Ex 4 SG Flashcards
1
Q
Learning Outcome: Explain the structure and function of the parts of the eye
A
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2
Q
Learning Outcome: describe the anatomy of the retina
A
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3
Q
Learning Outcome: explain the signal transduction mechanisms of photoreceptor cells
A
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4
Q
Learning outcome: Understand the functions of bipolar and ganglion cells in signal transduction
A
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5
Q
What are the “two functions” of the eye?
A
- it’s a camera-like system to focus light on the back of the eye
- action potentials are generated by photoreceptors
6
Q
in regard to the eye’s function: How does the generation of action potentials work?
A
many photons hit photoreceptors
7
Q
In regard to the eye’s function: What is the result when photons hit photoreceptors?
A
light energy is converted to electrical or chemical energy
8
Q
Information gathered in the retina is sent to the _____ _____ _____ (3 words)
A
Primary Visual Cortex (PVC)
9
Q
Information from the retina is also used for? (4 concepts)
A
- biological rhythm
- eye movement
- pupillary light reflex
- lens shape
10
Q
What is the electromagnetic frequency of light on the electromagnetic spectrum in nanometers (nm)?
A
400-700
11
Q
Define frequency:
A
waves per second
12
Q
What is the relationship between frequency and energy?
A
Higher frequency = Higher energy
13
Q
Why are frequency and energy directly correlated?
A
When one increases, so does the other. When one decreases, so does the other.
14
Q
Define Wavelength:
A
Distance between peaks
15
Q
What does wavelength determine and what other factor is affected by it?
A
It determines frequency and thus energy
16
Q
Define Amplitude:
A
Peak minus trough (how bright light is)
17
Q
Name the 4 properties of light:
A
Reflection, Absorption, Refraction, Cornea
18
Q
Define reflection:
A
bouncing of light rays off a surface. Most of the light we see.
19
Q
Define absorption:
A
transfer of light energy; compounds absorb light of specific wavelengths and reflect others
20
Q
Define refraction:
A
bending of light rays when traveling from one transparent medium to another
21
Q
Why does refraction occur?
A
the speed of light differs in two media (air and water)
22
Q
What light property is most relevant to eye function?
A
Refraction
23
Q
Define the cornea:
A
main refractive component
24
Q
What is the structure of the cornea?
A
air in front, fluid (aqueous humor) behind
25
Why is chlorophyll green?
It absorbs blue and red light, reflects greenW
26
What are the 8 major components of the eye?
Pupil, Iris, Cornea, Sclera, Conjunctiva, Optic Nerve, Nasal Cavity and Temporal Region
27
Describe the pupil:
appears dark because of light absorbing retinal pigments
28
What is the iris?
It gives the eye it's color
29
How does the iris structurally contribute to the eye?
there are two muscles that control pupil size (one contracts and one expands)
30
Describe the sclera:
the wall of the eyeball. It's the eye's white, very tough and attached to 3 extraocular muscles
31
Describe the conjunctiva:
the mucous membrane that covers the front of the eye and attaches the eyelids to the sclera
32
What is the optic nerve:
it carries axons from retina to the brain
33
Describe the optic nerve:
It exits the back of the eye, reaching the base of the brain near the pituitary gland
34
Where does the optic nerve end near the brain?
near the pituitary gland
35
Where is the nasal cavity?
the side of the eye closest to the nose
36
In regard to eye anatomy, what is the temporal region?
the side closer to the temple
37
What are the 5 major components of the retina?
the retina, optic disk, macula, fovea, lens
38
Describe the retina:
neural tissue at the back of the eye and the main sensory organ
39
Is the retina part of the peripheral nervous system or the central nervous system?
Central Nervous System. Even though it's a nerve, it's still attached to the brain, being part of the brain and spinal cord region of the CNS.
40
What is the optic disk? (3 descriptions)
1. The area where blood vessels originate
2. area where optic nerve exits the retina
3. blind spot
41
What is the macula? (3 descriptions)
1. Middle of each retina
2. meant for central vision as opposed to peripheral
3. important for fine vision
42
In regards to the retina, what is another word for "fine vision"?
acuity
43
Why can the macula allow for fine vision?
Due to lack of blood vessels
44
What is the fovea? (4 descriptions)
1. the dark spot thinning on the retina
2. center of the macula
3. important for high acuity vision
4. densely populated with cone photoreceptors
45
Why are cone photoreceptors important in the fovea?
They allow for the retina to sense color
46
In regards to the retina, describe the lens:
it concentrates and focuses light at the retina
47
in regard to the retina, what is the lens similar to?
A magnifying glass
48
Image shows the path taken by light as it passes through the _____ toward the _____
cornea ; retina
49
the transparent lens is suspended by _____ forming a ring inside of the eye
ligaments
50
What muscle controls the shape of the lens?
Ciliary muscle
51
How does the ciliary muscle help adjust vision?
It enables the eye to adjust focus to different viewing distances
52
What helpful image can help envision what the ciliary muscle looks like in the eye?
the lens is a strawberry suspended in the center of a bagel (ciliary muscle) by two toothpicks
53
What "two toothpicks" suspend the lens in the ciliary muscle?
zonule fibers
54
If the ciliary muscle contrasts, the lens gets _____ and when it expands, the lens gets _____ (width)
thicker, thinner
55
What structure is between the cornea and the lens?
Aqueous humor
56
What liquid stays inside the eyeball?
Vitreous humor
57
What 12 structures compose the entire eye? (14)
1. zonule fibers
2. iris
3. lens
4. cornea
5. aqueous humor
6. ciliary muscle
7. vitreous humor
8. sclera
9. optic disk
10. optic nerve
11. fovea
12. retina
13. pupil
14. conjunctiva
58
What are the 7 given eye disorders from lecture?
1 esotropia
2. exotropia
3. cataracts
4. glaucoma
5. detached retina
6. macular degeneration
7. retinitis pigmentosa
59
What is esotropia and what causes it?
Cross-eyed, an extraocular muscular imbalance
60
What is exotropia and what causes it?
Wall-eyed, an extraocular muscular imbalance
61
What are cataracts?
the clouding of the lens
62
What is hypotropia and what causes it?
Bottom-eyed, an extraocular muscular imbalance
63
What is hypertropia and what causes it?
Top-eyed, an extraocular muscular imbalance
64
What is glaucoma and what causes it?
increased intraocular pressure due to poor fluid drainage or damage of the optic nerve
65
What is a detached retina and what causes it?
shrinking of vitreous fluid inside eye which pulls on retina, can be due to aging
66
What is a macular degeneration and what causes it?
loss of central vision over a vast majority of people 65 and up. can be due to protein deposits (dry) or abnormal blood swelling in vessels (wet)
67
What is a retinitis pigmentosa and what causes it?
loss of peripheral and night vision due to degeneration of photoreceptors
68
How do images form in the eye?
the eye collects light rays which are emitted or reflected by other surroundings and focuses them into the retina
69
Cornea and lens bring objects into ______
focus
70
In regard to images forming in the eye:
The cornea is the site of:
the most refractive power
71
In regard to images forming in the eye:
The lens forms:
crisp images of objects less than 9 meters away from the eye
72
As light passes through a medium where it's speed is slowed, it will:
bend
73
Light is ____ as it moves from one medium (air) to another (water)
refracted
74
What degree is the bending of light measured in?
diopters
75
How many diopters does the cornea have? the lens?
42 ; a dozen more
76
Do prescription sunglasses have many diopters?
No; They have just a few
77
In regards to the lens, what is accomodation?
contraction of ciliary muscles to change the shape (rounder/curved) of the lens
78
In order to form the image, why does our lens need accomodation?
Objects 9 meters or less require accommodation because light rays emanated at steeper angles require more refraction
79
How is accommodating affected with age?
It decreases
80
What are the two diseases mainly associated with vision correction?
Hyperopia and Myopia
81
What is Hyperopia and what causes it?
Farsightedness because the eyeball is too short and the point of focus is behind the retina
82
How can you correct hyperopia?
use a convex lens (magnifier) to make the image larger and shorten the point of focus so the image hits the retina like it should
83
What is Myopia and what causes it?
