Physiology of Acoustic & Vestibular analyzer

1. Physiology of acousticPhysiology of acoustic
and vestibular analyzerand vestibular analyzer

2. Sound conducting apparatusSound conducting apparatus
1. directs the sound1. directs the sound
2. increases sound intensity2. increases sound intensity
3. protects the ear from3. protects the ear from
intensive soundintensive sound

5. SponsoredSponsored
Medical Lecture Notes –Medical Lecture Notes – All SubjectsAll Subjects
USMLE Exam (America) –USMLE Exam (America) – PracticePractice

7. Functions of receptors in acousticFunctions of receptors in acoustic
analyzeranalyzer
 Detection of sound pitchDetection of sound pitch
 Detection of sound intensityDetection of sound intensity
 Detection of sound directionDetection of sound direction
 Coding of information into a specialCoding of information into a special
pattern of action potentialspattern of action potentials

10. Functions of ascending pathways inFunctions of ascending pathways in
acoustic analyzeracoustic analyzer
 Transmission of information to cerebralTransmission of information to cerebral
cortexcortex
 Detection of sound direction, produced byDetection of sound direction, produced by
superior olivary nucleussuperior olivary nucleus
 Organization of primary reflexes byOrganization of primary reflexes by
midbrainmidbrain

11. Functions of the cortex in hearingFunctions of the cortex in hearing
 The main function- formation of acoustic sensationsThe main function- formation of acoustic sensations
 Location-Heshle gyrus (superior temporal gyrus)Location-Heshle gyrus (superior temporal gyrus)
 Functions: 1. discrimination of sound frequencesFunctions: 1. discrimination of sound frequences
 Psychic sensations of sound pitchesPsychic sensations of sound pitches
 Detection of the direction of the soundsDetection of the direction of the sounds
 Detection of special modulation of sounds, such as noiseDetection of special modulation of sounds, such as noise
versus pure frequency soundsversus pure frequency sounds
 Function of association cortex: Recognition of soundsFunction of association cortex: Recognition of sounds
 Associate sound information with information from otherAssociate sound information with information from other
sensory areas of the cortexsensory areas of the cortex
 recognition of words (Wernike’s area)recognition of words (Wernike’s area)

13. Determination of sound frequencyDetermination of sound frequency
 Place principle for determination of sound frequency:Place principle for determination of sound frequency:
 Low frequency sounds cause maximal activation of theLow frequency sounds cause maximal activation of the
basilar membrane near the apex of the cochleabasilar membrane near the apex of the cochlea
 High frequency sounds cause maximal activation of theHigh frequency sounds cause maximal activation of the
basilar membrane near the basis of the cochlea (oval &basilar membrane near the basis of the cochlea (oval &
round windows)round windows)
 Intermediate distances activate the basilar membraneIntermediate distances activate the basilar membrane
between these two extremesbetween these two extremes
 Thus, there is spatial organization of the nerve fibersThus, there is spatial organization of the nerve fibers
from the cochlea to the cerebral cortex. Specific brainfrom the cochlea to the cerebral cortex. Specific brain
neurons are activated by specific sound frequencies.neurons are activated by specific sound frequencies.

16. Determination of sound frequencyDetermination of sound frequency
 Sounds up to 1000 Hz are coded bySounds up to 1000 Hz are coded by
frequency principle, i.e. by the number offrequency principle, i.e. by the number of
action potentials caused in n.cochlearisaction potentials caused in n.cochlearis
 700 Hz = 700 AP, 900 Hz = 900 AP700 Hz = 700 AP, 900 Hz = 900 AP
 This coding is restricted by 1000 HzThis coding is restricted by 1000 Hz
because of nerve labilitybecause of nerve lability

19. Sensory
cells of
cochlear
Spiral
ganglion
Cochlear
nuclei
Olives nuclei
Inf.
col.
MGB
Temporal
lobe
Cochlear
nuclei
Olives nuclei
Inf.
col.
MGB
Temporal
lobe

20. ADEQUATE STIMULIADEQUATE STIMULI
 For otolit apparatus – gravitationalFor otolit apparatus – gravitational
acceleration (disposition of the center ofacceleration (disposition of the center of
gravity)gravity)
 For semicircular channels receptors –For semicircular channels receptors –
angular acceleration (turning of the head)angular acceleration (turning of the head)

24. Vestibulo
receptors
Vestibular nuclei
R, B, Sh. D
γ & α motoneurons
extensors
Neck muscles
cerebellum
hypothalamus
Midbrain
III,IV, VI
thalamus
VPL
Somato-sensory cortex
Life important centers
Eye nystagmus
Movement disorde
Vegetative disorde
Sensor disorders