Neuroscience Test 3 (Chapter 7)

images viewed by the eye are converted into

neural impulses that are sent to the brain

what part of the eye do images fall onto?

retina at the back of the eye

images in the eyes are

inverted and flipped around

the retina contains specialized neurons called

photoreceptor cells

photoreceptor cells include

rods & cones

the purpose of photoreceptor cells is to

convert light energy into changes in membrane potentials that lead to action potentials

where are the action potentials sent to and how is it sent there

sent to the brain and other areas via the optic nerve

why are action potentials sent to the brain

for integration & processing of visual information

how many layers does the eye have and what are those layers called

the eye had three major layers: the outer sclera, the middle choroid, and the inner retina

the pupil is the ___

opening by which light enters the eye

the iris can vary the

size of the pupil and gives the eye its color

the cornea is

the transparent external surface that is continous with the sclera

the lens helps to

focus images onto the retina

the lens is controlled by

the ciliary muscles

the conjunctiva is a

membrane that folds back from the inside of the eyelids and attaches to the sclera

the optic nerve contains

axons and blood vessels that carry visual information in the form of action potentials to the brain

the optic nerve enters the eye

medially

the fovea is located at

the back of the eye and its where you have the greatest visual acuity (sharpness)

location/ order of the cornea, pupil, iris, & lens

cornea, then pupil, iris, & lens

location/order of retina, choroid, & sclera

sclera, choroid, retina (top to bottom)

the eye is continuously ___

bathed in fluid

what muscles serve to move the eyeball

six extraocular muscles

what are the types of muscles included in the six extraocular muscles

4 rectus muscles, 2 oblique muscles

light is the

part of electromagnetic radiation that is visible to our eyes

light from a single wavelength appears as

one of the colors of the rainbow

light is described as a ___ characterized by ___

a wave characterized by wavelength, frequency, & amplitude

refraction is

the bending of light rays

light rays bend when

light rays travel from one medium into/through another medium

refraction is due to

the changes in density of the medium

the cornea and lens use ___ to focus ___

refraction to focus light rays directly onto the retina

emmetropia is

normal vision that occurs when light rays fall directly onto the back of the retina

when light rays do not fall directly on the retina, a person has

myopia or hyperopia

what is myopia

nearisightedness due to the focal point occurring before the retina

what is hyperopia

farsightedness due to the focal point occurring behinf the retina

is myopia or hyperopia more common in young people

myopia

what is accommodation

when the ciliary muscles use additional focusing power to control the shape of the lens

what happens when you correct myopia & hyperopia with corrective lens

it moves the focal point

visual processing begins in the

retina

photoreceptor cells convert

light into changes in the membrane potential

these graded potentials are relayed first to the ___ then to the ___

bipolar cell layer, ganglion cell layer

bipolar cells include

horizontal & amacrine cells

bipolar cells are involved with

modifying graded potentials as they are relayed to the ganglion cells

ganglion cells generate ___

action potentials in response to changes in membrane potentials

the rate or frequency of the action potential generated by ganglion cells is dependent upon

the magnitude of the input/stimulus

the magnitude changes between

depolarizing and hyperpolarizing currents

the magnitude controls

the rate at which ganglion cells generate actions potentials that are sent to the brain

light passes through the

• inner part of the eye through the ganglion cell layer, then bipolar cell layer, then to the rods and cones

• inner part of the eye to the outer part of the eye

nerve impulses/graded potentials move in the

• Opposite direction from that of light rays (outer part of the eye to the inner part of the eye)

• Rods and cones send graded potentials from the outer part of the eye back to the bipolar cell layer then to the ganglion cell layer

rods have a ___ but are sensitive to ___

low spatial resolution but are very sensitive to light

rods are sensitive to light because _____ and ____

• they contain more disks meaning they have more photopigment

• they amplify the response to light more than cones do

rods allow us to

see in the dark

true or false: all rods contain the same type of photopigment

true

cones have a ___ and are somewhat ____

high spatial resolution and are somewhat insensitive to light

cones allow us to

see color

how many types of cones are there and what pigment do they contain

there are three types of cones, each containing a different pigment

converting light into changes in membrane potentials involves the

G-protien transducin

the transduction of light energy into electrical signals is analogous/ the same as

the transduction of chemical energy into electrical signals during synaptic transmission

in a photoreceptor, light stimulating a photopigment activates

g-protiens

g protiens then activate

effector enzymes

what do effector enzymes do

change the cytoplasmic concentration of second messenger molecules that cause ion channels to close

photoreceptors respond to light by

releasing less neurotransmitters

the g protein transducin is inactivated ___

in the absence of light

in the dark, photoreceptors are

Continuously depolarized

in the dark, cGMP has a

a high concentration in the dark

In the light, cells become

hyperpolarized

light causes a conformational change in

rhodopsin receptor protien

the conformational change in rhodopsin causes

the activation of the g-protien/ transducin

transducin (the activated g-protein) activates

cGMP-phosphodiesterase (effector enzyme)

the activated cGMP-phosphodiesterase ___

breaks down cGMP (2nd messenger) and reduces its concentration

the breakdown/ decreased concentration of cGMP causes

the sodium channel to close & hyperpolarize the cell

when the cell is hyperpolarized _

less neurotransmitters are released causing less action potentials to be sent to the brain

what type of enzyme is cGMP phosphodiesterase

an effector enzyme

cGMP is a

second messenger

all photopigments contain

opsin & retinal

opsin is a

glycoprotien

retinal is a

derivative of vitamin A

in the dark, retinol is in the

cis-configuration (it’s bent)

when cis-retinal absorbs light

it changes to the trans-configuration (it’s straight)

what happens during the bleaching of a photopigment

retinal is converted from the cisconfiguration to the transconfiguration

the enzyme retinal isomerase converts

trans-retinal back to cis-retinal

what happens during regeneration

cis-retinal binds to opsin, reforming the functional photpigment

opsin is

colorless

when you go from dark to light, light adaptation occurs within

seconds to the brighter environment

while light is bleaching some photopigment molecules others are

being regenerated

in daylight, regeneration of rhodopsin cant

keep up with the bleaching process so rods contribute little to daylight vision

photopigments found in cones regenerate

rapidly so some of the cis form is always present

under condition of light adaptation, sensitivity depends on

cones

when you go from light to dark, dark adaptation occurs over

several minutes as sensitivity slowly increases

if the level of light decreases quickly, sensitivity

increases rapidly at first and then more slowly

what happens in complete darkness

full regeneration of cone pigments occur during the first 8 minutes of adaptation

under conditions of dark adaptation, sensitivity to light depends on

rods

true or false: rods adapt more slowly than cones

true

calcium ions act in a

negative feedback manner to prevent runaway increase in cGMP during visual transduction

in the dark, calcium enters

through the nonselective channel to inhibit guanylyl cyclase and stimulate phosphodiesterase (PDE)

guanylyl cyclase is the enzyme that generates

cGMP

in the dark, Ca 2+

decreases, and the decrease in calcium stops inhibiting of guanylyl cyclase, inhibits PDE, and increase cGMP

the increase in cGMP causes

the channel to reopen

photoreceptors continually release

neurotransmitters onto bipolar cells in the dark

in th dark, bipolar cells are

continuously depolarized by the influx of Na+ ions

the sodium channel is kept open due to

cGMP binding to the channel