Nearsightedness because the eyeball is too long and the point of focus is before the retina
84
How can you correct Myopia?
use a concave lens to make the image smaller and lengthen the point of focus so the image hits the retina like it should
85
How does the pupil contribute to optical functioning?
It adjusts for different ambient levels of light
86
What is the pupillary light reflex?
connections between the retina and brainstem which control the iris muscles, constricting the pupils
87
In regard to the pupillary light reflex, what is a consensual reflex?
when you shine a light in one eye and both pupils contract
88
In regard to the pupillary light reflex, what is a non-consensual reflex?
indication of a neurological disorder
89
Why would the constriction of pupil reflexes be benenficial?
it increases depth of focus/field (two distances away from the eye can both be in focus)
90
What determines the visual field? What does it determine?
the structure of the eyes, and where they are positioned on the head. Limits how much of the world we can see at one time
91
Define visual field:
area seen by the eyes when looking forward
92
Each eye has a visual field of: (degrees)
150*
93
What field of vision composes each eye's visual field? (name two and their degrees)
Temporal: 90* or more
Nasal: 60* (nose gets in the way)
94
Image is _______ on the retina
Inverted
95
What is visual acuity?
the ability to distinguish between nearby points due to refractive power and distance of photoreceptors
96
Distance across the retina is described in terms of:
degrees of visual angle
97
The conversion of visual activity to neural activity is done by the _____
retina
98
The most direct pathway for visual information to exit the eye is: (3 structures)
Photoreceptors > Bipolar Cells > retinal ganglion cells (RGCs)
99
Photoreceptors respond to _____
light
100
Since photoreceptors respond to light, they are:
excitatory
101
What does it mean when a cell is excitatory?
they release glutamate
102
What is another word for excitatory?
glutamic
103
In regards to the direct pathway for visual information, how does the excitatory response from photoreceptors affect bipolar cells?
the glutamate influences membrane potential of bipolar cells
104
In regards to the direct pathway for visual information, how does the membrane potential response from bipolar cells influence RCGs?
the membrane potential from bipolar cells sends a response to retinal ganglion cells (RCGs) for them to fire an action potential, sending a response through the forebrain
105
What two cell types influence retinal processing?
horizontal cells and amacrine cells
106
What do horizontal cells do?
They receive input from photoreceptors and project neurites laterally to affect surrounding bipolar and photoreceptor cells
107
Are horizontal cells inhibitory or excitatory? Why?
Inhibitory. They laterally send neurites to influence surrounding bipolar and photoreceptor cells
108
What is another term for inhibitory?
GABAergic
109
What do amacrine cells do?
they receive input from bipolar cells and project neurites laterally to influence surrounding ganglion and bipolar cells
110
Are amacrine cells inhibitory or excitatory? Why?
Inhibitory. They laterally send neurites to influence surrounding ganglion and bipolar cells
111
What light-sensitive cells do we have?
Photoreceptors
112
Are photoreceptors the only light sensitive cells we have?
Yes
113
What is a small exception to photoreceptors being the only light sensitive cells we have?
Retinal ganglion cells that influence our circadian rhythm
114
What cells are our only source of input from the retina?
Retinal ganglion cells
115
Retinal Ganglion Cells are the ____ _____ of _____ from the retina
only source of input
116
What axons make up the optic nerve?
Retinal ganglion cells
117
What retinal neurons fire action potentials? (only one)
Retinal Ganglion Cells
118
Retinal Ganglion Cells are the ____ _____ to _____ action potentials
only neurons to fire action potentials
119
What is our neuronal path from photoreceptors to the forebrain?
Photoreceptors ->
Photoreceptors are connected laterally to bipolar cells with a horizontal cell (GABA), horizontally with glutamate ->
Bipolar cells are connected laterally to ganglion cells with amacrine (GABA), horizontally with glutamate
Ganglion axons project to the forebrain
120
The retina has a _____ organization
laminar (layers)
121
Concerning the retina, it's laminar organization has layers which are seemingly ___ ___ or ____ ____
inside-out or upside-down
122
How many layers must light pass through to reach photoreceptors
several
123
Light must pass through ____ ____ before reaching photoreceptors
several layers
124
Name the seven layers light must pass through in the retina before reaching photoreceptors:
1. Ganglion cell layer
2. inner plexiform layer
3. Inner nuclear layer
4. Outer plexiform layer
5. Outer nuclear layer
6. Layer of photoreceptor outer segments
7. Pigment epthelium
125
In regard to the layers light must pass through before reaching photoreceptors, what is the ganglion cell layer?
cell bodies of retinal ganglion cells
126
What are the 6 cell types in the retina?
1. Rod photoreceptors
2. Cone photoreceptors
3. Bipolar Cells
4. Retinal Ganglion Cells (RGCs)
5. Horizontal Cells
6. Amacrine Cells
127
In regard to retina layers:
What is the Inner Plexiform Layer?
Synaptic connections between bipolar, amacrine cells and RGCs
128
In regard to retina layers:
What is the Inner Nuclear Layer?
Cell bodies of bipolar, horizontal and amacrine cells
129
In regard to retina layers:
What is the Outer Plexiform Layer?
Synaptic connections between photoreceptors, bipolar and horizontal cells
130
In regard to retina layers:
What is the Outer Nuclear Layer?
cell bodies of photoreceptors
131
In regard to retina layers:
What is the layer of Photoreceptor Outer Segments?
light sensitive part of retina
132
In regard to retina layers:
What is the Pigment Epithelium?
it absorbs stray light and minimizes things that may blur image by maintaining photoreceptors and photopigments
133
the conversion of electromagnetic radiation into neural signals occurs:
in the photoreceptors, at the back of the retina
134
How many photoreceptors do we have in the back of the retina?
Around 100 million
135
What two types of photoreceptors do we have?
Rods and Cones
136
What are rods meant for?
Night time, sensitive vision
137
What are cones meant for?
Daylight vision, less sensitive but are better for high acuity vision
138
What three parts does each photoreceptor have?
1. outer segment
2. inner segment
3. synaptic terminal
139
In regards to photoreceptors, what is an outer segment needed for?
It absorbs light using membranous disks
140
In regard to photoreceptors, what does the inner segment include?
the cell body and nuclei of photoreceptors
141
Do we have more rods or cone photoreceptors in our retina?
Rods
142
How many photopigments does a rod contain?
One
143
How many photopigments does a cone contain?
three (red, blue, green)
144
Are rods or cones more sensitive to light?
Rods
145
When do rods shut down?
in bright light
146
Do rods or cones have more disks?
Rods
147
Define scotopic
used for night vision
148
Define photopic
used for daylight lighting
149
Are rods scotopic or photopic?
scotopic
150
Are cones scotopic or photopic?
photopic
151
What do cones detect?
color using different wavelengths of light
152
Are cones very active in the dark?
No
153
What can be described as intermediate light levels?
indoor lighting or outdoor traffic lighting at night time
154
What are mesopic (twilight) conditions?
intermediate light levels
155
When are both rods and cones responsible for vision?
in mesopic conditions
156
Are more photons required to activate cones or rods?
Cones
157
Where are most of the cones photoreceptors?
Inside of the fovea, in the central retina
158
What is the purpose of the fovea?
High resolution and color (no rods)
159
Does the peripheral retina contain more rods or cones?
Rods
160
Can the peripheral retina discriminate color or details well?
No
161
Why is the peripheral retina so sensitive to light?
rods respond more strongly to low light than cones
162
Where is visual acuity maximized?
At the fovea
163
What is the fovea?
A thinning of the retina
164
Where is the fovea?
center of the macula
165
Why does the fovea appear as a pit?
lateral displacement of all the cells above
166
Since the fovea has lateral displacement with the above cells. what does this allow for?
light can directly hit the photoreceptors, reducing light scatter
167
Are cones or rods more apparent in the fovea?
Cones (important for visual acuity)
168
Are rods or cones more sensitive to light?
Rods. They work best in dark, low light
169
Are cones or rods more adapted for high acuity vision?
Cones, especially in the daytime
170
What is the name of the photo-sensitive pigment in photoreceptors?
