Visual system physiology

Question 1

What is cones and rod mediated vision and what happen if you lose them

Answer 1

Rod mediated vision is called scotopic vision
-lose you have night blindness

cone mediated vision is photopic vision
-lose you are blind

Question 2

What is mesopic vision

Answer 2

Vision that occurs when both rods and cones are activated by the light levels of the environment

Question 3

convergence of cells for rods

Answer 3

Rods need one photon and multiple rods converge onto a single bipolar cell which contact a single macrine cell

-allows for the highest levels of sensitivity but lower resolution

Question 4

Convergence of cells for cones

Answer 4

Need 100 photons to respond

One cone directly contacts one bipolar cell

this allows for best resolution but low sensitivity

Question 5

Dark Current

Answer 5

Gutamate release is highest when it is dark which leads to depolarization

this is because for rods, photons act as a hyperpolarizor of the cell

Question 6

What types of potentials do Neuronal cells use

Answer 6

Graded potentials rather than Action potentials

therefore the varying streams of glutamate lead to various degrees of neurotransmitter release

not binary

Question 7

ON-center bipolar cells

Answer 7

Activation of a photoreceptor in the center of this bipolar cells receptive field causes depolarization of this bipolar cell

contains a glutamate receptor called mGluR6 which is a Gi GPCR receptor

glutamate binds to the mGluR6 receptor that decreases cation influx by closing cGMP-gated Na+ channels

high levels of glutmate closes the channel and the ON-center bipolar cell remains inactive

Low levels of glutamate allows the channel to be open nd the ON-center bipolar cell will depolarize

works with light

Question 8

OFF center bipolar cells

Answer 8

Activation of a photoreceptor in the center of this bipolars cell receptive field causes hyperpolarization of this bipolar cell

express ionotropic receptors for glutamate (non-NMDA) AMPA that when glutamate is present it binds the receptor and the ion channel opens and the cell will depolarize

works at night

Question 9

Ganglion cell

Answer 9

If the associated bipolar cell is depolarized it releases glutmate on to the ganglion cell to depolarize it
-contain NMDA or Non-NMDA receptors

Ganglion cells use Action potentials rather than graded potentials

become the optic nerve and release glutmate at the cortex

Question 10

Amacrine cells

Answer 10

inhibitory and release GABA or glycine

suppresses nearby activity

important in allowing to see in low light conditions to enhance edges, shadows, and contrasting areas of luminance

Question 11

Lateral Genticulate body

Answer 11

Direct target of the retina

Control the motions of the eye to converge on a point of interest

control focus of the eyes based on distance

Determine relative position of objects to map them in space

Detect movement relative to an object

Question 12

Suprior Colliculus

Answer 12

Creates a mp of visual space to activte appropriate motor responses required to move the eyes into their intended position within the orbits

coordinates head and eye movement to visual targets

Question 13

Pretectum

Answer 13

Reflex control of pupil and lens, sends projections to Edinger-Westphal then on to ciliary ganglion

Question 14

Hypothlamus

Answer 14

Small number of fibers branch off the optic tract, forming the retinohypothalamic trct and terminate in the supraoptic, suprachiasmatic and paraventricular nuclei of the hypothalamus

visual input to the hypothalamus drives the light-dark entrainment of neuroendocrine function and other circadian rhythms

Question 15

Medial Temporal area

Answer 15

Contains neurons that responds selectively to the direction of a moving edge

tracks the motion across a scene in terms of directionality and background/foreground context

ignores color

also called V5

Question 16

Accessory optic system

Answer 16

Consists of several small nuclei

advanced visual processing

important role in eye movements of compensation and pursuit, particularly in alternation with saccadic-type eye movements responding to prolonged watching of large field motion

Question 17

Primary Visual Cortex

Answer 17

V1 (striate cortex)

Constructs local image features including size, shape, orientation local direction of movement, and binocular disparity

Mostly excitaatory and has some GABAnergic interneurons

Identify the edges and contours of Objects

Question 18

Visual association cortex V2

Answer 18

V2 (extrastriate)

Depth perception occurs by analyzing the disparities between the two eyes

Question 19

Visual association cortex V3a

Answer 19

Identification that motion is occuring

Question 20

Visual association cortex V4

Answer 20

Complete processing of color inputs

Question 21

Visual association cortex V5

Answer 21

Medial Temporal Area

identifies the direction of a moving edge in terms of context with background and foreground

Question 22

Ocular dominance columns

Answer 22

Found in the primary visual cortex

A slab of cells that preferentially respond to input from one eye or the other

are found in stripes

Question 23

Orientation columns

Answer 23

Found in primary visual cortex

organized region of neurons that are excited by visual line stimuli of varying angles

Orientated perpendicular to the cortical surface

mapped in swirls

Question 24

Blobs

Answer 24

Found in the primary visual cortex

Organized region of neurons that are sensitive to color that assemble into cylindrcal shapes

All 3 color coding cones are required for accurate color detection

Question 25

Achromatopsia

Answer 25

Three types of cones in the retina function normally

but damage to specific extrastriate cortical areas that render patients unable to see information supplied by the retina

Question 26

Color blinding

Answer 26

Improper function at the level of the cones

Question 27

Melanopsin ganglion (MG)

Answer 27

Photosensitive ganglion that project directly to the suprachiasmatic nucleus of the hypothalamus, the light sensitive nucleus of the pretectum and the limbic system

does not project to the visual cortex so it is called the non image light responsive system

play a role in regulation of circadian rhythms, sleep, and mood

Question 28

Ventral pathway

Answer 28

V1 to V2 to V4 and then to the Temporal lobe (what pathway)

involved in interpreting images (reckognizing or copying shapes, forms, faces, and complex patterns)

selectively activated by shape color, texture, and object recognition

face recognition is specialized area

Question 29

Dorsal Pathway

Answer 29

V1 to V2, V3 to MT/V5 and then to Parietal lobe (where pathway)

Primary pathway with associating vision with movement

also complete motor actions based on visual input through this pathway

selectivity activated by directionality and speed of movement

Question 30

Agnosia

Answer 30

see an object but is either unable to copy or identify what it is. Cant see parts of an object contributing to a whole or cannot interupt, understand, or assign meaning to the object

inabillity to construct or draw visual stimuli or they cannot recognize a picture of an object

damage to the temporal lobe and interruption of the ventral pathway

Question 31

Prosopagnosia

Answer 31

A type of agnosia that results in the abillity to identify a face as a face, recognize its parts, and detect facial expressions indictative of emotion but cannot recognize a particular face as belonging to a specific person

damage to the temporal lobe and interruption of the ventral stream