Superior olivary complex: Difference between revisions
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The [[lateral superior olive]] (LSO) is believed to be involved in measuring the level difference of sounds between the ears (the [[interaural level difference]] or ILD). The ILD is a major cue in determining the azimuth of high frequency sounds. |
The [[lateral superior olive]] (LSO) is believed to be involved in measuring the level difference of sounds between the ears (the [[interaural level difference]] or ILD). The ILD is a major cue in determining the azimuth of high frequency sounds. |
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==Relationship to auditory system== |
==Relationship to auditory system== |
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The [[superior olivary complex]] is located in the [[pons]] and receives projections predominantly from the anteroventral cochlear nucleus, although the posteroventral nucleus projects there as well, via the ventral acoustic stria. It is at this site where the first binaural interactions occur (4). The superior olivary complex is divided into three parts; the medial, lateral and the Trapezoid body (3). |
The [[superior olivary complex]] is located in the [[pons]] and receives projections predominantly from the anteroventral cochlear nucleus, although the posteroventral nucleus projects there as well, via the ventral acoustic stria. It is at this site where the first binaural interactions occur (4). The superior olivary complex is divided into three parts; the medial, lateral and the Trapezoid body (3). |
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Summary of SOC |
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• It is a group of nuclei in the pons. |
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• It is made up of 3 major nuclei: medial superior olive, lateral superior olive and medial nucleus of the Trapezoid body (MNTB). |
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• These three nuclei are surrounded by smaller and more diffuse nuclei, collectively called the periolivary nuclei. The best understood of these are called the olivocochlear bundle. These are involved in efferent pathways. |
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• The superior olivary nucleus receives inputs primarily from bushy cells of the anterior ventral cochlear nuclei (AVCN) bilaterally, and passes on information to the lateral lemnisci. This input occurs primarily via the ventral acoustic stria. |
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• The superior olivary nucleus is the first point where binaural input is combined. |
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====Medial superior olive==== |
====Medial superior olive==== |
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The projections of the ipsilateral medial superior olive terminate densely in the central nucleus of the [[inferior colliculus]]. The majority of these axons are considered to be “round shaped” or type R. These R axons are mostly glutamatergic and contain round synaptic vesicles and form asymmetric synaptic junctions (4) |
The projections of the ipsilateral medial superior olive terminate densely in the central nucleus of the [[inferior colliculus]]. The majority of these axons are considered to be “round shaped” or type R. These R axons are mostly glutamatergic and contain round synaptic vesicles and form asymmetric synaptic junctions (4) |
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Summary of Medial Superior Olive (MSO) |
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• This is the largest of the nuclei. |
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• Each MSO receives low-frequency bilateral inputs from the right and left AVCNs. |
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• The output is to the ipsilateral lateral lemniscus and ultimately to the inferior colliculus. |
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• The MSO responds better to binaural stimuli. |
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• Its main function involves detection of differences in arrival time of sounds to the two ears which is part of localization process (ITD). |
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====Lateral superior olive==== |
====Lateral superior olive==== |
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The projections of the ipsilateral lateral superior olive project equal proportions of round and pleomorphic axons. The densities of the axons termination spots of this olivary pathway are not uniform, and contributes the highest density of PL axons to the inferior colliculus. |
The projections of the ipsilateral lateral superior olive project equal proportions of round and pleomorphic axons. The densities of the axons termination spots of this olivary pathway are not uniform, and contributes the highest density of PL axons to the inferior colliculus. |
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Summary of Lateral Superior Olive (LSO) |
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• The LSO is considerably smaller than the MSO. |
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• The LSO receives high-frequency inputs from the ipsilateral AVCN and also from contralateral AVCN via the ipsilateral MNTB. Due to this arrangement, this is another site of binaural integration. |
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• Its output is to the lateral lemnisci on both sides (in contrast to MSO) and ultimately to Inferior Colliculus. |
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• The LSO is primarily sensitive to high frequencies and therefore to intensity differences between the ears and can detect differences as small as 10 dB SPL. |
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Summary of Medial Nucleus of Trapezoid Body (MNTB) |
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• The MNTB is the smallest part of SOC. |
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• The neurones only get high-frequency input from contralateral AVCN, and its output projects to ipsilateral LSO. |
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• There are two response types found: a ‘chopper type’ similar to spindle cells in the AVCN and a primary type which is similar to those of Bushy Cells in the AVCN. |
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==See also== |
==See also== |
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Revision as of 11:45, 1 December 2006
| Superior olivary complex | |
|---|---|
 Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red. (Superior olivary nucleus is labeled at center right.) | |
| Details | |
| Identifiers | |
| Latin | nucleus olivaris superior |
| MeSH | D065832 |
| NeuroNames | 569 |
| NeuroLex ID | birnlex_1307 |
| TA98 | A14.1.05.415 |
| TA2 | 5937 |
| FMA | 72247 |
| Anatomical terms of neuroanatomy | |
The superior olivary nucleus (or superior olive) is a small mass of gray substance situated on the dorsal surface of the lateral part of the trapezoid body. Small in man, but well developed in certain animals, it exhibits the similar structure as the inferior olivary nucleus, and is situated immediately above it. Some of the fibers of the trapezoid body end by arborizing around the cells of this nucleus, while others arise from these cells.
Physiology
The superior olivary nucleus plays a number of roles in hearing. The medial superior olive (MSO) is a specialised nucleus that is believed to measure the time difference of arrival of sounds between the ears (the interaural time difference or ITD). The ITD is a major cue for determining the azimuth of low frequency sounds, i.e. localising them on the azimuthal plane - their degree to the left or the right.
