Visual System Flashcards
What is the fovea?
Small depression in the eye socket where visual acuity is the highest
Why does the fovea have high visual acuity?
Contains mostly cones
The displacement of retinal layers in the middle allow for more light to reach the photoreceptors
Light travels from ____ to ____ through the retina
Anterior to posterior
The external nuclear layer of the retina contains
Cell bodies of photoreceptors
The internal nuclear layer of the retina contains
Cell bodies of bipolar neurons, horizontal cells, amacrine cells, Muller supporting cells
The third group of cells in the retina is called the …. and contains ….
Retinal ganglion neurons
Cell bodies of these ganglia
What are the 3 groups of cells in the retina going anterior to posterior?
Retinal ganglion neurons
Internal nuclear layer
External nuclear layer
Retinal detachment occurs between layers __ and ___
1 and 2
Rods are responsible for
Vision in light of low intensity
Predominate in periphery of retina
Responsible for sensing something in the dark
Cones are responsible for
Visual acuity and color vision
Concentrated at fovea
Move eyes so fovea gets input
What is phototransduction?
Conversion of light into electrical signals
The visual pathway consists of
Photoreceptors
Bipolar neurons
Retinal ganglion neurons
LGN (lateral geniculate nucleus) of the thalamus
Primary visual cortex
Where does more complicated visual processing occur?
Downstream of the primary visual cortex
The retrolenticular limb of the internal capsule contains axons from ___ that lead to _____
From LGN (lateral geniculate nucleus)
Leads to primary visual cortex
What is the optic radiation?
LGN neurons that project from thalamus to primary visual cortex
Neurons go through retrolenticualr limb of the internal capsule to become the optic radiation
The lateral inferior optic radiation is also referred to as … goes through …
Called Meyer’s loop
Goes through temporal lobe to inferior back of calcarine sulcus (lingual gyrus)
The medial super optic radiation goes through
Parietal lobes to superior bank of calcarine sulcus (cuneus gyrus)
Peripheral retina information goes to which part of the primary visual cortex?
Anterior
Fovea information goes to which part of the primary visual cortex?
Posterior
What is the cuneus?
Superior part of the occipital lobe
What is the lingual gyrus?
Inferior portion of the occipital lobe
What are other targets of retinal ganglion neurons?
Superior chiasmatic nucleus of hypothalamus for diurnal rhythms (day length)
Pretectal area: pupillary light reflex
Superior colliculus: eye movements
The retina and optic nerve are provided blood supply from
Opthalmic artery of internal carotid artery
The optic chiasm receives blood supply from?
ACA and anterior communicating artery
The optic tract receives blood supply from?
Anterior choroidal artery of internal carotid artery
The LGN (lateral geniculate nucleus) receives blood supply from?
Thalamogeniculate artery of PCA
The lateral inferior optic radiation (Meyer’s loop) receives blood supply from?
MCA
The medial superior optic radiation receives blood supply from?
PCA
The primary visual cortex receives blood supply from?
Calcarine artery of PCA
The dorsal stream of the visual association cortex provides information about
Where
Location of stimulus and movement direction
The ventral stream of the visual association cortex provides information about
What
Form (shape) and color perception
The dorsal stream primarily contains …. and sends information to ….
Contains rods
Sends information to anterior primary visual cortex and dorsal association visual cortices
The ventral stream primarily contains ….. and sends information to …..
Contains cones
Sends information to posterior primary visual cortex and ventral association visual cortical areas
What happens with damage to the dorsal stream?
Patient can still identify objects but cannot tell which is closest to each other
The four quadrants of the visual field are made up of
Nasal (medial) and temporal (lateral) halves
The visual field is ___ and ____ on retina
Reversed and inverted
Retinal ganglion neurons from the nasal (medial) half of retina cross at the …
Those from temporal (lateral) half of the retina ….
Optic Chiasm
Do not cross
Retinal ganglion neurons transmitting information about an object located in one half of the visual field ends up in ___ tract
Contralateral
What is an anopia?
Visual field cut
What is hemianopia?
Loss of one half of the visual field
What is quadrantanopia?
Loss of one quarter of the visual field
What does it mean if the anopia is homonymous?