Opsins
171
What gene family are opsins a part of?
GCPR (7-TM domain)
172
What photo-sensitive pigment is expressed in rods? (GCPR gene family)
Rhodopsin
173
What was studied first, rods or cones?
Rods
174
How does a GCPR's response affect the second messenger?
It increases the amount of the second messenger
175
How does a photopigment (opsin) affect the second messenger?
it decreases the amount of the second messenger
176
How does a GCPR's response affect ion channel response?
it increases or decreases it's conductance
177
How does a photopigment's (opsin) response affect ion channel response?
it decreases Na+ conductance
178
What is the stimulus of a GCPR?
a neurotransmitter (NT)
179
What is the stimulus of a photopigment?
Light
180
What is the "agonist" for the GCPR, Rhodopsin?
Light
181
In complete darkness, what is the Vm of the outer segment rod?
-30mV (relative to resting potential)
182
In complete darkness, is the outer rod segment hyperpolarized or depolarized?
Depolarized
183
What does "dark current" mean?
the movement of positive charge across the membrane, occurring in the dark
184
Why can rods have a dark current?
due to special cGMP-gated Na+ channels
185
How are membranes opened in rods?
by cyclic guanosine monophosphate (cGMP)
186
How are rod membranes made?
by guanylyl cyclase
187
When are guanylyl cyclase enzymes active?
continuously in the dark
188
What does light do to cGMP levels?
reduces cGMP levels
189
What happens when light reduces cGMP levels? (2 things)
1. the cGMP-gated channels close
2. Vm becomes more negative (began as depolarized, went to hyper polarized)
190
How are photopigments affected by electromagnetic radiation?
the pigments absorb light
191
Where are photopigments located?
in membranes of stacked disks
192
What is the photopigment in rods called?
Rhodopsin
193
What does Rhodopsin consist of? (2 things)
1. opsin (receptor protein)
2. retinal (prebound agonist from vitamin A, found in carrots)
194
What change is found in retinal due to light?
a conformational change which activates opsin (bleaching)
195
What does retinal look like when it's active (light shines on it)?
It's bleached (due to activated opsin)
196
Describe the 5-step process of phototransduction in rods:
1. light bleaches rhodopsin
2. transducin (G-protein) stimulated
3. phosphodiesterase (PDE; effector enzyme) activated
4. PDE cleaves cGMP and decreases its levels
5. cGMP-gated channels close, cell membrane hyperpolarizes
197
What is a key advantage to the phototransduction system in rods?
signal amplifaction
198
What does signal amplification do to phototransduction in rods? (2 things)
1. photopigment molecules activate many G-proteins
2. PDE breaks down many cGMP molecules
199
How much light is needed to activate signal transduction in rods?
Very little
200
Rods become _____ in response to bright light
saturated
201
Does increasing light level in rods cause additional hyperpolarization?
No, since rods are saturated in response to bright light
202
What are two differences of phototransduction between rods and cones?
1. Cones use three types of opsin
(blue, green, red)
2. Cones do not saturate in normal daylight
203
Why don't cones saturate in normal daylight? (2 reasons)
1. They are less sensitive to light than rods so their photopigments require more energy to bleach
2. Day vision is dependent on cones
204
Why do cone photopigments require more energy to become bleached than rods?
They are less sensitive to light
205
From shortest to longest, what are the wave lengths of cone opsins? (3 kinds)
blue=short
green=medium
red=long
206
What are the four main photopigment genes (OPSINs or OPN)
OPN1LW, OPN1MW, OPN1SW, OPN2 (RHO)
207
Describe the OPN1LW photopigment gene
It's the red opsin to process yellow color in cones
208
Describe the OPN1MW photopigment gene
It's the green opsin to process green color in cones
209
Describe the OPN1SW photopigment gene
it's the blue opsin to process violet color in the cones
210
Describe the OPN2 (RHO) photopigment gene
it's rhodopsin in rods
211
What determines color perception?
contributions of the short/med/long wavelength cones to the retina
212
Who were the gentlemen that determined how we perceive color? (2 guys)
Hermann von Helmholtz and Thomas Young
213
What is the color perception theory called?
Young-Helmholtz Trichromacy Theory
214
Why do we not name spectral sensitivities by their peak response?
each wavelength cone overlaps (ex: red does not consist of a single wavelength)
215
Why can all three cones photopigments activate at once?
colored lights contain a broad spectrum of wavelengths
216
How does the brain assign color?
based on a comparative readout of the three cone types (ex: if all cones are equally active, we perceive white)
217
Is the transition from all-cone daytime vision to all-rod nighttime vision instantaneous?
No, due to adaptation
218
in regard to vision transition, what is dark adaptation?
your eyes switch from cones to more sensitive rods, causing roughly 20 minutes for your eyes to adapt
219
What does dark adaptation result from? (3 things)
1. pupil dilation
2. adjustment of retinal circuitry
3. synthesis of unbleached (inactive) RHO
220
In regard to vision transition, how long does it take for your eyes to adjust to the light?
roughly 15-20 minutes
221
What does the ability to adapt to light changes rely on?
Ca2+ concentration within the cones
222
What can also conduct Ca2+ changes in cones?
cGMP-gated Na+ channels
223
In regard to light adaptation, what does Ca2+ inhibit?
cGMP synthesis by guanylyl cyclase
224
In regard to light adaptation, why does Ca2+ inhibit cGMP synthesis by guanylyl cyclase?
The cones are very hyper-polarized when switching from dark to light so the dark current channels rapidly close.
225
in regard to light adaptation, why does the hyper-polarization of cones inhibit cGMP synthesis?
PDE is activated when the dark current Na+ channels close.
This leads to less CA2+ entering since the channel denies access
Less Ca2 = more cGMP production.
more cGMP = cGMP-gated channels open gradually, depolarizing cones to -35mV
226
Why is the steady state between PDE and guanylyl cyclase unique to cones?
After PDE activates, it causes less Ca2+ to enter the cell. This causes more cGMP to produce which allows gradual depolarization to cones
227
light initially ____ the cone channel, similar to rods
closes
228
A mechanism in cones allows cGMP to do what?
Rise
229
What does increasing cGMP levels do for cones?
Slowing opens cone channels (depolarization) so cones can detect relative light difference during the day
230
How can cGMP levels affect rods?
When there is light differentiation during the day, rods completely shut down. Low cGMP = hyperpolarization
231
In the field of view, can cones LOCALLY adapt to light differentiation areas?
Yes
232
How can you demonstrate local cone adaptation to light-dark areas?
fixate on a plus sign with a white circle on the left, dark circle on the right. Take them away but keep the cross and see how your vision adapts (white should appear black, vice versa)
233
Between cones and rods, what photopigment responds to relative light differences BUT not absolute levels of light?
Cones
234
Why can't cones respond to absolute levels of light? (2 reasons)
1. They have short-term memory so it rapidly fades in seconds
2. cGMP levels and the Vm of cones have to rapidly readjust
235
How is neural activity to the retina coded to pass information to the brain? (3 steps)
1. most direct: from cones to bipolar cells to RGC
2. at each synaptic relay, responses are modified by lateral connections of horizontal and amacrine cells (inhibitory)
3. photoreceptors (release GLU) depolarize in the dark (inc. GLU) and hyperpolarize in the light (dec. GLU)
236
What is the preferred stimulus of photoreceptors (light vs. dark)? Why
Dark. They can release more glutamate this way.
237
How can you study a neuron?
Pick one, ex: RGC, and record its activity by using an electrode in the optic nerve for its action potential
Next, shine a light on different areas of the retina. See where the neuron fires. Now you know it's mapped receptive field.
238
Can any neuron in the visual system have mapped visual systems?
For its receptive field, yes. This applies to any sensory system.
239
What are the two areas of the bipolar receptive field?
