Sensory Flashcards
1
Q
What is the CNS made up of?
A
The brain and spinal cord
2
Q
What afferents?
A
Neurons that deliver information to the CNS(sensory input)
3
Q
Where are the cell bodies and axons of afferents located?
A
Cells bodies: Outside of CNS
Axons: Stick into the CNS in the brain or spinal cord
4
Q
What are the spinal nerve afferents responsible for?
A
Where somatosensation (touch, temperature and pain) enter the spinal cord
5
Q
What are the cranial nerve afferents responsible for?
A
Carry information about visual, olfactory, somatic into the brain
6
Q
How many cranial nerves and how many go into the brainstem?
A
12 cranial nerves
10 out of 12 go into the brainstem
7
Q
What is visceral input?
A
Somatosensation from within your body
8
Q
What are efferents?
A
Neurons that send outputs out of the CNS (motor outputs)
9
Q
Where are the cell bodies of efferent?
A
In the CNS and their Axons are outside of the CNS
10
Q
T/F: cranial nerves and spinal nerves have efferents?
A
True
11
Q
What somatic efferents?
A
Motor neurons with their cell bodies in the CNS and axons innervating the skeletal muscles to make you move
12
Q
What are autonomic efferents?
A
Innvervate things other than skeletal muscle such as smooth muscle, interneurons and cardiac muscle
13
Q
What are gyrus?
A
Wirnkles in the cerebral cortex responsible for out smartness
14
Q
What are sulcus?
A
The cracks in between the gyrus
15
Q
What is the central sulcus?
A
Separates the gyrus responsible for primary somatosensory processing from the gyrus responsible for primary motor cortex
16
Q
What is grey matter?
A
Location of the cell bodies for the neurons in the cerebral cortex
17
Q
What is white matter?
A
Axons travelling from different areas of the brain
18
Q
What is the basal nuclei/ganglia?
A
A bunch of cell bodies together inside the cerebral cortex
19
Q
What do cervical nerves innervate?
A
-Neck, shoulders, arms and hands
20
Q
What do Thoracic nerves innervate?
A
-Shoulders, chest, upper abdominal wall
21
Q
What do the lumbar nerves innervate?
A
-Lower abdominal wall, hips, legs
22
Q
What do the sacral nerve innervate?
A
-Genital and lower digestive tract
23
Q
How many spinal nerves?
A
31
24
Q
What is the butterfly shape of the spinal cord?
A
THe grey matter
25
What is the central canal and where is it located?
In the middle of the gray matter of the spinal cord and it is a canal for CSF
26
Ventral horn vs Dorsal horn
Ventral horn: Area of the grey matter closest to the stomach
Dorsal horn: Area of the grey matter closest to the back
27
What does the dorsal root carry?
Sensory afferent (inputs) into the spinal cord
28
What does the ventral root carry?
Motor efferent axons (output)
29
Where are the cell bodies of the seonsory afferents located?
Dorsal root ganglion
30
Where are the cell bodies of the motor efferents located?
Ventral horn
31
What would happen if you damage the dorsal root?
Somatosensory input would be affected bu motor output would be fine
32
What two nerves don't go into the brainstem?
1. Olfactory nerve
2. Optic Nerve
33
What is brain edema?
Brain bleeding`
34
How does a brain bleed affect pupillary response?
When your brain bleeds there is increase intercranial pressure which compresses the brain stem and cranial nerves that regulate the pupillary response. Now you pupil will no longer dilate when light is flashed into it
35
What are the three layers of the embryonic disk?
1. Ectoderm
2. Mesoderm
3. Endoderm
36
What occurs during week 3 and 4 of embryonic development?
The ectoderm folds up into a neural groove and then becomes the neural tube
37
Where do the cells of the CNS come from in development?
Ectoderm
38
Where do the cells that become the organs and muscles come from during development?
Mesoderm
39
Where does the digestive system come from during development?
Endoderm
40
What does the neural tube become?
THe CNS and part of the PNS
41
Neural crest cells become?
