Question

Briefly explain (less than 50 words/cell), the cause, origin, outer/inner hair cell functions, frequency processing, intensity coding, and bone/air conduction thresholds in the following: Noise Induced Hearing Loss

Cause (Congenital or acquired or both)?

Origin?

Outer Hair Cell Function?

Inner Hair Cell Function?

Frequency Selectivity or processing?

Intensity coding?

Bone conduction thresholds?

Air conduction thresholds?

Otoacoustic emissions?

Speech recognition in quiet?

Speech recognition in noise?

Answer 1

NOISE INDUCED HEARING LOSS

Noise-induced hearing loss is the second most common form of sensory neural hearing deficit, after age-related hearing loss. It resulting from exposure to loud sound. Shearing forces caused by any sound have an impact on the stereocilia of the hair cells of the basilar membrane of the cochlea; when excessive, these forces can cause cell death, and hearing loss

1. CAUSE (CONGENITAL OR ACQUIRED OR BOTH)?

Workplace exposure

The following is a list of occupations that are most susceptible to hearing loss:

· Agriculture

· Mining

· Construction

· Manufacturing

· Utilities

· Transportation

· Military

· Musicians

· Orchestra conductors

Acute acoustic trauma

NIHL commonly results from exposure to high-intensity sounds such as explosions, gunfire, a large drum hit loudly, and firecrackers

Gradually developing

Gradually developing NIHL refers to permanent cochlear damage from repeated exposure to loud sounds over a period of time.

2. ORIGIN?

NIHL occurs when sound with loud intensity is transmitted into and through the auditory system. An acoustic signal from a sound source enters into the external auditory canal (ear canal), and is passed through to the tympanic membrane (eardrum), causing it to vibrate. The vibration of the tympanic membrane moves the middle ear ossicles, the malleus, incus, and stapes to vibrate in along with the eardrum. The middle ear ossicles transfer mechanical energy to the cochlea by way of the stapes footplate hammering against the oval window of the cochlea, effectively amplifying the sound signal. This hammering causes the perilymph and endolymph to be displaced. Displacement of the fluid causes movement of the hair cells (sensory cells in the cochlea) and an electrochemical signal to be sent from the auditory nerve (CN VIII) to the central auditory system within the brain. This is where sound is perceived. There are two known biological mechanisms of NIHL from excessive sound intensity: damage to the structures called stereocilia .

3. OUTER HAIR CELL FUNCTION?

The outer hair cells mechanically amplify low-level sound that enters the cochlea. The amplification may be powered by the movement of their hair bundles, or by an electrically driven motility of their cell bodies.

4. INNER HAIR CELL FUNCTION?

Inner hair cells (IHCs), the sensory cells of the cochlea, are responsible for signal transduction.