The Inferior Colliculus

Inferior colliculus

The Inferior colliculus is the main midbrain nucleus and important structure of the auditory passage. It is not just a point on the way up. It is a receiver of essential information from various sources, and processing this information.

Auditory signals

inferior coliculusThe sensory auditory signals, comes as electrochemical current from some brainstem nuclei that are more peripheral in the auditory pathway. The central auditory inputs from the auditory cortex of the cerebrum.

Anatomical structure

The anatomical structure of the inferior colliculus has 3 sub structures: (1) the central nucleus of Inferior colliculus. (2) dorsal cortex of Inferior colliculus by which it is surrounded. (3) Inferior colliculus external cortex which is located laterally.

Its neurons are receiving input from somatosensory nuclei. This is the anatomical basis for the statement that they are involved in auditory-somatosensory interaction.

This multisensory integration may explain the ability to ignore self induced sounds that are generated by vocalization, chewing, or respiration activities.

The anatomic structure that includes inferior colliculi and the superior coliculi forms two parts: (1) the eminences of the corpora quadrigemina. (2) part of the tectal region of the midbrain.

The inferior colliculus is located near the following structures: (1) the superior colliculus. (2) the trochlear nerve. (3) the base of the projection of the medial geniculate nucleus. (4) the lateral geniculate nucleus.

Midbrain inferior colliculi

The inferior colliculi of the midbrain are placed immediately under the site of visual processing centers known as the superior colliculi.

The functional hypothesis is that the inferior colliculus contains many biological processors that unify the "vertical" signals from the fusiform cells in the dorsal cochlear nucleus and the "horizontal" signals that come from directly from the sense organ.

These paired mesencephalic functions are acting to unify all the data about sound location.

superior coliculusThe activity of the inferior colliculus can be compared to a "master electronic computer" both in regard to its hardware (complex connections) and its software (internal organization).

The macro anatomy of the Inferior colliculus is dominated by large auditory nuclei that are located on the right and left sides of the midbrain.

Central Nucleus of Inferior colliculus

The Central Nucleus of Inferior colliculus is the main part for biological processing of the ascending hearing data via the signals in the Inferior colliculus. The incoming auditory data to the inferior colliculus involve links to many brainstem nuclei.

All the brainstem nuclei have bi-lateral connection with the Central Nucleus of Inferior colliculus, except one. It is the contralateral ventral nucleus of the lateral lemniscus.

Experimental works showed that the majority of auditory fibers ascending in the lateral lemniscus terminate in the Central Nucleus of Inferior colliculus. In addition, the Inferior colliculus receives descending inputs from 3 sources: (1) auditory cortex. (2) medial geniculate body. (3) superior colliculus.

Electrochemical signal

The inferior colliculus receives electrochemical signals from both the same side and the opposite side cochlear nucleus and accordingly the matched ears and their cochlear nerves.

Crossing the midline is part of the distribution of auditory signals. The dorsal signal transmission (containing vertical data) project only to the inferior colliculus of the opposite side.

The inferior colliculus contralateral to the source of sound is sending the processed signal to the ipsilateral medial geniculate nucleus.

Medial Geniculate Body

The two functions of the medial geniculate body are: (1) Provides output connection from inferior colliculus. (2) Serves as the last subcortical "biological processor".

The Medial Geniculate Body is made of 3 sub structures: (I) Ventral division. (II) Dorsal division. (III) Medial division. The ventral division of the Medial Geniculate Body collects auditory data from the central nucleus of the Inferior colliculus.

The majority of the rising nerve fibers from lateral lemniscus transmit their data to the Inferior colliculus. In the terminology of electronic computation, the Inferior colliculus serves as an integrative part of the auditory CNS and switchboard for the "biological circuitry" as well.

High metabolism and blood flow

The relatively high metabolism and high blood flow in the inferior colliculus when compared to other parts of the brain, indicates that many important activities are done in this area of the CNS.

Most probably, only part of it is known today (multi-modal sensory perception and spatial localization by binaural hearing).

Generation of tinnitus

There are no reports about tumors or structural abnormalities in the Inferior colliculus that can be related to the generation of tinnitus sound in the meniere disease or tinnitus sufferers.

When MRA of tinnitus sufferers with effective masking sound was compared to those without masking, the imaging showed a significant difference.







































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