Ocular Physiology Flashcards
1
Q
What is the most common type of blinking?
A
Spontaneous
2
Q
Average blinks per min?
A
12-15
3
Q
Which part of the eyes allows for spontaneous blinking?
A
palpebral
4
Q
What is the main function for spontaneous blinking?
A
maintain optics and comfort of the eye by stabilizing the tear film
5
Q
Which CN are responsible for sensory blinking?
A
2 (dazzle and menace)
5 (reflex)
8 (loud noises)
6
Q
Which CN are responsible for motor blinking?
A
CN 7
7
Q
Which reflex blink does NOT involve the cortex?
A
2 (dazzle)
8
Q
The efferent loop of reflex blinking in response to auditory, touch/irritation, and menacing stimuli begins where?
A
frontal lobe
only dazzle reflex blinking does NOT involve the cortex
9
Q
Which portion of the eyelid is responsible for spontaneous and reflex blinking?
A
palpebral portion
10
Q
Winking requires contraction of what?
A
orbital and palpebral portion of the orbicularis oculi
11
Q
Benign essential blepharospasm is caused by spasms of which muscles?
A
orbicularis oculi, procerus, corrugator
12
Q
Tight or forced eyelid closure is a contraction of which part of the eye?
A
orbicularis oculi
13
Q
Bells Phenomenon
A
normal defense reflex that occurs after forced eyelid closure and is characterized by up and outward rotation of the globe
14
Q
what type of gland is the MG and zeiss?
A
holocrine
15
Q
Krause and wolfring are what type of glands?
A
accessory lacrimal glands that contributes to the aqueous layer of the tear film
16
Q
Which muscle surrounds the canaliculi for drainage?
A
muscle of horner contracts causing the canaliculi to shorten as they move medially to the lacrimal sac
remember that the muscle of horner’s is part of the palpebral ortion of the orbicularis oculi
17
Q
What helps w/ tear drainage?
A
temporal to medial eyelid closure during blink, contraction of muscles of horner, and negative pressure of the lacrimal sac (stretch of lacrimal sac away from the nose)
18
Q
How many eyelashes do we have on the upper lid and lower lid?
A
150 on UL and 75 on LL
19
Q
The palpebral portion of the eyelid is further divided into which 2 muscles?
A
horners and riolan
20
Q
Why is the tear film important?
A
- Optical (largest change in refractive index occurs btw air/tear film interface)
- Nutritional (primary source of O2)
- Mechanical (remove debris and metabolic waste)
- Antibacterial (tear film contains lysozyme, lactoferrin, and IgA, and other proteins of the immune system)
- Corneal transparency (the tear film has a specific osmolarity (308) and corneal epithelial cells helping to prevent corneal edema)
21
Q
What is the osmolarity of tears?
A
308, anything higher = dry eye
22
Q
What is the tear film thickness?
A
3um
23
Q
What is the anterior lipid composed of?
A
free fatty acid, cholesterol, waxy esters
24
Q
What are the main functions of the aqueous layer?
A
- protection (via antibacterial proteins)
- provides glucose to corneal epithelium
- adds thickness to the tear film
25
What does the aqueous layer contain?
1. Water (main component)
2. Electrolytes Na, K, Cl-
3. Antimicrobial: IgA, lactoferrin (chelates Fe2+), lysozyme (chelates peptidoglycans), betalysin (destroys cytoplasmic membrane), interferin
4. Lipocalins (enhance spreadability and acts like a carrier for all-trans retinol, blocks FE2+ from binding on bacteria)
5. Vit A (imp for goblet cells)
6. Enzyme cofactors: Fe2+ Mg2+, Cu2+, Ca2+ (helps maintain membrane permeability of corneal epithelial cells)
7. HCO3 (buffer for tears)
8. Solutes: glucose, urea, lactate, citrate, ascorbate, AA
9. Additional proteins: albimumin, GF, interleukins, VEGF
26
Is there more K+ blood in the tears or blood
tears
27
the main lacrimal gland is innervated by which CN?
