Optic radiation

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Brain: Optic radiation

Deep dissection of cortex and brain-stem. (Optic radiation labeled at center left.)
Latin	radiatio optica
NeuroNames	ancil-529
Dorlands/Elsevier	r_01/12686139

The optic radiation (also known as the geniculo-calcarine tract or as the geniculostriate pathway) is a collection of axons from relay neurons in the lateral geniculate nucleus of the thalamus carrying visual information to the visual cortex (also called striate cortex) along the calcarine fissure.

There is one such tract on each side of the brain.

[edit] Parts

A distinctive feature of the optic radiations is that they split into two parts on each side:

Source	Path	Information	Damage
Fibers from the inferior retina (also called "Meyer's loop" or "Archambault's loop")	must pass into the temporal lobe by looping around the inferior horn of the lateral ventricle.	Carry information from the superior part of the visual field	A lesion in the temporal lobe that results in damage to Meyer's loop causes a characteristic loss of vision in a superior quadrant (quadrantanopia.)
Fibers from the superior retina	travel straight back to the occipital lobe in the retrolenticular limb of the internal capsule to the visual cortex.	Carry information from the inferior part of the visual field	Taking the shorter path, these fibers are less susceptible to damage.

Right superior quadrantanopia. The areas of the visual field lost in each eye are shown as black areas. This visual field defect is characteristic of damage to Meyer's loop on the left side of the brain.

[edit] Additional images

Horizontal section of right cerebral hemisphere.

Diagram of the tracts in the internal capsule.

3D schematic representation of optic tracts

[edit] External links

Optic+radiation at eMedicine Dictionary
Kier LE, Staib LH, Davis, LM, Bronen, RA (2004). "MR Imaging of the Temporal Stem: Anatomic Dissection Tractography of the Uncinate Fasciculus, Inferior Occipitofrontal Fasciculus, and Meyer’s Loop of the Optic Radiation.". Am J Neuroradiology 25: 677-691. PMID 15140705.
http://www2.umdnj.edu/~neuro/studyaid/Practical2000/Q34.htm

v • d • e Sensory system – Visual system and eye movement

Vision	Retina → Optic nerve → Optic chiasm → Optic tract → Lateral geniculate nucleus → Optic radiation → Visual cortex (Cuneus, Lingual gyrus) → Blobs

Tracking	Smooth pursuit: Parietal lobe - Occipital lobe Saccade: Frontal eye fields Physiologic nystagmus

Horizontal gaze	Abducens nucleus → PPRF → MLF → Oculomotor nucleus → Medial rectus muscle

Vertical gaze	Rostral interstitial nucleus → Oculomotor nucleus, Trochlear nucleus → Muscles of orbit

Pupillary dilation	Ciliospinal center → Superior cervical ganglion → Long ciliary nerves → Iris dilator muscle

Pupillary light reflex (constriction)	Retina → Optic nerve → Optic chiasm → Optic tract → Pretectum → Edinger-Westphal nucleus → Oculomotor nerve → Ciliary ganglion → Short ciliary nerves → Iris sphincter muscle

Accommodation	Retina → Optic nerve → Optic chiasm → Optic tract → Visual cortex → Brodmann area 19 → Pretectum → Edinger-Westphal nucleus → Short ciliary nerves → Ciliary ganglion → Ciliary muscle

Vestibulo-ocular reflex	Semicircular canal → Vestibulocochlear nerve → Vestibular nuclei → Medial rectus muscle

Circadian rhythm	Retina → Hypothalamus (Suprachiasmatic nucleus)

v • d • e Nervous system: Sensory systems / sense

Special senses	Visual system – visual perception • Auditory system – hearing • Chemoreception (Olfactory system – olfaction • Gustatory system – taste)

Somatosensory system	Nociception • Thermoreception • Vestibular system • Mechanoreception (pressure, vibration, proprioception)

Other	Sensory receptor

v • d • e White matter fibers

Association fibers	Uncinate fasciculus - Cingulum - Superior longitudinal fasciculus/Arcuate fasciculus - Inferior longitudinal fasciculus - Inferior occipitofrontal fasciculus - Fornix (Columns of fornix, Crus of fornix)

Commissural fibers	Corpus callosum (Genu, Splenium, Tapetum, Rostrum) - Anterior commissure - Posterior commissure - Commissure of fornix

Projection fibers	(none named)