Part of the PNS
42
What is the dura, where does it come from and what does it become?
Cells from the mesoderm become the dura which is the covering/liniing of the CNS
43
What occurs during week 4 of embryonic development?
The neural tube forms vesicles with a cavity in the middle that later become parts of the brain (forebrain, midbrain and Hindbrain)
The neural tube also form a part with no vesicles that becomes the spinal cord
44
What is the cavitiy used for in the neural tube?
Becomes the ventricles of the brain and central canal of the spinal cord
45
What produces CSF?
The ventricles
46
What are the four ventricles?
1. Lateral ventricles
2. Third ventricle
3. Fourth ventricle
47
What are the largest types of ventricles?
Lateral ventricles
There is one in each hemisphere of the brain
48
Which ventricles produce the most CSF?
The lateral ventricles
49
Do all ventricles produce CSF?
Yes
50
What is the choroid plexus?
Lines the inside of all of the ventricls and is repsonsible for oozing out CSF(produces CSF) produces 500mL per day
51
How much CSF is in the brain?
150mL
52
What are the functions of the CSF?
1. Supports and cushions the CNS (the brain floats in CNS)
2. Provides nourishment to the brain (contains glucose)
3. Removes metabolic waste through absorption at the arachnoid villi
53
How is CSF removed from the brain?
Absorption by the arachnoid villi
54
Composition of the CSF?
-Sterile, colourless fluid that contains glucose
55
How does the CSF flow throughout the brain?
Passively flows throughout the brain and ventricles and requires no energy
56
What is the Foramen of Monro?
COnnects the two lateral ventricles to the third ventricle
57
What is the cerebral aqueduct?
Connects the third ventricle to the fourth ventricle
58
What is the role of the subarachnoid space?
THe CSF created by the chroid plexus passively moves around the subarachnoid space until it gets to the very top(midline). Where the arachnoid villi are located
59
Where does the subarachnoid space come from in development?
The dura
60
What is the role of the arachnoid villi?
Found at the midline of the brain, the acrachnoid villi take CSF out of the subarachnoid space and empty it into the venous blood supply
61
How hoes the CSF enter the subarachnoid space?
Via 3 foramens and 2 lateral and magendie
62
What happens if the CSF is not taken up by the arachnoid villi?
If the ventricle cannot empty CSF, yet it continues to produce it this will cause pressure on the brain
63
Communicating hyrocephalus vs noncommunicating?
Hydrocephalus - Water on the brain
Communication - blockage outside of the ventricles
Noncommunicating - blockage between ventricles
64
What are meninges?
Membranes that cover the CNS(brain and spinal cord)
65
What are the three meninges?
1.Dura
2. Arachnoid membrane
3. Pia matter
66
What helps produce the subarachnoid space?
1. Arachnoid membrane
2. Trabeculae( legs)
67
What is the pia matter?
Thin membrane that attaches to the brain below it
68
What is the dural venous sinus?
Dura open and creates a cavity at the midline of the head. Arachnoid villi line the dural sinus and take up CSF from the subarachnoid space and empty it into the dural sinus which goes to the venous blood supply
69
Where does CSF return to the blood?
At the dural sinus
70
Only substrate metabolized by the brain?
Glucose
71
Do neurons keep a back up supply of glycogen in the brain ?
No
72
Does the brain reuqire insulin to uptake glucose?
No
73
The brain needs a constant supply of...
Glucose and oxygen
74
What happens if there is a lack of blood supply to the brain?
Few seconds: Loss of conciousness
Few minutes: stroke which leads to neuronal death
75
Is glucose transported into neurons?
No, it diffuses in
76
Describe blood flow to brain?
Aorta diverges into the common carotid artery which then diverges into the external carotid (supplies blood to outside of the skull) and the internal carotid(supplies bloos to the base of the brain).
77
What is the basilar artery?
Where the two vertebral arteries come together
78
What is the circle of Willis?
Where the basilar artery and the two internal carotid arteries come together and form a loop and then they branch off to different parts of the brain
79
How is the cricle of willis a safety factor?
