensity of the sound waves.

4. The Sound then goes into….the Middle Ear The middle ear amplifies the sound waves. Its made up of the Hammer, anvil and stirrup – These are 3 tiny bones in your middle ear – Their joint action doubles the amplification of sound. And, the oval window… – The stirrup transmits the amplified vibrations to the oval window – Which is a small membrane separating the middle ear from the inner ear. It relays the vibrations to…..

5. The Inner Ear The inner ear transfers sound waves into neural messages… – The Cochlea Receives vibrations from the oval window It’s a spiral-shaped, fluid filled membrane that contains the basilar membrane and hair cells – Basilar Membrane Runs the length of the cochlea Holds the hair cell receptors for hearing – Hair Cells Sensory Receptors embedded in the basilar membrane The hair cells transfer the physical vibration of the sound waves into neural impulses

6. So basically….it’s a “chain reaction” – Chain Reaction…explained: Outer ear channels sound waves through canal to the eardrum. This vibrates with the waves and then the middle ear transmits to the cochlea. The vibrations cause the cochlea to vibrate, which moves fluid which affects the hair cells in the basilar membrane. (Damage to hair cells account for most hearing loss) This triggers nerve cell impulses which will form the auditory nerve and sends neural messages to the brain.

7. The Neural impulses then go to the….. The BRAIN – As the hair cells bend, they stimulate the cells of the auditory nerve. – The auditory nerve carries the neural messages to the thalamus and then to the temporal lobe’s auditory cortex.

8. Hearing is highly adaptive…(audition) – Sound waves are moving air molecules. Our ears detect air pressure changes. – Transmitted into nerve impulses and our brains decode as sounds. Amplitude: Strength of sound waves (loudness) Frequency: variance in wavelength which affects pitch. (the highness or lowness of a tone) Sound measured in decibels.

9. Distinguishing Pitch Pitch is the relative highness or lowness of a sound. – There are two theories associated with this.. Frequency Theory – Brain reads pitch by monitoring frequency of neural impulses…at the same rate as the sound wave. – Helps explain how we sense low pitch sounds. Place Theory – Different places in the cochlea are stimulated by different sound waves (pitches) (Explains high pitched sounds) – Difficult to explain low pitched sounds…not so neatly organized in the basilar membrane…where the hair cells are)

10. Frequency Theory According to the frequency theory, the basilar membrane vibrates at the same frequency as the sound wave. Explains how low-frequency sounds are transmitted to the brain. However, since individual neurons cannot fire faster than about 1000 times per second, the frequency theory does not explain how the much faster high-frequency sounds are transmitted.

11. Hermann von Helmholtz’s Place Theory According to this theory, different frequencies excite different hair cells at different locations along the basilar membrane Different places in the cochlea are stimulated by different sound waves (pitches) (Explains high pitched sounds) Difficult to explain low pitched sounds…not so neatly organized in the basilar membrane…where the hair cells are) High-frequency sounds cause maximum vibrations near the stirrup end of the basilar membrane Lower-frequency sounds cause maximum vibrations at the opposite end.

12. Hearing Loss: Two major causes Cause 1: Conduction deafness – Caused when the tiny bones in the middle ear are damaged and cannot transmit sound waves to the inner ear. (Physical damage to the ear) – Hearing aids can amplify sound and help overcome conduction deafness.

13. Hearing loss, Con’t. Cause 2: Nerve deafness – Caused by damage to the cochlea, hair cells, or auditory nerve – Exposure to noises such as headphones playing at full blast can damage hair cells and cause permanent hearing loss!!! – Hearing aides cannot help nerve deafness since damage to the hair cells and auditory nerve is almost always irreversible.