Chapter 51

Question 1

Outline the neural pathway for vision form the stimulus to the cortex

Answer 1

visual stimulus –> CN II –> optic chiasm –> optic tract –> dorsal LGB –> optic radiations –> primary visual cortex (V1)

Question 2

What are the 2 main fxns of the LGB?

Answer 2

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

Question 3

Where are the 2 inibitory signals to the LGB to turn off transmission through selected portions?

Answer 3

Corticofugal fibers (from V1) and raticular areas of the mesencephalon

Question 4

Where is V1 and secondary visual areas of the occipital lobe?

Answer 4

medial aspect along the calacrine sulcus

Question 5

What field of vision is represented in the lingual portion of the occipital lobe?

Answer 5

upper visiual field

Question 6

What field of vision is represented in the cuneus portion of the occipital lobe?

Answer 6

Lower visual field

Question 7

What is the fxn of the secondary visual Cx?

Answer 7

Analysis of visual meaning

Question 8

Geniculocalcarine fibers (optic radiation fibers) terminate mainly in which layer of V1?

Answer 8

IV

Question 9

What are “Y” ganglion cells?

Answer 9

Magnocellular
Fast, Black and white
Analyzes the 3-D position of the object and its general physical form and motion

Question 10

What are “X” ganglion cells?

Answer 10

parvocellular
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.

Question 11

What is stereopsis?

Answer 11

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/

Question 12

How does V1 process contrast?

Answer 12

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

Question 13

What is the role of simple cells to show the orientation of lines and borders?

Answer 13

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

Question 14

How does V1 process displacement?

Answer 14

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.

Question 15

What can cause Monocular scotoma?

Answer 15

Damage to the optic nerve or lens causes one sided blindness to the affected eye

Question 16

What can cause bitemporal hemianopsia in both eyes?

Answer 16

Damage to the optic chiasm

Question 17

What can cause Homoymous hemianopsia?

Answer 17

Damage to optic tract

Question 18

What can cause Contralateral inferior/superior quadrantanopia?

Answer 18

Damage to optic radiation

Question 19

What can blindness in the Contralateral quadrant?

Answer 19

Damage to visual cortex

Question 20

What is macular sparing/Contralateral homonymous hemianopia?

Answer 20

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.

Question 21

Go over the movements of the MR, LR, SR, IR, SO, and IO muscles

Answer 21

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

Question 22

What muscles are innervated by CN III?

Answer 22

Superior rectus, inferior rectus, medial rectus, inferior oblique

Question 23

What muscles are innervated by CN IV?

Answer 23

SO

Question 24

What muscles are innervated by CN VI?

Answer 24

IR

Question 25

Where are all the eye CN’s connected together?

Answer 25

medial longitudinal fasciculis

Question 26

What is voluntary fixation?

Answer 26

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)

Question 27

What is involuntary fixation?

Answer 27

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)

Question 28

What are saccadic movements?

Answer 28

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)

Question 29

What are pursuit movements?

Answer 29

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

Question 30

What is the role of the superior colliculis?

Answer 30

superior colliculi play a role in orienting eyes, head and body with respect to external disturbances whether they are visual, auditory or somatic.

Question 31

What is the “fusion” of visual image?

Answer 31

Visual images from each eyes fuse with each other at a corresponding point of the two retinas to make the complete picture

Question 32

What is the mechanism for fusion of visual images?

Answer 32

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

Question 33

What is strabismus?

Answer 33

: 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)

Question 34

Is stabismus permanent after childhood?

Answer 34

Yesh

Question 35

What is the mechanism for accomodation?

Answer 35

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

Question 36

What is the mechanism for pupillary light reflex?

Answer 36

First, the retina picks up the light, which sends signals to the pretectal nuclei, which then synapse and then go to the Edinger Westphal nucleus, which then go to the ciliary body and constrict the pupil so that less light comes in. This process is inhibited in darkness. In by Pretectal nucleus, out by Edinger Westphal nucleus. This can reduce the amount of light by almost 30 times.