Physiology-Visual Pathways Flashcards
Areas of the visual field
Central binocular zone + lateral monocular crescents (only seen by the ipsilateral side)
What does the lens do to the image as it projects it onto the retina?
Inverts and reverses it.
Areas of the retina
*
What axons are contained in the optic tract posterior to the optic chiasm?
Ipsilateral temporal retinal ganglion cell axons and contralateral nasal retinal ganglion cell axons. Both of these axons convey information from the contralateral hemifield to the lateral geniculate body.
How does the structure indicated below coordinate with the optic tract to give us a sense of a 3-D image?
There are 6 different layers of the LGB that correspond to different locations in the visual field. Synapses on these layers gives us an idea about spatial relationships of objects we see.
What pathway is involved in the pupil constriction reflex in response to light?
Retinal ganglion axons project through the optic tract to the pre-tectal area where they turn and synapse on the occulomotor complex’s presynaptic parasympathetic fibers that go on to cause pupillary constriction.
What visual pathway is involved in reflex changes in response to visual stimulus?
Optic tract -> superior colliculus -> Pulvinar
What visual pathway is involved in setting our circadian rhythm?
Optic tract -> Suprachiasmatic nucleus
How are the eye inputs segregated as signals are transferred to the lateral geniculate body?
The temporal axons go to layers 2, 3 & 5. The Nasal axons go to layers 1, 4 & 6.
What type of retinal ganglion cells are more sensitive to movement, exist in the periphery of the retina and are largely composed of rods? What type of cells are more sensitive to color, resolution and are centrally located in the retina? Where do they all land in the lateral geniculate body?
Changes in motion = magnocellular layer (m-cells). Changes in resolution = parvocellular layer (p-cells)
The lateral geniculate body receives information from the contralateral visual field. Where does the information from the superior and inferior portions travel to after leaving the lateral geniculate body?
Inferior visual field -> internal capsule -> superior bank of cuneus. Superior visual field -> Meyer’s loop -> inferior bank of lingual gyrus
What would the clinical symptoms be in each lesion seen below?
A) Lesion of the right optic nerve results in complete blindness of the right eye. B) Lesion of the optic chiasm affects axons that cross (nasal hemiretinal axons) and causes bitemporal heteronymous hemianopsia C) Lesion of the right optic tract causes loss of information from the contralateral hemifield D) Lesion of the arching axons causes loss of the superior part of the contralateral hemifield (pie in the sky). E) Lesion of the left optic tract causes right homonymous hemianopsia.
In what layer of the primary visual cortex do the axons of the lateral geniculate body terminate?
The thick myelin layer 4 (striate cortex) of the calcarine sulcus.
What optic pathways converge at the calcarine sulcus? What ones don’t?
Lateral geniculate body axons converge, but the M & P pathways and information from the left and right eye remain segregated
What cortical regions end up receiving signals from the M-pathway? The P-pathway?
M = LGB -> layer IV of V1 (primary visual cortex) -> dorsal pathway -> superior parietal cortex. P = LGB -> layer IV of V1 -> ventral pathway -> inferior temporal cortex.
A patient presents to the clinic after having a stroke. He is unable to recognize and identify objects or people, but has perfectly fine vision. What arteries may have been affected in this patient?
PCA or MCA. Either of these can affect the inferior ventral cortex or superior parietal cortex.
A patient presents who is unable to perceive more than one object at the same time. What is causing this?
He has simultanagnosia. This is an inability to perceive more than one object at the same time due to lesion in the M pathway (superior parietal cortex)
A patient presents who feels like she is looking through the world in a strobe light. What is causing this?
She has akinetopsia. This is due to an inability to perceive motion due to lesion of the dorsal M pathway in the superior parietal cortex.
A patient presents with an inability to identify people’s faces. What is causing this?
She has prosopagnosia. This is due an inability to integrate the facial features they are seeing. This is caused by lesions in the ventral P pathway in the inferior temporal cortex.
A patient presents with perfectly fine cones, but can no longer see color after his stroke. What is causing these symptoms?
This patient has cortical color blindness (achromatopsia). This is caused by a lesion in the P pathway in inferior temporal cortex.
