From the ear to the brain cortex, sound signals are transmitted and processed by the auditory neural pathway in the central nervous system (CNS). Here, let’s learn the sequential steps through which the auditory information is passed to the cortex of the brain.
Table of Contents
Auditory Pathway
The auditory pathway is primarily located in the midbrain, medulla oblongata and thalamic region. The primary receptors for hearing are located in the cochlea. The cochlea is filled with ear fluids, namely perilymph and endolymph. The auditory pathway fibres pass through the cochlear division of the vestibulocochlear nerve, also called the auditory nerve.
Auditory Receptors – The temporal lobe of the cerebral cortex houses the higher centre for hearing, where the auditory pathway’s fibres finally come to an end. The auditory sense is processed by hair cells in the organ of Corti. Inner and outer hair cells are two different types of hair cells. Afferent and efferent nerve fibres innervate each and every hair cell. The auditory nerve is made up of afferent nerve fibres from the hair cells.
Physiology of Hearing
Sound waves pass through the external auditory meatus and cause the tympanic membrane to vibrate. The stapes move as a result of tympanic membrane vibrations that pass through the malleus and incus on their way to the stapes. The fluids in the cochlea vibrate as a result of stapes movements. In the organ of Corti, these vibrations activate the hair cells. As a result, the auditory nerve fibres begin to produce auditory impulses or action potentials.
Hearing is perceived when auditory impulses enter the cerebral cortex. The ear transforms the energy of sound waves into action potentials in the auditory nerve fibres during the hearing process. This process is also termed sound transduction. The organ of Corti contains the sound transduction site. The process by which the auditory information is conveyed to the brain is explained in the auditory pathway steps.
Also Check: MCQs on Structure of Ear
Auditory Pathway Steps
The brain receives the majority of its auditory information from the inner hair cells. In most cases, afferent neurons receive information from inner hair cells and each hair cell synapses with about ten other neurons. The auditory information is conveyed by bipolar afferent neurons that travel from the cochlea to the medulla, via the midbrain and pons in the brainstem, and finally to the primary auditory cortex in the temporal lobe. These auditory nerves pass through the cochlear division of the vestibulocochlear nerve (CN â…§). The sequential steps are as follows:
- The bipolar cells of the spiral ganglion, which are located in the cochlea’s modiolus, are the first-order neurons of the auditory pathway.
- The second-order auditory pathway neurons are made up of neurons from the dorsal and ventral cochlear nuclei in the medulla oblongata.
- Both the superior olivary nuclei and the lateral lemniscus nucleus comprise the third-order neurons.
- The subcortical auditory centre is formed by the medial geniculate body, where the fibres of third-order neurons terminate.
- The nerve fibres from the medial geniculate body travel as auditory radiation via the internal capsule to the temporal cortex.
- In the midbrain, the inferior colliculus of the tectum receives some fibres from the medial geniculate body.
- The reflex movements in response to auditory stimuli are mediated by the auditory radiation fibres.
- The temporal lobe of the cerebral cortex houses the cortical auditory centres. The perception of auditory impulses, analysis of sound pitch and intensity, and identification of sound source are all concerns of the cortical auditory centres.
Auditory Pathway Flowchart
Action potential generated in the cochlea
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Mid pons (superior olive)
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Pons-midbrain junction (lateral lemniscus)
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Caudal midbrain (inferior colliculus)
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Rostral midbrain (medial geniculate complex of the thalamus)
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Primary auditory cortex
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