Brain viewed from below; the front of the brain is above. Visual pathway with optic chiasm (X shape) is shown in red (image from Andreas Vesalius' Fabrica, 1543).
This article is about the optic chiasm of vertebrates, which is the best known nerve chiasm, but not every chiasm denotes a crossing of the body midline (e.g., in some invertebrates, see Chiasm (anatomy)). A midline crossing of nerves inside the brain is called a decussation (see Definition of types of crossings).
In all vertebrates, the optic nerves of the left and the right eye meet in the body midline, ventral to the brain. In many vertebrates the left optic nerve crosses over the right one without fusing with it.[4]
In vertebrates with a large overlap of the visual fields of the two eyes, i.e., most mammals and birds, but also amphibians, reptiles such as chameleons, the two optic nerves merge in the optic chiasm. In such a merged optic chiasm, part of the nerve fibres do not cross the midline, but continue towards the optic tract of the ipsilateral side. By this partial decussation, the part of the visual field that is covered by both eyes is fused so that the processing of binocular depth perception by stereopsis is enabled (see Figure 2).
In the case of such partial decussation, the optic nerve fibres on the medial sides of each retina (which correspond to the lateral side of each visual hemifield, because the image is inverted) cross over to the opposite side of the body midline. The inferonasal retina are related to the anterior portion of the optic chiasm whereas superonasal retinal fibers are related to the posterior portion of the optic chiasm.
The partial crossing over of optic nerve fibres at the optic chiasm allows the visual cortex to receive the same hemispheric visual field from both eyes. Superimposing and processing these monocular visual signals allow the visual cortex to generate binocular and stereoscopic vision. The net result is that the right cerebral hemisphere processes left visual hemifield, and the left cerebral hemisphere processes the right visual hemifield.
During development, the crossing of the optic nerves is guided primarily by cues such as netrin, slit, semaphorin and ephrin; and by morphogens such as sonic hedgehog (Shh) and Wnt.[6] This navigation is mediated by the neuronal growth cone, a structure that responds to the cues by ligand-receptor signalling systems that activate downstream pathways inducing changes in the cytoskeleton.[7]Retinal ganglion cell (RGC) axons leaving the eye through the optic nerve are blocked from exiting the developing pathway by Slit2 and Sema5A inhibition, expressed bordering the optic nerve pathway. Ssh expressed at the central nervous system midline inhibits crossing prior to the chiasm, where it is downregulated.[8][9] The organization of RGC axons changes from retinotopic to a flat sheet-like orientation as they approach the chiasm site.[10]
Most RGC axons cross the midline at the ventraldiencephalon and continue to the contralateralsuperior colliculus. The number of axons that do not cross the midline and project ipsilaterally depends on the degree of binocular vision of the animal (3% in mice and 45% in humans do not cross).[8]Ephrin-B2 is expressed at the chiasm midline by radial glia and acts as a repulsive signal to axons originating from the ventrotemporal retina expressing EphB1 receptor protein, giving rise to the ipsilateral, or uncrossed, projection.[8] RGC axons that do cross at the optic chiasm are guided by the vascular endothelial growth factor, VEGF-A, expressed at the midline, which signals through the receptor Neuropilin-1 (NRP1) expressed on RGC axons.[11] Chiasm crossing is also promoted by Nr-CAM (Ng-CAM-related cell adhesion molecule) and Semaphorin6D (Sema6D) expressed at the midline, which form a complex that signals to Nr-CAM/Plexin-A1 receptors on crossing RGC axons.[12]
Since all vertebrates, even the earliest fossils[13] and modern jawless ones,[5] possess an optic chiasm, it is not known how it evolved.[14] A number of theories have been proposed for the function of the optic chiasm in vertebrates (see theories). According to the axial twist hypothesis the optic chiasm develops as a consequence of a twist in the early embryo.[15]
In Siamese cats with certain genotypes of the albino gene, the wiring is disrupted, with more of the nerve-crossing than normal.[16] Since siamese cats, like albinotigers, also tend to cross their eyes (strabismus), it has been proposed that this behavior might compensate the abnormal amount of decussation.[17][18]
In cephalopods and insects the optic tracts do not cross the body midline, so each side of the brain processes the ipsilateral eye.
