Physio ear


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Physio ear

  2. 2. KEY TERMS <ul><li>Auditory periphery : The outer ear, middle ear, and inner ear, ending at the nerve fibers exiting the inner ear. </li></ul><ul><li>Auditory central nervous system : The ascending and descending auditory pathways, which centers in the brainstem and cortex. </li></ul><ul><li>Tonotopic organization : The systematic mapping of sound frequency to the place of maximum stimulation within the auditory system that begins in the cochlea and is preserved through the auditory cortex. </li></ul>
  3. 3. MAIN COMPONENTS OF THE HEARING MECHANISM: <ul><li>Divided into 4 parts (by function): </li></ul><ul><li>Outer Ear </li></ul><ul><li>Middle Ear </li></ul><ul><li>Inner Ear </li></ul><ul><li>Central Auditory Nervous System </li></ul>
  4. 4. STRUCTURES OF THE OUTER EAR <ul><li>Auricle (Pinna) </li></ul><ul><li>Gathers sound waves </li></ul><ul><li>Aids in localization </li></ul><ul><li>Amplifies sound approx. 5-6 dB </li></ul>
  5. 5. <ul><li>The outer ear serves a variety of functions: </li></ul><ul><ul><li>1. It protects the more delicate middle and inner ears from foreign bodies. </li></ul></ul><ul><ul><li>2. It boosts or amplifies high-frequency sounds. </li></ul></ul><ul><ul><li>3. The outer ear provides the primary cue for the determination of the elevation of a sound’s source. </li></ul></ul><ul><ul><li>4. The outer ear assists in distinguishing sounds that arise from in front of the listener from those that arise from behind the listener. </li></ul></ul>
  6. 6. EXTERNAL AUDITORY CANAL: <ul><li>Approx. 1 inch long </li></ul><ul><li>“ S” shaped </li></ul><ul><li>Outer 1/3 surrounded by cartilage; inner 2/3 by mastoid bone </li></ul><ul><li>Allows air to warm before reaching TM </li></ul><ul><li>Isolates TM from physical damage </li></ul><ul><li>Cerumen glands moisten/soften skin </li></ul>
  7. 7. TYMPANIC MEMBRANE <ul><li>Thin membrane </li></ul><ul><li>Forms boundary between outer and middle ear </li></ul><ul><li>Vibrates in response to sound waves </li></ul><ul><li>Changes acoustical (sound) energy into mechanical energy </li></ul>
  8. 8. <ul><li>Middle Ear </li></ul><ul><li>The middle ear consists of a small air-filled cavity lined with a mucous membrane that forms the link between the air-filled outer ear and the fluid-filled inner ear. </li></ul><ul><li>This link is accomplished mechanically via three tiny bones, the ossicles: </li></ul><ul><ul><li>Malleus </li></ul></ul><ul><ul><li>Incus </li></ul></ul><ul><ul><li>Stapes </li></ul></ul>
  9. 9. <ul><li>The purpose of the elaborate link between the air-filled outer ear and the fluid-filled inner ear is to compensate for the loss of energy that would occur if sound waves struck the fluid-filled inner ear directly. </li></ul><ul><li>The middle ear compensates for this loss of sound energy through two primary mechanisms: </li></ul><ul><ul><li>1. The areal ratio of the tympanic membrane to the footplate of the stapes </li></ul></ul><ul><ul><li>2. The lever action of the ossicles </li></ul></ul>
  10. 11. EUSTACHIAN TUBE ( “THE EQUALIZER”) <ul><li>Mucous-lined (protection), connects middle ear cavity to nasopharynx </li></ul><ul><li>“ Equalizes” air pressure in middle ear </li></ul><ul><li>Normally closed, opens under certain conditions </li></ul><ul><li>May allow a pathway for infection </li></ul><ul><li>Children “grow out of” most middle ear problems as this tube lengthens and becomes more vertical </li></ul>
  11. 12. STAPEDIUS MUSCLE <ul><li>Attaches to stapes </li></ul><ul><li>Contracts in response to loud sounds; (the Acoustic Reflex) </li></ul><ul><li>Changes stapes mode of vibration; makes it less efficient and reduce loudness perceived </li></ul><ul><li>Built-in earplugs! </li></ul><ul><li>Absent acoustic reflex could signal conductive loss or marked sensorineural loss </li></ul>
  12. 13. STRUCTURES OF THE INNER EAR: THE COCHLEA <ul><li>Snail shaped cavity within mastoid bone </li></ul><ul><li>2 ½ turns, 3 fluid-filled chambers </li></ul><ul><li>Scala Media contains Organ of Corti Converts mechanical energy to electrical energy </li></ul>
  13. 14. TRANSMISSION OF SOUND TO THE INNER EAR <ul><li>The route of sound to the inner ear follows this pathway: </li></ul><ul><ul><li>Outer ear – pinna, auditory canal, eardrum </li></ul></ul><ul><ul><li>Middle ear – malleus, incus, and stapes to the oval window </li></ul></ul><ul><ul><li>Inner ear – scalas vestibuli and tympani to the cochlear duct </li></ul></ul><ul><ul><ul><li>Stimulation of the organ of Corti </li></ul></ul></ul><ul><ul><ul><li>Generation of impulses in the cochlear nerve </li></ul></ul></ul>
  14. 15. ORGAN OF CORTI <ul><li>The end organ of hearing </li></ul><ul><ul><li>Contains stereocilia & receptor hair cells ( contains auditory sensory cells) </li></ul></ul><ul><ul><li>3 rows OHC, 1 row IHC </li></ul></ul><ul><ul><li>Tectorial and Basilar Membranes </li></ul></ul><ul><ul><li>Cochlear fluids </li></ul></ul>(From Augustana College, “Virtual Tour of the Ear”)
