Optic chiasm

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Optic chiasm
1543,Visalius'OpticChiasma.jpg
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).
Gray773.png
Optic nerves, chiasm, and optic tracts
Details
System Visual system
FunctionTransmit visual information from the optic nerves to the occipital lobes of the brain
Identifiers
Latin chiasma opticum
MeSH D009897
NeuroNames 459
NeuroLex ID birnlex_1416
TA98 A14.1.08.403
TA2 5668
FMA 62045
Anatomical terms of neuroanatomy

In neuroanatomy, the optic chiasm, or optic chiasma ( /ɒptɪkkaɪæzəm/ ; from Greek χίασμα 'crossing', from Ancient Greek χιάζω '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]

Contents

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).

Structure

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=fovea Optical-transformations.png
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=fovea

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]

Arterial supply

The optic chiasma receives its arterial supply from the anterior cerebral arteries, and from branches of the internal carotid artery which ascend along the pituitary stalk (the latter supplying the midline portion of the chiasma). [6]

Development in mammals

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. [7] 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. [8] 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. [9] [10] The organization of RGC axons changes from retinotopic to a flat sheet-like orientation as they approach the chiasm site. [11]

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). [9] 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. [9] 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. [12] 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. [13]

Other animals

Mammals

Since all vertebrates, even the earliest fossils [14] and modern jawless ones, [5] possess an optic chiasm, it is not known how it evolved. [15] A number of theories have been proposed for the function of the optic chiasm in vertebrates (see theories). According to the Axial Twist theory the optic chiasm develops as a consequence of a twist in the early embryo. [16]

In Siamese cats with certain genotypes of the albino gene, the wiring is disrupted, with more of the nerve-crossing than normal. [17] 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. [18] [19]

Cephalopods and insects

In cephalopods and insects the optic tracts do not cross the body midline, so each side of the brain processes the ipsilateral eye.

History

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). [20]

Additional images

See also

Related Research Articles

<span class="mw-page-title-main">Optic nerve</span> Second cranial nerve, which connects the eyes to the brain

In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

<span class="mw-page-title-main">Visual system</span> Body parts responsible for vision

The visual system is the physiological basis of visual perception. The system detects, transduces and interprets information concerning light within the visible range to construct an image and build a mental model of the surrounding environment. The visual system is associated with the eye and functionally divided into the optical system and the neural system.

<span class="mw-page-title-main">Lateral geniculate nucleus</span> Component of the visual system in the brains thalamus

In neuroanatomy, the lateral geniculate nucleus is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve. There are two LGNs, one on the left and another on the right side of the thalamus. In humans, both LGNs have six layers of neurons alternating with optic fibers.

<span class="mw-page-title-main">Pupillary light reflex</span> Eye reflex which alters the pupils size in response to light intensity

The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness. A greater intensity of light causes the pupil to constrict, whereas a lower intensity of light causes the pupil to dilate. Thus, the pupillary light reflex regulates the intensity of light entering the eye. Light shone into one eye will cause both pupils to constrict.

<span class="mw-page-title-main">Retinal ganglion cell</span> Type of cell within the eye

A retinal ganglion cell (RGC) is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance. Retinal ganglion cells collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain.

<span class="mw-page-title-main">Optic tract</span> Neural pathway within the human visual system

In neuroanatomy, the optic tract is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus.

<span class="mw-page-title-main">Precentral gyrus</span> Motor gyrus of the posterior frontal lobe of the brain

The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecturally defined as Brodmann area 4.

Axon guidance is a subfield of neural development concerning the process by which neurons send out axons to reach their correct targets. Axons often follow very precise paths in the nervous system, and how they manage to find their way so accurately is an area of ongoing research.

<span class="mw-page-title-main">Abducens nucleus</span>

The abducens nucleus is the originating nucleus from which the abducens nerve (VI) emerges—a cranial nerve nucleus. This nucleus is located beneath the fourth ventricle in the caudal portion of the pons near the midline, medial to the sulcus limitans.

<span class="mw-page-title-main">Facial motor nucleus</span>

The facial motor nucleus is a collection of neurons in the brainstem that belong to the facial nerve. These lower motor neurons innervate the muscles of facial expression and the stapedius.

<span class="mw-page-title-main">Trochlear nucleus</span> Motor nucleus of cranial nerve IV

The nucleus of the trochlear nerve is a motor nucleus in the medial midbrain giving rise to the trochlear nerve.

<span class="mw-page-title-main">Decussation</span> Biological term to describe a crossing

Decussation is used in biological contexts to describe a crossing. In Latin anatomical terms, the form decussatio is used, e.g. decussatio pyramidum.

