Senses

1. Senses Hearing

2. Structures of the EAR • Outer Ear • Pinna • External auditory canal • Tympanic membrane (ear drum) • Middle Ear • Malleus (hammer) • Incus (anvil) • Stapes (stirrup) • Inner Ear • Cochlea • Semicircular canals (labyrinth)

3. Ear and Hearing • Outer ear – funnels sound waves into the outer ear canal, to the eardrum, which cause it to vibrate • Middle ear – vibrations are conducted through 3 “air filled” ossicles – amplify and transmit mechanical movements to oval window (cochlea) • Inner ear – vibrations of the oval window produce pressure waves in the “fluid” within the cochlea. Cochlea transduces energy of vibrating fluid into action potentials

4. Cochlea • Cochlea is filled with fluid • The middle ear passes sound vibrations along to the cochlea • The waves in the fluid cause hair cells (mechanoreceptors to vibrate) • The vibration of these cells causes a action potential to be sent to the brain via the auditory nerve.

5. Detection of Sound • Sound is detected by the frequency of impulses in the sensory neuron. Quality of sound is determined by: • Volume (loudness) of a sound depends on amplitude of sound waves produced. • Pitch (shrillness) is determined by number of vibrations per second. Humans can hear pitch in range of 20 to 20,000 Hz. Dogs 40,000 Hz.

6. Equilibrium - Semicircular Canals • Detect orientation (body position) and gravity • Hair cells along 3 planes respond to shifts of liquid within the cochlea. • The signals from this part of this organ are sent to the cerebellum

7. Deafness • 1 in every 1,000 newborns is profoundly deaf, while 1 in 20 has significant hearing impairment. • Most of the 28 million deaf or hearing-impaired people in the United States were born with normal hearing. • Deafness usually results from overexposure to loud noise, disease or old age. Genetics is also a cause of hearing loss, especially children.