Auditory pathway

The auditory pathway is a complex neural route that transmits sound information from the external environment to the auditory cortex of the brain. It involves a series of synapses and relays within the brainstem and midbrain, enabling perception and localization of sound.

Anatomical Description

The auditory pathway is a four-neuron pathway that transmits auditory information from the organ of Corti of the inner ear to the primary auditory cortex.

The pathway begins in the cochlea, where sound waves are transduced into neural signals by hair cells in the organ of Corti.

The first neurons of the auditory pathway are bipolar cells whose bodies lie in the ganglion spirale cochleae. The dendrites of these cells form synapses with the hair cells of the organ of Corti. The axons of the bipolar cells form the pars cochlearis nervi vestibulocochlearis and enter the brainstem, in the region of the pontocerebellar angle , where they end in the cochlear nuclei (nucleus cochlearis ventralis and nucleus cochlearis dorsalis) located at the interface between the medulla oblongata and the pons.

The second neurons arise from the cells of the cochlear nuclei and form three bundles:

• Corpus trapezoideum (from nucleus cochlearis ventralis);
• Stria acustica intermedia (from nucleus cochlearis ventralis);
• Stria acustica dorsalis (from nucleus cochlearis dorsalis).

These bundles cross the midline and proceed upward in the contralateral part of the brainstem, where they unite to form the massive bundle of lemniscus lateralis ending in the colliculi inferiores of the midbrain. Some fibers arising from the nucleus cochlearis ventralis make synapses in the nucleus olivaris superior and nucleus corporis trapezoidei. Some fibers of the lateral lemniscus connect in the nucleus lemnisci lateralis.

The third neurons arise from the colliculi inferiores and terminate in the corpus geniculatum mediale in the thalamus.

The fourth neurons begin in the corpus geniculatum mediale, form the tractus geniculocorticalis (or radiatio acustica) and end in the primary auditory cortex located in the upper part of the gyrus temporalis superior (area 41, 42).

Clinical Relevance

Lesions at different levels of the auditory pathway can cause various forms of hearing loss. Due to the bilateral nature of the pathway beyond the cochlear nuclei, unilateral lesions in the brainstem usually do not result in complete deafness in one ear but may affect sound localization or discrimination.

References

• ČIHÁK, Radomír – GRIM, Miloš. Anatomie 3. 2.. edition. Grada, 2004. 673 pp. vol. 3. ISBN 80-247-1132-X.

• KRÁLÍČEK, Petr. Introduction to Special Neurophysiology. 1. edition. Karolinum, 1997, c1995. ISBN 8071840149.

• Sobotta Atlas of Human Anatomy, 16th edition
• Gray’s Anatomy for Students, 4th edition
• Neuroanatomy through Clinical Cases by Hal Blumenfeld, 2nd edition