HistoryEdit
The crossing of nerve fibres, and the impact on vision that this had, was probably first identified by Persian physician "Esmail Jorjani", who appears to be Zayn al-Din Gorgani (1042–1137).[19]
Additional imagesEdit
Scheme showing central connections of the optic nerves and optic tracts.
Brain seen from below, with the optic chiasm seen in yellow in the centre.
Transformations of the visual field toward the visual map on the primary visual cortex.
Brain and brainstem seen from below
Left hemisphere of the brain seen in a cadaveric specimen from the side, with the optic chiasm labelled.
Cerebrum, inferior view, deep dissection.
Guidance of axon crossing and non-crossing during development.
^Colman, Andrew M. (2006). Oxford Dictionary of Psychology (2nd ed.). Oxford University Press. p. 530. ISBN978-0-19-861035-9.
^Bainbridge, David (30 June 2009). Beyond the Zonules of Zinn: A Fantastic Journey Through Your Brain. Harvard University Press. p. 162. ISBN978-0-674-02042-9. Retrieved 22 November 2015.
^de Lussanet, Marc H.E.; Osse, Jan W.M. (2012). "An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates". Animal Biology. 62 (2): 193–216. arXiv:1003.1872. doi:10.1163/157075611X617102. ISSN 1570-7555. S2CID 7399128.
^Stephen, Polyak (1957). The vertebrate visual system. Chicago: Chicago Univ. Press.
^ abNieuwenhuys, R.; Donkelaar, H.J.; Nicholson, C.; Smeets, W.J.A.J.; Wicht, H. (1998). The central nervous system of vertebrates. New York: Springer. ISBN9783642621277.
^Erskine, L.; Herrera, E. (2007). "The retinal ganglion cell axon's journey: Insights into molecular mechanisms of axon guidance". Developmental Biology. 308 (1): 1–14. doi:10.1016/j.ydbio.2007.05.013. PMID 17560562.
^Gordon-Weeks, PR (2005). Neuronal Growth Cones. Cambridge University Press. ISBN9780511529719.
^ abcHerrera, E; Erskine, L; Morenilla-Palao, C (2019). "Guidance of retinal axons in mammals". Seminars in Cell & Developmental Biology. 85: 48–59. doi:10.1016/j.semcdb.2017.11.027. PMID 29174916. S2CID 24381059.
^Guillery, RW; Mason, CA; Taylor, JS (1995). "Developmental determinants at the mammalian optic chiasm". The Journal of Neuroscience. 15 (7): 4727–4737. doi:10.1523/JNEUROSCI.15-07-04727.1995. PMC6577905. PMID 7623106.
^Erskine, L; Reijntjes, S; Pratt, T (2011). "VEGF signaling through neuropilin 1 guides commissural axon crossing at the optic chiasm". Neuron. 70 (5): 951–965. doi:10.1016/j.neuron.2011.02.052. PMC3114076. PMID 21658587.
^Kuwajima, T; Yoshida, Y; Pratt, T (2012). "Optic chiasm presentation of Semaphorin6D in the context of Plexin-A1 and Nr-CAM promotes retinal axon midline crossing". Neuron. 74 (4): 676–690. doi:10.1016/j.neuron.2012.03.025. PMC3361695. PMID 22632726.
^Janvier, P. (1996). Early vertebrates. New York: Clarendon Press, Oxford University Press. ISBN978-0198540472.
^de Lussanet, M.H.E.; Osse, J.W.M. (2012). "An ancestral axial twist explains the contralateral forebain and the optic chiasm in vertebrates". Animal Biology. 62 (2): 193–216. arXiv:1003.1872. doi:10.1163/157075611X617102. S2CID 7399128.
^de Lussanet, M.H.E. (2019). "Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis". PeerJ. 7: e7096. doi:10.7717/peerj.7096. PMC6557252. PMID 31211022.
^Schmolesky MT, Wang Y, Creel DJ, Leventhal AG (2000). "Abnormal retinotopic organization of the dorsal lateral geniculate nucleus of the tyrosinase-negative albino cat". J Comp Neurol. 427 (2): 209–19. doi:10.1002/1096-9861(20001113)427:2<209::aid-cne4>3.0.co;2-3. PMID 11054689. S2CID 32536933.
