THE AUDITORY SYSTEM AND THE CHEMICAL SENSES

1
THE AUDITORY SYSTEM AND THE CHEMICAL SENSES

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

2
THE NATURE OF SOUND

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

3
CHARACTERISTICS OF A PRESSURE WAVE
A
T WAVELENGTH A AMPLITUDE f 1/T FREQUENCY
4
ANATOMY OF THE EAR

• OUTER EAR
• MIDDLE EAR
• INNER EAR

5
OUTER EAR

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

6
OUTER EAR
PINNA
CANAL
7
MIDDLE EAR

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

8
MIDDLE EAR
BONES OF MIDDLE EAR
COCHLEAR FLUID
SOUND WAVE IN EAR CANAL
TYMPANIC MEMBRANE
OVAL WINDOW
9
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

10
INNER EAR
COCHLEA
OVAL WINDOW
11
STRUCTURE OF THE COCHLEA
OVAL WINDOW
SCALA VESTIBULI
COCHLEAR DUCT
SCALA TYPANI
ROUND WINDOW
12
STRUCTURE OF COCHLEAR DUCT

TECTORIAL MEMBRANE ORGAN OF CORTI
BASILAR MEMBRANE
13
TRANSDUCTION MECHANISM
TECTORIAL MEMBRANE STATIONARY
STEROCILIA
HAIR CELLS
AUDITORY NERVE
BASILAR MEMBRANE..VIBRATES
14
TRANSDUCTION MECHANISM
TECTORIAL MEMBRANE STATIONARY
STEROCILIA BEND
AUDITORY NERVE
HAIR CELLS
BASILAR MEMBRANE..VIBRATES
15
FREQUENCY DISCRIMINATION LOCALIZATION OF
DISPLACEMENT OF BASILAR MEMBRANE
BASE
APEX
HIGH
MID
LOW
16
AUDITORY PATHWAYS
INFERIOR COLLICULUS
SUPERIOR OLIVE
VENTRAL COCHLEAR NUCLEUS
VENTRAL COCHLEAR NUCLEUS
COCHLEA
MIDLINE
17
AUDITORY PATHWAYS (CONT.)
TEMPORAL CORTEX
TEMPORAL CORTEX
MEDIAL GENICULATE
MEDIAL GENICULATE
INFERIOR COLLICULUS
INFERIOR COLLICULUS
SUPERIOR OLIVE
MIDLINE
18
CHARACTERISTICS OF A PRESSURE WAVE
A
T WAVELENGTH A AMPLITUDE f 1/T FREQUENCY
19
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

20
SOUND LOCALIZATION

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

21
DISORDERS OF AUDITION

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

22
TASTE SENSATION

• GUSTATORY RECEPTORS
• GUSTATORY PATHWAYS

23
GUSTATORY RECEPTORS

• TASTE BUDS ON TONGUE LOCALIZED
• SWEET TIP
• BITTERBACK
• SOUR SIDES
• SALT FRONT

24
GUSTATORY PATHWAYS

• VII, IX, X CRANIAL NERVES
• TO GUSTATORY NUCLEUS IN BRAIN STEM
• VPM NUCLEUS OF THALAMUS
• GUSTATORY AREA OF NEOCORTEX
• VIA LIMBIC SYSTEM TO HYPOTHALAMUS

25
THE OLIFACTORY SYSTEM

• RECEPTOR CELLS IN OLIFACTORY MUCOSAL MEMBRANE
• AXONS CROSS CRIBIFORM PLATE AND TERMINATE ON
  MITRAL CELLS IN OLIFACTORY BULB-FORM OLIFACTORY
  TRACT
• OLIFACTORY TRACT GOES TO LIMBIC SYSTEM AND TO
  ORBITOFRONTAL CORTEX
• CLOSELY ASSOCIATED WITH EATING AND MATING BEHAVIOR