Cortical Auditory Centers and there function

CORTICAL AUDITORY CENTERS

Cortical auditory centers are in the temporal lobe of cerebral cortex.

Auditory areas are:

1. Primary auditory area, which includes area 41, area 42 and Wernicke area

2. Secondary auditory area or auditopsychic area, which includes area 22.

Areas 41 and 42 are the primary auditory areas situated in the anterior transverse gyrus and lateral surface of superior temporal gyrus. Wernicke area is in upper part of superior temporal gyrus, posterior to areas 41 and 42. Area 22 occupies the superior temporal gyrus.

 FUNCTIONS OF CORTICAL AUDITORY CENTERS

Cortical auditory centers are concerned with the perception of auditory impulses, analysis of pitch and intensity of sound and determination of source of sound. Areas 41 and 42 are concerned with the perception of auditory impulses only. However, analysis and interpretation of sound are carried out by Wernicke area, with the help of area 22.

APPLIED PHYSIOLOGY – EFFECT OF LESION

1. Lesion of cochlear nerve causes deafness of the ear

2. Unilateral lesion of auditory pathway, above the level of cochlear nuclei causes diminished hearing

3. Degeneration of hair cells in the organ of Corti leads to presbycusis. Presbycusis is the gradual loss of

hearing. It is common in old age.

4. Lesion in superior olivary nucleus results in poor localization of sound.

Sound waves travel through external auditory meatus and produce vibrations in the tympanic membrane.

Vibrations from tympanic membrane travel through malleus and incus and reach the stapes resulting in the movement of stapes. Movements of stapes produce vibrations in the fluids of cochlea. These vibrations stimulate the hair cells in organ of Corti. This, in turn, causes generation of action potential (auditory impulses) in the auditory nerve fibers. When auditory impulses reach the cerebral cortex, the perception of hearing occurs. Thus, during the process of hearing, ear converts energy of sound waves into action potentials in auditory nerve fibers. This process is called sound transduction.

ROLE OF EXTERNAL EAR

External ear directs the sound waves towards tympanic membrane. Sound waves produce pressure

changes over the surface of tympanic membrane. Accumulation of wax prevents conduction of sound.

In many animals, the auricle (pinna) can be turned to locate the source of sound. Auricle can be folded to

avoid unwanted sound. But in man, the extrinsic and intrinsic muscles of auricle are rudimentary and the

movement is not possible. auditory nerve fibers. This process is called sound transduction.

ROLE OF EXTERNAL EAR

External ear directs the sound waves towards tympanic membrane. Sound waves produce pressure

changes over the surface of tympanic membrane. Accumulation of wax prevents conduction of sound.

In many animals, the auricle (pinna) can be turned to locate the source of sound. Auricle can be folded to

avoid unwanted sound. But in man, the extrinsic and intrinsic muscles of auricle are rudimentary and the

movement is not possible.

ROLE OF MIDDLE EAR

ROLE OF TYMPANIC MEMBRANE

Due to the pressure changes produced by sound waves, tympanic membrane vibrates, i.e. it moves in

and out of middle ear. Thus, tympanic membrane acts as a resonator that reproduces the vibration of sound.

ROLE OF AUDITORY OSSICLES

Vibrations set up in tympanic membrane are transmitted through the malleus and incus and reach

the stapes, causing to and fro movement of stapes against oval window and against perilymph present in

scala vestibuli of cochlea.