MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 3. ANATOMICAL AND PHYSIOLOGICAL ASPECTS OF BODY FUNCTION SELFREGULATION

GENERAL ISSUES OF THE ANATOMY AND PHYSIOLOGY OF SENSORY SYSTEMS

2. PHYSIOLOGY OF THE AUDITORY ANALYZER

The Auditory Analyzer (auditory sensory system) ranks second in importance and volume of information processed. This is closely linked to The Emergence of human speech. The auditory analyzer is responsible for sound perception. From a physical perspective, sound is defined as air vibrations. Depending on the physical parameters of the sound wave, a person perceives a particular sound. Pitch, loudness, and timbre are the Main characteristics of sound. Sound pitch is determined by the frequency of air vibrations. Low-pitched tones have a lower frequency, whereas high-pitched tones have a higher frequency. Sound intensity (loudness) depends on the amplitude of vibration; a larger vibration amplitude produces a louder sound.

Timbre allows us to distinguish the sound of various musical instruments (even when they have the same loudness and pitch) as well as the voices of different people.

The human ear can perceive sound frequencies ranging from 16 to 20,000 Hz. With Aging, the upper limit of sound pitch perception decreases to 15,000 Hz. Speech sounds typically range in frequency from 150 to 2,500 Hz.

The minimum sound intensity perceived by a person in half of the cases is referred to as absolute auditory sensitivity. Sensitivity thresholds depend on sound frequency. Human Hearing exhibits maximum sensitivity within the frequency range of 1,000 to 4,000 Hz.

Loudness is another key characteristic of sound, determined by the interplay between sound intensity and pitch. In practice, the decibel (dB) is used as the unit of loudness. The maximum loudness level at which sound causes pain is 120-140 dB.

Before sound vibrations reach the Inner ear, they pass through the outer and Middle ear. The auricle collects sound waves and channels them through the external acoustic meatus to the tympanic membrane. The tympanic membrane captures sound vibrations and transmits them to the auditory ossicles of the middle ear (malleus, incus, and stapes), which amplify the sound wave while reducing its amplitude. As a result, the pressure of the sound wave on the oval window membrane is amplified 22-fold.

The presence of two windows in the inner ear wall—the oval and round windows—allows for the vibration of perilymph. Perilymph vibrations are transmitted to the endolymph and the basilar membrane, which houses the receptor Cells. The Organ of Corti contains approximately 2,400 Hair (receptor) cells, positioned beneath a movable tectorial membrane. These vibrations generate a receptor potential within the receptor cells. The excitation of the receptors in the organ of Corti is transmitted via nerve fibers to subcortical centers and subsequently to the cortical auditory centers (the middle Regions of the superior temporal gyrus). A distinct perception of sound arises only within the Cerebral Cortex.