<span class="mw-page-title-main">Retinohypothalamic tract</span> Neural pathway involved with circadian rhythms

In neuroanatomy, the retinohypothalamic tract (RHT) is a photic neural input pathway involved in the circadian rhythms of mammals. The origin of the retinohypothalamic tract is the intrinsically photosensitive retinal ganglion cells (ipRGC), which contain the photopigment melanopsin. The axons of the ipRGCs belonging to the retinohypothalamic tract project directly, monosynaptically, to the suprachiasmatic nuclei (SCN) via the optic nerve and the optic chiasm. The suprachiasmatic nuclei receive and interpret information on environmental light, dark and day length, important in the entrainment of the "body clock". They can coordinate peripheral "clocks" and direct the pineal gland to secrete the hormone melatonin.

<span class="mw-page-title-main">Chiasmal syndrome</span> Set of signs and symptoms that are associated with lesions of the optic chiasm

Chiasmal syndrome is the set of signs and symptoms that are associated with lesions of the optic chiasm, manifesting as various impairments of the affected's visual field according to the location of the lesion along the optic nerve. Pituitary adenomas are the most common cause; however, chiasmal syndrome may be caused by cancer, or associated with other medical conditions such as multiple sclerosis and neurofibromatosis.

<span class="mw-page-title-main">Anatomical terms of neuroanatomy</span> Terminology used to describe the central and peripheral nervous systems

This article describes anatomical terminology that is used to describe the central and peripheral nervous systems - including the brain, brainstem, spinal cord, and nerves.

<span class="mw-page-title-main">Contralateral brain</span> Each side of the forebrain represents the opposite side of the body

The contralateral organization of the forebrain is the property that the hemispheres of the cerebrum and the thalamus represent mainly the contralateral side of the body. Consequently, the left side of the forebrain mostly represents the right side of the body, and the right side of the brain primarily represents the left side of the body. The contralateral organization involves both executive and sensory functions. The contralateral organization is only present in vertebrates.

<span class="mw-page-title-main">Axial twist theory</span> Scientific theory in vertebrate development

The axial twist theory is a scientific theory put forward to explain a range of unusual aspects of the body plan of vertebrates. It proposes that the rostral part of the head is "turned around" regarding the rest of the body. This end-part consists of the face as well as part of the brain. According to the theory, the vertebrate body has a left-handed chirality.

Carol Ann Mason is a Professor of Pathology and Cell Biology at Columbia University in the Mortimer B. Zuckerman Mind Brain Behavior Institute. She studies axon guidance in visual pathways in an effort to restore vision to the blind. Her research focuses on the retinal ganglion cell. She was elected a member of the National Academy of Sciences in 2018.

<span class="mw-page-title-main">Chiasm (anatomy)</span> Nerve crossings outside the central nervous system

In anatomy a chiasm is the spot where two structures cross, forming an X-shape. Examples of chiasms are:

<span class="mw-page-title-main">Visual pathway lesions</span> Overview about the lesions of visual pathways

The visual pathway consists of structures that carry visual information from the retina to the brain. Lesions in that pathway cause a variety of visual field defects. In the visual system of human eye, the visual information processed by retinal photoreceptor cells travel in the following way:
Retina→Optic nerve→Optic chiasma →Optic tract→Lateral geniculate body→Optic radiation→Primary visual cortex

References

  1. ↑ Colman, Andrew M. (2006). Oxford Dictionary of Psychology (2nd ed.). Oxford University Press. p. 530. ISBN   978-0-19-861035-9.
  2. ↑ 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.
  3. ↑ 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.
  4. ↑ Stephen, Polyak (1957). The vertebrate visual system. Chicago: Chicago Univ. Press.
  5. 1 2 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.
  6. ↑ Standring, Susan (2020). Gray's Anatomy: The Anatomical Basis of Clinical Practice (42th ed.). New York: Elsevier. p. 420. ISBN   978-0-7020-7707-4. OCLC   1201341621.
  7. ↑ 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 . hdl: 10261/338550 . PMID   17560562.
  8. ↑ Gordon-Weeks, PR (2005). Neuronal Growth Cones. Cambridge University Press. ISBN   9780511529719.
  9. 1 2 3 Herrera, 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.
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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.
  14. ↑ Janvier, P. (1996). Early vertebrates. New York: Clarendon Press, Oxford University Press. ISBN   978-0198540472.
  15. ↑ 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.
  16. ↑ 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.
  17. ↑ 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.
  18. ↑ 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.
  19. ↑ 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.
  20. ↑ 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.
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