^Guillery, RW; Kaas, JH (June 1973). "Genetic abnormality of the visual pathways in a "white" tiger". Science. 180 (4092): 1287–9. Bibcode:1973Sci...180.1287G. doi:10.1126/science.180.4092.1287. PMID 4707916. S2CID 28568341.
^Davis, Matthew C.; Griessenauer, Christoph J.; Bosmia, Anand N.; Tubbs, R. Shane; Shoja, Mohammadali M. (2014-01-01). "The naming of the cranial nerves: A historical review". Clinical Anatomy. 27 (1): 14–19. doi:10.1002/ca.22345. ISSN 1098-2353. PMID 24323823. S2CID 15242391.
Jeffery G (October 2001). "Architecture of the optic chiasm and the mechanisms that sculpt its development". Physiol. Rev. 81 (4): 1393–414. doi:10.1152/physrev.2001.81.4.1393. PMID 11581492. S2CID 203231.
External linksEdit
Wikimedia Commons has media related to Optic chiasm.
. Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-11-07.
September 13, 2023
optic, chiasm, neuroanatomy, optic, chiasm, optic, chiasma, from, greek, χίασμα, crossing, from, ancient, greek, χιάζω, mark, with, part, brain, where, optic, nerves, cross, located, bottom, brain, immediately, inferior, hypothalamus, optic, chiasm, found, ver. In neuroanatomy the optic chiasm or optic chiasma ɒ p t ɪ k k aɪ ae z em from Greek xiasma crossing from Ancient Greek xiazw to mark with an X is the part of the brain where the optic nerves cross It is located at the bottom of the brain immediately inferior to the hypothalamus 1 The optic chiasm is found in all vertebrates although in cyclostomes lampreys and hagfishes it is located within the brain 2 3 Optic chiasmBrain viewed from below the front of the brain is above Visual pathway with optic chiasm X shape is shown in red image from Andreas Vesalius Fabrica 1543 Optic nerves chiasm and optic tractsDetailsSystemVisual systemFunctionTransmit visual information from the optic nerves to the occipital lobes of the brainIdentifiersLatinchiasma opticumMeSHD009897NeuroNames459NeuroLex IDbirnlex 1416TA98A14 1 08 403TA25668FMA62045Anatomical terms of neuroanatomy edit on Wikidata This article is about the optic chiasm of vertebrates which is the best known nerve chiasm but not every chiasm denotes a crossing of the body midline e g in some invertebrates see Chiasm anatomy A midline crossing of nerves inside the brain is called a decussation see Definition of types of crossings Contents 1 Structure 2 Development in mammals 3 Other animals 3 1 Mammals 3 2 Cephalopods and insects 4 History 5 Additional images 6 See also 7 References 8 External linksStructure Edit nbsp Figure 2 Transformations of the visual field toward the visual map on the primary visual cortex in vertebrates U up D down L left R right F foveaMain article Chiasm anatomy Structure In all vertebrates the optic nerves of the left and the right eye meet in the body midline ventral to the brain In many vertebrates the left optic nerve crosses over the right one without fusing with it 4 In vertebrates with a large overlap of the visual fields of the two eyes i e most mammals and birds but also amphibians reptiles such as chameleons the two optic nerves merge in the optic chiasm In such a merged optic chiasm part of the nerve fibres do not cross the midline but continue towards the optic tract of the ipsilateral side By this partial decussation the part of the visual field that is covered by both eyes is fused so that the processing of binocular depth perception by stereopsis is enabled see Figure 2 In the case of such partial decussation the optic nerve fibres on the medial sides of each retina which correspond to the lateral side of each visual hemifield because the image is inverted cross over to the opposite side of the body midline The inferonasal retina are related to the anterior portion of the optic chiasm whereas superonasal retinal fibers are related to the posterior portion of the optic chiasm The partial crossing over of optic nerve fibres at the optic chiasm allows the visual cortex to receive the same hemispheric visual field from both eyes Superimposing and processing these monocular