OS III Exam I Flashcards
(86 cards)
0
Q
Secondary neuralization
A
Mesenchyme condenses to form rod which undergoes epithelial transition to become the neural tube.
1
Q
Primary neuralization
A
Columnarization of existing epithelial cells to form a neural tube, then rolling or folding of tube
2
Q
When does the neural tube close in five seperate waves?
A
Day 19-20
3
Q
Where does the final closure of the neural tube occur?
A
Caudal region, sacral part of the spinal cord
4
Q
What is anencephaly?
A
Lack of skull and cerebrum formation with only brain stem intact, due to failure of wave 2 closures
5
Q
What is spina bifida?
A
Incomplete closure of caudal neuropore, located at junction of waves 1 and 5.
6
Q
Diencephalon
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Thalamus, hypothalamus, and epithalamus
7
Q
Cephalic flexure
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Ensure the optical axes are at right angles to vertebral column
8
Q
Pontine flexure
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Derives cerebellum
9
Q
White matter is divided into which three funiculi?
A
Dorsal, ventral, lateral
10
Q
Dorsal funiculus
A
Dorsal columns carry tactile info to brain stem and thalamus
12
Q
What is the vitreous body?
A
Clear gel-like fluid contains hyaluronic acid and type II collagen fibrils. 99% water.
13
Q
What is the hyaloid artery and what did it do?
A
Vessel that nourished the lens and vitreous body while they were developing.
14
Q
What are floaters?
A
Black or gray specks, strings that drift when you move your eyes. Collagen fibers clump together.
15
Q
Compare the sclera to the cornea.
A
Sclera is dense, white CT that muscles attach to. Cornea is transparent and avascular.
16
Q
How does the cornea get its nutrients?
A
Diffusion from the aqueous humor
17
Q
How much do the cornea and the lens each contribute to light refraction?
A
The cornea contributes 2/3 of the refractory power. The lens 1/3.
18
Q
What is the cellular and CT makeup of the lens and how is it attached within the orbit? </p>
A
Intrinsic elastic fibers encased in a capsul of collagen and glycoprotein. Held in place by zonule fibers from ciliary body.
19
Q
What happens to the lens with age?
A
Decreased elasticity, presbyopia
20
Q
How does the lens accommodate to near and far vision?
A
Increase or decrease convexity using the ciliary muscle.
21
Q
What happens to the lens in near vision?
A
Thick, increased convexity
22
Q
What happens to the lens in far vision?
A
Thin, less convexity
23
Q
What are cataracts?
A
Opaqueness of the lens often caused by oxidative damage.
24
Q
Describe aqueous humor and its circulation.
A
Aqueous humor is secreted from the ciliary processes then move into Schlemm’s canal (scleral venous sinus). Flows between iris and lens.
25
How does it compare to the vitreous body?
Vitreous body is in the main cavity of the eye ball, whereas the aqueous humor is between the lens and the cornea.
26
What is glaucoma?
Build up of fluid pressure due to inadequate drainage into Schlemms' canal. Adherence of iris to lens can block flow.
27
Describe the iris in terms of CT, blood vessels, smooth muscles, innervation and pigments.
Stroma has CT and radiating and circular patterns of blood vessels. Dilator and sphincter pupillae.
28
What is the pigment epithelium?
Continuous on the posterior surface of iris; completely absorb all light restricting incoming light to within pupil
29
What pattern of melanin accounts for blue eyes?
Melanin is modtly on the deep surface of the iris.
30
What pattern of melanin accounts for brown or green eyes?
Melanin evenly distributed through the iris.
31
How does it affect entry of light into the orbit?
Sphincter pupillae (parasympathetic) and dilator pupillae (sympathetic)
32
Account for the different colors of the eye.
Different distributiong of melanin in the iris.
33
Describe the circuit and action of the consensual pupillary reflex.
Light activates melanopsin ganglioan cells which feedback to the Pretectal n. to the E.W. nucleus to the ciliary gangiion, to pupil.
34
What is the Edinger-Westphal nucleus?
Nuclei of the oculomotor nerve in midbrain. Parasympathetic.
35
What is the ciliary ganglion?
Post ganglionic neurons that activate the sphincter pupillae and ciliary muscle to contract lens.
