CN II-Optic Nerve and Visual System Flashcards Preview

DPT 736 Neuroanatomy > CN II-Optic Nerve and Visual System > Flashcards

Flashcards in CN II-Optic Nerve and Visual System Deck (13)
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1

Visual System

-most highly developed of sensory modalities
-optic nerve and retina grow out of diencephalon
-retina encodes visual information and projects that info to brain via myelinated fibers in optic nerve
-optic nerve fibers undergo hemidecussation (part of fibers cross) in optic chiasm and project to primary visual cortex of the occipital lobe via thalamus (lat geniculate body)
-from eye --> optic chiasm = optic nerve
-optic chiasm to lateral geniculate body = optic tract
-lat geniculate body --> 1* visual cortex = optic radiation

2

The Eye

-optic nerve (II) emerges from posterior pole
-sclera: white, fibrous, protective outer layer of eye; over the anterior pole it is transparent and called cornea-light passes through to lens and then retina
-iris: fibers arranged in circular and radial fashion (under control of autonomic nervous system): circular (pupil constriction)-parasympathetic; radial (dilate pupil): sympathetic
-pupil: central aperture
-transition from eye into optic thalamus nerve = optic disc/blind spot
-ciliary body: contains ciliary muscle (parasympathetic innervation), alters shape of lens
-choroid: dark pigmented inner surface of sclera that absorbs light and reduces reflection
-retina: inner surface of choroid, photoreceptive

3

Diabetic Retinopathy

-eye filled with vitreous fluid
-diabetics who aren't under good control --> leaky vessels in eye --> min bleeds --> see floaters in vision

4

Retina

-photoreceptors: transduce light to electrical impulses by a series of photochemical reactions and physicochemical changes
-two varieties: rods-20x more numerous, very sensitive to light; cones-responsible for color
-highest acuity and high spatial and temporal resolution in cones
-more cones at fovea
-photoreceptor (rods and cones) --> bipolar cells --> optic nerve

5

Visual Field

-visual field consists of four quadrants
-image formed is inverted both vertically and laterally
-objects that lie in left half of visual field form an image on the right half of right eye and the right half of the left eye

6

Visual Pathways

-retinal ganglion axon travel in optic nerve and converge in optic chiasma
-axons from medial portions of retina decussate at chiasma and pass into contralateral optic tract
-axons from lateral portions of retina remain ipsilateral through chiasma
-axons then travel to thalamus, a relatively small number of axons bypass thalamus and go to pretectal region and superior colliculi for mediation of pupillary light reflex

7

Thalamocortical Neurons (3rd Order)

-project to primary visual cortex of occipital lobe: primarily on medial aspect of the occipital lobe above and below calcarine sulcus

8

Visual Association Cortex

-surrounding primary visual cortex
-interpretation of visual images
-recognition
-depth perception
-color vision

9

Visual Field Disorders

-monocular blindness: cataract, intraocular hemorrhage, retinal detachment
-bitemporal hemianopia: compression of optic chiasma by pituitary tumor
-homonymous hemianopia: vascular or neoplastic lesions of the optic tract, optic radiation

10

Meyer's Loop

-medial is parietal lobe goes to upper bank of calcarine fissure and receives images from lower visual field
-temporal is meyer's loop white matter tracts that go to lower bank of calcarine fissure and receives vision from upper visual quadrant from opposite eye
-look at drown out schematics

11

Optic Chiasm Pressure

-pituitary gland lies under optic chiasm --> tumor here would put pressure on optic chiasm at central fibers = tunnel vision
-bitemporal hemianopia

12

L Optic Nerve Disruption

-monocular anopia
-blindness in left eye

13

Lesion on L optic Tract

-affects right side of both eyes
-right homonymous heminaopia