Deficit in the same half or quadrant of the visual field for each eye
What does it mean if the anopia is heteronymous?
Deficit is in the different half or quadrant of the visual field for each eye
Ipsilateral blindness occurs when there is destruction to …
Optic nerve or retina
Blindness is paired with loss of pupillary light reflex
Bitemporal (lateral) hemianopia occurs with
Destruction of crossing axons at the optic chiasm
Also called tunnel vision
Person cannot see laterally
Right hemianopia (half) occurs with
Destruction of lateral aspect of optic chiasm (usually due to aneurysm of internal carotid artery)
Also called nasal hemianopia (medial)
Right homonymous hemianopia occurs with
Destruction of optic tract, LGN, optic radiation, or primary visual cortex
Also called contralateral homonymous hemianopia
Lose visual field on the right in both eyes
What is macular sparing?
Loss of right side of visual field as well as around the pupil
Occurs due to occlusion of calcarine artery
What is left superior quadrantanopia?
Loss of left upper quadrant on both sides
Due to damage at Meyer’s loop
Also called contralateral superior quadrantanopia
What happens with direct light reflex?
Pupil constricts in eye stimulated by light
What happens with consensual light reflex?
Pupil constricts in contralateral eye
What is the order of pupillary light reflex synapsing?
Retinal ganglion neurons > pretectal neurons (afferent lim) > Edinger-Westphal nuclei (parasympathetic) > ciliary ganglion (efferent limb) > pupillary sphincter muscle and causes contraction
Pupillary dilation reflex: Hypothalamic neurons synapse at
T1 to T3 of spinal cord
Pupillary dilation reflex: Sympathetic preganglionic neurons synapse in
Superior cervical region
Pupillary dilation reflex: sympathetic postganglionic neurons synapse on
Pupillary dilator muscle and cause contraction
What are the 3 ways that eyes accommodate and maintain a clear visual image as gaze shifts from distant to near point?
- 2 eyes converge to midline from contraction of medial rectus muscles
- constriction in pupil from pupillary sphincter muscles
- Lens thickens due to contraction of ciliary muscles from ciliary ganglia
What are extraocular muscles and cranial nerves associated?
CN III: oculomotor nerve, superior rectus, inferior rectus, medial rectus, inferior oblique muscle
CN IV: trochlear nerve, superior oblique muscle
CN VI: abducens, lateral rectus muscle
What muscles are involved in horizontal eye movements?
Lateral rectus (CN VI) abducts the eye
Medical rectus (CN III) adducts the eye
What are conjugate eye movements?
Both eyes move in the same direction
What are vergent eye movements?
Eyes move in opposite directions
What is the horizontal gaze center?
PPRF, paramedian pontine reticular formation
What is the frontal eye field center?
Frontal lobe
There is an eye field in ___ lobes
All lobes
What is the pathway for voluntary horizontal gaze to the right?
Activate left frontal eye field
Right PPRF excited
Righ abducens nucleus excited
Internuclear neurons (MLF)
Left oculomotor nucleus excited (MLF)
What muscles contract with horizontal gaze to the right? This leads to ….
Right lateral rectus muscle
Medial rectus muscle
Both eye gazes right
What eye fields are responsible for saccades?
Frontal eye fields
Shifting gaze from one stationary object to another
What eye fields are responsible for smooth pursuit?
Multiple
Done to track a moving object
The cerebral eye fields are supplied by the
MCA
The midbrain structures are supplied by
PCA
The pontine structures are supplied by
Basilar artery
Lesion to the left frontal eye field leads to
Transient (temporary) paralysis of gaze to right
It is temporary due to redundant connections, bilateral cortical connections to brainstem gaze centers
Lesion to right PPRF (paramedian pontine reticular formation) leads to
Paralysis of gaze to the right
Permanent loss due to no redudancy
Lesion to left MLF (medial longitudinal fasciculus) leads to
Paralysis of gaze to right of left eye only
Right eye not affected because the pathway to the lateral rectus is intact
Also called left internuclear ophthalmoplegia
Lesion to the right abducens nerve leads to
Paralysis of gaze to right of right eye only