visual signals allow the visual cortex to generate binocular and stereoscopic vision The net result is that the right cerebral hemisphere processes left visual hemifield and the left cerebral hemisphere processes the right visual hemifield Beyond the optic chiasm with crossed and uncrossed fibers the optic nerves are called optic tracts The optic tract inserts on the optic tectum in mammals known as superior colliculus of the midbrain In mammals they also branch off to the lateral geniculate body of the thalamus in turn giving them to the occipital cortex of the cerebrum 5 Development in mammals EditDuring development the crossing of the optic nerves is guided primarily by cues such as netrin slit semaphorin and ephrin and by morphogens such as sonic hedgehog Shh and Wnt 6 This navigation is mediated by the neuronal growth cone a structure that responds to the cues by ligand receptor signalling systems that activate downstream pathways inducing changes in the cytoskeleton 7 Retinal ganglion cell RGC axons leaving the eye through the optic nerve are blocked from exiting the developing pathway by Slit2 and Sema5A inhibition expressed bordering the optic nerve pathway Ssh expressed at the central nervous system midline inhibits crossing prior to the chiasm where it is downregulated 8 9 The organization of RGC axons changes from retinotopic to a flat sheet like orientation as they approach the chiasm site 10 Most RGC axons cross the midline at the ventral diencephalon and continue to the contralateral superior colliculus The number of axons that do not cross the midline and project ipsilaterally depends on the degree of binocular vision of the animal 3 in mice and 45 in humans do not cross 8 Ephrin B2 is expressed at the chiasm midline by radial glia and acts as a repulsive signal to axons originating from the ventrotemporal retina expressing EphB1 receptor protein giving rise to the ipsilateral or uncrossed projection 8 RGC axons that do cross at the optic chiasm are guided by the vascular endothelial growth factor VEGF A expressed at the midline which signals through the receptor Neuropilin 1 NRP1 expressed on RGC axons 11 Chiasm crossing is also promoted by Nr CAM Ng CAM related cell adhesion molecule and Semaphorin6D Sema6D expressed at the midline which form a complex that signals to Nr CAM Plexin A1 receptors on crossing RGC axons 12 Other animals EditMammals Edit Main article Contralateral brain Theories Since all vertebrates even the earliest fossils 13 and modern jawless ones 5 possess an optic chiasm it is not known how it evolved 14 A number of theories have been proposed for the function of the optic chiasm in vertebrates see theories According to the axial twist hypothesis the optic chiasm develops as a consequence of a twist in the early embryo 15 In Siamese cats with certain genotypes of the albino gene the wiring is disrupted with more of the nerve crossing than normal 16 Since siamese cats like albino tigers also tend to cross their eyes strabismus it has been proposed that this behavior might compensate the abnormal amount of decussation 17 18 Cephalopods and insects Edit Main article chiasm anatomy In cephalopods and insects the optic tracts do not cross the body midline so each side of the brain processes the ipsilateral eye History EditThe crossing of nerve fibres and the impact on vision that this had was probably first identified by Persian physician Esmail Jorjani who appears to be Zayn al Din Gorgani 1042 1137 19 Additional images Edit nbsp Scheme showing central connections of the optic nerves and optic tracts nbsp Brain seen from below with the optic chiasm seen in yellow in the centre nbsp Transformations of the visual field toward the visual map on the primary visual cortex nbsp Brain and brainstem seen from below nbsp Left hemisphere of the brain seen in a cadaveric specimen from the side with the optic chiasm labelled nbsp Cerebrum inferior view deep dissection nbsp Guidance of axon crossing and non crossing during