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