Neuro week 14-15 (1-4) Flashcards
1
Q
Role of Vision
What is the purpose of photoreceptors of the retina of the eye
A
To convert photonic energy within the electromagnetic spectrum with wavelengths between 400 to 700 nm to electrical signals.
2
Q
The range of the electromagnetic spectrum that is “visible light” represents
A
< 1.5% of the entire spectrum.
3
Q
Electrical signals are then sent to the brain which generates .
A
A complex 3 dimensional world from a 2 dimensional input on the retina
4
Q
In addition to vision being an important form of sensation it is also one of three critical systems for
A
balance
5
Q
How many major classes of cells does the Retina have?
A
7 in 10 histologically distinct layers
6
Q
What is found in the deepest cellular layer of retina?
A
Photoreceptors,
Rods and cones,
7
Q
Rods are scotopic which means that they are sensitive to
A
Low light levels across the entire specturm so do not provide color vision
8
Q
Cones are photopic
A
They work at higher light levels
9
Q
T / F- Cones come in 3 forms with each sensitive to different part of the spectrum and provide color vision
Each eye has 80-110 million rods & 4-5 million cones
A
True
10
Q
Rods & Cones Both have
A
Photosensitive outer segment
11
Q
Photosensitive pigments, Inner cytoplasmic segement are rich in
A
Mitochondria and has an innermost Nuclear region
12
Q
T / F- There is Specialized presynaptic endings with invaginations which interfold with bipolar & horizontal cells and releases transmitter molecules onto these cells
A
True
13
Q
Are Rods found in the fovea/macula lutea retina?
A
No
14
Q
Where are rods found in highest concentrations?
A
Just lateral to fovea.
15
Q
T / F- Although there is a decline in density as you move to the periphery of the retina, there is still maintained a relatively high concentration of rods in the peripheral
A
True
16
Q
Where are the highest density of cones found?
A
Fovea/macula lutea - cones are the only photoreceptors in this area,
17
Q
T/F- Cones decline in density very rapidly as you move to the periphery and so are found in very low densities elsewhere
A
True
18
Q
Which area has the highest visual acuity and why?
A
Fovea/macula lutea - because it has the highest density of photoreceptors
19
Q
Due to the lack of rods in the fovea and high densities in the retinal periphery, the periphery of the field of vision has a
A
higher low light sensitivity
20
Q
Cell types vary by
A
region of the retina.
21
Q
T /F- In the Fovea there are direct cone to bipolar to ganglion cells, but in the Peripheral retina additional cells to allow interaction between photoreceptor & ganglion cells.
A
True
22
Q
Bipolar cells are analogous to
A
Primary afferent neuron,
23
Q
Bipolar cells receive input from photoreceptors and transmit the signal to the
A
ganglion cells.
24
Q
Bipolar cells are specific to the types of photoreceptors and come in
A
ON & OFF varieties
25
Laterally interconnecting interneurons which integrate and regulate the input from multiple photoreceptor cells. are called
Horizontal cells
26
T / F - Horizontal cells can produce an integrated “lateral inhibition” on photoreceptor cells to Enhance contrast of the image
True
27
Laterally interconnecting interneurons which integrate and regulate the input from multiple bipolar cells onto the ganglion cells.
Amacrine cells
28
T/F- Amacrine cells produce an integrated “lateral inhibition” on both bipolar & ganglion cells
True
29
Role of Amacrine cells
Enhancing image contrast
30
Which cells are analogous to the 2° neurons of relay nuclei of other sensory systems
Ganglion cells
31
Ganglion cells are the
Most superficial layer of neurons
32
axons of ganglion cells exit retina as
optic nerve.
33
T/F- There are >100 million retinal receptor cells but only about 1 million ganglion cells
True
34
Convergence of photoreceptor cells onto Ganglion cells is greatest with
Peripheral rods
35
Convergence of photoreceptor cells onto Ganglion cells is least with.
Foveal cones
36
There are two types of ganglion cells:
M (magnocellular) type & P (parvocellular) type.
37
P (parvocellular) type are associated with
Cones
38
type of receptor field of Paevocellular type?
Small receptive fields, that are very specific to detail and sensitive to color & visual acuity (form)
39
M (magnocellular) type are those assoicated with
Rods
40
What type of receptive field does M (magnocellular) type have?
