1. Biophysics of Hearing Ján Jakuš

2. Hearing – is very important human sense because through the ear we can receive sound, music or noise. Sound - is a kind of mechanical (pressure) energy, that results from vibration of air molecules. Thus, in a vaccum there is no sound, because no molecules that could undergo the vibration. Velocity of sound in air is approx. 330 m/ s. However, in liquids the velocity of sound is 5-times higher, in solids there is a velocity even 20-times higher, but its intensity (amplitude ) is lower.

3. Frequency of the sound – is the number of waves that pass a given point, in a given time. The shorter is the wavelenght ( λ ), the higher is the sound frequency, and vice versa. Most sounds are mixtures of several frequen- cies. Harmonic sounds with the same frequency enable the perception of music. There are 4 subjectively perceiving sound properties : Pitch, Color, Strenght,Duration of the sound Frequency of the sound – is the number of waves that pass a given point, in a given time. The shorter is the wavelenght ( λ ), the higher is the sound frequency, and vice versa. Most sounds are mixtures of several frequen- cies. Harmonic sounds with the same frequency enable the perception of music. There are 4 subjectively perceiving sound properties : Pitch, Color, Strenght,Duration of the sound. Watch! For physical properties of sound, also a light, electricity or magnetism, look Nave &Nave

4. Among the subjectively percieved properties of sound, the most important is the Strenght. The human ear can dis- tinguish the sound within the frequency range from 16 Hz – 20 000 Hz, but it is the most sensitive for sound frequen-cies between 1500 – 4000 Hz. The higher is the frequency, the bigger is the pitch of the sound, and vice versa. The Loudness of the sound closely co- rrelates with the Amplitude of the sound. The higher is the amplitude, the louder is the sound, and vice versa.

5. Intensity of the sound in created in environment is mea- sured in units named decibels (dB). The ear threshold for the minimal sound intensity coming from environment is 0 dB. Subjectively percieved soud intensity is measured in units named Phons (Ph). At frequency of 1 kHz the scale for sound intensity (given in dB ) equals to scale for subjectively percieved intensity (given in Phons) The perception of sound changes into the pain sensa- tion at the sound intensity around 130 dB (the pain threshold). The hearing threshold is examined by a diagnostic method – AUDIOMETRY. Audiometer is an electronic generator of a sound frequencies at different intensities. Audiometry enables to obtain a graphical record of hea- ring loss for right and left ears.

6. EAR - scheme EAR - scheme

7. EAR ANATOMY. EAR ANATOMY. Ear consists of: I. Outer Ear – composed of the Pinna (auricula), and the Auditory canal (Ear canal) II. Middle Ear – composed of Tym- panic membrane (Ear drum) + 3 ossicles: Maleus (Hammer), Incus (Anvil), Stapes ( s tirrup) + Oval win- dow and the Round window + Two tiny musles (the stapedius muscle and tensor tymphani muscle) being connected with the ossicles + Eustachian tube (3.5 cm long tube connecting the middle ear with pharynx, thus balancing the air pressures within the middle ear and in the atmosphere. ( Inflammation can enter from nasopharynx to the middle ear in children, because ET is short) III. Inner Ear - Cochlea with Organ of Corti

8. SOUND PERCEPTION

9. Composition of Inner Ear

10. Organ of Corti - composition Organ of Corti - composition

11. Mechanism of hearing: The pinna captures the sound energy from the envi- ronment and directs it through the auditory canal to the eardrum. Then, the sound passes three small ossic- les, being located within the midle ear. Mechanism of hearing: The pinna captures the sound energy from the envi- ronment and directs it through the auditory canal to the eardrum. Then, the sound passes three small ossic- les, being located within the midle ear. Next, when pas- sing the last ossicle – stapes - the sound comes throu- ght the Oval window into the Cochlea of the inner ear.The Cochlea is divided into three parts: SCALA VESTIBULY (is filled in with a perilymph, that consists of a high concentration of Na + cations, and Cl - anions and higher amount of proteins), SCALA MEDIA (filled with endolymph consisting a high concentration of K + cations and lower concentration of Na + and Cl - ions) and SCA- LA TYMPANI (filled again with perilymph). The different concentrations of ions (mainly K + ) play a key role in production of local electrical changes (GP and AP).

12. Within the Scala Media there is the Corti´s Organ, placed on the basilary membrane, consisting of one row of the INNER HAIR CELLS (they serve as proper receptors for hearing) + three rows of OUTER HAIR CELLS (serving as pre-amplifier) both equipped with stereocilia. Entering the Inner Ear, the sound pushes both the perilymph and endolymph, resulting in the liquid movements. Such liquid oscillations bend the stereocilia of the hair cells within the Corti´s Organ of the Scala Media. One direction of bending causes the depola- rization of the Hair cells, an opposite bending results in their hyperpolarization. GP rises up within the filaments of Inner Hair cells. AP is created in the axons leaving the Inner Hair Cells.

13. These APs are transmitted through the These APs are transmitted through the Cochler nerve ultimately reaching the Temporal lobe of the Auditory brain cortex, where they are processed and perceived as a sound.

14. According to BEKESY´S HEARING THEORY: we are able to perceive the high frequencies of sound at the base (at a botom) of the cochlea. Contrary, the sound with a low frequencies stimulates the hair cells near the top of the cochlea, named the helicotrema. Thus, the high pitch sound (e.g. 10,000 Hz) is detected by the hair cells placed on the basilary membrane at the base of the Cochlea, whereas the low pich sound (e.g. 200 Hz) is detected by the receptors near the helicotrema.

15. ANIMATION ANIMATION

16. HAVE A NICE, BEAUTIFUL & PLEASANT DAY !