Center and the surrond
240
What input does the center area of the bipolar receptive field receive?
direct from one BiP neuron in the fovea to thousands of photoreceptors in the periphery
241
What accounts for high resolution in the fovea?
many small receptive fields
242
What input does the center area of the bipolar receptive field receive?
indirect from photoreceptors in the surround via inhibitory horizontal cells
243
What affects do direct and indirect pathways have on a single bipolar cell?
opposite/antagonistic
244
What determines the two types of bipolar cells? (2 reasons)
1. the way they respond to direct (center) stimulation from photoreceptors
2. response to GLU released by photoreceptors
245
What are the two types of bipolar cells? (based on the type of GLU receptor they express)
1. OFF-center
2. ON-center
246
What are OFF-center bipolar cells?
They respond in the same way the communicating photoreceptors do;
they use ionotropic AMPA GLU receptors (depolarized by GLU)
247
What are ON-center bipolar cells?
they respond in the opposite way the communicating photoreceptors do;
metabotropic GLU receptors (hyperpolarized by GLU)
248
Describe OFF-center Bipolar cells
1. Light turns them off
2. they lead to decreased release GLU on the ganglion cells (hyper polarizes ganglion cells)
249
Describe ON-center Bipolar cells
1. light turns them on
2. they lead to increased release of GLU on ganglion cells (depolarize ganglion)
250
What pathway to OFF and ON bipolar cells come from?
direct (one cone)
251
Why is the direct pathway important in the retina?
left-right eyes, ON-OFF cells come from one cone
252
In a INDIRECT pathway for an ON-center bipolar cell, the horizontal cell is:
inhibitory (uses GABA) to decrease release of GLU from photoreceptors in the receptive field.
253
If a horizontal cell in the INDIRECT pathway for an ON-center cell is hyper-polarized, it:
releases less GABA
254
In an INDIRECT pathway of an ON-center cell, if a horizontal cell is hyper-polarized and releases less GABA, the center photoreceptor:
depolarizes and releases more GLU (hyper-polarizes ON-center bipolar cells)
255
The antagonistic effect of light on direct (center) bipolar cells causes ____ for center and ____ for surround
depolarization ; hyperpolarization
256
The antagonistic effect of light on indirect (surround) bipolar cells causes ____ for center and ____ for surround
hyperpolarization ; depolarization
257
The antagonistic effect of dark on indirect (surround) bipolar cells causes ____ for center and ____ for surround
depolarization ; hyperpolarization
258
The antagonistic effect of dark on direct (surround) bipolar cells causes ____ for center and ____ for surround
hyperpolarization ; depolarization
259
RCGs have the (same/opposite) center-surround organization as bipolar cells
same
260
ON and OFF-center ganglion cells receive input from the _______ type of bipolar cells
corresponding
261
When do ganglion cells fire action potentials?
All the time ; whether or not they are exposed to light (center or surround may increase or decrease firing rate)
262
The stimulation at the center of an OFF-center ganglion cell tends to be _____ by the stimulation of the surround
canceled
263
Concerning the RGC receptive field, they like to respond to (center/edges):
edges
264
For an OFF-center RGC: light at the center turns it (ON/OFF), light at surround (ON/OFF)
OFF ; ON
265
For an OFF-center RGC: dark at the center turns it (ON/OFF), dark at surround (ON/OFF)
ON ; OFF
266
In regard to color opponency: what are color-opponent cells?
in the ganglion receptive field, they respond to one color in the center and is canceled by another in the surround
267
In regard to color opponency: how does the inhibitory surround use inhibitory horizontal cells?
As mentioned with RGC receptive fields
268
In regard to color opponency: green light and green cones in the surround maximally _____ red center cells
inhibit
269
Main opponent colors are: (2 answers)
1. Green and Red
2. Blue and yellow (yellow = red + green)
270
How can ganglion cells be classified? (3 groups)
1. P-type
2. M-type
3. nonM-nonP type
271
What sizes are the 3 groups of ganglion cells?
1. P-type: small
2. M-type: large
3. non: neither
272
Between the 3 groups of retinal ganglion cells, which type is composes the most ganglion cells?
P-type (90%)
273
Between the 3 groups of retinal ganglion cells, which types are sensitive to color?
P-types and non types
274
Between the 3 groups of retinal ganglion cells, do they play different or similar roles in visual perception?
Different
275
The receptive field of a bipolar cell consists of two parts that are _____
antagonistic
276
What does it mean when the receptive field of bipolar cells are antagonistic?:
the center response is opposite to the surround response in the same cell
277
Antagonistic bipolar cells are called?:
center-surround receptive fields (responding to edges of light/dark, in/activating many pixels at once)
278
Retinal ganglion cells _____ the center-surround receptive fields of bipolar cells
recapitualte
279
RGCs in the retina (only output) respond to ______ _____ across their receptive fields
light-dark edges
280
RGCs in the retina (only output) detect _____
contrast
281
the role of the ganglion cell as the only output from the retina is to ______ _____
encode information
282
What information does the ganglion cell encode to the retina? (5 answers)
light-dark, red-green, blue-yellow, movement, detail and sends it to the brain
283
What are the 5 steps to phototransduction in rods?
1. Light activates/bleaches rhodopsin
2. Transducin/G-protein stimulated
3. Phosphodiesterase/effector enzyme activate
4. PDE activity cleaves cGMP and dec. its levels
5. cGMP-gated channels close, cell membrane hyperpolarizes
284
In your field of vision at night, areas of light projected onto your retina will have (low/high) or (hyperpolarized/depolarized) cGMP:
low ; hyperpolarized
285
In your field of vision at night, areas of dark projected onto your retina will have (low/high) or (hyperpolarized/depolarized) cGMP:
high ; depolarized
286
Photoreceptors in local areas of your retina will have (low/high) cGMP if there is light and (low/high) cGMP if there is no light
low ; high
287
Learning Objective: can you describe the anatomy of the central visual system including the LGN and primary visual cortex (V1):
rate 1-5 on confidence level
288
Learning Objective: can you explain the "flow" of information from the retina to the layers of V1?
rate 1-5 on confidence level
289
Learning Objective: are you able to understand the visual information channels?
rate 1-5 on confidence level
290
Learning Objective: can you describe the role of extra-striate areas in vision (V2 and beyond)
rate 1-5 on confidence level
291
For each of us to sense shape, color, position, and movement, we must have:
neurons at different places in the visual system
292
Retina extracts _____:
information
293
How many cells does the retina have?
1 million ganglion cells < 10 million bipolar cell < 100 million photoreceptors
294
What is the overview of the visual process (4 structures)
conscious visual perception pathway from retina > lateral geniculate nucleus (LGN) of thalamus > primary visual cortex (V1, striate cortex) > over two dozen temporal and parietal lobe areas
295
How is information separated for the visual overview?
into parallel pathways for analyzing different features of input
296
What is retinofugal projection?
the neural pathway that leaves the eye, beginning with the optic nerve
297
Define fugal:
latin for a pathway that is directed away from a structure
298
in regard to retinofugal projection:
Where must ganglion cell axons go before forming synapses in the thalamus?
they go away from the retina to pass through 3 structures (optic nerve, optic chiasm, optic tract)
299
In regard to retinofugal projection, what 3 structures must ganglion cell axons pass through before forming synapses in the thalamus?
