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Special senses I.
The sense of hearing and equilibrium
„Anatomy“ of sound
Wavelenght in the air
1. Sound is a mechanical wave eitherlongitudinaly or transversaly betweenwithin the frequency of• it can be bend, broken or rebound
2. under 16 Hz • infrasound
3. above 16 kHz • ultrasound
Sound is described by these characteristics: • speed, wavelenght, frequency, intesity, color, pitch
The number of pressure changes in 1 second is called frequencyIts unit is Herz (Hz=s-1), and sign f.
According to frequency, we recognize
Each tone is recognized by the pitch. The higher frequency, thehigher pitch.
Frequency
infrasound16Hz 16 kHzaudible sound ultrasound
Substanace Temperature Speed [m/s]
Gases
Carbon dioxide 0 259
Oxygen 0 613
Air 0 331
Air 20 343
Helium 0 965
Liquids
Chlorophorm 20 1004
Ethanol 20 1162
Mercury 20 1450
Water 20 1482
Rigid material
Plumbum - 1960
Copper - 5010
Glass - 5640
Metal - 5960
Speed of the sound
EAR ANATOMY
Hearing is the perception of energies which are carried by the
sound waves between the 16/20-16 000/20 000 Hz range and
safe loudness of 1-80 dB.
Sound transmission includes transformation to mechanical
waves, propagation by liquid, chemical signals and action
potential.
Primary center of pitch, loudness and duration is in cochlea.
Sound localization is the function of CNS.
HEARING
I. Area of TM / Area
stapes
+
II. Ossicular chain
lever
=
Matches impedance
between air in ME &
fluid in inner ear
Sound amplification by the middle ear
M. stapedius & m. tensor tympani
Attached to stapedius and malleus
Contraction as a response to loud sounds(acustic reflex)
They decrease the stapedius vibration, and thus preception is decreased as well
Response time 40-80 ms
Sound transmission/conversion
Scala vestibuli
Scalamedia/cochle
ar
Scala tympani
1. Sound waves come to and „collide“ with tympanus
2. Created energy istransfered to ossicles ofmiddle ear
3. Vibrations of middle earossicles are transferedthrough ovale foramen to perilymph in vestibular canal. Waves inside the coclea are formed
4. The wave pushes theflexible membrane (Meisnerimembrane) of cochlear canal
5. Sound waves are transferedto tympanic canal and are transformed back to airenergy through the roundforamen
6. Deformation od cochlearcanal will cause the movementof tectorial membrane, so thestereocilia of hairy cells are activated
6
CochleaCochlea is organ, where soundwaves are changed into liquidwaves and then to chemicalsignals and action potentials
Movement of tectorial membrane willmove the cilia on surface of hairycells, so the neurotransmiter isreleased after depolarization.
Or
T
Signal transduction by hairy cells
-30mV
0 mV
++
+
Code
Basal membrane of cochlearcavity is rigid and narrow nearthe oval foramen. It becomeswider and more flexible on distalend
Frequency of sound wavedetermines layout of sound on basal membrane. High frequencyis localised near the stapedius, lower frequency near thehelicotrema (distal end)
Localization of hairy cells on membrane creates code, thatbrain transforms into pitch. Amplitude is coded by theimpulse frequency of actionpotential
Sound localizationApart from time difference, brainuses also difference in
• sound intesity
• period and
• sound wavelenght
when calculating the sound source
Moving with head allows to calculate the 3D space of soundsource.
Practicals
Otoscopy – page 22
Audiometry – page 25
Ear test with tuning forks – page 23
Nystagm examination – page 27
Otoscopy
Practicals
Otoscopy – page 22
Audiometry – page 25
Ear test with tuning forks – page 23
Nystagm examination – page 27
Audiometry
Examination of hearing thresholds
Practicals
Otoscopy – page 22
Audiometry – page 25
Ear test with tuning forks – page 23
Nystagm examination – page 27
Examination with tuningforks
Before audiometry introduced served to helprecognize hearing disorders
– Perception In the brain – problems with detecting and interpreting the sound
– Conduction Outer, middle and partly
inner ear problem
Problem with stimulating the
hairy cells that are otherwise
intact
– Mixed
Weber test• If lateralization occurs then either:
A. Perception disorder in opposite earB. Conduction disorder in the
lateralized ear
Rinne testair conductance > bone conductance
conduction disorder
Practicals
Otoscopy – page 22
Audiometry – page 25
Ear test with tuning forks – page 23
Nystagm examination – page 27
Equilibrium is state which allows the body to be laid down in
3D space under normal gravitational circumstances
Equilibrium is maintained by the hairy cells and liquid filled
space in vestibular organ, and by hairy cells in semicircular
canals of inner ear.
Gravitation and acceleration form force that moves the cilia.
Hairy cells act then as mechanoreceptors
Equilibrium has 2 components: dynamic – detects rotational
movement of head, and static – detects the position of head
according to linear acceleration and gravitation.
Rotation movements are detected by hairy cells in ampula
that is connected to semicircular canals
Gravitational changes are detected by otholits in macula that
are located on base of semicircular canals
Equilibrium
Vestibular system and equilibrium
Rotation and gravitation
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