Visual System 1 Flashcards
Brings visual fields from the eye to the primary visual cortex
Visual System (In occipital lobe)
Goldman perimetry test of visual fields shows that larger and brighter objects have larger
Visual Fields
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)
Relatively small visual loss
Scotoma
Relatively large visual loss, usually the whole eye visual field
Anopia (anopsia)
Both eyes open during visual field testing can mask a deficit because of
Binocular Vision
Temporal retinas receive information from
Nasal hemifields
Nasal retinas receive information from
Temporal hemifields
A cause for complete lesion of the optic nerve is
-Rare
Occlusion of central artery of retina
Provide myelin for the optic nerve
-affected in MS
Oligodendrocytes
Similar to the brain, the optic nerve has
Meninges (dura, arachnoid, and pia)
Axons from the nasal halfs of the retina (from the temporal visual hemifields) will
Cross at optic chiams
Axons from the temporal halfs of the retina (from the nasal hemifields) will
NOT cross at optic chiasm
The right optic tract has all the visual information from the
Left
The left optic tract has all the visual information from the
Right
The optic tract has axons from the
Ipsilateral temporal retina and contralateral nasal retina
The optic tract carries visual field information from the
Ipsilateral nasal field and contralateral temporal field
The major destination of the optic tract is the
Lateral Geniculate nucleus (90%)
The remaining 10% of optic tract axons will go to one of which three areas?
- ) Hypothalamus (via suprachiastamtic n.)
- ) Pretectum
- ) Superior Colliculus
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.
Responsivle for the pupillary light and accommodation reflexes
Axons from retina to pretectum
Responsible for coordinating vision with other sensory inputs
Axons from retina to superior colliculus
Allows us to follow visual subjects clearly
-Responsible for visual motor reflexes
Axons from retina to superior colliculus
The thalamic nucleus for the visual system
Lateral Geniculate Nucleus (LGN)
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?
- ) 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
4
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