1. optic nerve
2. optic chiasm
3. optic tract
300
In regard to retinofugal projection, where is the optic chiasm located at?
anterior to the pituitary
301
In regard to retinofugal projection, where does the optic tract run about in the brain?
under pia along lateral diencephalon
302
Define decussation:
the crossing of a fiber bundle from one side of the brain to the other
303
In terms of the visual field:
what is the left visual hemifield composed of?
everything left of the midpoint (left of your nose)
304
In terms of the visual field:
what is the right visual hemifield composed of?
everything right of the midpoint (left of your nose)
305
In terms of the visual field:
what is the binocular visual field viewed by?
both retinas (center of both hemifields ; the nasal side)
306
Image of the right visual field gets sent to the (left/right) brain:
left
307
Image of the left visual field gets sent to the (left/right) brain:
right
308
In terms of the visual field:
nasal axons (cross/remain) and temporal axons (cross/remain)
cross ; remain on the same side
309
Left visual hemifield is "viewed or analyzed" by the (left/right) hemisphere
right
310
Right visual hemifield is "viewed or analyzed" by the (left/right) hemisphere
left
311
In regard to the optic tract:
where do most neurons connect?
the lateral geniculate nucleus (LGN) of the dorsal thalamus
312
In regard to the optic tract:
what is the pathway for most neurons to send their signal? (3 locations)
1. LGN of the dorsal thalamus
to
2. ipsilateral cortex
via
3. optic radiation
313
In regard to the optic tract:
what is the portion of the pathway for most neurons to send their signal a part of?
the internal capsule
314
What is the optic tract pathway responsible for?
conscious visual perception
315
When there are lesions from the eye to the LGN to the visual cortex, how does this affect retinofugal projection?
blindness in part or all the visual field
316
In regard to retinofugal projection lesions, how does transection of the left/right optic nerve affect vision? (2 things)
loss of peripheral vision on the ipsilateral side (same as closing one eye) and depth perception lost
317
In regard to retinofugal projection lesions, how does transection of the left/right optic tract affect vision? (one thing)
loss of complete contralateral (opposite) visual hemifield
318
In regard to retinofugal projection lesions, how does transection of the optic chiasm affect vision? (two things)
produces a "tunnel vision" effect due to damage of nasal or crossing axons, loss of peripheral vision
319
In regard to non-thalamic targets of the optic tract, what can some axons do? (3 things)
1. connect to the hypothalamus
2. synchronize sleep and wakefulness with light/dark cycles
3. maintain biological rhythms
320
In regard to non-thalamic targets of the optic tract:
when axons connect to the pretectum, what can they control? (2 things)
1. control pupil size, lens
2. control eye movement
321
In regard to non-thalamic targets of the optic tract, how many ganglion cells are connected to the superior colliculus (tectum)?
10% of ganglion cells are connected to the superior colliculus
322
In regard to non-thalamic targets of the optic tract:
What is the role of ganglion cells in the superior colliculus (tectum) ?
for mammals: orient head and eye movements in response to stimuli
323
In regard to non-thalamic targets of the optic tract:
How do ganglion cells of the superior colliculus (tectum) communicate?
They receive input from both eyes in response to new stimuli while LGN neurons receive input from only one eye or the other
324
In regard to control of pupillary reflex and lens shape:
what is the purpose of the ciliary ganglion?
it mediates the pupillary reflex and lens shape
325
What cranial nerve number is the ciliary ganglion?
Cranial nerve 3
326
What does the pretectum receive? What does it do with that information?
visual signals ; feeds back to eye to control pupillary reflex and lens shape
327
What is the anatomy and location of the superior colliculus in regard to a mouse?
dorsal part of the brain (sensory)
328
What is the anatomy and location of the superior colliculus in regard to humans?
medial ; inside of the thalamus, inferior to the LGN
329
In regard to the layered structure of the LGN, where is the right and left LGN located?
Laterally in the posteroventral thalamus
330
In regard to the layered structure of the LGN, what are the right and left LGN targets for?
the two optic tracts
331
In regard to the layered structure of the LGN, how are the layers arranged?
In six distinct layers of cells
332
What is the LGN?
the gateway to the visual cortex and conscious visual perception
333
The MGN of the auditory pathway is _____ to LGN
medial
334
Within each side of the LGN, each eye is represented in separate layers of the (same/other) eye:
other
335
What kind of map is the LGN thought to be?
retinotopic
336
The Right LGN represents the (left/right) visual field:
left
337
The Left LGN represents the (left/right) visual field:
right
338
The left visual field is the (left/right) side of each eye:
right
339
The right visual field is the (left/right) side of each eye:
left
340
Where do LGN neurons receive input from?
they receive synaptic input from the retinal ganglion cells
341
What does the segregation of LGN neurons suggest?
different types of retinal information are being kept separate at the synaptic relay
342
In each layer of the LGN, (one/both) eye(s) are represented (mono/binocular)
one ; monocular
343
LGN neurons have (similar/different) center-surround receptive fields as the RGC's in the retina
similar
344
LGN neurons have light-dark (and/or) color opponency
or
345
Separate layers of the LGN support what notion?
parallel but separate pathways course from one retina to the LGN to layer IV of the V1, THEN convergence and integration in layers 2/3 of V1 AND on to cortical processing sites beyond V1
346
What are other synaptic inputs to the LGN? (2 inputs)
1. primary visual cortex (V1
2. other parts of the thalamus
3. other parts of the brain stem
347
When synaptic input is sent from the V1 to the LGN, what is it's function? provide an example:
Modulates responses to stimuli through top-down processing (since LGN is not a relay station)
ex: V1 could pay selective attention to parts of the visual field while suppressing others
348
What is the LGN's single major synaptic target?
primary visual cortex (V1) in the occipital lobe
349
Why is the primary visual cortex called the V1?
it is the first cortical area to receive information from the LGN
350
Besides the primary visual cortex being called the V1, what are two other names for it?
The striate cortex or Brodman area 17
351
What is retinotopy of the LGN?
an organization where neighboring cells in the retina feed information to neighboring places in target structures (LGN. striate/V1)
352
What does retinotopy allow for in the LGN?
the two-dimensional surface of the retina to be mapped onto the 2D surface of the subsequent structures
353
What are the three important points to remember about retinotopy?
1. mapping of the visual field onto retinotopically organized structure is often distorted due to the visual field being non-uniform in retina cells
2. a discrete point of light can activate many cells in the retina and far more in the target structure due to overlap of receptive fields
3. "map" is misleading ; there are no snapshots in the V1 of a person
354
In regard to retinotopy:
What does non-uniform retina cells in the visual space mean?
the fovea has many small ganglion cell receptie fields than the periphery. Therefore, less photoreceptors feed into the RGC's. Yet now, it's spatially over-represented in the V1. It composes little space in the retina versus how it looks in the V1.
354
In regard to retinotopy:
What does an overlap of receptive fields mean?
When the retina is stimulated by a small point of light, the striate cortex activates on a broad distribution with a peak at the corresponding location
355
In regard to retinotopy:
What does it mean when the fovea/central retina is much more represented in the striate cortex than the periphery?
there is more info to process since there are many more but smaller receptive fields
356
In regard to lamination of the striate cortex:
What do the six layers suggest?
segregation of input and analysis
357
Layer 1 of 6 in the striate cortex has (few/many) neurons:
few
358
Layers 5 and 6 of the striate cortex have (smaller/larger) pyramidal neurons:
larger
359
Layers 2 and 3 of the striate cortex have (smaller/larger) pyramidal neurons:
smaller
360
Layer 4 of the striate cortex has (many/few) pyramidal neurons:
few
361
In regard to the striate cortex:
Which two layers do the stellate cells in layer 4 project to?
Layers 2 and 3
362
In regard to the striate cortex:
Where do the pyramidal neurons in layers 2 and 3 signal to?
the dendrites of pyramidal neurons in layers 5 and 6
363
In regard to the striate cortex:
Inputs from LGN target to layer ? out of 6:
layer IVC (4C)
364
stopped on beginning of slide 24
out of 45
365
From the LGN, what is the pathway of inputs to the striate cortex?
to the striate cortex, there is no cross over as there is a direct path from LVN via optic radiation; information from each eye is still separate?
366
In regard to the inputs to the striate cortex:
In the LGN, every layer receives ? as an input and ? as an output to the visual cortex?:
receives retinal afferents ; sends efferents
367
In regard to the inputs to the striate cortex:
why is the visual cortex different of receiving input versus the LGN? (2 reasons)
1. only subset of layers receive input from LGN
2. sends output to a different cortical/subcortical area
368
in regard to the inputs to the striate cortex:
Where do most of the inputs from the LGN go?
to the stellate cells in layer IVC (4C)
369
In regard to the inputs to the striate cortex:
what are the stellate cells in layer 4C for?
they are interneurons which communicate with other layers
370
In regard to the inputs to the striate cortex:
What is the alternating retinotopic pattern of inputs for layer 4C meant for? What is the process called?
they alternate bands of cells receiving input from only one eye
Called ocular dominance columbs
371
In regard to the inputs to the striate cortex:
What is the retinotopic pattern of all inputs for layer 4C meant for?
