The Human Bio-Amplifier—Electrifying - PowerPoint Presentation

1. The Human Bio-Amplifier—Electrifying!September 28, 2021

2. We have learned that electricity is the hearing “language” for the brain. We will review the most accepted theory regarding the creation and transmission of this “language” to the brain.

3. The displacement of hair cells produces responses within these cells which cause a “transmitter release” (electric shock) from the base of the hair cell.This “transmitter release” ultimately generates electrical nerve impulses into the fibers of the eighth nerve.Electrical Events Within the Cochlea

4. A positive electrical potential has been found within the endolymph fluid of the cochlear duct (scala media).This positive potential is maintained by the Stria Vascularis, which is also responsible for the maintenance of the chemical composition of the endolymph fluid.Electrical Events Within the Cochlea

5. The inside composition of outer hair cells have been found to have a negative electrical potential.This electrical difference potential between the inner structure of the outer hair cells (negative) and the endolymph fluid (positive) is very large for a biologic system.Electrical Events Within the Cochlea

6. When an acoustic stimulus is delivered to the cochlea, this electrical positive—negative balance is disturbed.When this acoustic disturbance occurs, two responses within the cochlea become apparent.Electrical Events Within the Cochlea

7. The two responses within the cochlea are:The frequency of the acoustic stimulus is reproduced by the cochlea (cochlear microphone).A sizable shift from the baseline resting electrical potential is produced (a summating electrical potential).Electrical Events Within the Cochlea

8. When both of these potentials (the frequency and the electrical potential) reach a maximum “best” frequency, which also corresponds to the maximum displacement peak of the travelling wave, the acoustic stimulus will transform into an electrical stimulus for the eighth nerve.Electrical Events Within the Cochlea

9. The cochlear microphone frequency response corresponds quite well with the summating potential created by the basilar membrane travelling wave displacement. Electrical Events Within the Cochlea

10. There is a shearing action which occurs when the tectorial membrane and the basilar membrane move, and the hair cells begin to move/shear.This creates the opportunity for electrical impulses to be generated within the cochlea.Hair Cells and the Cochlear Microphone

11. This shearing occurs due to the different hinge points of each membrane and the traveling wave movement which initiates the mechanical articulation at these pivot points. Hair Cells and the Cochlear Microphone

12. Note, how embedded OHCs actually pull the Tectorial Membrane downOuter Hair Cells:The Active Cochlear Mechanism

13. This mechanical action results in the stereocilia on top of the hair cells to bend—thus, creating a certain amount of mechanical gain due to the shearing force between the two membranes.Hair Cells and the Cochlear Microphone

14. The outermost row of outer hair cells are attached to the tectorial membrane.The other rows drag across the tectorial membrane and are influenced more by the eddy movement of the endolymph fluid than by the shearing action.Hair Cells and the Cochlear Microphone

15. This shearing force plus the viscous streaming of endolymph is thought to be the initial disturbance of the stereocilia that generates a receptor current which flows through the rest of the hair cell body. Hair Cells and the Cochlear Microphone

16. The identification of positive and negative electrical potentials were clearly defined by Davis in 1960. He placed the cochlear electrical potentials into four classes.Cochlear Electrical Potentials

17. The four potentials are:DC (direct current) resting potential with no acoustic stimulation.CM (cochlear microphonics) which are alternating current in response to acoustic stimulation.SP (summating potential) which is direct current but only appears with acoustic stimulation.AP the (action potential) of the VIIIth nerve fibers.

18. The cochlea is controlled by two “bio” batteries. The first battery is the hair cells (negative) and the second is the endolymph (maintained by the stria vascularis) positive.The “variable resistor” (gain knob) are the stereocilia located on top of each hair cell.This variable resistance changes as the stereocilia move, bend, and swirl.Cochlear Electrical Potentials

19. PLEASE NOTE: When the blood supply to the stria vascularis or the basilar membrane is modified or compromised, the electrical current generated from the bio-batteries may deteriorate thus, creating hearing loss.Hair Cell Movement & Electrical Potentials

20. When the hair cells move to and fro, this creates alternating current and the cochlear microphone (CM) is created.When the hairs cells all move in the same direction, a summating gain potential (SP) is created. How much movement and how many hair cells move, determine the amount of gain.Hair Cell Movement & Electrical Potentials

21. This active gain/amplification process is located between the basilar membrane and the eighth nerve and also produces additional frequency sharpening.It is only present in life, as it requires bio-energy to function.Hair Cell Movement & Electrical Potentials

22. The cochlea is:A sixty decibel WDRC amplifier (due primarily to outer hair cell movement).A mechanical frequency analyzer (basilar membrane).A cochlear microphone w/gain control (outer hair cell movement).Cochlea Performance Summary

23. The type of electrical current received (alternating or direct), and the amount of electrical current received by the eighth nerve create/generate the appropriate afferent information for the central pathways to disburse/process.Hair Cell Movement & Electrical Potentials

24. THANK YOUANY QUESTIONS?