36
What is the tarsal muscle and how does it function?
SM deep to levator palpebrae superioris. Sympathetically innervated to raise eyelid in emotional states.
37
Describe the embryonic development of the eye: retina
An optic vesicle forms from the neural tube which become the neural layer (retina)
38
Describe the embryonic development of the eye: meninges
Extension of brain meninges: sclera and choroid. Optic nerve is surrounded by dura, arachnoid, pia and a subarachnoid space.
39
Sympathetic control of the iris and upper eyelid is regulated by:
Local reflexes, descending influences from limbic and hypothalamus during emotional states.
40
How does sympathetic activity increase light entry into the eye?
Preganglionic neurons in T1 and T2 invervate superior cervical ganglion cells. Postganglionic SCG neurons activate dilator pupillae and the tarsal muscle.
41
Describe the embryonic development of the eye: lens
Comes from ectoderm.
42
Describe the blood supplies associated with the retina: choroid and central artery of the retina.
Central artery is a branch of the internal carotid surround macular region and radiates out. Choroid is the outer vascular layer that feeds the retina.
43
Describe the fovea.
Central point of retina with only cones, imparing high levels of visual acuity.
44
Describe the macula.
Yellow area surrounding fovea. Rich in lutein and zeaxanthins, caratenoids derived from the diet.
45
Describe the optic disc.
Containes axons of ganglion cells, but no receptor cells.
46
What is the blind spot?
The optic disc, where there are no receptor cells.
47
Describe the layers of the retina and what the different cells do.
From outer to inner: Retinal pigmented epithelium, photoreceptors to absorb visible light, neural cells to integrate light information, ganglion cells to project visual information to thalamus.
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What are the differences between rods and cones?
Rods have rhodopsin and low acuity, high sensitivity "night vision." Cones have three types of pigment and are concentrated iin the fovea.
49
How does light activate rods and cones?
Pigments (iodopsin in cones, rhodopsin in rods) respond to different wavelengths within the visible light spectrum. Hyperpolarization of the cell through a G cell mechanism closing Ca and Na channels, eventually causing the cel decrease the release of glutamate.
50
Describe the fovea in terms of receptor cells and retinal organization.
The fovea contains the highest density of cones. The cones are more exposed to light due to the outward dispersal of ganglion and other cells. Acuity and color are key here. Avascular! Capillaries encircle.
51
How does this differ from the peripheral retina?
Peripheral retina is dominated by rods which do not code for color.
52
Describe the functions of the retinal pigmented epithelium in regards to retinal support.
1) Provides visual acuity by absorbing light which limits reflection 2) Acts as and antioxidant by absorbing blue light 3) Maintain photoreceptor excitability 4) Transports nutrients such as glucose and retinol 5) Phagocytosis cell debris.
53
What kinds of retinal detachment are there?
Wet and dry. Wet involves leaking blood vessels causing detachment (visual loss can be sudden), whereas dry involves waste product build up (visual loss can be gradual)
54
Between which layers does retinal detachment occur?
Retinal pigmented epithelium and the neural retina.
55
Describe the optic nerve/tract in terms of neurons, glia, meninges and CSF.
Ganglion cells converge to form the optic tract; it is covered by a dura, arachnoid (with subarachnoid space), and pia mater. Oligodendrocytes myelinate the axons. Astrocytes surround cell bodies and dendricites (contact blood vessels)
56
What is papilledema?
Increased CSF pressure that limits venous return from retina.
57
Describe the neural sequence from retina to primary visual cortex.
Cones/rods -> bipolar cells -> lateral cells -> LGN -> simple cells ->complex cells -> association cortices (ventral and dorsal)
58
What is partial decussation?
The image is split between the sides of the brain, but does not complete cross. What you see with the right side of your eye (left visual field) goes to the right visual cortex. Visa versa.
59
What is the difference between homonymous and heteronymous hemianopsia?
Heteronymous is caused by a lesion at the optic chiasm, whereas homonymous is caused by a lesion of the optic tract between chiasm and visual cortex.
60
Describe the differences between ON and OFF retinal cells.
Light inhibits glutamate release from rods/cones; darkness enhances it. ON bipolar cells are activated by decrease in glutamate. OFF bipolar cells are activated by increase of glutamate. Active response to darkness. (Black is different than absence of light)
61
What are center-surround receptive fields in the retina?
