Sensorineural Hearing Loss (SNHL)
This chapter covers sensorineural hearing loss disorders. Sensorineural hearing loss is considered one of the major causes of hearing impairment that affects the quality of life and ability to communicate with others which can affect human well-being and
- PDF / 579,060 Bytes
- 9 Pages / 504.567 x 720 pts Page_size
- 66 Downloads / 250 Views
10
Aisha Larem, Zaid Altamimi, and Adham Aljariri
10.1 Introduction Hearing loss can be defined as an impairment in the ability to perceive sound stimulus. It includes three types: Conductive, Sensorineural, and Mixed hearing loss. Sensorineural hearing loss (SNHL) occurs due to defect in the sensory apparatus of the cochlea (sensory), or the peripheral pathways of conduction of nerve impulses (XIII CN) to the brain or in the central auditory pathway or cortex (neural). Knowledge of growth, development, and functional anatomy of the inner ear is important to be able to identify the pathology and diagnose it. Membranous labyrinth develops from otic placode from the third week of the gestational age (GA) and then it becomes otocysts subdivided into vestibular and cochlear compartments. Cochlea reaches the shape of adult form at 10 weeks and adult size at 20 weeks GA. Cochlea is composed of a 35 mm coiled bony tube with 2.5 turns, and it is divided into scala vestibuli, scala tympani, and scala media. Scala vestibuli and scala tympani contain perilymph, scala media is located between scala vestibuli and tympani, and A. Larem (*) · Z. Altamimi · A. Aljariri Hamad Medical Corporation, Doha, Qatar e-mail: [email protected]; [email protected]; [email protected]
it contains the endolymph. Scala media is bounded by Reissner’s membrane, basilar membrane, osseous spiral lamina, and stria vascularis in the lateral wall, and it contains the organ of Corti. Organ of Corti is the receptor organ for hearing, composed of outer and inner hair cells, supporting cells, and the tectorial membrane. Inner and outer hair cells are differing in morphology and innervation. Inner hair cells’ neural innervation is by type I neurons which are predominantly afferent neurons, where 15–20 of these neurons innervate each inner hair cell. Outer hair cells’ neural synapses are by type II neurons which are predominantly efferent, where each type II neuron branches to innervate around ten outer hair cells. Sound transduction is defined as converting sound vibrations (mechanical energy) into neural impulse (electrical energy) by the movement of the basilar membrane with the hair cells against the tectorial membrane, stimulating generation of nerve ending impulses in spiral ganglion. The spiral ganglion sends axons into the cochlear nerve. The cochlear nerve transmits auditory information up a series of nuclei to the auditory cortex where perception occurs. These nuclei include: (1) cochlear nucleus, (2) superior olivary nuclei, (3) lateral lemniscus, (4) inferior colliculus, and (5) medial geniculate nuclei. Sensorineural hearing loss (SNHL) is featured with the following
© Springer Nature Switzerland AG 2021 A. Al-Qahtani et al. (eds.), Textbook of Clinical Otolaryngology, https://doi.org/10.1007/978-3-030-54088-3_10
111
A. Larem et al.
112
• Normal examination of the external ear canal and tympanic membrane. • Weber and Rinne’s tests show a positive Rinne’s test (air conduction (AC) > bone conduction (BC)). Weber’s lateralized to the better
Data Loading...
