Optic radiation: Definition from Answers.com

Brain: Optic radiation

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

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.

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 (also called "Shin's loop" or "Baum's loop")	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.

Additional images

Horizontal section of right cerebral hemisphere.

Diagram of the tracts in the internal capsule.

3D schematic representation of optic tracts

External links

Optic+radiation at eMedicine Dictionary
Kier LE, Staib LH, Davis, LM, Bronen, RA (01 May 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 (5): 677–691. PMID 15140705. http://www.ajnr.org/cgi/content/abstract/25/5/677. Retrieved 2007-12-19.
http://www2.umdnj.edu/~neuro/studyaid/Practical2000/Q34.htm

Sensory system: Visual system and eye movement pathways

Visual perception

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

Muscles of orbit

Tracking	Smooth pursuit: Parietal lobe · Occipital lobe Saccade: Frontal eye fields Physiologic nystagmus → Fixation reflex → PPRF

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

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

Vestibulo-ocular reflex	Semicircular canal → Vestibulocochlear nerve → Vestibular nuclei → Abducens nucleus → MLF → Oculomotor nucleus → Medial rectus muscle

Pupillary reflex

Pupillary dilation	1 (Posterior hypothalamus → Ciliospinal center) → 2 (Superior cervical ganglion) → 3 (Sympathetic root of ciliary ganglion → Nasociliary nerve → Long ciliary nerves → Iris dilator muscle)

Pupillary light reflex (constriction)	1 (Retina → Optic nerve → Optic chiasm → Optic tract → Pretectal nucleus) → 2 (Edinger-Westphal nucleus) → 3 (Oculomotor nerve → Parasympathetic root of ciliary ganglion → Ciliary ganglion) → (4 Short ciliary nerves → Iris sphincter muscle)

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

Circadian rhythm

Retina → Hypothalamus (Suprachiasmatic nucleus)

eye navs: anat/adnexa anat/pathways/physio/dev, noncongen/congen/neoplasia, eponymous signs, proc

Human brain: diencephalon (TA A14.1.08, GA 9.807)

Epithalamus

Surface	Pineal body · Habenula · Habenular trigone · Habenular commissure

Grey matter	Pretectal area · Habenular nuclei · Subcommissural organ

Thalamus

Surface	Stria medullaris of thalamus · Thalamic reticular nucleus · Taenia thalami

Grey matter/ nuclei	paired: AN · Ventral (VA/VL, VP/VPM/VPL) · Lateral (LD, LP, Pulvinar) · Metathalamus (MG, LG) midline: MD · Intralaminar (Centromedian) · Midline nuclear group · Interthalamic adhesion

White matter	Mammillothalamic fasciculus · Pallidothalamic connections (Ansa lenticularis, Lenticular fasciculus, Thalamic fasciculus) · PCML (Medial lemniscus, Trigeminal lemniscus) · Spinothalamic tract · Lateral lemniscus · Dentatothalamic tract · Acoustic radiation · Optic radiation · Subthalamic fasciculus · Anterior trigeminothalamic tract Medullary laminae

Hypothalamus

Surface

Median eminence/Tuber cinereum · Mammillary body · Infundibulum

Grey matter

Autonomic zones	Anterior (parasympathetic/heat loss) · Posterior (sympathetic/heat conservation)

Endocrine	posterior pituitary: magnocellular/Paraventricular/Supraoptic (oxytocin/vasopressin) other: parvocellular/Arcuate (dopamine/GHRH) · Preoptic (GnRH) · Suprachiasmatic (melatonin)

Emotion	Lateral (hunger) · Ventromedial (satiety) · Dorsomedial (rage)

White matter

afferent (SN → Medial forebrain bundle) · efferent (Mammillothalamic fasciculus → AN, Stria terminalis → Amygdala, Dorsal longitudinal fasciculus → SC)

Pituitary

Posterior is diencephalon, but anterior is glandular

Subthalamus

Subthalamic nucleus · Zona incerta

Ventricular system:
Third ventricle

recesses: (Optic recess, Infundibular recess, Suprapineal recess, Pineal recess)

Hypothalamic sulcus · Tela chorioidea of third ventricle

Subfornical organ

Apertures: Interventricular/Monro

Posterior commissure

Human brain, cerebrum, Interior of the cerebral hemispheres - Rostral Basal ganglia and associated structures (TA A14.1.09.321-552, GA 9.832-837)

Basal ganglia

Grey matter

Corpus striatum	striatum: Putamen · Caudate nucleus lentiform nucleus: Putamen · Globus pallidus (GPe, GPi)

Ventral striatum	Nucleus accumbens · Olfactory tubercle · Islands of Calleja

Other	Amygdala · Claustrum

White matter

Semioval center

Internal capsule (Anterior limb · Genu · Posterior limb, Optic radiation)

Corona radiata · External capsule · Extreme capsule

Pallidothalamic connections: Thalamic fasciculus (Ansa lenticularis, Lenticular fasciculus) · Subthalamic fasciculus

Rhinencephalon

Grey matter	Anterior olfactory nucleus · Anterior perforated substance · Olfactory bulb

White matter	Olfactory tract (Medial olfactory stria, Lateral olfactory stria) · Olfactory trigone

Other basal forebrain

Grey matter	Substantia innominata (Basal optic nucleus of Meynert) · Nucleus of diagonal band

White matter	Diagonal band of Broca · Stria terminalis

Archicortex:
Hippocampal formation/
Hippocampus anatomy

Grey matter	Hippocampus proper: CA1 · CA2 · CA3 · CA4 Dentate gyrus: Fascia dentata Subiculum

White matter	Alveus · Fimbria · Perforant path

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