Eyes Flashcards
CNS:
Brain & Spinal Cord
Contains what
Contains Integration Centers that organize and prioritize sensory input that enters from the periphery
PNS:
Cranial & Spinal Nerves
Brings sensory in to the CNS, and carries motor/effector messages out.
Cranial nerves =
sensory, motor, or both
Spinal nerves =
“mixed”– both sensory and motor
Sensation:
the triggering of a sensory receptor to fire, and that firing being communicated to neurons within the central nervous system.
Perception:
How the brain interprets sensory inputs that it receives.
In this way, “Sensation” is processed to create “_________”– not always the same thing.
Perception
Sensory receptors are ….
cells that generate graded potentials called RECEPTOR POTENTIALS in response to a stimulus.
Receptors typically have a _______ _______ range that they respond to.
specific stimulus
There are five major types of sensory receptors based on the type of stimuli that they respond to:
- Mechanoreceptors
- Thermoreceptors
- Photoreceptors
- Chemoreceptors
- Nociceptors- pain
Bipolar Cell:
1 cell to 1 interneuron
Coding
the conversion of a stimulus into an signal that is conveyed to the central nervous system, where it is perceived.
In sensory coding, Information is conveyed by both the ________ and _________ of the resulting signals.
frequency and amplitude
A stimulus that persists will cause ……
repeated action potentials, which happen as frequently as the nerve can repolarize.
A more intense stimulus causes…..
slide 17
more frequent neuronal firing.
More intense stimuli =
more frequent action potentials.
More intense stimuli usually =
a larger affected area, which causes action potentials in more afferent neurons (recruitment).
Increasing the surface area that’s stimulated causes firing of more action potentials. Your brain perceives this as a ______ _______ ________.
more intense stumulus.
slide 21
Lateral inhibition enhances the ________ between the center and periphery of a stimulated region, thereby increasing the brain’s ability to localize a sensory input.
Lateral inhibition enhances the contrast between the center and periphery of a stimulated region, thereby increasing the brain’s ability to localize a sensory input.
in lateral inhibition, Exact localization is possible because
lateral inhibition removes the information from the peripheral regions.
The afferent sensory neuron is the beginning of a chain of neurons that form an _______ _______ to the CNS.
*ascending pathway
Processing of afferent information does not end in the primary receiving areas of the cerebral cortex; it continues from these areas to ______ ________ in the cerebral cortex where complex integration occurs.
*association areas
Central control of sensory information (e.g., inhibition of pain messages) occurs via _______ _______, from the CNS to the sensory (afferent) neuron.
descending pathways
Those descending pathways carry an inhibitory message from the brain to pain fibers in the skin.
Ascending pathways involve three or more ______, and always involve at least one __________ (remember, interneurons are the most numerous of neurons).
neurons, interneuron
Most pathways are ________– carrying only one type of message. These travel to the thalamus and brainstem (except for smell!)
specific
Smell is specific, but it sends messages to two places:
to the limbic system (“the emotional brain”) and straight to the olfactory cortex.
This is partly why smells can evoke such strong memories and feelings.
Some afferent messages also join with other afferent messages to activate _______ pathways.
nonspecific
Their purpose: control alertness or awareness–
The _______ _______ _______ relies upon various association areas of the cortex to properly process sensory information.
primary somatosensory cortex
Association areas close to the somatosensory cortex do …..
broad, basic message processing.
Association areas further away process in a …..
complex, “fine tuning” way.
slide 33
Complex perceptual processing involves ….
arousal, attention, learning, memory, language, and emotions… but also comparison of the information presented via one type of sensation with that presented through another.
Factors that Affect Perception
Receptor adaptation and afferent processing
Emotions and experiences
Not all stimuli give rise to a conscious sensation
For example: stretch receptors monitor blood pressure in several large arteries
Lack of receptors for certain stimuli
For example: radio waves
Damaged neural pathways
Drugs
The eyes are composed of:
An optical component,
which focuses the visual image on the receptor cells
The eyes are composed of:A neural component,
which transforms the visual image into a pattern of action potentials
Wavelength =
how long one complete wave is.
Frequency =
how many waves travel by a point in one second.
Longer wavelength =
Lower frequency
Shorter wavelength =
higher frequency
Fovea is the most central spot in the visual field, with
highest cone density.
Optic Disc is where optic _____ and _______ come through.
nerve and vessels
Your iris actually is made of two separate sets of fibers;
radial and circular.
When your circular muscles contract, ……
the pupil gets smaller.
When your circular muscles relax,…..
the pupil gets bigger.