Cells in all layers of the striate respect the same retinotopic organization and maintain radial connections
372
In regard to the inputs to the striate cortex:
Layer 4C stellate cells contact what retinotopic layers and their pyramidal neurons? What do those layers then do after receiving input?
Layers 2 and 3. They make horizontal connections across the layer
373
In regard to ocular dominance columns:
most intracortical connections extend (parallel/perpendicular) to the cortical surface
perpendicular
374
In left eye ocular dominance columns and right eye ocular dominance columns, do the intracortical connections ever together? (Y/N, why?)
No. Most of the information that runs across the lays stay separated in each eye
375
In regard to ocular dominance columns:
how do you get binocular cells? Why is that?
How: For the first time layers 2 and 3 send information, it is mixed from the two eyes, resulting in binocular cells
Why: there is a combination of layer 4C stellate cell axons which cross borders and horizontal connections of layer 3 pyramidal cells
376
Briefly describe the study of Hubel and Weisel
They determined how the left and right eye LGN inputs were arranged in the striate cortex. This was done by tracking ganglion cell axons in the LGN using radioactive amino acid. This acid shows what proteins were released and transmitted across terminals to target striate cortex cells
377
What did the Hubel and Wiesel study reveal to the science community?
The silver grains (marked proteins) represented the location of radioactive LGN inputs.
This revealed the left and right eye inputs to layer 4 are laid out in alternating bands. They stay segregated rather than mix.
378
In regard to striate cortex input and output:
the pyramidal cells send axons out of the striate cortex into:
white matter
379
In regard to striate cortex input and output:
the pyramidal cells in different layers innervate:
different structures
380
In regard to striate cortex input and output:
layers 2 and 3 play a key role in visual processing. What would that be?
they provide most of the information that leaves V1 for other cortical areas
381
ON and OFF signals from retina remain segregated in layer 4 (simple cells) but what?
integrate in layers 2 and 3 (complex cells)
382
ON and OFF signals from the retina are though to encode object contrast which signal "____ _____" renderings of the same image. These are integrated where?
mirror symmetric ; in primary V1 and beyond
383
In regard to receptive field maps in the striate cortex:
Hubel and Wiesel were the first to explore the physiology of the striate cortex using:
microelectrodes
384
In regard to receptive field maps in the striate cortex:
The receptive fields in the retina, LGN (thalamus) and layer 4C of the striate cortex are (mono/biocular) and (circular/pointed) with greatest response at the (center/surround).
monocular ; circular ; center
385
In regard to receptive field maps in the striate cortex:
Receptive fields are (similar/different) in striate cortex outside of layer 4C
different
386
What are 4 other levels of receptive field maps in regard to layer 4C of the striate cortex?
1. Binocularity
2. Orientation Selectivity
3. Direction Selectivity
4. Blob Receptive Fields
387
In regard to binocularity:
What retinotopic layers are binocular? Which ones are monocular?
Layers 2 and 3 are binocular. All others are mostly monocular
388
In regard to binocularity:
What retinotopic layers do most of the projections leave from? What do we call this?
Layers 2 and 3. Stereo vision/3D
389
What is binocularity?
It's the ability to focus on an object with both eyes to create a single image
390
In regard to binocularity:
How many receptive fields do binocular neurons have? In which eye?
Two ; one in the ipsilateral and one in the contralateral eye
391
In regard to binocularity:
What visual field do binocular neurons observe when looking at one object?
contralateral visual field
392
In regard to orientation selectivity:
Where does the eye respond to a bar of light? What is this called for a particular cell? Why?
1. neurons in V1 respond
2. called optimal orientation for that particular cell. It has the highest cell discharge compared to other orientations
393
In regard to orientation selectivity:
Does the orientation of a light bar matter?
Yes
394
In regard to orientation selectivity:
What orientation of the light bar elicits the weakest response?
perpendicular (90*) to the optimal orientation
395
In regard to orientation selectivity:
When bars are oriented 90* to the most optimal orientation, what is this called?
orientation selectivity
396
What is orientation selectivity?
When arranged columns cross multiple layers
397
In regard to orientation selectivity:
What relationship is there between single and neighboring layers?
There is an orientation relationship
398
Systematic variation of orientation selectivity in neighboring regions of a single layer is (random/not random)? What example could explain this? What does this represent?
Not random. It's like the sweep of the minute hand on a clock. It represents the analysis of object shape.
399
What layers are systematic variation of orientation selectivity encoded in?
layers 2 and 3
400
In regard to direction selectivity:
are neurons responding to optimal orientation bidirectional? (Y/N, why?)
No. They respond to orientation of one direction but not the opposite.
401
In regard to direction selectivity: what are direction-selective neurons thought to be specialized for?
the analysis of object motion
402
Direction selectivity is a hallmark of what area:
V1 (striate cortex) neurons getting input from M-Cell layers of the LGN
403
In regard to Blobs,
neurons which express higher levels of mitochondrial cytochrome oxidase are identified where?
In the primary visual cortex
404
What are blobs aggregates of? What are it's characteristics?
cells within the visual cortex. They are sensitive to color and arrange in cylinder shapes
405
What are interblobs?
The area between blobs which receive the same input yet are sensitive to orientation/shape (rather than color)
406
What do blobs represent? What about interblobs?
non-MP ganglion cells from the retina. inter: parvocellular P ganglion cells but this can be oversimplified
407
In parallel pathway models, what is the foundation (cell types)?:
P, M and nonMP ganglion cells of the retina
408
In parallel pathway models, what areas receive P, M and nonMP ganglion cells?
segregated areas of the LGN and projections in layer 4C of the striate cortex
409
In regard to parallel pathway models:
What might magnocellular cells be involved in?
the analysis of object motion and guidance of motor actions
410
In regard to parallel pathway models:
What might parvo-interblob cells be involved in?
the analysis of fine object shape
411
In regard to parallel pathway models:
What might blob cells be involved in?
analysis of object color
412
In regard to cortical modules, what might 0.5-1.5* of light include? (4 concepts)
1. two complete sets of ocular dominance columns
2. 16 blobs
3. complete sampling (twiceover) of all possible 180* orientations
4. all cells needed to "see" the light
413
In regard to cortical modules, what might 0.5-1.5* of light include in the V1?
nearly 1000 modules
414
In regard to cortical modules, what might be needed to perceive 0.5-1.5* of light?
further projections to many extrastriate cortical regions
415
What two areas lie beyond the striate cortex?
1. two dozen distinct extra-striate areas of the cortex
2. two large-scale cortical streams of visual processing (one stretches dorsally toward the parietal lobe and other goes ventrally toward the temporal lobe)
416
What is another name for the dorsal stream pathway?
Where? pathway
417
What 5 things are involved in the dorsal stream?
1. large receptive fields
2. direction and motion sensitive cells (more important than shape)
3. direction of motion columns
4. MT (perception of motion)
5. MST (perceives linear, radial and circular motion)
418
What is another name for the dorsal stream pathway?
What? pathway
419
Where is the ventral stream located?
Area V4 and Area 1T (inferior temporal)
420
In regard to the ventral stream,
what 3 things can Area V4 help perceive?
1. receive input from (inter)blob regions of V1
2. Receptive field for orientation/color selection
3. Shape and Color perception (!!!)
421
If there is damage to Area V4, specifically for people with achromatopsia, what can this cause issues with?
color perception; the world has no color but is only grey
422
In regard to the ventral stream,
what 3 things can Area IT help perceive?
1. input from the V4
2. perception of color and abstract objects (such as faces) (!!!)
3. object and facial memory
423
What does the IT in Area IT stand for?
Inferior Temporal
424
What is the hierarchy of receptive fields? (4 structures)
The retina to higher cortical regions goes from:
simple center-surround receptive fields ->
orientation (shape) selectivity ->
motion/direction selectivity ->
abstract object selectivity
425
In regard to the hierarchy of receptive fields:
What can help in the perception of your "grandmother"?
Broadly tuned and cells and distributed signals across many regions
426
In regard to the hierarchy of receptive fields:
What is parallel processing? What can it be compared to?
A division of labor; an "orchestra of visual areas, not a single musician"
427
For an ON-center retinal ganglion receptive field, what is it's optimal stimulus?