7
28
What increases under closed eye conditions
albumin and IgA
29
What produces the aqueous layer?
main lacrimal gland, krause, and wolfring
30
Which glands are responsible for reflex and emotional tearing?
lacrimal
31
Which glands are responsible for maintenance tearing?
acessory glands
32
Which glands are responsible for basal tearing?
main and accessory lacrimal gland
33
Which CN causes lacrimation
V1
CN7
CN 2
34
What are the main functions of the mucin layer?
spread tears across corneal surface
removes debris, bacteria and sloughed epithelial cells
able to mix lipid and water
35
What produces mucin
goblet cells
36
Where are goblet cells predominantly found?
inferonasal fornix and bulbar conjunctiva
37
What do goblet cells require?
Vit A which is found in the aqueous layer of the tears as all-trans retinol
38
Deficiency in Vit A can cause what?
Bitot spot = keratinization of the cornea and conjunctiva, which can cause night blindness
usually found in underdeveloped countrys
39
Mucous fishing syndrome
occur as a result of pts fishing for and removing excess mucous in the conjunctiva
damage to the conjunctival epithelium can increase mucous production
40
What does the mucin layer interact with?
glycocalyx of the corneal epithelium, allowing tear film to be evenly spread across the corneal and conjunctival epithelium
41
What does TBUT test for?
evaporation of the aqueous layer due to insufficient lipid layer
less than 10 sec is abnormal
42
Elimination of tears
25% evaporation
75% drains through the nasolacrimal system or via absorption into the conjunctival or nasolacrimal vasculature
43
What is the total tear volume?
7-9uL
44
max amount of fluid teh eye can hold within the tear film
20-30uL
45
What is the normal tear production
1uL/min
46
An average eye drop contains how many uL?
50uL
47
What is the osmolarity of the eye?
308 mOsm/L and isotonic
48
What are the main contributors to tear osmolarity?
Na+, cl-, ca2+, K+
49
What is calcium important for in the eye?
hemidesmosomes
too much calcium can cause "jelly bumps" on cls
49
Does dry eye increase or decrease tear osmolarity?
increase
49
Eye drops for dry eyes have an osmolarity of?
150 mOsm/L
hypotonic eye drops
50
What is the average pH of tears?
7.45
50
pH of tears during sleep becomes more ___ ?
acidic due to byproducts of anaerobic respiration
51
Most ophthalmic solution are __?
weak bases
52
What does the middle ear contain?
tympanic cavity
auditory ossicles (malleus, incus and stapes) MIS
53
Which muscles of the ear dampens sound? What CN are they innervated by?
stapedius (CN 7) and tensor tympani muscle (V3)
54
What carries taste sensation to the anterior 2/3 of the tongue?
chorda tympani nerve of CN 7
55
What is the main function of the inner ear?
converts mechanical vibrations to neural signal
56
What does the vestibulocochlear organ help with?
maintain balance, receive sound, contribute to ocular reflex actions
57
What does the bony labyrinth consist of? What are the functions of each?
located in the middle ear and consists of
1. Cochlea - shell shaped & contains organ of corti that contains hair cells that control hearing
2. Vestibule - Detect linear acceleration (mvmt of head or body from side to side) and cause reflex eye mvmts (linear VOR) that are equal and opposite to the motion of the head
3. Semicirculuar canal - detect angular acceleartion ( rotational mvmts and angular VOR)
58
What does the vestibule contain?
ultricle - horizontal linear mvmt
saccule - vertical linear mvmt
vestibule - continuous with the cochlear duct for hearing
59
What separates the external and middle ear?
tympanic membrane
60
Voluntary mvmts are a combination of?
saccades and pursuits
61
What is saccades controlled by?
rapid eye mvmts that maintain fixation on the object of regard
FEF and superior colliculus
ex. right frontal lobe controls saccades toward the left
62
What is pursuits controlled by?
smooth tracking mvmts that maintain foveation on slow moving objects
ipsilateral parietal lobe
ex. right pursuit is driven by the right parietal lobe
63
What is vergence driven by?
control vergences is presumably located at the level of the brainstem
driven by retinal disparity and help maintain sensory fusion and stereopsis
64
The corneal epithelial has what type of junctions?
zonula occludens
65
Which layers are hydrophilic and lipophilic
epithelium (lipophilic)
stroma (hydrophilic)
endothelium (lipophilic)
66
What type of junctions do endothelial cells have?
macula occludens
67
What type of junctions does the stroma have?
zonula adherens
68
Which layers absorb shorter wavelenghts of UV light?
corneal epithelium and bowman's layer, protect inner layers from UVB and UVC (below 300 nm)
69
the lens absorbs which wavelenghths of UV light?