If an internal carotid artery or vertebral artery is blocked blood is still able to flow to the other side of the brain due to the loop
80
What is between the endothelial cells of the capillaries in the brain and what do they do?
There are tight junctions between endothelial cellsthat prevent anything from leaving/entering the blood from the ECF of the brain.
81
What can pass through the blood-brain barrier?
Lipid soluble substance
- things such as O2, CO2, H2O, alcohol, caffeine, nicotine, heroine
82
Can ions cross the blood brain barrier?
Barely
83
How does glucose cross the blood-brain barrier?
Active transport brings glucose into the ECF of the brain from the blood
84
What are astrocytes ?
Cells that maintain the blood-brain barrier(induce tight junctions)
-Non neuronal cells of the CNS(glial)
85
Role of astrocytes?
1. Induce tight junctions by putting their foot processes on capillaries
2. Provide structural support for the brain
3. Take up extra neurotransmitters/ions to keep everything regulated
4. Phagocyte debris
86
Sensation vs Perception?
Sensation: Awarness of sensory information(im aware something is hurting)
Perception:Understanding of a sensation's meaning (My finger hurts because I bumped it)
87
T/F: We percieve the energy of a seonsory stimulus?
False, we do not percieve the photons striking out retina
88
T/F: We perveice the neural activity that is produced by a sensory stimulation
True
89
What is the law of specific nerve energies and give an example?
Does not matter how you activate the receptor on an afferent, what your brain perceives is what it is designed to detect
ex. When you rub your eeyes in the dark you may see some light becaus eyou are putting pressure on the retina
90
What is the law of projection?
Regardless of where in the brain you stimulate a sensory pathway, the sensation is always felt at the sensory receptors location
Ex. Phantom limb pain, axons carry the somatosensory information regrow in the wrong spots and then are activated for the worng reasons
91
What is the labeled line code?
Every afferent that arrives in the CNS carrying sensory information is labeled both on the modality and location
92
What is modality?
Class of stimulus (ex. pain, auditory, visual)
93
T/F: THe brain knows the modality and location of every sensory afferent?
True
94
What is an adequate stimulus?
In order for the membrane receptor channels to open the stimulus must match what the membrane is designed to transduce. If it is not a match channels will not open
- Ex. Somatosensory receptors in the finger are designed to detect deforamtions of the skin
95
What happens to sensory receptors when they are activated?
1. Stimulus energy
2. Receptor Membrane is depolarized by opening/closing ion channels
3. Transduction
4. Ion channel activation
5. Afferent
96
How is a weak stimulus encoded by the afferent?
1. Lower magnitude of receptor potential
2. Frequency of action potentials decreases
3. Less neurostransmitter is released
97
How is a strong stimulus encoded by the afferent?
1. Bigger magnitude of receptor potential
2. Frequency of action potentials increases
3. Lots of neurotransmitter released
98
How is a subthreshold stimulus encoded by the afferent?
-Produces a receptor potential that is not strong enough to produce an action potential
- No neurostransmitter is released
99
What is adaptation?
Change in the frquency of action potentials, even though the stimulus is constant
100
What are non-adapting afferents?
Continuously discharges action potentials due to an ongoing stimulus
-Not coomon
-Encodes stimulus energy just as it is
101
What are slowly adapting afferents?
-Starts as a strong action potential than as time goes on the action potentials occur less frequently
-Moderate stimulus changes
102
What is a rapidly adapting stimulus?
-Fires rapidly when a stimulus is presented, then falls silent in the prescence of the stimulus
103
What is a receptive field?
Region in space that activates a sensory receptor or neuron
104
What happens when there is is a deformation in the middle of the RF vs the outskirts of the RF?
Middle of the RF will produce more action potentials
Outsides of the receptive field will produce less action potentials
This explains the graded response of the RF
105
What happens if an action potential occurs outside of the Receptive Field ?
No action potentials will be fired by that receptor
106
What is a population code how is it produced?