Parasympathetic =
constriction
Constriction is caused by…
bright light, PNS stimulation, opioids
Sympathetic=
dilate
dilation is caused by….
low light, ins stimulation, nervous system injury, oxytocin, drugs
Stimulus=
light into eye
Afferent =
optic nerve (CNII)
Interneurons =
midbrain
- Carry light information to the pretectal nucleus
- from there to the Edinger-Westphal nucleus;
- from there to parasympathetic centers;
- and from there to the oculomotor nucleus.
Efferent=
oculomotor nerve (CNIII)
Response=
irises constricts and less light comes in
how does the image appear in the visual cortex?
flipped
what focuses the eye?
cornea and lens
what does lassie surgery do?
permanently changes the shape of your cornea
what does the Cornes do?
refracting (more than lens)
What does the lens do?
fine tuning of refraction. its the part of refraction that can be controlled
what controls accommodation for distance?
lens
what controls the lens?
ciliary muscles (circular muscles)
what happens when ciliary muscles contract?
they narrow the “circle” around the lens, thus loosening tension on the lens—cause it to become more spherical. Now it will focus on things that are near.
what happens when ciliary muscles relax?
they enlarge the “circle” around the lens, pulling it outward and making it flatter- improving focus on things that are farther away.
Myopic=
Nearsighted: can only see NEAR.
Eyeball is too wide (shaped like a near-seeing lens)
To correct: wear glass that are the opposite—narrower in the middle area.
Hyperopic =
Farsighted: can only see FAR.
Eyeball is too narrow (shaped like a far-seeing lens)
To correct: wear glass that are the opposite—fatter in the middle area.
To see things up close:
contract ciliary muscles and make lens rounder
To see things far away:
relax ciliary muscles and make lens flatter.
F= Flat= Far away
Rods and Cones– differ in what way?
light sensitivity
Cones =
color perception
Rods =
low-light vision
Choroid and pigment epithelium:
work like a sponge to “soak up” any light not directed at rods and cones, so there won’t be a lot of reflected light confusing the picture.
Rods use _______
Rhodopsin (rod-opsin) only.
Cones = 3 types, and which tones do they see
which specialize in detecting 3 different sets of wavelengths:
“S” = SHORT (blue tones)
“M”= MEDIUM (green tones)
“L” = LONG (red tones)
Our ability to discriminate color depends on the ________ __ _______ striking the retina. In brightly lit conditions, the differential response of the cones allows for good color vision.
intensity of light
In dim light, only the _____ are able to respond, and they have no mechanism for distinguishing between frequencies. Thus, objects that appear vividly colored in bright daylight are perceived in shades of gray at night.
rods
In their resting state (in the dark), rods and cones are depolarized and they’re sending _________ to the next cell in line (bipolar cells).
glutamate
When stimulated by light, the rods and cones quickly ___________. This causes less glutamate release.
hyperpolarize
Glutamate is
an inhibitor for bipolar cells. With less glutamate, they release more neurotransmitter to the ganglion cells you see in the picture, which become the optic nerve.
Photoreceptors release _________
glutamate
The optic nerves come together, and partially cross, at the _____ ______
optic chiasm.
Depth perception occurs in the area of your field of vision that …..
is able to stimulate receptors on both eyes.
the two messages from the area of vision that is stimulated by both eyes is processed in the….
occipital lobe, converted to information about three dimensional position in space.
Some neurons of the visual pathway skip the visual cortex, going to …
other regions of the brain instead.
melanopsin
carry visual information to the suprachiasmatic nucleus– just above the optic chiasm. It functions as part of the “biological clock.”
It appears that information from these cells is used to entrain your neuronal clock to a 24-hour day – the circadian rhythm.
macula lutea
region of the retina is specialized to provide the highest visual acuity.
macular degeneration
Macula lute becomes impaired producing a defect characterized by loss of vision in the center of the visual field.
AMD- most common, 1/3 people over 75
Six skeletal muscles attach to the outside of each eyeball
-Superior rectus Lateral rectus inferior oblique inferior rectus medial rectus superior oblique
eye muscle mission
keep the most important point on the fovea centralis (the center of the macula lutea).
The fast movements, (saccades)
are small, jerking movements that rapidly bring the eye from one fixation point to another to allow a search of the visual field.
Saccades also occur during certain periods of sleep when dreaming occurs.
Slow eye movements
involved both in tracking visual objects as they move through the visual field and during compensation for movements of the head.
The control centers for these compensating movements get their information about head movement from the vestibular system (inner ear).