development See also EditChiasmal syndrome Chiasm anatomy Definition of types of crossings Contralateral brainReferences Edit Colman Andrew M 2006 Oxford Dictionary of Psychology 2nd ed Oxford University Press p 530 ISBN 978 0 19 861035 9 Bainbridge David 30 June 2009 Beyond the Zonules of Zinn A Fantastic Journey Through Your Brain Harvard University Press p 162 ISBN 978 0 674 02042 9 Retrieved 22 November 2015 de Lussanet Marc H E Osse Jan W M 2012 An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates Animal Biology 62 2 193 216 arXiv 1003 1872 doi 10 1163 157075611X617102 ISSN 1570 7555 S2CID 7399128 Stephen Polyak 1957 The vertebrate visual system Chicago Chicago Univ Press a b Nieuwenhuys R Donkelaar H J Nicholson C Smeets W J A J Wicht H 1998 The central nervous system of vertebrates New York Springer ISBN 9783642621277 Erskine L Herrera E 2007 The retinal ganglion cell axon s journey Insights into molecular mechanisms of axon guidance Developmental Biology 308 1 1 14 doi 10 1016 j ydbio 2007 05 013 PMID 17560562 Gordon Weeks PR 2005 Neuronal Growth Cones Cambridge University Press ISBN 9780511529719 a b c Herrera E Erskine L Morenilla Palao C 2019 Guidance of retinal axons in mammals Seminars in Cell amp Developmental Biology 85 48 59 doi 10 1016 j semcdb 2017 11 027 PMID 29174916 S2CID 24381059 Rasband Kendall Hardy Melissa Chien Chi Bin 2003 Generating X Formation of the Optic Chiasm Neuron 39 6 885 888 doi 10 1016 S0896 6273 03 00563 4 PMID 12971890 Guillery RW Mason CA Taylor JS 1995 Developmental determinants at the mammalian optic chiasm The Journal of Neuroscience 15 7 4727 4737 doi 10 1523 JNEUROSCI 15 07 04727 1995 PMC 6577905 PMID 7623106 Erskine L Reijntjes S Pratt T 2011 VEGF signaling through neuropilin 1 guides commissural axon crossing at the optic chiasm Neuron 70 5 951 965 doi 10 1016 j neuron 2011 02 052 PMC 3114076 PMID 21658587 Kuwajima T Yoshida Y Pratt T 2012 Optic chiasm presentation of Semaphorin6D in the context of Plexin A1 and Nr CAM promotes retinal axon midline crossing Neuron 74 4 676 690 doi 10 1016 j neuron 2012 03 025 PMC 3361695 PMID 22632726 Janvier P 1996 Early vertebrates New York Clarendon Press Oxford University Press ISBN 978 0198540472 de Lussanet M H E Osse J W M 2012 An ancestral axial twist explains the contralateral forebain and the optic chiasm in vertebrates Animal Biology 62 2 193 216 arXiv 1003 1872 doi 10 1163 157075611X617102 S2CID 7399128 de Lussanet M H E 2019 Opposite asymmetries of face and trunk and of kissing and hugging as predicted by the axial twist hypothesis PeerJ 7 e7096 doi 10 7717 peerj 7096 PMC 6557252 PMID 31211022 Schmolesky MT Wang Y Creel DJ Leventhal AG 2000 Abnormal retinotopic organization of the dorsal lateral geniculate nucleus of the tyrosinase negative albino cat J Comp Neurol 427 2 209 19 doi 10 1002 1096 9861 20001113 427 2 lt 209 aid cne4 gt 3 0 co 2 3 PMID 11054689 S2CID 32536933 Guillery RW Kaas JH June 1973 Genetic abnormality of the visual pathways in a white tiger Science 180 4092 1287 9 Bibcode 1973Sci 180 1287G doi 10 1126 science 180 4092 1287 PMID 4707916 S2CID 28568341 Guillery RW May 1974 Visual pathways in albinos Sci Am 230 5 44 54 Bibcode 1974SciAm 230e 44G doi 10 1038 scientificamerican0574 44 PMID 4822986 Davis Matthew C Griessenauer Christoph J Bosmia Anand N Tubbs R Shane Shoja Mohammadali M 2014 01 01 The naming of the cranial nerves A historical review Clinical Anatomy 27 1 14 19 doi 10 1002 ca 22345 ISSN 1098 2353 PMID 24323823 S2CID 15242391 Jeffery G October 2001 Architecture of the optic chiasm and the mechanisms that sculpt its development Physiol Rev 81 4 1393 414 doi 10 1152 physrev 2001 81 4 1393 PMID 11581492 S2CID 203231 External links Edit nbsp Wikimedia Commons has media related to Optic chiasm Anatomy diagram 13048 000 1 Roche Lexicon illustrated navigator Elsevier Archived from the original on 2014 11 07 Retrieved from https en wikipedia org w index php title Optic chiasm amp oldid 1161690803, wikipedia, wiki, book, books, library,