Receptive Fields overlap. When a stimulus is presented it will mainly activate one afferent but it will also activate other afferents around it slightly less(less action potentials) because it will be at the edge of its RF
107
How does the brain utilize the population code?
The brain knows where every receptive field is located. The brain uses the population code to determine which afferents are active and which receptive fields were activated in the middle vs edge to determine the precise location of the stimulus
108
Define acuity?
Ability to differentiate one stimulus from another
109
How do receptive fields relate to acuity?
Small RF = High Acuity
Large RF = Low acuity
110
What is lateral inhibition?
When afferents adjacent to eachother try to inhibit each other
111
How does lateral inhibition occur ?
The main receptive field afferent (B) has inhibitory interneurons that inhibit the 2nd order neurons of the afferents nearby (reducing their activity)
112
What is the goal of lateral inhibition?
"sharpen" the population code, makes it easier for the brain to distiguish where the stimulus is
113
How is lateral inhibition a bottom up mechanism?
Way of making sense of the stimuli starting with the receptors and working its way up to the brain(happens automatically)
114
Does lateral inhibition inhibit first order neurons?
No, only second order neurons are inhibited , the first order will still fire more action potentials when the stimulus is at the edge of their RF
115
How is sensory information shaped?
By both bottom-up(lateral inhibition) and top-down mechanisms(descending pathways)
116
What are the modalities of somatosensory information?
-Touch
-Pain
-Proprioception
-Thermal
117
Receptors classes for somatosensory information?
1. Chemoreceptors
2. Mechanoreceptors(touch)
3. Thermoreceptors(thermal)
4. Nociceptors(pain)
118
What are the two types of touch mechanoreceptors in the deep layers?
Pacinian corpuscle
Ruffini endings
119
Where are the pacinian corpuscle and ruffini endings found?
In the deep layers of the skin
120
Pacinian Corpuscle Vs Ruffini Endings
Pacinian Corpuscle: Rapidly Adapting. Detects vibrations
Ruffini endings: Slowly adapting afferents. Signal how the body is bending/stretching (tells you the shape of an object you are touching)
121
What is proprioception?
Sense of body awareness (the state of your body)
122
How are mechanoreceptors activated?
Stretching the cytoskeletal strands
123
Describe the transduction mechanism of somatosensory receptors?
1. Deformation of the skin results in deformation of the cell membrane of an afferent
2. Afferents have cytoskeletal strands that attach to ion channels, when the cell membrane deforms it causes sytoskeletal strands to pull on the ion channels and open them
3. Open ion channels causes a receptor potential. If it is big enough it will produce an action potential sent to the brain/CNS
124
What kind of ion channels are found in the afferents cell membrane?
Mechanically-gated(this is why they open due to cytoskeletal strands pulling)
125
What are the two types of mechanoreceptors of touch in the superficial layers?
1. Meissner's corpuscle
2. Merkel disk
126
What is the role of specialized end organs on mechanoreceptors?
Only allow selective mechanical information to activate the nerve terminal
127
Describe the Meissner's Corpuscle?
-Superficial layers
- Rapidly adapting
- Signal light stroking and fluttering
128
Describe the Merkel disk?
- Superficial layers
- Slowly Adapting
- Sensitive to pressure and texture
129
What are the two types of thermoreceptors?
1. Cold Afferents
2. Warm Afferents
130
Sense of temperature is mediated by....
Free nerve endings
Afferents that don't have specialized end organs wrapped around them
131
T/F : Free nerve endings of the thermoreceptors are located near the surface of the skin?
True
-This allows them to ge the most accurate reading of temperature
132
T/F: Free nerve endings have ion channels?
True, they open/close depending on temperature
133
Describe the cold afferents?
-Ion channels open between 0 and 35 degrees
-Also activated by menthol (Vick's)
134
Describe the warm afferents?
-Ion channels open between 30 and 50 degrees
-Also activated by capsaicin and ethanol
135
What are the pain receptors?
Nociceptors
136
Are pain receptors free nerve endings or do they have specialized ned organs?
