Sound Transmission Sound is produced by vibrations which causes bands of compression and rarefaction in molecules of air The ear drum will vibrate sympathetically if the vibration is between If the wave is within this range and of sufficient amplitude the sound will be perceived

The ear has two separate functions: Hearing and (balance) The ear can be divided into three sections: the outer ear, the middle ear and the inner ear. The Ear

The Outer Ear: Consists of the and the a. Pinna – external ear flap designed to sound into ear b. Auditory canal - channel leading into the eardrum - lined with glands which a yellowish/brown waxy substance [ ] which and the ear [can interfere with sound transmission if too much builds up] The Anatomy of the Ear

Anatomy of the Ear Middle ear – Sound waves travel auditory canal and strike the [ear drum] between the outer and middle ear – Behind the membrane is an air-filled chamber that contains three tiny bones called – Movements of the tympanic membrane cause the three small bones [ossicles] of the ear to move transmitting sound to the which separates the middle ear from the inner ear

Anatomy of the Ear Ossicles are named for their shape – 1. Malleus [] – touches tympanic membrane – 2. Incus [] – between malleus and stapes – 3. Stapes [] – touches oval window Bones act as levers the movement of the tympanic membrane Vibration is increased by before it reaches the oval window Pressure differential across tympanic membrane -> inefficient sound transmission [the allows equalization of pressure in middle ear] Video

Inner ear [labyrinth] functions: – Converts sound impulses to which get sent to the brain – Maintenance of & recognition of oval window movement transmits sound waves to inner ear Fluid Filled

Inner Ear: Three distinct structures: – Vestibule: – Involved with balance – Contains two small sacs called the and (function to establish head position) – Cochlea: – Involved with balance – Involved in hearing – Converts sound waves to Semicircular Canals – Identifies Anatomy of the Ear

The Ear Mechanoreceptors for hearing and balance are located in the inner ear.

Cochlea Bony, snail shaped structure leading from the oval window which performs the of vibrations to impulses Contains special called and

Cochlea Three channels of the cochlea: – 1. scala – 2. cochlear – 3. choclear duct

Cochlear Implants /

Organ of Corti Contains connected to neurons Hairs sway against the membrane & bend -> a nerve impulse being sent to the brain along the

Organ of Corti Hair cells are different lengths thus are stimulated by different wavelengths – Low frequency - hairs near tip of cochlea – High frequency - hairs near base of cochlea Brain distinguishes sound frequency differences by which part of brain is stimulated

Sound enters the ear () Tympanic membrane () vibrates Ossicles vibrate Sound is transmitted as bony vibrations through the,, and finally. Vibrations from the stapes cause the of the inner ear to vibrate, which pushes it inward and the pushes the outward This causes a in the inner ear This wave bends the hair cells of the Hair cells stimulate the Signal sent to the central nervous system () Process of Hearing

Loudness perception Depends on of wave Measured on logarithmic decibel () [Alex Bell] (0 dB threshold of human hearing -> 100+ painful/damage to ear) Contraction of middle ear muscles can dampen loud sounds by up to 40 dB

Loudness Perception How loudness is perceived by the brain: – 1. Amplitude of vibration - loud sounds cause large of hair cells --> many sent to brain – 2. Summation - loud sounds move hair cells resulting in many – 3. Variation in threshold - some hair cells only depolarize at - if brain interprets as a loud sound

Two types of Deafness 1. Conduction – Bones of middle ear become “" due to calcification or other problems – Surgery may cure or hearing aid 2. Nerve – Conduction system is functional but or auditory nerve is impaired – Age -> loss of acuity to high frequencies – Exposure to loud sounds -> loss of acuity to low frequencies – Cochlear implants can now restore hearing by electronically stimulating the auditory nerve

Equilibrium The cochlea, semicircular canals, utricle, and saccule all contain hair cells that react to movement.

Equilibrium Inside the vestibule, the utricle and saccule detect gravity and use it to maintain. The which fills these structures contains (calcium carbonate) which move with movements of head, & hair cells. Together these two structures are very important in determining minor (1/2 o ) changes in head position.

EEEEEEEEEEEEEEEEEEEEEEE EEEEEEEEEEEEEEE

Equilibrium The three semicircular canals are involved in maintenance dynamic equilibrium (stopping, starting, turning). They are oriented at 90 o to each other. Hair cells in these canals respond to endolymph motion sending messages to brain allowing motor impulses to be sent to the muscles of the body. [alcohol affects flow of impulses - slows body reaction time - motor neurons do not respond quickly enough to accommodate body position changes]

Equilibrium Proprioceptors in the, joints, and also inform the brain about the position of body parts.

Mechanoreception and Chemoreception Sensory receptors in the tongue ( ), nose ( ), and skin (temperature,, and pain receptors) provide additional information the brain.

Taste () Most of the >10,000 taste buds in the mouth are on the tongue. The tongue is covered with surrounded by Buried taste buds Taste buds are which pick up dissolved chemicals and send to the brain. The brain responds to a combination of these tastes, similar to the way the eye responds to visual stimuli.

Taste (gustation) Four Tastes – Sweet – Sour – Salt – Bitter Taste buds are but quickly. With age the number of active taste buds decreases. How Stuff Works video clip - Tastebuds

Smell () Not well understood and often combined with taste as a sensation. Cells that recognize smell become fatigued easily leading to accommodation to the smell. Olfactory cells are located in the upper part of the nasal cavity in 2 small patches of about 5 cm 2 with > 100 million olfactory cells. Food smells pass up the into the nose to increase the sensation of taste (note reduction of taste when you have a cold)

Touch Receptors in the skin include: – touch – pressure – pain – temperature TLC - Touch

Chapter 12 Concept Organizer