Physiology of acoustic Physiology of acoustic and vestibular analyzerand vestibular analyzer

Sound conducting apparatusSound conducting apparatus1. directs the sound1. directs the sound2. increases sound intensity2. increases sound intensity3. protects the ear from 3. protects the ear from

intensive soundintensive sound

Functions of receptors in acoustic Functions 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 special Coding of information into a special

pattern of action potentials pattern of action potentials

Functions of ascending pathways in Functions of ascending pathways in acoustic analyzeracoustic analyzer

Transmission of information to cerebral Transmission of information to cerebral cortexcortex

Detection of sound direction, produced by Detection of sound direction, produced by superior olivary nucleussuperior olivary nucleus

Organization of primary reflexes by Organization of primary reflexes by midbrainmidbrain

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 sounds Detection of the direction of the sounds Detection of special modulation of sounds, such as noise Detection 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 other Associate 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)

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 the Low 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 the High 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 membrane Intermediate distances activate the basilar membrane between these two extremesbetween these two extremes

Thus, there is spatial organization of the nerve fibers Thus, there is spatial organization of the nerve fibers from the cochlea to the cerebral cortex. Specific brain from the cochlea to the cerebral cortex. Specific brain neurons are activated by specific sound frequencies.neurons are activated by specific sound frequencies.

Determination of sound frequencyDetermination of sound frequency

Sounds up to 1000 Hz are coded by Sounds up to 1000 Hz are coded by frequency principle, i.e. by the number of frequency 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 Hz This coding is restricted by 1000 Hz

because of nerve labilitybecause of nerve lability

Sensory cells of cochlear

Spiral ganglion

Cochlear nuclei

Olives nuclei

Inf. col.

MGB

Temporallobe

Cochlear nuclei

Olives nuclei

Inf.col.

MGB

Temporallobe

ADEQUATE STIMULIADEQUATE STIMULI For otolit apparatusFor otolit apparatus – – gravitational gravitational

accelerationacceleration ( (disposition of the center of disposition of the center of gravitygravity))

For semicircular channels receptorsFor semicircular channels receptors – – angular accelerationangular acceleration ( (turning of the headturning of the head))

Vestibuloreceptors

Vestibular nucleiR, B, Sh. D

γ & α motoneurons

extensors

Neck muscles

cerebellum

hypothalamus

MidbrainIII,IV, VI

thalamusVPL

Somato-sensory cortex

Life important centers

Eye nystagmus

Movement disorders

Vegetative disorders

Sensor disorders