The document summarizes the anatomy and physiology of the human auditory system. It describes how sound is collected by the outer ear and transmitted through the middle ear. It then explains how the inner ear performs spectral and temporal analysis of sounds through structures like the cochlea. The cochlea uses tonotopic organization and traveling waves to convert sounds into neural signals. These signals are then transmitted by the auditory nerve pathway to the brain for interpretation.

1. Anatomy and Physiology of the Speech and Hearing Mechanisms: Auditory Physiology Wilhelmina Wright-Harp, Ph.D. Associate Professor Department of Communication Sciences and Disorders Howard University 2009 Fall Semester

2. W. Wright-Harp, Ph.D. 2002 Fall Semester Auditory Physiology Organizing Principles of Hearing Physiology: The external ear collects sound (acoustic energy) and shapes its frequency components; The middle ear matches the air-borne acoustic signal, transforms it into mechanical energy, with the fluid medium of the cochlea; The inner ear performs spectral and temporal analyses on the acoustic signal; The auditory pathway conveys and processes the signal; The cerebral cortex interprets the signal.

3. W. Wright-Harp, Ph.D. 2002 Fall Semester Auditory Physiology The ear is capable of responding to: Frequencies ranging from 20 to 20,000 Hz Intensities ranging from 1 to 10 trillion.

4. W. Wright-Harp, Ph.D. 2002 Fall Semester External Ear: Acoustic System The auricle: serves as a “sound funnel” by channeling acoustic energy into the EAM. Aids in localization of sound The EAM: funnels sound to the TM. functions as a closed tube resonator.

5. W. Wright-Harp, Ph.D. 2002 Fall Semester Middle Ear: Mechanical System The middle ear: Functions to convert acoustic energy into mechanical energy. Serves as an impedance-matching device. Impedance-matching is achieved through two mechanisms: Area effect Lever effect

6. W. Wright-Harp, Ph.D. 2002 Fall Semester Inner Ear: Vestibular Mechanism The inner ear is comprised of two divisions: Vestibular Mechanism The semicircular canals help maintain balance. Provide input to the proprioceptive system Aids in perception of body position

7. W. Wright-Harp, Ph.D. 2002 Fall Semester Inner Ear: Auditory Mechanism The cochlea is designed to: sort out the frequency components of an incoming signal, determine their amplitude, and identify basic temporal aspects of that signal.

8. W. Wright-Harp, Ph.D. 2002 Fall Semester Inner Ear: Hydraulic System Hydraulic energy results from movement of the stapes footplate in and out against the perilymph in the oval window of the vestibule.

9. W. Wright-Harp, Ph.D. 2002 Fall Semester Inner Ear: Auditory Mechanism The frequency analysis ability of the basilar membrane is influenced by three variables: Graded Stiffness Graded Mass Graded Width

10. W. Wright-Harp, Ph.D. 2002 Fall Semester Inner Ear: Auditory Mechanism Von Bekesy’s research revealed that the vibration is transmitted along the basilar membrane as a traveling wave. As the traveling wave moves along the basilar membrane, it builds to a peak and then ends abruptly. The cochlea has a tonotopic arrangement.

11. W. Wright-Harp, Ph.D. 2002 Fall Semester Inner Ear: Auditory Mechanism Excitation of hair cells of the cochlea. The inner hair cells are excited by fluid flow and turbulence of endolymph. The outer hair cells are excited by shearing effect on the cilia. Movement of the hair cells generates a neural impulse.

12. W. Wright-Harp, Ph.D. 2002 Fall Semester Neural Pathway of CN VIII Pfeiffer (1966) described six different types of neural responses to auditory stimulation: Single-unit response Primary-like Onset Chopper Pausers Build-up