  15. 16. HAIR CELLS <ul><li>Frequency specific </li></ul><ul><ul><li>High pitches= base of cochlea </li></ul></ul><ul><ul><li>Low pitches= apex of cochlea </li></ul></ul><ul><ul><li>Fluid movement causes deflection of nerve endings </li></ul></ul><ul><ul><li>Nerve impulses (electrical energy) are generated and sent to the brain </li></ul></ul>
  16. 17. VESTIBULAR SYSTEM <ul><li>Consists of three semi-circular canals </li></ul><ul><li>Monitors the position of the head in space </li></ul><ul><li>Controls balance </li></ul><ul><li>Shares fluid with the cochlea </li></ul><ul><li>Cochlea & Vestibular system comprise the inner ear </li></ul>
  17. 18. CENTRAL AUDITORY SYSTEM <ul><li>VIII th Cranial Nerve or “Auditory Nerve ” </li></ul><ul><ul><li>Bundle of nerve fibers </li></ul></ul><ul><ul><li>Travels from cochlea through internal auditory meatus to skull cavity and brain stem </li></ul></ul><ul><ul><li>Carry signals from cochlea to primary auditory cortex, with continuous processing along the way </li></ul></ul><ul><li>Auditory Cortex </li></ul><ul><ul><li>Wernicke’s Area within Temporal Lobe of the brain </li></ul></ul><ul><ul><li>Sounds interpreted (analyze) based on experience/association </li></ul></ul>
  18. 19. MECHANISMS OF HEARING <ul><li>Acoustic energy, in the form of sound waves, is channeled into the ear canal by the pinna. </li></ul><ul><li>Sound waves hit the tympanic membrane and cause it to vibrate, like a drum, changing it into mechanical energy . </li></ul><ul><li>The malleus, which is attached to the tympanic membrane, starts the ossicles into motion. </li></ul><ul><li>The stapes moves in and out of the oval window of the cochlea creating a fluid motion, or hydraulic energy . </li></ul>
  19. 20. NEXT..... <ul><li>The fluid movement causes membranes in the Organ of Corti to shear against the hair cells. </li></ul><ul><li>The neurotransmitter released by hair cells to stimulate the dendrites of afferent neurons </li></ul><ul><li>This creates an electrical signal which is sent up the Auditory Nerve to the brain. </li></ul><ul><li>The brain interprets it as sound! </li></ul>
  20. 22. Mechanisms of Hearing Slide 8.29 Figure 8.14
  21. 23. 6 STEPS OF HEARING PROCESS Figure 17–29
  22. 24. BALANCE AND ORIENTATION PATHWAYS <ul><li>There are three modes of input for balance and orientation </li></ul><ul><ul><li>Vestibular receptors </li></ul></ul><ul><ul><li>Visual receptors </li></ul></ul><ul><ul><li>Somatic receptors </li></ul></ul><ul><li>These receptors allow our body to respond reflexively </li></ul>
  23. 25. MECHANISMS OF EQUILIBRIUM AND ORIENTATION <ul><li>Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule </li></ul><ul><ul><li>Maintains our orientation and balance in space </li></ul></ul><ul><ul><li>Vestibular receptors monitor static equilibrium </li></ul></ul><ul><ul><li>Semicircular canal receptors monitor dynamic equilibrium </li></ul></ul>
  25. 27. Organs of Equilibrium Slide 8.30a <ul><li>Receptor cells are in two structures </li></ul><ul><ul><li>Vestibule </li></ul></ul><ul><ul><li>Semicircular canals </li></ul></ul>Figure 8.16a, b
  26. 28. Organs of Equilibrium Slide 8.30b <ul><li>Equilibrium has two functional parts </li></ul><ul><ul><li>Static equilibrium – sense of gravity at rest </li></ul></ul><ul><ul><li>Dynamic equilibrium – angular and rotary head movements </li></ul></ul>Figure 8.16a, b
  27. 29. Static Equilibrium - Rest Slide 8.31 <ul><li>Maculae – receptors in the vestibule </li></ul><ul><ul><li>Report on the position of the head </li></ul></ul><ul><ul><li>Send information via the vestibular nerve </li></ul></ul><ul><li>Anatomy of the maculae </li></ul><ul><ul><li>Hair cells are embedded in the otolithic membrane </li></ul></ul><ul><ul><li>Otoliths (tiny stones) float in a gel around the hair cells </li></ul></ul><ul><ul><li>Movements cause otoliths to bend the hair cells </li></ul></ul>
  28. 30. Function of Maculae Slide 8.32 Figure 8.15
  29. 31. Dynamic Equilibrium - Movement Slide 8.33a <ul><li>Crista ampullaris – receptors in the semicircular canals </li></ul><ul><ul><li>Tuft of hair cells </li></ul></ul><ul><ul><li>Cupula (gelatinous cap) covers the hair cells </li></ul></ul>
  30. 32. Dynamic Equilibrium <ul><li>Action of angular head movements </li></ul><ul><ul><li>The cupula stimulates the hair cells </li></ul></ul><ul><ul><li>An impulse is sent via the vestibular nerve to the cerebellum </li></ul></ul>
  32. 34. DON’T FORGET… <ul><li>The vestibular apparatus DOES NOT automatically compensate for forces acting on the body… it sends warning signals to the CNS which initiates the appropriate “righting” compensations to keep your body balanced, weight distributed, & eyes focused on location . </li></ul>
  33. 35. AUDITORY PATHWAY TO THE BRAIN <ul><li>Organ of Corti  spiral ganglion (in cochlear nerve)  cochlear nuclei of medulla  superior olivary nucleus (pons/ medullary junction)  along the lateral lemniscal tract to inferior colliculus (midbrain)  medial geniculate body of thalamus  auditory cortex in temporal lobe </li></ul>