300-400 UVB
70
the retina absorbs which wavelength of UV light?
400-700 UVA
71
UVC causes what damages to the eye?
snow-blindness, welder's keratitis, tanning sun lamps
72
Which factors contribute to minmize light scattering and optimal corneal transparency?
1. corneal crystallins
2. Ascorbate (Vit C) and glutathione
3. collagen fibrils that have uniform size and are precisely spaced (less than 1/2 the wavelength of visible light from one another)
4. Avascular nature of the cornea
5. Proteoglycans and precise spacing
6. High water content
73
Where are corneal crystallins located?
cytoplasm of epithelial and endothelial cells - help maintain corneal transparency by limiting light scattering
74
What type of collagen does the cornea have?
Type 1
75
What are proteoglycans composed of?
core protein with one or more covalently linked GAG side chains
76
What is the major proteoglycan in the corneal stroma?
keratin sulfate
77
Deturgescence relies on which part of the cornea?
endothelium and epithelial transport
and aquaporins are imp for deturgescence
78
The basal membrane of the epithelium contains what 2 transport mechanism?
Na+/K+ ATPase pump :
uses energy to transport Na into the corneal stroma (higher Na in the stroma than the epithelium)
Na+/K+/Cl- co transporter:
passively tranports Na/K/Cl from the stroma into the epithelial cells
79
Movement of K+ into the aqueous humor will stimulate what?
cl- to move into the tears, water will follow cl- contributing to dehydration of the cornea
80
Which channel responds to pH changes?
K+ channels
K+ channels move more K+ into the aqueous causing more cl- and H2O to move into the tear film to restore normal corneal thickness
81
The endothelium uses which pump?
Na+/K+ ATPase pump, located on the basolateral memebrane and Na/H+ pump
Na/K+ ATPase pumps Na out into the aqueous humor (higher Na concentration in the aqueous humor)
Na/H+ pumps H+ out into the aqueous humor and Na+ into the endothelium and Co2 diffuses into the endothelial cell
82
Where does bicarb move from the endothelium
Bicarb and cl- will move to the aqueous humor, H2O will follow
83
What are the major factors for water transport across the epithelium and endothelium?
cl- excretion and N+ absorption
aquaporins (bidirection water transport)
84
What is the total amount of pressure in the atmosphere
760mmHg
85
What is the partial pressure of oxygen in the air and tears (open eyed conditions)?
155mmHg, oxygen is 1/5 of the atmosphere 760mmHg
86
What is the partial pressure in closed eye conditions?
55mmHg
87
What supplies oxygen to the front and back of the eyes during closed eye conditions?
superior palpebral conjunctiva (anterior) and the aqueous humor (posterior)
88
When is the cornea the thickest and why?
Morning, due to build-up of lactate from anaerobic respiration and the limited O2 supply when the eyes are closed
89
What is the critical PPO2 of the cornea?
10-20mmHg, partial pressure must be above the critical value when wearing cls while sleeping (minus lens are thinner and more capable of transporting O2 compared to plus lens)
90
What is the formula for looking at how O2 flows to the cornea during cls wear?
J/A = Dk/t (P1-P2)
J/A = oxygen flow over a certain area
Dk = oxygen permeability
Transmissibility (Dk/t) = measures how much O2 will diffuse through a cls of a given thickness
91
What happens to the ions during corneal hypoxia?
accumulation of H+ produced via glycolysis resulting in acidity of corneal cells
Decreased corneal pH causes a massive efflux of K+ from keratocytes causing collagen damage and scar formation
92
What is the primary contributor of glucose to the cornea?
aqueous humor (as well as AA and vitamins for the cornea)
93
Where is glucose stored in the cornea?
corneal epithelium (for basal cell mitosis & wound healing)
the endothelium also uses glucose for Na+/K+ ATPase pumps
94
How many days does it take for the cornea to regenerate itself?
7-14 days
95
Where are limbal stem cells located
Palisade of Vogt
96
What are the only mitotic cells in the epithelium?
Basal cells
97
What is the process of epithelial regeneration?
