Chapter 7 (part 2) Sensory Physiology Flashcards
The eyes are composed of:
An optical component, which focuses the visual image on the receptor cells.
A neural component, which transforms the visual image into a pattern of graded and action potentials.
The Optics of Vision: Refraction
Relaxed ciliary muscles, tension on zonular fibers, flattened lens.
Light rays from distant objects are nearly parallel.
In focus
The Optics of Vision: Refraction
Relaxed ciliary muscles.
Light rays from near objects diverge.
Out of focus:
The Optics of Vision: Refraction
Near object with accommodation
Firing of parasympathetic nerves, contracted ciliary muscles, slackened zonular fibers, rounded lens.
In focus
eyeball too long
nearsighted
eyeball too short
farsighted
nearsighted glasses
concave
farsighted glasses
convex
Neural Pathways of Vision
Light signals are converted into action potentials by the interaction of _________, ______, and ____________
photoreceptors, bipolar cells and ganglion cells.
Neural Pathways of Vision
Photoreceptor and bipolar cells only undergo graded responses due to lack of
voltage-gated channels.
Neural Pathways of Vision
________ are the first cells in the pathway where action potentials can be initiated.
Ganglion cells
Photoreceptors interact with bipolar and ganglion cells in two distinct ways
“ON-pathways” and “OFF-pathways”
Light striking the photoreceptors of either pathway _________ the photoreceptors, resulting in a __________ in glutamate release onto bipolar cells.
hyperpolarizes, decrease
in both “ON-pathways” and “OFF-pathways”, photoreceptors are depolarized in the ___________of light, causing the neurotransmitter __________ to be released onto bipolar cells
absence, glutamate
which neural pathway is this
Bipolar cells spontaneously depolarize in the absence of input,
(ON-pathway)
which neural pathway is this
bipolar cells hyperpolarize in the absence of input
(OFF-pathway)
which neural pathway is this
Glutamate receptors bipolar cells are inhibitory
(ON-pathway)
which neural pathway is this
glutamate receptors bipolar cells are excitatory.
(OFF-pathway)
ON-pathway steps
Photoreceptor is depolarized in the absence of light rays
LIGHT RAYS ⇄
Light hyperpolarizes photoreceptor cell
Decreased glutamate release onto bipolar cell
Bipolar cell depolarizes and releases more excitatory neurotransmitter
Ganglion cell depolarizes and generates more action potentials
OFF-pathway steps
Photoreceptor is depolarized in the absence of light rays
LIGHT RAYS ⇄
Light hyperpolarizes photoreceptor cell
Decreased glutamate release onto bipolar cell
Bipolar cell hyperpolarizes and releases less excitatory neurotransmitter
Ganglion cell hyperpolarizes and generates fewer action potentials
Co-existence of ON and OFF pathways in the retina greatly improves image resolution by
increasing the brain’s ability to perceive contrast.
related to the wavelengths of light that the pigments in the objects of our visual world reflect, absorb, or transmit.
Color Vision
an object appears red because it absorbs ___________, while it reflects the __________
shorter wavelengths
longer wavelengths
Light perceived as ___________ is a mixture of all wavelengths
white
________ is the absence of all light.
black
three kinds of cones with the wavelengths they respond to
“L” cones respond optimally at long wavelengths
“M” cones respond at medium wavelengths
“S” cones best stimulated at short wavelengths
most common form of color blindness, is present predominantly in men, affect 1 out of 12
either lack the red or the green cone pigments entirely or have them in an abnormal form
red-green color blindness
results from a recessive mutation in genes encoding the cone pigments
Color Blindness
macula lutea becomes impaired in __________ producing a defect characterized by loss of vision in the center of the visual field.
Macular Degeneration
- The ___________ region of the retina provide the highest visual acuity.
macula lutea
Incidence of age-related macular degeneration ______________ (approx. 30% of individuals over the age of 75)
(AMD)increases with age
- small, jerking movements that rapidly bring the eye from one fixation point to another to allow a search of the visual field
- move the visual image over the receptors, thereby preventing adaptation
- occur during certain periods of sleep when dreaming occurs, though not thought to be involved in “watching” the visual imagery of dreams
Eye Movement
Involved in tracking visual objects as they move and during compensation for movements of the head
Slow eye movements
in Slow eye movements, Control centers obtain information about head movement from the vestibular system; require
continuous feedback of visual information about the moving object
