THE AUDITORY SYSTEM AND THE CHEMICAL SENSES

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THE AUDITORY SYSTEM AND THE CHEMICAL SENSES

• D. C. MIKULECKY
• PROFESSOR OF PHYSIOLOGY
• AND
• FACULTY MENTORING PROGRAM

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THE NATURE OF SOUND

• COMPRESSION AND RARIFICATION OF AIR
• WAVES OF HIGH AND LOW PRESSURE
• TRANSMIT MECHANICAL FORCES

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CHARACTERISTICS OF A PRESSURE WAVE
A
T WAVELENGTH A AMPLITUDE f 1/T FREQUENCY
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ANATOMY OF THE EAR

• OUTER EAR
• MIDDLE EAR
• INNER EAR

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OUTER EAR

• ACTS TO FOCUS SOUND WAVES ON THE TYMPANIC
  MEMBRANE
• SHAPED LIKE A SOUND CONE

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OUTER EAR
PINNA
CANAL
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MIDDLE EAR

• THREE BONES LINK TYMPANIC MEMBRANE TO OVAL WINDOW
  
• VIBRATIONS TRANSMITTED MECHANICALLY

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MIDDLE EAR
BONES OF MIDDLE EAR
COCHLEAR FLUID
SOUND WAVE IN EAR CANAL
TYMPANIC MEMBRANE
OVAL WINDOW
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INNER EAR

• SITE OF TRANSDUCTION
• VIBRATION OF COCHLEAR FLUID CAUSES BASILAR
  MEMBRANE TO VIBRATE
• HAIR CELLS ARE DEFORMED
• AUDITORY NERVE BECOMES EXCITED AS HAIR CELLS
  DEPOLARIZE

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INNER EAR
COCHLEA
OVAL WINDOW
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STRUCTURE OF THE COCHLEA
OVAL WINDOW
SCALA VESTIBULI
COCHLEAR DUCT
SCALA TYPANI
ROUND WINDOW
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STRUCTURE OF COCHLEAR DUCT

TECTORIAL MEMBRANE ORGAN OF CORTI
BASILAR MEMBRANE
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TRANSDUCTION MECHANISM
TECTORIAL MEMBRANE STATIONARY
STEROCILIA
HAIR CELLS
AUDITORY NERVE
BASILAR MEMBRANE..VIBRATES
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TRANSDUCTION MECHANISM
TECTORIAL MEMBRANE STATIONARY
STEROCILIA BEND
AUDITORY NERVE
HAIR CELLS
BASILAR MEMBRANE..VIBRATES
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FREQUENCY DISCRIMINATION LOCALIZATION OF
DISPLACEMENT OF BASILAR MEMBRANE
BASE
APEX
HIGH
MID
LOW
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AUDITORY PATHWAYS
INFERIOR COLLICULUS
INFERIOR COLLICULUS
SUPERIOR OLIVE
DORSAL COCHLEAR NUCLEUS
VENTRAL COCHLEAR NUCLEUS
COCHLEA
MIDLINE
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AUDITORY PATHWAYS (CONT.)
TEMPORAL CORTEX
TEMPORAL CORTEX
MEDIAL GENICULATE
MEDIAL GENICULATE
INFERIOR COLLICULUS
INFERIOR COLLICULUS
SUPERIOR OLIVE
MIDLINE
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CHARACTERISTICS OF A PRESSURE WAVE
A
T WAVELENGTH A AMPLITUDE f 1/T FREQUENCY
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PROPERTIES OF AUDITORY NERVE CELLS

• EACH AUDITORY NERVE FIBER HAS AN OPTIMUM
  FREQUENCY
• THIS TONOTOPIC ORGANIZATION ARISES FROM POSITION
  IN THE COCHLEA
• TONIC AND PHASIC NEURONS IN EACH AREA
• SOME RESPOND TO CHANGE IN FREQUENCY
• SOME RESPOND TO CHANGE IN AMPLITUDE

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SOUND LOCALIZATION

• INTERAURAL TIME DIFFERENCE
• TIME DELAY BETWEEN TWO EARS
• ALSO INTENSITY DIFFERENCES

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DISORDERS OF AUDITION

• LOSS OF HAIR CELLS FREQUENCY SPECIFIC
• TINNITUS RINGING
• CONDUCTIVEl DAMAGE TO MIDDLE EAR
• CENTRAL BRAIN TUMORS AND LESIONS

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THE VESTIBULAR APPARATUS

• SEMICIRCULAR CANALS HAIR CELLS SENSE MOTION
• THREE COORDINATE PLANES SUPERIOR, INFERIOR, AND
  HORIZONTAL
• UTRICLE AND SACCULE DETECT LINEAR ACCELERATION IN
  HORIZONTAL AND VERTICLE PLANES

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THE VESTIBULAR APPARATUSUTRICLE SACCULUS
ONE CANAL IN EACH COORDINATE PLANE
UTRICLE SACCULUS
AMPULLA
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THE UTRICLE SACCULUS
OTOCONIA (CALCIUM CARBONATE CRYSTALS)
OTOLITHIC MEMBRANE- GELATINOUS LAYER
HAIR CELLS
NERVE CELLS
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THE UTRICLE SACCULUS
HEAD MOVEMENT
OTOCONIA (CALCIUM CARBONATE CRYSTALS)
OTOLITHIC MEMBRANE- GELATINOUS LAYER
HAIR CELLS
NERVE CELLS
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THE VESTIBULAR APPARATUS SEMICIRCULAR CANALS
ONE CANAL IN EACH COORDINATE PLANE
UTRICLE SACCULUS
AMPULLA
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THE AMPULLA
HAIR CELLS
NERVE CELLS
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THE AMPULLA
MOVEMENT OF HEAD
INERTIAL FLUID MOVEMENT
HAIR CELLS BENT
NERVE CELLS FIRE
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VESTIBULAR INFLUENCE ON EYE MOVEMENTS

• VESTIBULO-OCULAR REFLEXCOMPENSATES FOR HEAD
  MOVEMENT WHILE GAZING ON OBJECT
• SACCADEFAST MOVEMENT OF EYES IN DIRECTION OF
  HEAD MOTION
• NYSTAGMUSSLOW AND FAST MOVEMENTS OF EYES DURING
  ANGULAR ACCELERATION