Basal cells differentiate into wing cells and then squamous cells before reaching the corneal surface. Superficial old cornea are shed as this process occurs
1. basal cell mitosis is inhibited
2. After injury of epithelium/stroma fibronectin is released, serves as a scaffold for epithelial cells to migrate over the wound in response to the release of cytokines and GF. Hemidesmosomes are then created to allow for proper adhesion between migrated epithelial cells and BM
3. Basal cell mitosis resumes at a rapid rate. This occurs once the wound is closed with a single layer of cells and cell to cell junctions are created
if BM is damaged then corneal regeneration occurs more slowly
98
Complete healing of the BM w/ intact hemidesmosomes takes how long?
8 weeks
99
What degrades hemidesmosomes formation?
MMPs
corticosteroids and tetracyclines are used to decrease activity of MMPs and used in tx of RCEs
100
RCE is the result of poor adhesion between which 2 layers?
epithelium and BM from previous abrasions or corneal dystrophy
101
Which layers CANNOT regenerate?
Bowmans and endothelium
"bowmans bows out if it's damaged, D-3 will regenerate via endothelium"
102
Which layers can regenerate?
Descemet's and epithelium
103
Where does the corneal nerves enter at what level?
mid stroma and up
104
majority of the nerves are considered ___ ?
nocioceptors (naked receptors) - low threshold and mediate pain
105
What are common causes of neurotropic keratitis (CN V damage)
Herpes simplex and zoster, stroke and DM
106
Aging changes of the cornea
more ATR
Light scattering incr
corneal sensitivity decr
corneal arcus
descemets thickens - incr hassall henle bodies in the corneal periphery
endothelial cell density decr as endothelium becomes thinner with age
107
the lens provide ___ of the total dioptric power of the eye
1/3
108
What changes occur in the lens during accommodation?
parasympathetic stimulation causes contraction of the ciliary muscle, resulting in a decrease in tension in the zonules
anterior pole moves forward and anterior curvature increases
the posterior pole moves back and posterior curvature increases
lens thickness and increases
anterior depth decr
lens diamter decr
lens power incr
109
does accommodation incr or decr IOP
Both!
decr b/c ciliary muscle contraction pulls the scleral spur posteriorly and opens up the pores of the TM
incr b/c the anterior pole of the lens move forward causing narrowing of the angle which may induce pupillary block (imp adverse effect of pilo)
110
What produces most of the glucose in the lens?
anaerobic glycolysis
111
What produces glucose in the epithelium
Krebs cycle (aerobic glycolysis)
112
What is the first step for both aerobic and anaerobic respiration?
conversion of glucose to glucose 6 phosphate via hexokinase
113
What causes too much water to enter the lens?
excess sorbital, creates an osmotic gradient that favors movement of water into the lens
too much sorbital can lead to cataracts
114
What protects the lens from oxidative damage?
1. Glutathione
2. Ascorbic acid (Vit C)
115
What is the function of glutathione and where does the lens get glutathione from?
Glutathione is a reducing agent and detoxifies hydrogen peroxide
It comes from the aqueous humor but can also be synthesized from the lens epithelial cells and superficial fiber transport
glutathione decreases with age resulting in cataracts
116
What is the function of ascorbic acid (vit C)?
protects lens from oxidative damage
higher concentration in lens compared to the aqueous humor
117
Review: What drugs can cause cataract formation?
PSC: steroids
ASC: Amiodarone, chlorpromazine, thioridazine, miotics
118
Which factors help with lens transparency?
1. Na/K pumps on the lens epithelium. (Na+ into the aqueous humor and K+ into the lens)
2. avascular
3. no membrane bound organelles in the lens fiber
4. packed lens fiber and uniformly spaced
5. crystallins in the cytoplasm of lens fibers
6. multiple transport that limits Ca2+ into the lens preventing cataract formation
119
Review: What are some significant age-related changes to the lens that can cause cataracts?
decreased glutathione
increased calcium
decreased alpha crystallin
120
What is the embryonic nucelus formed from?
primary lens fiber of the lens epithelium
the remaining growth of the lens are from 2' lens fibers of the anterior epithelium
121
Which part of the lens has the greatest metabolic demand?