The lateral superior olive (LSO) is believed to be involved in measuring the level difference of sounds between the ears (the interaural level difference or ILD). The ILD is a major cue in determining the azimuth of high frequency sounds.
Relationship to auditory system
The superior olivary complex is located in the pons and receives projections predominantly from the anteroventral cochlear nucleus, although the posteroventral nucleus projects there as well, via the ventral acoustic stria. It is at this site where the first binaural interactions occur (4). The superior olivary complex is divided into three parts; the medial, lateral and the Trapezoid body (3).
Summary of SOC
• It is a group of nuclei in the pons. • It is made up of 3 major nuclei: medial superior olive, lateral superior olive and medial nucleus of the Trapezoid body (MNTB). • These three nuclei are surrounded by smaller and more diffuse nuclei, collectively called the periolivary nuclei. The best understood of these are called the olivocochlear bundle. These are involved in efferent pathways. • The superior olivary nucleus receives inputs primarily from bushy cells of the anterior ventral cochlear nuclei (AVCN) bilaterally, and passes on information to the lateral lemnisci. This input occurs primarily via the ventral acoustic stria. • The superior olivary nucleus is the first point where binaural input is combined.
Medial superior olive
The medial superior olive is thought to help locate the position of a sound on the azimuth axis (3). The azimuth axis is the angle from a certain direction, ie: 32 degrees from north. One’s first instincts may be to think that this nucleus includes vertical information, but this is not the case. The fusiform cells do not project to anything in the level of the pons, and only come into play at the inferior colliculus. Only horizontal data is present, but it does come from two different ear sources, which aides in the localizing of sound on the azimuth axis (2). The way in which the superior olive does this is by measuring the differences in time between two ear signals recording the same stimulus. Traveling around the head takes about 700 μs, and it is assumed that the medial superior olive is able to detect this. In fact, it is observed that people can detect interaural differences down to 10 microseconds (2). Kandell claims that this nucleus is tonotopographically organized, but recent evidence (3) disagrees. Dr. Douglas Oliver claims that the tonotopographical map of the medial superior olive is “most likely a complex, nonlinear map.”
The projections of the ipsilateral medial superior olive terminate densely in the central nucleus of the inferior colliculus. The majority of these axons are considered to be “round shaped” or type R. These R axons are mostly glutamatergic and contain round synaptic vesicles and form asymmetric synaptic junctions (4)
Summary of Medial Superior Olive (MSO)
• This is the largest of the nuclei. • Each MSO receives low-frequency bilateral inputs from the right and left AVCNs. • The output is to the ipsilateral lateral lemniscus and ultimately to the inferior colliculus. • The MSO responds better to binaural stimuli. • Its main function involves detection of differences in arrival time of sounds to the two ears which is part of localization process (ITD).
Lateral superior olive
This olive has similar functions to the medial superior olive, but employs intensity to home in on a sound source. This is the part of the brain stem that labels the louder sound form the left ear as being on the left hand side. The lateral olive receives input from both cochlear nuclei, although the contralateral projections are received indirectly through the nucleus of trapezoid body. The contralateral and ipsilateral inputs are in stark opposition to one another, and thusly the cells in the lateral superior olive fire accordingly when one lateral input is greater than the other.
The projections from the contralateral lateral superior olive go to the central nucleus of the inferior colliculus. The types of axonal projections are both round (or R), as seen above, and also a small amount of pleomorphic or PL axons. Pleomorphic is a synonym for polymorphic or protean, and means the axons are capable of being found in many forms (5). The pleomorphic axons are mostly inhibitory, with the neurotransmitters glycine and GABA at their disposal, stored inside pleomorphic synaptic vesicles. These axons form symmetrical synapses with the neurons of the inferior colliculus and terminate in a less dense fashion.
The projections of the ipsilateral lateral superior olive project equal proportions of round and pleomorphic axons. The densities of the axons termination spots of this olivary pathway are not uniform, and contributes the highest density of PL axons to the inferior colliculus.
Summary of Lateral Superior Olive (LSO)
• The LSO is considerably smaller than the MSO. • The LSO receives high-frequency inputs from the ipsilateral AVCN and also from contralateral AVCN via the ipsilateral MNTB. Due to this arrangement, this is another site of binaural integration. • Its output is to the lateral lemnisci on both sides (in contrast to MSO) and ultimately to Inferior Colliculus. • The LSO is primarily sensitive to high frequencies and therefore to intensity differences between the ears and can detect differences as small as 10 dB SPL.
Summary of Medial Nucleus of Trapezoid Body (MNTB)
• The MNTB is the smallest part of SOC. • The neurones only get high-frequency input from contralateral AVCN, and its output projects to ipsilateral LSO. • There are two response types found: a ‘chopper type’ similar to spindle cells in the AVCN and a primary type which is similar to those of Bushy Cells in the AVCN.
See also
References
2) Kandel, et al Principles of Neuroscience. Fourth ed. pp 591-624. Copyright 2000, by McGraw-Hill Co.
3) Oliver, Douglas L. et al. Topography of Interaural Temporal Disparity Coding in Projections of Medial Superior Olive to Inferior Colliculus. The Journal of Neuroscience, August 13, 2003, 23(19):7438-7449
4) Oliver DL, et al. Axonal projections from the lateral and medial superior olive to the inferior colliculus of the cat: a study using electron microscopic autoradiography. J Comp Neurol. 1995 Sep 11;360(1):17-32
5) Medical Online Dictionary http://www.medterms.com/script/main/art.asp?articlekey=4943
External links
This article incorporates text in the public domain from page 787 of the 20th edition of Gray's Anatomy (1918)