A spot surrounded by dark shades
428
For a simple cell in V1 and its receptive field, what is the optimal stimulus?
An elongated bar of light
429
For the infero-temporal visual cortex and its receptive field, what is its optimal stimulus?
A face
430
Learning Objective: can you explain the receptors and pathways involved in touch?
Rate on confidence scale, 1-5
431
Learning Objective: can you explain the receptors and pathways involved with pain?
Rate on confidence scale, 1-5
432
Learning Objective: do you understand how the somatosensory cortex organizes input?
Rate on confidence scale, 1-5
433
What is the somatic sensory system?
catch-all name for all of the sensations that are not seeing, hearing, tasting, smelling and the vestibular sense of balance
434
How is the somatic sensory system different from that of other systems? (2 reasons)
1. different type of receptor cells
2. different stimuli for receptor cells
435
In regard to the somatic sensory system:
how are receptor cells distributed throughout the system?
they are distributed throughout the body rather than being concentrated at small, specialized locations
436
In regard to the somatic sensory system:
what is the purpose of a single receptor?
it provides information about intensity, position and duration of a stimulus
437
In regard to the somatic sensory system:
What is the relationship between a single stimulus and many receptors?
A single stimulus can activate many receptors
438
In regard to the somatic sensory system:
How is the CNS involved?
the CNS interprets the activity of vast receptor arrays, using it to generate coherent perceptions
439
In regard to the somatic sensory system:
(similar/different) receptor cell types respond to (similar/different) kinds of stimuli
Different ; Different
440
In regard to the somatic sensory system:
What is the name of touch receptors?
mechanoreceptors
441
In regard to the somatic sensory system:
What is the same for temperature and pain receptors?
nociceptors
442
In regard to the somatic sensory system:
What is the name for body position receptors?
proprioceptors
443
In regard to the somatic sensory system:
The skin is a _____ organ
social
444
In regard to the sense of touch:
skin is the largest ______ organ
sensory
445
In regard to the sense of touch:
Why is skin protective?
it prevents evaporation of needed fluids
446
Most sensory receptor cells in the somatic nervous system are:
mechanoreceptors
447
In regard to mechanoreceptors of the skin:
what is a pacinian corpuscle (PC)?
it's deep in the dermis, allowing for high density for sensing touch in the fingers
448
In regard to mechanoreceptors of the skin:
what are Ruffini's endings in contrast to PC's?
they are slightly smaller
449
In regard to mechanoreceptors of the skin:
what are Meissnger's corpuscles in contrast to PC's?
They are a fraction of the size, found in ridges of your fingerprints
450
In regard to mechanoreceptors of the skin:
what are merkel's discs?
They reside in the epidermis with a nerve terminal and a flat non-neural epithelial cell
451
In regard to mechanoreceptors of the skin:
what may other mechanoreceptors than the main 4 detect?
blood pressure, bladder extension to name a few
452
In regard to mechanoreceptors of the skin:
What are the 4 main cell types?
1. Pacinian corpuscles
2. Ruffini's endings
3. Meissner's corpuscles
4. Merkel's discs
453
In regard to mechanoreceptors of the skin:
how to mechanoreceptors vary?
In receptive field sizes, stimulus frequencies and pressure
454
In regard to mechanoreceptors of the skin:
How do receptive fields vary? (2 differences)
1. Meissner's corpuscles and Merkel's disks have small receptive fields (important for fingertips)
2. Pacinian Corpuscles and Ruffini's endings have large receptive fields
455
In regard to mechanoreceptors of the skin:
How does adaptation among the 4 main cells vary? (2 differences)
What does each group respond to?
1. Meissner's and Pacinian Corpuscles are fast adapting; responding to change in pressure (touch and release)
2. Merkel's discs and Ruffini's endings are slow adapting; they sustain responses with applied pressure
456
In regard to mechanoreceptors of the skin:
Ruffini's endings detect: (2 things)
stretch and deformation in joints
457
In regard to the somatic sensory system:
Is hair a sensory organ? Why or why not?
Yes. Animals use their whiskers. When the follicles detect change, they fire AP from free nerve endings
458
In regard to different mechanical sensitivities of mechanoreceptors:
What is an example of touch response for Pacinian Corpuscles?
Putting your hand on a loudspeaker helps to "feel" the music
459
In regard to different mechanical sensitivities of mechanoreceptors:
What is an example of touch response for Meissner's corpuscles?
Feeling a rough or bumpy surface
460
Vibration sensitivity of Pacinian corpuscles depends on the:
fluid-filled capsule; not the axon alone
461
Adaptation in the Pacinian corpuscle
depends on the special ending called the:
capsule
462
What happens to Pacinian corpuscle adaptation if you take away the capsule?
the nerve ending responds to constant pressure only ; it's no longer sensitive to vibration
463
How does the capsule benefit a Pacinian Corpuscle?
It allows for insensitivity to low frequency stimulation and constant pressure ; sensitive only to high frequency vibration
464
In regard to mechanosensitive ion channels:
it can respond to what two things?
1. stretch force within the lipid bilayer
2. stretch of an extracellular protein or intracellular protein
465
What is the two point discrimination test?
our ability to discriminate details of a stimulus (usually with our fingertips)
466
In regard to primary afferent axons:
how does it transmit touch information?
into the spine at specific levels depending on where the stimulus came from
467
How do axons bring information in regard to primary afferent axons?
It comes from somatic sensory receptors to the spinal cord
468
Where do primary afferent axons enter?
the spinal cord through dorsal roots
469
Where is the soma of primary afferent axons located?
dorsal root ganglion
470
Do primary afferent axons have the same diameters?
No. Size is correlated with the sensory receptor
471
What primary afferent axons convey pain?
C fibers are the slowest but convey pain, temperature and itch
472
What primary afferent axons convey sensation?
AB fibers
473
What composes the spinal cord (overview)
30 pairs of dorsal and ventral roots
474
How many groups is the spinal cord divided into? Name them.
4 groups; Cervical, Thoracic, Lumbar, Sacral
475
What are dermatones?
The area of skin innervated by the left and right dorsal roots of a single spinal segement
476
What is the relationship between spinal segments and dermatones?
One-to-one
477
Multiple dorsal roots innervate each _____
dermatone
478
When a single dorsal root is cut, what happens?
the corresponding dermatone on that side of the body does not lose all sensation
479
Adjacent dorsal roots innervate ____ _____
overlapping areas
480
In regard to dorsal roots and dermatones:
to lose all sensation from an area, what must happen?
all three dorsal roots would need to be cut
481
What is a factoid?
Shingles virus and dermatones
482
Where does shingles reside?
sensory ganglia
483
What happens to the dermatone when shingles emerges?
it's infected
484
Primary afferent axons participate in ____ and _____ through bifurcating projections
reflex control and perception of touch
485
What composes a primary afferent axon?
Inner core of gray matter surrounded by a thick white matter covering
486
What is a dorsal horn in regard to primary afferent axons?
second-order cells that receive input from sensory neurons
487
What is a ventral horn in regard to primary afferent axons?
motor neurons
488
What is the intermediate zone in regard to primary afferent axons?
interneurons
489
What are columns in regard to primary afferent axons?
fibers and white matter
490
What do primary afferent neurons synapse on?
second-order sensory neurons within the dorsal horn
491
What happens to primary afferent neurons after they synapse onto second-order sensory neurons?
they project to motor neurons in the ventral horn or to other interneurons, while sending a bifurcating process to the brain
492
What two things does a primary afferent axon do?
1. initiate or modify a variety of rapid and unconscious reflexes
2. responsible for perception
493
What pathway is the dorsal column a part of?
the Medial Lemniscal Pathway
494
What is the medial lemniscal pathway for?
touch and vibration through AB fibers and limb position through Aa proprioceptors
495
Is the medial lemniscal pathway different from pain and temperature?
Yes. That is associated with C fibers
496
AB sensory axons travel to the brain on ipsilateral side through the _____ ______
dorsal column
497
Dorsal column axons connect to _____ ______ ______ in medulla near the medulla-spinal cord junction
dorsal column nuclei
498
What is the medial lemniscal pathway (actual pathway)?
