Sensori – Neural & Mixed Hearing Loss

Sensori Neural Hearing Loss


A hearing loss is sensori-neural when there is damage to the inner ear.

The inner ear consists of:

  1.  The Cochlea
  2.  Auditory Nerve

1. The Cochlea:


The cochlea is a shell-shaped structure containing sensory hair cells, lying deep in the temporal bones of the skull. The force of vibrations from the stirrup in the middle ear onto the oval window of the cochlea is converted into hydraulic pressure waves. The waves pass swiftly through the fluid-filled inner ear, stimulating thousands of sensory hair cells which produce small electrical charges.

Damage to the inner ear can result in Sensori-neural hearing loss. Outer hair cell loss results in a loss of volume of sound. They get damaged first. Continual damage results in inner hair cell loss and that results in loss of clarity of sound. It has an impact on a person’s ability to follow conversation.

Factors that can cause damage to the hair cells of the cochlea include:


 

  • Noise exposure
  • Congenital conditions
  • Ototoxic drugs
  • Environmental causes
  • Prematurity
  • Age deterioration
  • Trauma
  • Lack of oxygen
  • Specific viral/ bacterial infections

A) Intact Cochlea, No Damage

B) Damaged Hair Cells

Damaged Hair Cells

2. Auditory Nerve:


The electrical signals from the cochlea travel along the auditory nerve and through enormously complex neural pathways to the brain. The brain recognizes analyses and interprets the signals. Where does the auditory pathway begin and where does it end? It begins with hair cells of the Organ of Corti and it ends at the transverse temporal Gyri of Hescl containing the primary auditory cortex.

Auditory Neuropathy is a term used to label a spectrum of auditory dysfunctions where normal outer hair cell functioning is present in the cochlea; with an absent or severely abnormal auditory brain stem response at high levels. This condition is differentiated from ‘typical’ sensori-neural hearing loss. Potential sites of lesion include the inner hair cells, the inner hair cell synapse to the nerve fibers, auditory neurons in the spiral ganglion, auditory nerve, brain stem auditory nuclei or any combination.

 

With Auditory Neuropathy Spectrum Disorder, older children and adults may display hearing thresholds ranging from within normal limits to profound hearing loss and poorer perception of speech than what would be expected when compared to the hearing thresholds.

 

Auditory Neuropathy Spectrum Disorder (ANSD) is prevalent with infants born prematurely and with low birth weight. The prevalence figures for ANSD in high-risk infant populations vary between 0.2% to 24%.

Mixed Hearing Loss


 

A mixed hearing loss occurs when there is a problem in both the middle and inner ear

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