Anterior lens epithelium
Mitosis of fiber cells occur in the germinative zone of the anterior lens epithelium which then migrate into the equator where fiber elongation occurs
aqueous humor provides nutrients for the ant epithelium
122
What part of the lens is responsible for transporting nutrients from the aqueous humor?
anterior lens epithelium
Na+/K+ ATPase pumps
123
List some age-related changes in the lens
1. decreased alpha crystallin
2. lens thickness increase 0.2mm per year
3. ant lens capsule thickness
5. decr radius of curvature of ant and post lens
6. lens move ant, decr ant chamber depth
7. AA decr with age
8. Glutathione decr, Na+, Ca2+, and water incr inside lens
9. Nuclear fibers begin to lose nucleus and organelles
124
What is the molecular chaperone of the lens?
alpha crystallins, reduces degradation of lens fiber cells
125
What's the thickest BM in the body?
lens capsule
thickest at anterior mid peripheral portion (pre-equatorial) of the lens and thinnest at the posterior pole
126
What is the refractive index of the embryonic nucleus?
1.41
highest refractive index in the lens
127
What are 2 drugs resistant to dilation?
1. flomax or ozin drugs (block alpha 1)
2. pilocarpine
128
T or F. Ciliary muscle contraction decreases with age
False. Loss of accommodation is due to lens changes.
129
List functions of the vitreous
1. passage of light
2. acts as a UV filter, transmission drops at 300-350nm
3. cushions the globe
4. storage for ions and nutrients (O2, H2O, Na,K, cl, phosphate, glucose and proteins)
130
What is the volume of the vitreous?
4 mL, 80% total volume of the eye
131
The lens is made up of what type of collagen?
4
132
The vitreous is made up of what type of collagen?
2
133
Is vit C greater in the vitreous or blood?
40X greater in the vitreous
134
What is the index of the vitreous?
1.3345-1.3348
135
wavelengths below 300 are absorbed by what part of the eye?
cornea
136
Wavelengths between 300 and 400 nm are absorbed by which part of the eye?
lens
137
Wavelengths above 400nm are transmitted to which part of the eye
retina
138
the lens absorbs a majority of which UV light?
UVA and UVB
139
age-related changes in the vitreous
1. liquefaction
2. condensation (aggregation of collagen fibers)
aka syneresis
140
What is the most common cause of PVD?
syneresis
141
collagen concentration is highest where in the vitreous?
base
142
What is the equation for blood flow?
F = Parteries - Pveins/ R
F = flow
P = pressure
R = Resistance
143
What is the mean arterial pressure for arteries entering the eye? veins leaving the eye?
65mmHg, 15mmHg
144
What is the perfusion pressure in the eye?
50mmHg
indicates how easily blood can pass through a given tissue nand is the difference between the pressure of blood flow entering and leaving the eye
145
What is the equation for ocular perfusion pressure (OPP)?
OPP = diastolic blood pressure - IOP
Glaucoma pts w/ low OPPs are 1.5X more likely to develop progressive optic neuropathy secondary to ischemia
146
If IOP increases, OPP ___
decreases
think glaucoma!
147
If diastolic BP decreases, OPP ___
decreases
148
What's responsible for autoregulation?
Pericytes within the blood supply of the retina and ON
149
What is autoregulation
the process by which blood vessels alter their diameter in absence of neural control to decrease or increase resistance to blood flow
allows blood flow to be maintained at a constant rate despite moderate variations in the mean arterial pressure and IOP
150
Transmural pressure
Transmural pressure = pressure outside the vessel - pressure inside the vessel
describes pressure across blood vessel wall and determined
151
What is the critical closing pressure?
pressure at which blood vessel collapse and blood flow stops
152
What is the threat to vision in acute angle closure?
CRAO
acute angle closure reduces blood flow in the CRA leading to decr perfusion pressure in the retinal tissue. The retinal vessels detect change in transmural pressure and increase vessel diameter through autoregulation to improve perfusion
If IOP remains acutely elevated long enough it can reach critical closing pressure causing a CRAO
153
Sympathetic innervates mostly what part of the eye?
uveal tract, does NOT innervate the CRA
sudden increase in blood flow = vasoconstriction
154
Where is parasympathetic innervation most prominent?
anterior uvea, causes vasodilation of blood vessels in respones to decreased blood vessels
155
Should IOP be greater or lower compared to the episcleral venous pressure?
greater, so aqueous humor can drain from anterior chamber, through the corneoscleral meshwork, and into the venous system
156
Should IOP be greater or lower than ICP?
