visual system Flashcards
Relationship between wavelength and frequency
inversely related (shorter wavelength = higher frequency )
Describe the order of eye (anterior -> posterior), leading up to the retina
cornea -> anterior chamber -> pupil/iris/ciliary body -> vitreous chamber -> retina
Where are the two parts of the retina (nasal and temporal)?
Nasal: medial / towards the nose
Temporal: lateral / away from the nose
What part of the retina is the maximum point of visual acuity (sharpness)?
The fovea
Where does the blind spot emerge from?
The optic disc / where the optic nerve emerges from
What layer borders the posterior aspect of the retina?
The pigmented epithelium (tapetum lucidum) of the choroid
What retinal layer do bipolar cells reside in?
Inner Nuclear Layer
What retinal layer do photoreceptor cells (rods & cones) reside in?
Outer Nuclear Layer
are modified bipolar neurons
What retinal layer do ganglion cells reside in?
Ganglion Cell Layer
What part of the photoreceptor releases glutamate when it synapses with bipolar cells, which transfers info to ganglion cells (for the pathway of vision)?
Synaptic Body
What opsins are present in rods vs. cones? Functions?
Cones: cone opsin
Rods: rhodopsins
Opsin = photosensitive transmembrane proteins that bind to photons and are a part of the photopigment complex => => vision, phototaxis, circadian rhythm, etc.
What are the two parts of the photopigment complex? How do they interact with one another?
- Retinal (formed from VitA)
- Opsin (G protein-coupled receptors) -> rhodopsin in rods (purple), 3 in cones (red, green, blue)
Opsin = transmembrane protein with retinal tucked into it
Differences b/w Rods and Cones (5)
Rods: most sensitive to light, night vision, low acuity, achromatic, peripheral vision (located throughout the retina and near the fovea)
Cones: less sensitive to light, day vision, high acuity, color vision, central vision (only near the fovea)
Describe the steps of transduction in the optic pathway
Opsin absorbs photon -> conformation change in retinal part of photopigment complex in photoreceptor -> associated G-protein activated -> Na+ channel closed -> hyperpolarization of cell -> NT released! @ synaptic body (UNSTIMULATED CELL!)
General flow of CONSCIOUS perception of vision pathway (retino-geniculo-striate system)
Photoreceptor -> bipolar cells -> ganglion cells -> thalamus -> primary visual cortex -> CONSCIOUS perception of vision
Where in the thalamus does synapse occur? Where do these neurons project to?
Synapse occurs in the LATERAL GENICULATE NUCLEUS
Project to the PRIMARY VISUAL CORTEX (“optic radiations”) in the OCCIPITAL REGION OF CEREBRUM
Which side of the retina crosses midline at the optic chiasm into the optic tract? How does visual field project?
The NASAL side of the retina (of the optic nerve) -> RIGHT visual field projects in LEFT primary visual cortex (and vice versa)
Where do photosensitive ganglion cells of the retino-tectal tract project to for REFLEXIVE vision (PLR, Dazzle)
To the MIDBRAIN:
- rostral colliculus (head & eye orientation to visual stimuli)
- pretectal nucleus in the midbrain (PLR & Dazzle)
What are the 3 innervations of the eye for REFLEXIVE vision?
- Somatic afferent = trigeminal (V) [sensation to medial canthus, cornea]
- Visceral efferent = parasympathetic = oculomotor (III) [motor to pupillary constriction, lens accommodation]
- Visceral efferent = sympathetic = cervical spinal nn.
Recall:
- SOMATIC NN. = Sense the external environment and respond by shaping bodily motions
- VISCERAL NN. = Sense the interior environment and respond by regulating vital functions
Describe Pupillary Light Reflex pathway
PLR:
Light -> retina -> CN II -> optic chiasm (nasal parts cross) -> optic tract -> pretectal nucleus -> pretectal neurons project to parasymp. nucleus of CN III -> pre-gang. neurons project to parasymp. gang. (ciliary gang.) -> post-gang. neurons project to pupillary constrictor muscle –> BILATERAL MIOSIS!
What is the Dazzle Reflex? What nucleus do pretectal neurons project to?
involuntary blinking in response to light; pretectal (midbrain) -> parasymp. nucleus CN 3 (midbrain) -> parasymp. nucleus CN 7 (medulla) -> orbicularis oculi m.
Describe Menace Response pathway
Rapid gesture toward face -> info transmitted to visual cortex via retino-geniculate-striate pathway -> interneurons connect sensory & primary motor cortices -> corticobulbar pathway to facial nucleus -> BILATERAL EYE CLOSURE/BLINKING
In the vestibulo-ocular reflex, what neurons project to the extra-ocular muscles, and what results?
Neurons of the vestibular nuclei -> extra-ocular mm. constriction and movement of eyes in OPPOSITE direction of head movement)?
Predatory vs prey animals’ eye position
PREDATORY: eyes @ front of head, move together, enhanced depth perception, decreased field of view
PREY: eyes @ sides of head, move independently, decreased depth perception, increased field of view
How do predatory and prey optic chiasm pathways differ?
Predators: only projections from the NASAL visual field of the retina CROSS @ optic chiasm
Prey: ALL projections from retina CROSS @ optic chiasm
A lesion in the optic nerve results in loss of vision in the ___ eye.
IPSILATERAL eye (b/c optic nerve is rostral to optic chiasm)
A lesion in the optic tract, optic radiation or visual cortex results in loss of vision in the ___ visual field.
CONTRALATERAL (b/c all are caudal to optic chiasm)
What occurs if you transect the optic chiasm in predators v. prey?
Predators: loss of peripheral vision
Prey: Blindness
