The tympanic membrane ear drum separates the external
The tympanic membrane (ear drum) separates the external ear (pinna, ext. auditory meatus) from the middle ear (contains ossicles: malleus, incus, stapes). From Noback & Demarest, The Human Nervous System
The vestibulocochlear nerve (C. N. VIII) enters the brainstem at the pontocerebellar angle. It has two divisions: auditory and vestibular. Abducens nerve Facial nerve Flocculus
Auditory fibers in CN VIII first synapse in the cochlear nuclei in the dorsolateral medulla. Inferior Cerebellar Peduncle Dorsal Cochlear Nucleus Ventral Cochlear Nucleus Pontocerebellar Angle Vestibulocochlear Nerve (C. N. VIII)
The medial geniculate nucleus projects to the superior transverse temporal gyri (primary auditory cortex) via the sublenticular part of the posterior limb of the internal capsule (“auditory radiations”).
Primary Auditory Cortex: Sup. Transverse Temporal Gyri Brodmann’s Areas 41, 42
The efferent cochlear bundle originates from the superior olivary nucleus and projects thru the VIIIth nerve to the auditory receptor organ (Organ of Corti) to focus auditory attention. From: Carpenter, Human Neuroanatomy
Dorsal Cochlear Nucleus Inferior Cerebellar Peduncle Ventral Cochlear Nucleus
Superior olive Lateral lemniscus Trapezoid body
Lateral Lemniscus ML
Inferior Colliculus Most of the fibers in the lateral lemniscus synapse in the inferior colliculus, and then auditory information is conveyed thru the brachium of the inferior colliculus to the medial geniculate nucleus. Commissure of the inferior colliculus
SC Brachium of the Inferior Colliculus Carries fibers from the inferior colliculus to the medial geniculate nucleus IC
Medial geniculate nucleus The medial geniculate nucleus projects to the primary auditory cortex (superior transverse temporal gyri, areas 41, 42).
Descending feedback pathways at all levels within the auditory system function in sound localization.
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