They are free nerve endings with ion channels that open in response to intense mechanical deformation, excessive temperature or chemicals
137
What does it mean when pain afferents are highly modulated?
Either enhanced or surpressed
138
Where are nociceptors located?
Close to the surface of the skin
139
What are visceral pain receptors?
Receptors inside you (stomach hurts, internal inflammation)
140
Describe what happens when you poke your finger?
1. Nociceptors activate
2. Nociceptors prodcue action potentials
3. These action potential go to the spinal cord and release substance P
4. Substance P activates second order neurons that go to the brain
5. Brain then registers the the poke in the thumb hurt
141
What is enhancement in terms of nociceptors?
A process by which the nociceptors become more sensitive to stimuli after having been previously activated
142
Give an example of nociceptor enhancement?
After you poked your finger, the next morning when you pick up an object with that finjet you will experience pain because the nociceptor became more sensotive
143
How does enhancement of nociceptors work ?
When the afferents were first activated they not only sent axons to the spinal cord but they also sent them to the surrounding tissue of the site of injury.
They released substance P on mast cells which causes the release of histamine which increases sensitivity of the nociceptors. They also release substance P which causes the blood vessels to dilate and the skin at the site of injury to be swollen and red. Mechanical swelling also causes nociceptors to be more sensitive
144
What is hyperalgesia?
-Bottom up mechanism
-When a stimulus activates nociceptors that the stimulus normally would not.
-Occurs at previous sites of injury
Body is telling you to not use it till it is healed
145
Describe the touch and proprioception pathway
1. Activation of the receptor
2. Afferent of the receptor then goes from the finger into the spinal nerve and then into the dorsal root ganglion
3. Afferent then enters the spinal cord and goes up through the dorsal columns(white matter)
4. Afferent then crosses the midline in the medula and synapses onto second order neurons
5. They then synapse onto the thalamus which then goes to the somatosensory cortex
146
What does the dorsal column carry in terms of touch and proprioception?
Ipsilateral touch and proprioception
147
Ipsilateral vs Contralateral
Ipsilateral : same side
Contralateral: opposite side
148
What does the somatosensory coretx recieve?
Contralateral touch and proprioception
149
If a patient has no sense of touch on the left side of the body from chest down, where could there be a lesion.
Thoracic damage to the dorsal columns
150
Describe the temperature and pain pathway?
1. Afferent enters through the dorsal root
2. Afferent synapses onto 2nd order neuron in the grey matter of the spinal cord and crosses the midline in the spinal cord
3. Afferent axons then go up a white matter track in the anterolateral column
4. Then synapses onto the thalamus which goes to the somatosensory cortex
151
Anterolateral columns carry what?
Contralateral temperature and pain
152
How does a lesion at the anterolateral column affect the body?
Temperature and pain from the segment with the lesion and down will be lost on the contrlateral side
153
What would happen if you cut a dorsal root?
Loss of temperature, pain, touch and proprioception at the level of the cut on the ipsilateral side
154
What regions of the body have higher acuity ?
Lips, face, fingers
155
Why do certain regions of the body have higher acuity?
These regions of the body have more neurons in the somatosensory cortrx that represent these parts of the body
156
Where is the somatosensory cortex located?
Behind the central sulcus
157
What would a lesion to the somatosensory cortex do ?
Loss of temperature, touch , proprioception and pain to the contralateral side
158
When is label line code not true?
For referred pain
159
What is referred pain caused by ?
Nociceptive afferents from the surface of the skin share the same 2nd order neurons as the nociceptors that are visceral
160
What is referred pain ?
When the brain puts the location of the pain of the skin rather than the visceral organ
ex. Heart attack = pain in right arm
161
What are descending pathways?
Originate in the brainstem and come down the spinal cord
Inhibit the neural transmission of substance P at the 2nd order neurons that are recieving pain information
162
What is analgesia?
Top-down mechanism
-Under your control
The reduction in pain
163
Describe a situation where descending pathways occur?
