HOW WE HEAR

THE OUTER EAR

• Sound waves enter through here
• Pinnae captures sound waves and channels them through the auditory canal
• The number of waves lengths (frequency) entering ear determines the pitch
• The amplitude will determine the strength of sound waves entering ear

AUDITORY CANAL

• Channels sound waves to eardrum

THE EARDRUM

• Skin stretched across opening of inner ear
• Vibrates the sound waves (amplifys)
• Sends sound waves to mid ear

THE MIDDLE EAR

• Vibrations go through ossicles (hammer -> anvil ->stirrup)
• Amplify and relay vibrations from ear drum
• The oval window is where the stirrup attaches to the cochlea
• Soundwaves from stirrup are sent to cochlea

THE COCHLEA

• Snail shaped and fluid filled
• Hearing receptor cells are located here and trigger nerve impulses
• Incoming vibrations jostle fluid (pressure change)
• Cause ripples in basilar membrane
• Place and frequency theory helps determine the pitch of waves

HELMHOLTZ PLACE THEORY

• Determines high pitch
• Cochlea is stimulated in different parts
• Each part of cochlea stimulated gives off a different pitch
• Brain determines pitch by recognizing place generating neural signal
• Many sound waves =high pitch

FREQUENCY THEORY

• Determines low pitch
• Rate of nerve impulses traveling through auditory canal =frequency of tone
• Volley Principle:
• Neural cells alternate firing in rapid succession to form a combined frequency
• Less amount of sound waves = lower pitch

BASILAR MEMBRANE

• Vibrations from cochlea to basilar membrane trigger hair cell movement
• Cilia: short, microscopic, hairlike vibrating structure- bend when stimulated
• Triggers adjacent nerve cells
• Causes neural impulses to be fired to auditory nerve

AUDITORY NERVE

• Basilar membranes adjacent neural cell axons form auditory nerve
• Send neural messages through thalamus
• Transduction: sound waves are being changed into electrical impulses
• From thalamus message sent to the temporal lobes auditory cortex
• As message hits the brain we are able to hear