greater to maintain an axoplasmic gradient that flows from the optic nerve toward the brain
157
What happens if there's a reversal in the axoplasmic gradient between the eye and the brain?
papilledema , this reversal cause sthe brain to spill CSF from the subarachnoid space onto the optic disc margins and surrounding the RNFL
158
Is IOP greater or lower than retinal and uveal arteries?
lower allowing nutrients to be delivered from the choriocapillaris to the RPE cells
159
Fenestrated vessels in the eye
1. choroidal
2. ciliary
160
2 non-fenestrated vessels in the eye
1. Iris
2. Retina
161
MACI (Major)
Located in the ciliary body, formed by ACA and LPCA
162
MACI (Minor)
located in the iris stroma, formed by anastomoses of iris radial vessels
Blood flows from Major > minor > pupillary margin
163
Where is watershed area located?
OPL - supplied by both CRA and choroid
164
the CRA forms 2 networks of capillaries in the retina, where are they located?
RNFL and INL (deep capillary)
165
Where are the retinal capillaries most dense?
around the fovea, but the fovea is avascular
166
What supplies the fovea?
underlying choriocapillaris
167
tight junctions are found in what 2 locations in the retina?
retina vessels and RPE
168
What's the most important risk factor for development of retinopathy in insulin-dependent diabetes?
duration of diabetes
169
Where is rhodopsin embedded?
within disc membranes of rod
170
Where is iodopsins stored in cones?
invaginations of the plasma membrane
171
Where are photopigments produced?
photoreceptor inner segment and then travel through the cilium to the outer segment
172
The disc and plasma membranes that enclose the photopigments are produce where?
outer segment
173
What does the photopigment consist of?
opsin and chromophore (11=cis retinal)
174
Vitamin A is an alcohol retinol that is oxidized into what?
oxidized in the RPE to for 11-cis-retinal
175
Light absorption occurs in which part of the photoreceptors?
OS
176
Rod and cone outer segments are shed when?
Rod - morning
cones = evening
177
Stages of the visual cycle
1. light absorption results in transformation of 11-cis retinal to all trans retinal
2. All-trans retinal moves from disc lumen into the cytoplasm where it is reduced to all-trans retinol
3. All-trans retinol is transported to RPE where it is converted to 11-cis retinol . 11-cis retinol is then oxidized to 11-cis retinal
4. 11-cis retinal shuttled back to the photoreceptor for incorporation into the disc OS
178
Photoreceptors ____ in the dark
depolarize
release glutamate to bipolar cells > release cGMP > Keeps Na+ channels open
179
What triggers phototransduction
absorption of light by rhodopsin = hyperpolarization of cells
which triggers transducin causing a decr of cGMP, closing of sodium channels, and increase negative charge (-65mV) > decrease release of glutamate to bipolar cells
180
What "shuts off" phototransduction?
closure of Na+ channels via hyperpolarization in the presence of light
Decr cGMP = closes sodium channels = -65mV (vs -50mv during depolarization)
181
Are photoreceptors action potential or graded potential?
graded potential
182
Excitatory retinal neurotransmitter
glutamate
183
Inhibitor retinal neural transmitter
GABA and Glycine
184
What is 11-cis retinal converted to after light absorption of a photoreceptor?
11- cis retinal (Vitamin A) > all trans retinal > all trans retinol > 11-cis retinol
11- cis retinal is incorporated into the disc OS
185
Which part of the retina stores vit A
RPE
186
What happens If all-trans retinal is accumulated with the photoreceptor disc?
Stargardt's disease (mutation of ABCA4)
leads to a degeneration of the photoreceptors and RPE
187
Bipolar cells have what type of receptive fields?
center-surround
188
What are the 2 types of cone bipolar cells?
Cone cells can hyperpolarize or depolarize the center of bipolar cells
ON-center = inhibited by glutamate and hyperpolarized in the dark
When light is present = more glutamate = depolarization of ON center
OFF-center = excited by glutamate and depolarized in the dark
When light is present = less glutamate = hyperpolarize of OFF center
189
Bipolar responds to glutamate with _____
graded potential
190
Horizontal cells respond w/ ____
graded potentials, they do NOT have center/surround receptive fields
191
What's the main function of horizontal cells?
provide lateral inhibition to fine-tune neural signal sent from neighboring photoreceptors
192
How does horizontal cell respond to light?
hyperpolarize
provides inhibitory feedback to PR cells or directly synapsing with bipolar cell (feed-forward synapse)
193
REVIEW: which cells hyperpolarize in response to light?
