The Ear Three parts of the ear Outer

The Ear

Three parts of the ear • Outer ear – The Pinna – what we see on the sides of our head – – The pinna gather sound into our ears • The Ear canal leads to the: • Middle Ear – The section from the ear drum to the oval window – Contains three small bones, the malleus, incus, and stapes (hammer, anvil, and stirrup), ILLUSTRATION 1

The Inner Ear • The inner ear is composed of the cochlea, from the Greek word for snail, and the semicircular canals • The cochlea is filled with fluid, and the pushing and pulling of the stapes on the oval window moves the fluid in this coiled tube ILLUSTRATION 1

External ear • The folds in the ear channel sounds into our inner ear. Since each person has slightly different folds and channels, we each hear slightly differently. ILLUSTRATION 1

Sound Amplification The Pinna and ear canal amplify sound coming into the ear 20 times Bonus slide –no illustration

Middle Ear • carries vibrations from the eardrum to the inner ear. • The stapes, pulls or pushes on the membranous oval window The oval window is a closed membrane, but acts as the entrance to the inner ear for sound energy. ILLUSTRATION 2

Inner Ear – Cochlea stretched out • The vibrations travel into the fluid of the upper tube of the cochlea and around the tip of the organ into the fluid of the lower tube. • the round window releases the pressure of this motion

Inner Ear • Mechanical to electrical impulse • Fluid -The motion of the stapes sets the fluid in the top moving • Hair Receptors

Hearing – Cochlear Duct • Hair Receptors - Displacement

Geography of the Cochlea 20, 000 Hz 1500 hz 500 Hz 20 Hz • Where different sound frequencies will trigger these hair cells has been mapped

20, 000 Hz 1500 Hz 20 Hz

Cochlear Duct • Vestibular duct and Tympanic duct – Fluid and bone

Equilibrium • Hair Cells • Vestibular complex – 3 basic directional movements • When you tilt your head the fluid in the cochlear duct pushes the hair receptors in different directions

Hearing Process • Step 1 –sound waves arrive at the tympanic Membrane • Directionality

Sound Location • We can distinguish the slightest variation in amplitude (volume) and therefore determine direction of sounds

Step 2 • Movement of the tympanic membrane causes displacement of the auditory ossicles

Step 3 • Movement of the stapes establishes pressure waves in the perilymph

Step 4 • Pressure waves distort the basilar membrane

Step 5 • Transformation of mechanical impulse

Step 6 • Information to the Nervous system

Organ of Corti

Nerves

Signals • Two types of signalling: • Dendrites • Axons

Chemical messengers

Space and joining • Synapse • Synaptic Cleft