If you get injured during a race but don't realize till after the race due to adrenaline
164
What are opiate receptors and how are they involved in the descending pathways?
Descending pathways of the brain release opiate neurostransmitters that bind to the opiate receptor and stop the release of substance P. Now you will feel no pain
165
T/F: Opiate receptors are sites for drugs such as morphine?
True, morphine is used to reduce pain
166
What is the stimulus energy for the visual system?
Light
167
What are the recepotrs for the visual system?
Photoreceptors
168
What controls the pupil?
Iris
169
What is the retinal pigment epithelium?
Lines behind the retina and helps with transduction
170
What is the Fovea Centralis?
-Point of highest visual acuity (smallest RF)
-Center of vision
-This is where you do all of your detailed looking and reading
-Photorecptors are only cones
171
What is the optic disk?
-Blind spot
- Where the optic nerve leaves
-No photoreceptors
172
What opens/closes ion channels in the eyes?
Photons
173
What is the retina?
-Lines back of eye
-Contains the photoreceptors where transduction occurs
-Contains neurons that start processing the visual information before it is sent out via the optic nerve
174
Role of the cornea and lens?
Focus light on the retina
175
T/F: refraction occurs at the cornea and lens?
True, photons light bends due to the cornea and lens
176
T/F: Cornea refracts light more than the lens?
True
177
What does it mean when something is in focus?
All of the different light rays are projected to a single point at the retina
178
Projection on the retina is upsidedown ?
Lnes inverts the image
179
What happens to the lens when an object is further away from you?
Lens becomes thinner to change refraction
180
What happens to the lens when an object is really close to you?
Lens becomes rounder so that there is more refraction of light
181
T/F: Lenses accomodate for changes in object location
True
182
What happens if an object is close to the eye but the lens does not become rounder?
Object will be out of focus
183
What is a myopic eye?
Nearsightedness
-When you can see objects up close just fine but at a distance there is too much refraction and the focus is in front of your retina
184
What is a hyperopic eye?
Farsightedness
-Can see things at a distance but objects thar are up close are focuse behind the retina
185
What is astigmatism?
The lens or cornea are not spherical
186
What is presbyopia?
When the lens gets stiff and is unable to accomodate for near vision as you get older
187
What is cataract?
Changes in the lens colour, it becomes opaque which blocks photons from the retina
188
What are the two types of photoreceptors?
1. Cones
2. Rods
189
Where are the photoreceptors found?
Lining the back of the retina
Right next to the retinal pigment epithelium since they undergo a biochemical reaction
190
How does light travel through the eye?
Photons travel through the cornea then the lens and then through the vitreous humor and then to the retina
191
What must photons go through before reaching the retina?
Must go through the neurons in the retina. The Bipolar, Horizontal and Amacrine neurons are transparent but help process the photons
192
What is convergence?
THe idea that the optic nerve has one million axons but there are 100 million photoreceptors. The ganglion cells (axons of the optic nerve) recieve information from many photoreceptors and put it together
193
Describe convergence in the fovea?
Since the fovea has higher acuity there are only 1-2 cones driving a ganglion cell
194
Describe convergence in the periphery(outside of the fovea)?
Since there is less acuity, there are lots of rods driving one single ganglion cell
195
Why is the fovea the clearest image?
All of the cells that distort the image normally are pushed out of the way at the fovea, this creates the little notch and creates the clearest image because photons do not need to pass by all of those cells
196
What are opsin molecules?
The proteins that capture photons
197
T/F: Photons cause ion channels to close?
True
198
What is phototransduction?
Process by which light is converted into electrical energy so that it can be understood by the nervous system
199
Explain phototransduction?
1. Photon is absorbed by chromophore which causes a conformational change and the chromophore to dettach
2. This then triggers a G-protein cascade which converts cGMP to GMP
3. As cGMP concentrations fall the sodium ion channels start closing
4. This results in the hyperpolarization of the photoreceptor and stops the release of neurotransmitters
200
When to photoreceptors release neurtransmitters?