Areas of cones that have a concentric circle around either OFF or ON cells. ON-center respond like stars in a dark sky. OFF-center respond like a fly in a bright sky.
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How do center-surround receptive field affect perception of visual boundaries?
They enhance the contrast and respond best when the receptive fields subtend light-dark edges.
63
What is the difference between the parvocellular and magnocellular pathways from retina to LGN and visual cortex?
Parvocellular pathway transmits color and shape information. Magnocelluar transmet movement information. They are parallel pathways that pass through the LGN to the primary visual cortex.
64
What type of cell transmits parvocellular information?
Midget cells (90% of axons in optic nerve). 1 or a few photoreceptors. High acuity with smaller center-surround receptive fields.
65
What type of cell transmits magnocellular information?
Parasol cells (5% of axons in optic nerve). Larger group of photoreceptors. Low acuity with large center surround receptive fields.
66
What is the lateral geniculate nucleus?
Visual thalamus, six-layered structure that receives input from each eye.
67
How do parvocellular and magnocellular pathways relate to ventral and dorsal streams cortical and processing of visual information?
Parvocellular relates the the ventral stream or "what" stream. Magnocellular relates to the dorsal or "where" stream.
68
Give a brief description of simple cells in the primary cortex.
Combine input from several geniculate cells that individually respond to continuous points along the bar of light. Respond to orientation, direction of movement and exact location within the receptive field.
69
Give a brief description of complex cells in the primary cortex.
Complex cells combine the information of several simple cells to detect position and orientation of the structure.
70
How do simple and complex cells differ from ganglion and lateral geniculate cells?
They deconstruct the image into edges. They combine the input, getting more and more information.
71
What characterizes visual cortical columns?
Orientation, color, shape/size, direction of movement, R or L eye.
72
What impact does cortical feedback have on incoming visual input?
Regulates how much information is coming to it, allows focus to particular aspects of the environment.
73
What impact does neuromodulation by the reticular formation have on incoming visual information?
This affects arousal or wakefulness. Stimulates LGN in the thalamus and cortex via forebrain (Ach and NO). Also occurs with increased emotions (flash of light).
74
What are the visual association cortices?
They integrate the information from the visual system with touch, proprioception, audition, etc.
75
How do the inferotemporal and fusiform cortices differ from the other visual association cortices?
These are connected to the limbic system and are impacted by the hippocampus and amygdala.
76
Describe visual neglect and its impact on perception of oneÕs visual field.
Loss of function in right visual association cortices. There is nothing there.
77
What does Wernickes area do?
Speech comprehension
78
Describe the visual pathways mediated by the superior colliculus (SC).
From the LGN to Superior Colliculi. Koniocellular ganglion cells. Non-conscious visual responses and behaviors.
79
What role does the SC have in eye movements?
It helps you orient yourself to the visual field including saccadic eye movement and head turning.
80
What are saccadic eye movements and how do they impact vision?
Quick, simultaneous movements of both eyes in same direction initiated cortically by the cortical eye fields or by superior colliculis.
81
Reflexive vs. scanning saccade
Exogenously triggered to orient vision vs. endogenously for exploring environment or reading.
82
What is blindsight and how does it relate to the SC?
Selective lack of vision conciousness, your are relying solely on your connection of the LGN to the SC. You still respond to image even though you can not connect to the primary visual cortex. SC projects to pulvinar nucleus then to posterior parietal cortex (dorsal stream) and amygdala.
83
What does the suprachiasmatic nucleus do?
Responds to light and dark cycles from the intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) which contain melanopsin. SCN projects axons to paraventricular hypothalamic nuclei (PVN) which then affect sympathetic and parasympathetic pathways as well as hypothalamic-pituitary release of hormones. Also regulates the pineal release of melatonin.
84
What are circadian rhythms?
Sleep wake, temperature, hormone cycles throughout the day, determined by light.
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How is melatonin released by the SCN?
Melatonin is released by the pineal gland which is stimulated by the SCN reponse to a decrease in light.
86
What impacts do melatonin have on the systems covered in class?
Sleep-wake cylce, temperature, cortisol release.
