From the cochlear nerve sound climbs through relays: the cochlear nuclei where the medulla meets the pons, the superior olive in the pons, where the two ears first meet, the lateral lemniscus to the midbrain’s inferior colliculus, the thalamus’s medial geniculate body and the auditory cortex on the superior temporal gyrus. [1][2]
A tract has no shape of its own in this atlas; lit: the parts it runs through, in order.
The 3D brain needs JavaScript. The steps below still say where the auditory pathway runs, in order.
The brain starts seen from the left, a little from behind and below, so the back of the brainstem, where the inferior colliculus and the medial geniculate body sit, and the superior temporal gyrus above it both show. Step through lights one step at a time, about 1.2 s each, bottom to top; tap a step below to light it. The lit step is in the bright highlight colour, the steps before it stay lit in a paler tint of it and the steps still ahead are grey. Drag to turn, pinch or scroll to zoom. Step through is off because your device asks for reduced motion; tap each step instead.
The atlas has no shape for the cochlear nuclei, the superior olive, the lateral lemniscus, the auditory cortex or Heschl’s (transverse temporal) gyrus, so those steps light the part that holds them, or nothing new. The superior temporal gyrus is lit whole, though the primary auditory cortex covers only its upper surface inside the lateral sulcus. [3][4][5]
The route, in 6 steps
Every fibre of the cochlear nerve, the hearing half of the vestibulocochlear nerve, ends in the cochlear nuclei: a ventral and a dorsal nucleus on the outer back side of the brainstem, where the medulla meets the pons. Not a separate shape in this atlas; lit: the part that holds them, the medulla oblongata. Each keeps the cochlea’s map of pitch, high and low tones apart. [6][7]Where is the medulla oblongata?
From the ventral cochlear nucleus fibres run to the superior olivary complex (the superior olive) in the pons on both sides, the first place where signals from the two ears meet. Not a separate shape in this atlas; lit: the part that holds it, the pons. Its medial nucleus compares when a sound reaches each ear, its lateral nucleus how loud it is at each, the two cues for where a sound comes from. [8][1]Where is the pons?
Many fibres cross to the opposite side in the trapezoid body, a band in the lower pons, so each superior olive takes signals from both ears. The atlas has no shape for the trapezoid body. [9][8]
The lateral lemniscus, a tract of fibres from the cochlear nuclei and the superior olive, with small nuclei of its own along the way, climbs the side of the pons to the inferior colliculus. The atlas has no shape for it, so this step lights nothing new: the pons it runs through stays lit. [10]
The inferior colliculi, the lower pair of bumps on the back of the midbrain, are the main hearing nucleus of the midbrain: nearly all the rising auditory paths meet here, and it also takes fibres down from the auditory cortex. From it the brachium of the inferior colliculus runs up to the thalamus. [11][1]Where is the inferior colliculus?
The medial geniculate body (nucleus) is the thalamic relay between the inferior colliculus and the auditory cortex, a small bump under the back of the thalamus. Its ventral part keeps the map of pitch and sends the acoustic radiation through the internal capsule to the primary auditory cortex. [12]Where is the medial geniculate body?
The radiation ends in the primary auditory cortex (Brodmann area 41) on Heschl’s gyrus, the transverse temporal gyrus, where the superior temporal gyrus folds into the lateral sulcus; belt and parabelt areas around it take the sound on. Neither the auditory cortex nor Heschl’s gyrus has a separate shape in this atlas; lit: the superior temporal gyrus that holds them. [4][5]Where is the superior temporal gyrus?
More about the auditory pathway
Other names: central auditory pathway, ascending auditory pathway, acoustic radiation (auditory radiation) [1][12]
Sound reaches the brain through the cochlear nerve, the hearing half of the vestibulocochlear nerve (cranial nerve VIII); its fibres are the axons of the spiral ganglion cells, which take signals from the hair cells of the cochlea. [7][6]
From the superior olive up the route is bilateral: each superior olive already takes signals from both ears, so the inferior colliculus, medial geniculate body and auditory cortex of each side carry sound from both ears, unlike touch or sight, where each side of the brain serves the opposite side of the body or visual field. [1][8]
The map of pitch (tonotopy) laid out along the cochlea is kept all the way up: in the cochlear nuclei, the inferior colliculus, the medial geniculate body and the primary auditory cortex, high and low tones lie in separate places. [1][4]
Hearing also runs back down: the auditory cortex sends fibres to the medial geniculate body and the inferior colliculus, and cells near the superior olive send the olivocochlear bundle out to the hair cells of the cochlea. [1][8]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); it has no shape for tracts, so a pathway is shown by the parts it runs through.