In the dark when the cGMP activates the sodium ion channels and the membrane is depolarized
201
Where are opsin molecules foundd?
In both rods and cones (photoreceptors)
202
Rod properties?
1. High sensitivity to photons (used as night vision)
2. Have more rhodopsin to capture as much light as possible at night
3. High amplification (one photon may close many Na+ channels)
4. Slow response time
5. More sensitive to scattered light
203
Cone properties?
1. Low sensitivity to photons(used as day visions)
2. Less opsin because photons are numerous during the day
3. Lower amplification
4. Faster response time
5. Most sensitive to direct axial rays
204
Describe the rod system?
-Low acuity: not present in the central fovea, highly convergent
-Achromatic: one type of opsin molecule(don't see colour at night)
205
Describe the cone system?
-High acuity: concentrated in the central fovea. less convergent
-Chromatic: three types of opsin molecules (colour perception)
206
Describe Dark Adaptation
1. Start with bright lights where the rods are inactivated and the cones are activated
2. IF you turn the light off you will have temporary blindness until the rods "reactivate"(opsin reattaches to chromophores) and take over
207
Why are rod inactive in bright lights?
Due to all of the photons which have broken down the opsin molecules in the rods (no more opsin attached to chromophore)
208
Why are cones inactive in the dark?
Not enough photons present
209
Describe Light Adaptation
1. Start in the dark where rods are active and cones are inactive
2. Turn on the lights this results in temporary blindness until the rods "inactivate" and the cones take over
The rods are initially saturated (all activated) when the lights turn on which is why it is incredibly bright.
210
Why are the rods near the retinal pigment epithelium?
When light breaks the chromophore from the opsin in rods, they have to go into the retinal epithelium is that they can be put back together
211
What determines the intensity of light ?
Depends on what is next to the image(contrast)
212
What is the role of the ganglion cells in contrast?
Compare the middle of the Receptive field to the surrounding and signal the relative difference of light (contrast) across their receptive fields
213
Patterns retinal ganglion cells like best with excitatory centre?
1. Bright center dark surround (fires a lot of action potentials)
2. Dark center bright surround(stops firing action potentials)
3. Uniforma light(center and surround cancel out, doesnt do anything when stimulus comes on)
214
Patterns retinal ganglion cells like best with inhibitory centers?
1. Bright center dark surround(stop firing action potentials)
2. Dark center bright surround(fires a lot of action potentials)
3. Uniform(center and surround cancel out, doesnt do anything when stimulus comes on)
215
Where does colour perception come from?
Cones
216
What determines the chromatic sensitivity of the photoreceptor?
The opsin molecule
217
T/F: Retinal ganglion cells don't only compare brightness between center and surrround but they also compare colour
True
218
Where is colour transmitted?
In the fovea because that is where the cones are
219
What are the two types of colour comparisons?
1. Red-Green
2. Blue-Yellow
220
Why is colourblindness common in males?
Opsin molecules are found on the X chromosome, since females have two X's they are less likely to be colour blind
221
What is colourblindness?
Missing an opsin molecule (only have two/one cones)
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What is the optic chiasm?
Where both optic nerves come together (fibers that cross come from the nasal side of the retina)
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What is the optic tract carrying?
Visual information from the contralateral visual fields
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What is optic nerve carrying?
Information from one eye but with both visual fields
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What does the left and right visual cortex recieve?
Left visual cortex recieves info about the right visual field
Left visual cortex recieves info about left visual field
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What is the primary visual cortex?
-Region of small RFs
-These RFs are sensitive to edges, the edges get put together to form a more complex strcuture
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Two pathways after the primary visual cortex ?
1. Parietal visual stream
2. Temporal visual stream
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What is the parietal visual stream?
-The "where" pathway
-RFs are larger
-Brain uses this pathway to determine where things are located and whether or not they are moving
-Get mixed up with touch
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What is the temporal visual stream?
-The "what" pathway
-RFs are larger (the entire image)
-Respond to complex features such as faces, hands and landmarks