Large receptive fields (due to lots of convergence onto them from the rods).
41
T / F- M (magnocellular) type are sensitive to color and are very sensitive to low illumination.
False- they are not
42
M (magnocellular) type are most sensitive to
gross patterns rather than detail and the location & movement of images across the retina
43
Photoreceptor Membranes are
depolarized so release glutamate in dark.
44
What happens when Light reacts with membrane bound opsins?
The membrane hyperpolarizes the membrane so glutamate release is decreased
45
T / F- Glutamate both depolarizes & hyperpolarizes bipolar cells depending upon type of glutamate receptor
True
46
Depolarization & hyperpolarization of bipolar cells produces
The two types of bipolar cells: OFF & ON bipolar cells.
47
OFF cells
depolarized by glutamate so active in dark.
48
ON cells
Are hyperpolarized inactive in dark and become activated by disinhibition of light lowering glutamate release
49
T / F- Bipolar & ganglion cells respond in an annular way to light on the retina with Inner “central” region responding one way and peripheral “surround” responding another due to action of horizontal & amacrine cells
True
50
Visual field
The portion of space that can be viewed from the retina when the eye is fixated straight ahead
51
Retinal field
The portion of retina that alters its firing rate in response
52
Lens reverses and inverts image so reversed & inverted relationship between the visual and retinal fields
true
53
1° afferent
Bipolar cells
54
2° neuron
Ganglion cells have their Axons form optic nerve
55
Axons from nasal retinal field decussate in optic chiasm but temporal retinal fields stay ipsilateral So this allows the right visual field goes to left brain & left visual field goes to right brain via the optic tract
T
56
Like other sensory pathways the 3° neurons are in the
Thalamus - Lateral geniculate nucleus
57
LGN neurons are
Retinotopic pattern with half of LGN devoted to fovea.
58
LGN neurons Respond to light similar to ganglion cells with “on” or “off” center and opposing surround. However only 10-20% synapses onto LGN neurons comes from optic tract
T
59
Most input onto these LGN neurons is from
Visual cortex & brainstem reticular formation
60
Cortical inputs provide feedback regulation of flow of information to cortex and is related to
visual attentiveness within the visual domain.
61
Brainstem input is part of the more global switch of attentiveness between various sensory inputs.
T
62
Neurons of the LGN project as
The optic radiation or geniculocalcarine tract to the occipital lobe -Primary visual cortex - striate cortex.
63
Dorsal axons (from the inferior visual field) project almost directly to
the occipital lobe
64
Ventral axons (from the superior visual field) Geniculocalcarine tract project .
Anteriorly and downward as Meyer's loop
65
Axons from the Superior retinal (inferior visual) field end in the superior aspect of calcarine sulcus
T
66
Neurons from the Inferior retinal (superior visual) field end in the
cortex inferior to the calcarine sulcus
67
There are a small contingent of optic tract axons that form a Direct retinohypothalamic projection that terminates in the suprachiasmatic nucleus of the hypothalamus. These projections have a role in
entraining circadian rhythms in day–night cycle
68
Some optic tract axons bypass the LGN and project to
midbrain.
69
Optic tract axons going to the superior colliculus are involved in
visual reflexes.
70
Projections to the Accessory optic & pretectal area function in
visual light reflexes (constriction of pupil with light)
71
Another important projection is the Pulvinar. It is the
The Largest and most posteriorly positioned thalamic nucleus.
72
Pulvinar receives input from the PVS
superior colliculus, visual cortex & pretectum.
73
The Pulvinar sends information to
visual association areas in the posterior parietal lobe to supplement dorsal stream pathway
74
Bipolar & Ganglion cells can have an
“On” center - “Off” surround
75
“On” center - “Off” surround
When light hits on the center of annulus on surface of retina – the bipolar cell or ganglion cell fires, but is then quiet when light off. When Light hits on surround of annulus the bipolar or ganglion cell is inactive until light turned off on that outer region, when the cell then becomes active
76
“On” center - “Off” surround bipolar or ganglion cells,
When Light shines on both center and surround, there is some activity in the cell but less activity than when light is only on the center
77
“Off” center - “On” surround Bipolar & Ganglion cells act in the exact opposite manner
Becomes inactive when Light shown on center of annulus on surface of retina and becomes active again when light goes off. Light shining on surround of annulus produces cell activity until light turned off then the cell becomes quiet again.
