The inferior colliculus is a pair of small rounded bumps on the back of the midbrain, directly below the superior colliculi and just above where the trochlear nerve leaves the brainstem. It is the main hearing centre of the midbrain: nearly all rising sound pathways meet here before the thalamus. [1]
The 3D brain needs JavaScript. The text below still says where the inferior colliculus is and what it does.
Slice
Opens cut by a side (sagittal) slice through the inferior colliculus. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Takes part in: hearing — see every part of each lit together.
Where it is
With the superior colliculi it forms the corpora quadrigemina and is part of the midbrain tectum, the roof that lies behind the cerebral aqueduct. [1][2]
It lies directly below (caudal to) the superior colliculus and above the trochlear nerve, at the base of the paths that run up to the medial and lateral geniculate nuclei of the thalamus. [1]
The trochlear nerve (IV), the only cranial nerve that leaves from the back of the brainstem, emerges just below the inferior colliculi. [3]
What it does
Most of the fibres rising in the lateral lemniscus end in its central nucleus, so the major ascending hearing pathways converge here; it acts as an integrating station and switchboard. [1]
It also takes part in routing signals from more than one sense, mainly for the startle response and the vestibulo-ocular reflex that keeps the eyes steady as the head moves. [1]
Some of its neurons take in touch signals as well as sound, which may help filter out the sounds you make yourself by speaking, chewing or breathing. [1]
Single neurons here are already sensitive to the tiny difference in when a sound reaches each ear, a cue for where the sound comes from. [1]
It is very active: in cats its blood flow measured 1.80 ml per gram per minute, ahead of the next region measured, the somatosensory cortex, at 1.53. [1]
Connections
In: from the cochlear nuclei of both ears and the other lower brainstem hearing nuclei, through the lateral lemniscus; also feedback from the auditory cortex and the medial geniculate body. [1]
Out: to the medial geniculate body of the thalamus on its own side, the last relay below the cortex; the central nucleus feeds the ventral division of the medial geniculate body. [1]
Inside it
Three subdivisions: the central nucleus, the main way station for rising sound signals; a dorsal cortex that wraps it; and an external cortex at the side. [1]
Other names
Inferior colliculi (the pair), IC; the name is Latin for “lower hill”. With the superior colliculi it makes up the tectum of the midbrain (the corpora quadrigemina). [1]
Size
On this model the left inferior colliculus measures about 8 mm front to back, 8 mm top to bottom and 8 mm side to side (the box it fits in, not its volume); the right one is its mirror image. [4]
Centre of the left inferior colliculus compared with the centre of the left superior colliculus: 8 mm lower; 8 mm apart in a straight line. [4]
Centre of the left inferior colliculus compared with the centre of the left medial geniculate body: 4 mm further back, 7 mm lower, 12 mm closer to the midline; 14 mm apart in a straight line. [4]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.