Flashcards in Chapter 51 Deck (36):
Outline the neural pathway for vision form the stimulus to the cortex
visual stimulus --> CN II --> optic chiasm --> optic tract --> dorsal LGB --> optic radiations --> primary visual cortex (V1)
What are the 2 main fxns of the LGB?
1. relays visual info from the optic tract to V1
2. it controlls how much of the signal is allowed to pass through to V1
Where are the 2 inibitory signals to the LGB to turn off transmission through selected portions?
Corticofugal fibers (from V1) and raticular areas of the mesencephalon
Where is V1 and secondary visual areas of the occipital lobe?
medial aspect along the calacrine sulcus
What field of vision is represented in the lingual portion of the occipital lobe?
upper visiual field
What field of vision is represented in the cuneus portion of the occipital lobe?
Lower visual field
What is the fxn of the secondary visual Cx?
Analysis of visual meaning
Geniculocalcarine fibers (optic radiation fibers) terminate mainly in which layer of V1?
What are "Y" ganglion cells?
Fast, Black and white
Analyzes the 3-D position of the object and its general physical form and motion
What are "X" ganglion cells?
Medium sized optic never fibers, very accurate and color. Recognizing letters, reading, determining the texture of surfaces, determining detailed colors of object and interpreting from all this information what the object is and what it means.
What is stereopsis?
Since we have binocular vision,t he left and right eyes are not in the same location in our head. This difference in our vision makes up the depth percetpion/ distance of an object/
How does V1 process contrast?
Area of maximum excitation occur along the sharp borders of the visual pattern. Visual signal in the primary visual cortex is concerned mainly with contrasts in the visual scene
What is the role of simple cells to show the orientation of lines and borders?
found mainly in layer IV of the primary visual cortex. Simple cells have excitatory or inhibitory zone which have mutual antagonistic function. So when there is a contrast edge, inhibition occurs all along that edge. A line orientated in different direction excites different sets of cells
How does V1 process displacement?
Some neurons respond to lines that are oriented in the same direction but are not position specific. So if a line is displaced moderate distances laterally or vertically in the field, the same neurons will still be stimulated if the line has the same direction. This is called complex cells.
What can cause Monocular scotoma?
Damage to the optic nerve or lens causes one sided blindness to the affected eye
What can cause bitemporal hemianopsia in both eyes?
Damage to the optic chiasm
What can cause Homoymous hemianopsia?
Damage to optic tract
What can cause Contralateral inferior/superior quadrantanopia?
Damage to optic radiation
What can blindness in the Contralateral quadrant?
Damage to visual cortex
What is macular sparing/Contralateral homonymous hemianopia?
Usually by vascular occlusion, blood supply to fovea is blocked. Fovea is supplied by both Posterior cerebral artery & Middle cerebral artery. For macular sparing PCA is blocked but MCA is spared.
Go over the movements of the MR, LR, SR, IR, SO, and IO muscles
Medial and lateral recti: moves eyes side to side
Superior and inferior recti: moves eyes up or down
Superior and inferior obliques: rotates the eyeball
What muscles are innervated by CN III?
Superior rectus, inferior rectus, medial rectus, inferior oblique
What muscles are innervated by CN IV?
What muscles are innervated by CN VI?
Where are all the eye CN's connected together?
medial longitudinal fasciculis
What is voluntary fixation?
This mechanism is controlled by our cortex that is located bilaterally in the premotor cortical region of the frontal cortext. If there is damage to this area bilaterally, a person will not be able to “unlock” their gaze from one point of fixation to another move. One will have to either blink or put a hand over the eyes for a short time for them to move from one object to another. (staring problem fo sho) (AKA I wil VOLUNTARILY stare at boobies for a long time)
What is involuntary fixation?
controlled by secondary visual area in the occipital cortex. (Anterior to the primary visual area). When this area is damaged bilaterally, one will have problem staring at a fixed point. (ADD fo sho) (AKA I will INVOLUNTARILY move my eyes around like I'm drunk)
What are saccadic movements?
When something is moving continually before the eyes. Ex: person riding in a car, causing the visual field to jump from one to another at 2-3jumps per second. The jumps are called saccades and the movements are called opticokinetic movements. (so fast u dont even notice it)
What are pursuit movements?
fixation on a moving object. Our brain automatically detects the course of the movement of an object then rapidly develops a similar course of movement for the eyes
What is the role of the superior colliculis?
superior colliculi play a role in orienting eyes, head and body with respect to external disturbances whether they are visual, auditory or somatic.
What is the "fusion" of visual image?
Visual images from each eyes fuse with each other at a corresponding point of the two retinas to make the complete picture
What is the mechanism for fusion of visual images?
Visual cortex plays an important role in this fusion. Correspond point of the two retinas transmit visual signals to different neuronal layers of the lateral geniculate body and these signals go to the neurons in the visual cortex
What is strabismus?
: Strabismus is squint or cross eyed due to lack of fusion of the eyes in one or more of the visual coordinates: horizontal, vertical or rotational. (derp)
Is stabismus permanent after childhood?
What is the mechanism for accomodation?
Contraction of the ciliary muscle causes the lens to get fatter, increasing refractive power, and allowing focus on a close object, whereas relaxation allows the lens to return to its original shape, so you can look at a faraway building