78
“Off” center - “On” surround Bipolar & Ganglion cells
When Light shines on both center and surround, there is some but less activity than when light is only on the outer annulus
79
This pattern of cell activity Enhances contrast with sharp delineations between active and not active at borders of light and dark regions. This particularly true in peripheral vision so that even if there is degeneration of cones of the fovea as is seen in macular degeneration, the person can still see contrasts but not detail using the peripheral retina.
True
80
The optic disk is
The Circular, elevated region where ganglion cell axons gather to leave the eye as the optic nerve.
81
Optic disc
Devoid of rods and cones and represents the blind spot in the visual field
82
The Neural retina receives 2 sources of blood supply
Outer retinal layers receives blood via choroidal capillaries
Inner retinal layers receives blood via central retinal artery, which is a Branch of the opthalmic artery from the internal carotid.
83
Blockage of central retinal artery can cause
Sudden blindness
84
Age-related macular degeneration (AMD)
Called age related because it increases in prevalence in sixth decade of life and is the Leading cause of blindness in the elderly
85
AMD involve degeneration of
Macular photoreceptor cells (cones) and produces Loss of central vision, color vision and visual acuity. There is Peripheral vision & ability to determine contrasts.
86
Age-related macular degeneration (AMD) comes in two forms
Dry & Wet
87
Dry AMD
Most common and is Due to atrophy of retinal pigmented epithelium
88
Wet AMD
Due to detachment of retinal pigmented epithelium due to hypervascularization
89
T / F- Some evidence that exercise can reduce retinal cell death (elevated retinal BDNF)
True
90
Optic nerve is formed by axons from the .
Ganglion cells of the ipsilateral eye and is part of the CNS because ganglion cells are the equivalent of the CNS relay nuclei neurons of other sensory systems
91
Axons of the optic nerve are myelinated by
oligodendrocytes
92
Optic nerve is ensheathed by .
Pia, arachnoid & dura, and thus has subarachnoid space with CSF
93
Papilledema
Increased intracranial pressure which causes bulging of the optic disc - occurs since the optic nerve exits the retina at the optic disc,
94
Vision optics is based upon
Refraction of Light using Convex lens.
95
T / F - Convex lenses will bend light at different angles along its curved surface & will focus light coming from a distant image at fixed point some distance from the convex lens
True
96
The point at which light is focused by the convex lens is called
Focal length and is dependent upon the shape of the lens
97
T / F -The greater the lens curvature, the shorter the focal length
True
98
T / F- Normally focal length matches the distance from lens of eye and retina so image is focused on the retina
True
99
Myopia or Nearsightedness
Focal length falls short of retina due to either an overly curved lens or elongated eyeball.
100
Myopia is corrected with the use of
Concave lens to lengthen the focal distance
101
Hyperopia or Farsightedness .
Focal length falls behind the retina and is due to either insufficiently curved lens or shortened eyeball
102
Hyperopia is Corrected with the use of
Convex lens to shorten the focal distance
103
In accommodation for near and far vision the lens is
pliable and changes shape
104
The lens is held by suspensory ligaments whose tightness is controlled by
Ciliary muscles.
105
For vision > 20 ft
Ciliary muscles relaxes and the lens is held tight by the suspensory ligaments in a thinner, less curved shape and is adapted for far vision
106
Greater curvature to adapt to close vision produced by ciliary muscles contracting and acting to take tension off the suspensory ligaments so the lens will assume its more curved shape.
T
107
Also as part of Accommodation, there is a Change in pupillary diameter. The pupils are constricted for close vision. Constricted pupils produce a greater depth of field so objects at different distances will still stay in focus. Depth of field need for reaching and manipulation of close objects
T
108
Accommodation involves
Parasympathetics to eye mediated by the Oculomotor nerve (CN III) from Edinger-Westphal nucleus via ciliary ganglion.
109
Accommodation produces both pupil constriction by activating the
pupillary sphincter muscles & ciliary muscles to contract
110
Lens hardens with age and produces Presbyopia
An age related loss of power accommodation even though ciliary muscles can still contract.
111
Presbyopia results in the inability to
Focus on near objects and is corrected for by the use of convex corrective lenses
