Visual System 1 Flashcards by Joel Glotfelty

Brings visual fields from the eye to the primary visual cortex

Visual System (In occipital lobe)

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Goldman perimetry test of visual fields shows that larger and brighter objects have larger

Visual Fields

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Are always named by the part of the visual field lost and not by the part of the retina that is damaged

Visual field defect (scotoma and anopia)

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Relatively small visual loss

Scotoma

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Relatively large visual loss, usually the whole eye visual field

Anopia (anopsia)

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Both eyes open during visual field testing can mask a deficit because of

Binocular Vision

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Temporal retinas receive information from

Nasal hemifields

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Nasal retinas receive information from

Temporal hemifields

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A cause for complete lesion of the optic nerve is

-Rare

Occlusion of central artery of retina

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Provide myelin for the optic nerve

-affected in MS

Oligodendrocytes

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Similar to the brain, the optic nerve has

Meninges (dura, arachnoid, and pia)

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Axons from the nasal halfs of the retina (from the temporal visual hemifields) will

Cross at optic chiams

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Axons from the temporal halfs of the retina (from the nasal hemifields) will

NOT cross at optic chiasm

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The right optic tract has all the visual information from the

Left

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The left optic tract has all the visual information from the

Right

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The optic tract has axons from the

Ipsilateral temporal retina and contralateral nasal retina

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The optic tract carries visual field information from the

Ipsilateral nasal field and contralateral temporal field

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The major destination of the optic tract is the

Lateral Geniculate nucleus (90%)

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The remaining 10% of optic tract axons will go to one of which three areas?

) Hypothalamus (via suprachiastamtic n.)
) Pretectum
) Superior Colliculus

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Responsible for the influence of light over the neuroendocrine functions and over the sleep/wake cycle through the pineal gland

Axons from the retina to the hypothalamus via the suprachiastamtic n.

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Responsivle for the pupillary light and accommodation reflexes

Axons from retina to pretectum

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Responsible for coordinating vision with other sensory inputs

Axons from retina to superior colliculus

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Allows us to follow visual subjects clearly

-Responsible for visual motor reflexes

Axons from retina to superior colliculus

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The thalamic nucleus for the visual system

Lateral Geniculate Nucleus (LGN)

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Has cell bodies organized in layers

The lateral Geniculate Nucleus

Each layer of the LGN receives on portion of the visual fields from

Each eye

LGN axons form the

Optic radiations

LGN axons form the optic radiations and synapse in the

Primary visual cortex

The left side of the world (both left visual fields) ends up in the

Right primary visual cortex

The right side of the world (both right visual fields) ends up in the

Left primary visual cortex

Is placed on the medial side of the occipital lobe

Primary visual cortex

Partial optic chiasm lesions result in

Bitemporal superior or inferior heteronymous quadrantanopia

What is a cause of partial optic chiasm lesion?

Pituitary tumors (Pituitary adenoma or craniopharyngioma)

Puts pressure on the optic chiasm from below -begins as superior quadrantonopia

Pituitary adenoma

Puts pressure on the optic chiasm from above -Begins as an inferior quadrantonopia

Craniopharyngioma

Occlusion of the superior branch of the right opthalamic artery results in a

Mononuclear visual defect

Aneurisms of the internal carotid artery put pressure on the temporal tract of the optic chiasm and cause

Nasal hemianopia

Meyer's loop vision system axons can be found in the

Temporal lobe

With lesions before the optic chiasm, deficits are

Ipsilateral and monocular

With lesions at the optic chiasm, deficits are

Binocular, bitemporal, and heteronymous

With lesions past the optic chiasm, deficits are

Binocular, contralateral, and homonymous

Lesions with abnormal pupillary reflex are lesions of the

Optic nerve and optic tract

Lesions with normal pupillary reflex are lesions of the

Optic radiation and visual cortex

Axons reaching pretectum will leave before synapse in

LNG

How can we differentiate optic tract lesions from primary visual cortex lesions?

Primary visual cortex lesions will have macular sparing

The macular representation is very large in the

Primary visual cortex

The macular representation is very large in the primary visual cortex and can receive blood supply from the

Posterior cerebral artery and middle cerebral artery

Lesions to the occipital pole cause

Macular visual field defects

A larger region of high visual acuity surrounding the fovea

Macula

Damage to the macula of the retina occurs in macular degeneration and results in loss of

Central Vision

Axons from RGCs coalesce and exit the eye through the

Optic Disk

Glaucoma first effects

Peripheral Vision

Age related macular degeneration results in

Central Blindness

Important for nutrients delivery to photoreceptors

Pigment Epithelium

The part of rods and cones where phototransduction occurs

Outer segments of Rods and Cones

The pigmented epithelium contains

Melatonin

The fovea is specialized for realizing

What the object is and what color it is

The neurotransmitter of all photoreceptors is

Glutamate

Used when light conditions are very low

Rods

In response to light, the rod cells

Hyperpolarize (dark current is lost)

This hyperpolarization results in the diminishment of

Neurotransmitter release

Photoreceptors do not have aciton potentials so their depolarizations and hyperpolarizations are

Graded

Turn off when exposed to light

Rods

The light receptor is

"Opsin" with Vitamin A Derivative

The light receptor in rods is

Rhodopsin

The light receptor in cones is

Conopsin

All light isomerizes 11-cis retinal to

All-trans retinal

All-trans retinal dissociates from Opsin. Opsin changes conformation and interacts with

G-protein -Signaling cascade starts

The G-protein acted upon by the opsin is

Transducin

Inhibitors of transducin fall off when

GDP is converted to GTP

This conversion of GDP to GTP results in the activation of

Transducin

The activated transducin's then target

Phosphodiesterase (PDE)

Removes the inhibitor from one or both PDEs

Transducin

Cleaves cGMP and inactivates it

PDE

The inner nuclear layer of the retina contains

Bipolar cells

Bipolar and ganglion cells have receptive fields with a

Center-surround (concentric) configuration

Are excited by the light in the center

On-center cells

A inhibited by the light in the center

Off-center cells

Center light results in less

Glutamate

How many Rods and cones can synapse on 1 bipolar retinal cell?

Up to 50 Rods Up to 5 cones

The inner nuclear layer of the retina also contains horizontal cells that provide

Lateral inhibition

Under most circumstances, horizontal cells will inhibit which 2 things?

1. ) Photoreceptor hyperpolarization | 2. ) Bipolar cell response

The primary point of signal compression

Horizontal cells

Cells in the inner nuclear layer of the retina that provide lateral inhibition, but at the opposite (optic nerve) side than horizontal cells

Amacrine cells

Intervene between bipolar cells and retinal ganglion cells

Amacrine cells

Second filter to reconsider what horizontal cells let through -Secondary point of signal compression

Amacrine cells

We need to detect boundaries form the background and also shape to figure out

Form of an object

Very good for spatial resolution but bad for temporal resolution -enable us to tell form of object

Parvocellular Pathway (P-cells)

Very good for temporal resolution, but has poor spatial resolution -Allows us to see motion of an object

Magnocellular pathway (M-cells)

Have small receptive fields and small caliber axons -Carry information on shape/form

P-cells

Have large receptive fields and large caliber axons -Carry information to the motion detectors

M-cells

M-cells can't detect motion themselves, but they relay information to cells that can in the

Visual cortex

Has to analyze motion, form, color, and depth

Primary visual cortex

The primary visual cortex is the

V1 (area 17: striate cortex)

V1 has 6 layers, but the special layer is layer

Layer 4 is special because it is where the massive

LGN projections end up

Each column in V1 analyzes a small region of the

Retina