1. dorsal columb nuclei axons decussate sensory info
2. they ascend into the medial lemniscus (white matter tract)
3. that travels through medulla, pons and midbrain to the ventral posterior (VP) nucleus of the thalamus
4. those neuons send processes to the primary somatosensory cortex (S1) through the internal capsule
499
Define ascending pathway"
proceeds from lower areas to higher areas (ex: spinal cord to dorsal column)
500
Lateral inhibition heightens the ____
of edges or points on the skin.
perception
501
The trigeminal touch pathway mediates somatic sensation of the _____
face
502
sensation in face carried mainly through
_____ nerves (cranial nerve ?)
trigeminal ; 5
503
Where is the somatosensory cortex located?
the parietal lobe
504
What area in the brain is considered the primary somatosensory cortex (S1)?
Brodmann's area 3b
505
Why is the Brodmann's area considered S1? (4 reasons)
1. receives dense input from ventral posterior nucleus of thalamus
2. the neurons are highly responsive to somatosenosary input only
3. lesions impair sensation
4. electrical stimulation causes sensation
506
What other areas of the brain also process somatosensory information?
Brodmann 1, 2, 3a and posterior parietal cortex 5 and 7
507
How many layers are there in the columnar organization of the somatosensory cortex?
6
508
What layer in the columnar organization of the somatosensory cortex is the thalamus?
Layer IV (4) (similar to visual system)
509
In regard to the columnar organization of the somatosensory cortex:
Cells with similar characteristics stacked in ____ ____
vertical columns
510
The receptive fields of many S1 neurons
produce an orderly ______ _____ of the
body on the cortex
somatotopic map
511
In regard to Whisker ”barrels” in rodent S1 cortex: Each whisker corresponds to a single ____
S1
512
In regard to Whisker ”barrels” in rodent S1 cortex: Whiskers are represented in a much
larger area than the ____ in S1
paws
513
Somatotopic map plasticity is noted as what common saying?
“use it or lose it”
514
Plasticity is _______ in the brain (visual, auditory, motor)
widespread
515
The Posterior parietal cortex are what areas of Brodmann?
areas 5 & 7
516
Somatosensory input integrated with what other systems?
visual, attention, movement
517
What is the function of the posterior parietal cortex?
perception & interpretation of spatial relationships, body image (where your body is in space), coordinated body movements
518
Damage to posterior parietal cortex causes what two things? What are they?
Astereognosia: inability to recognize objects by touch
Neglect Syndrome: part of the body or world would be ignored (dress one side of body, eat one side of the plate)
519
Pain signals are transmitted by sensory cells called:
nociceptors
520
What is nociception?
The sensory process that provides signals that we perceive as pain (is not the same as pain)
521
What are nociceptors?
(sensory cells) respond specifically to harmful stimuli that are perceived as painful, and are different from mechanoreceptors for touch
522
What is pain?
the perception of noxious stimuli
523
What are the names of the three types of nociceptors?
1. Mechanical
2. Thermal
3. Chemical
524
The transduction of painful stimuli occurs in the _____ _____ ______ of unmyelinated C fibers and lightly myelinated Aδ fibers
free nerve endings
525
The transduction of painful stimuli occurs in what fibers?
unmyelinated C fibers and lightly myelinated Aδ fibers
526
Most nociceptors are ____modal
poly
527
How are touch mechanoceptors different from nociceptors?
mechanoceptors don't have free nerve endings
528
What is primary hyperalgesia?
area of damaged tissue
529
What is secondary hyperalgesia?
surrounding area caused by variety of substances in PNS and CNS
530
What fibers bring pain to the spinal afferents and mechanisms?
AB and C fibers
531
the projection pathway is different from the touch pathway how?
1. Touch projections are dorsal column; pain
pathway is lateral column
2. Touch and pain signals remain segregated
532
mechanoreceptors:
each have what? (3 things)
1. different receptive field size
2. stimulus frequencies
3. pressure response
533
Vibration sensitivity of PCs
depends on ____?
capsule
534
If no capsule on a PC = no ___ __ ___?
no response to vibration
535
Define dermatones:
Area of skin innervated by the right and left dorsal roots of a single spinal segment
536
PC are dependent on what? (3 things)
1. nerve
2. pressure
3. fluid-filled capsule
537
Dorsal root is what?
sensory
538
If you cut one dorsal root, can you still feel the sensation somewhere else in the body?
YES
539
What is the medial lemniscal pathway for?
touch, vibration, and limb position
540
The medial lemniscal pathway connects to what?
dorsal column nuclei in medulla and cross over to ventral posterior nucleus of the thalamus
541
After the medial lemniscal pathway connects to the dorsal column nuclei and crosses over to the thalamus, what does the thalamus connect to?
primary somatosensory cortex via internal capsule
542
Lateral inhibition heightens what?
perception of edges or points on the skin
543
Compared to vision, Lateral inhibition is the same idea as what?
horizontal cells
544
Trigeminal touch pathway is for?
the face
545
Is the medial lemniscal pathway an ascending or descending pathway?
ascending
546
What is nociception?
sensory process that provides signals we perceive as pain
547
What do nociceptors do?
respond to harmful stimuli that are perceived as painful
548
Are nociceptors or mechanoreceptors the same or different?
different
549
Nociceptors can be *three things*:
mechanical, thermal or chemical
550
Nociceptor transduction occurs on the free nerve endings of what two fibers?
unmyelinated C fibers and lightly myelinated Aδ fibers
551
With afferent pathways, what fiber causes you to feel pain FIRST?
AB fibers
552
With afferent pathways, what fiber causes you to feel pain SECOND?
C fibers
553
With afferent pathways, what is the main neurotransmitter?
Glutamate
554
With afferent pathways, what substance plays a role with inflammation?
Substance P
555
What is the Spinothalamic pain pathway?
From spine to thalamus, relay pain and temperature from limbs and torso
556
What is the Trigeminal pain pathway?
CN V → spinal trigeminal nucleus → trigeminal lemniscus → thalamus
557
With respect to objects in our field of vision, most of the light coming from an object is from which optical phenomenon?
Reflection
558
The opening that allows light to enter the eye is the _____
pupil
559
The part of the eye that can be adjusted to better refract and focus the light of close objects (<9M) is called the _____
lens
560
Which pathway describes the conversion of light energy into neural activity and neural output in the retina?
Photoreceptor > Bipolar Cell > Retinal Ganglion Cell
561
Of the ~100 million photoreceptors in the retina the majority are cones in the peripheral retina (T/F)
false
562
When both rods and cones are switched from dark to light the immediate effect on these cells is ____ due to cleavage of cGMP
Na+ channel CLOSING and HYPERPOLARIZATION
563
What property of cones is different from rods and causes cones to reactivate after initally being hyperpolarized by the transition from dark to light?
decreased intracellular Ca2+ and increased cGMP
564
What is faster to perceive, touch or pain?
Touch is fast ; Pain is slower
565
An OFF-center ganglion cell that is switched from light to dark at its visual field center will be _____
depolarized
566
Transection (cutting) of the left optic tract would result in _____
loss of the right visual hemifield
567
Transecting the optic chiasm would sever the _____ projection of each eye and disrupt the ______ field of vision
nasal; PERIPHERAL
568
Information from the two eyes remains segregated in the _____ subregion of the thalamus and in layer _____ of the primary visual cortex (V1), but binocular cells receiving information from both eyes can first be observed in layer _____ of V1
lateral geniculate nucleus (LGN); IVS; II/III
569
ON and OFF visual pathways first emanating from the retina are thought to encode ______
object contrast
570
Cells with receptive fields in both eyes (binocular cells) are first observed in _____
layer II/III of the striate cortex
571
In the primary visual cortex (V1) orientation selective cells encode ________
object SHAPE
572
The right visual field is represented ______
on the left retina of both eyes
573
The left primary visual cortex receives visual information from ______
the left retina of both eyes
574
____ (#) dorsal roots need to be severed (cut) in order to lose ALL sensation from a corresponding dermatone
3
575
Loss of a finger would cause neurons representing that finger in the somatosensory cortex to ____
respond to adjacent digits instead