Horizontal cells and Bipolar OFF center cone bipolar cells
194
How do amacrine cells respond to light?
depolarize, respond via action potentials
195
Amacrine have ____
center/surround receptive fields
196
What is the main function of amacrine cells?
fine-tune signal between bipolar and ganglion cells
197
Ganglion cells have ____
center-surround receptive fields
198
How does ganglion cells respond to bipolar cells?
action potentials
199
What are the 2 types of response that ganglion cells have to light?
ON-center/OFF-surround = synapse w/ ON-center Bipolar cells and depolarize in response to light
OFF-center/ON-surround ganglion cells synapse with OFF-center bipolar cells and hyperpolarize in response to light
200
What do midget ganglion cells synapse with?
one midge bipolar cells which synapse with a single cone in the fovea allowing for resolution of very fine details
201
Acton potentials?
All or nothing
202
Graded potentials
response influenced by the number of photos absorbed
203
Amacrine and ganglion cells
responds with action potential, all other retinal cells respond with graded potentials
204
Aging changes in the retina
1. RNFL within the ON decr = incr diameter of the vertical cup
2. ILM thickens, fovea dims
3. Rod density decr, scotopic function does NOT decline
4. RPE cells decr, lipofuscin and drusen incr
5. Atrophy in the retina (peripapillary atrophy, paving stone degen, RPE/choroid)
205
Where does the pyramidal motor pathway begin
motor cortex
206
Pyramidal motor pathway plays a large role in what?
complicated voluntary movements (muscle control)
207
Where does the pyramidal motor cells travel?
forms a the internal capsule in the forebrain> travel through cerebral peduncles, pons, and medulla and forms the medulla pyramid
decussates at the medulla
208
What are the 2 tracts associated with the pyramidal motor pathway?
1. Corticospinal tract (control distal musculature)
75% decussate, 25% ipsilateral
2. Corticobulbar tract (voluntary control of face, head, neck)
209
What occurs with a lesion above the medulla?
motor control on the contralateral side
210
What is an alternative pathway for the pyramidal motor pathway?
Reticulospinal pathway, descends ipsilaterally
211
What does the tectospinal pathway play a role in?
reflexive head mvmts in response to visual stimuli
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Where does the reticulospinal pathway originate?
from the reticular formation within pons and medulla, descends ipsilaterally and eventually synapse with neurons at all levels of the spinal cord
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Where do tectospinal pathway fibers originate?
superior colliculus - they immediately cross the midline and then descend through pons and medulla, traveling ant to the medial longitudinal fasciculus (MLF)
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Where do the cochlear nerve fibers originate?
spiral ganglion of the cochlea. These fibers travel from the organ of corti before exiting the internal meatus and ending their cell bodies in the cochlear nuclei of the medulla
2nd order neuron axons ascend on both sides of the trapezoid body > superior olivary complex (first location of auditory input > fibers from superior olivary complex (third order neuron) for the lemniscus pathway > synapse in inferior colluclus of the midbrain and medial geniculate body in the thalamus (forth order neuron) before traveling to the primary auditory cortex
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Where do the vestibular nerve axons originate?
vestibular ganglia at the distal end of the internal auditory meatus
these fibers join the cochlear nerve of CN 8 and carry sensory info from the semicircular canals and otolith organs of the ear
most of the fibers synapse with 4 vestibular nuclei in the medulla and pons
the remaining fibers directly project to the cerebellum via the inferior cerebellar peduncle to control mvmts necessary for balance
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What is the pathway of the vestibular nerve?
Primary ascending fibers from superior and lateral vestibular nuclei carry sensory info to the thalamus > sends fibers to primary vestibular cortex
Ascending fibers from superior and vestibular nuclei travel through MLF tonuclei of CN 3,4,6 to help coordinate head and eye movements
Ascending fibers from the inferior and medial vestibular nuclei travel to the cerebellum to help coordinate balance
Descending fiber from the lateral vestibular nuclei forms the lateral vestibulospinal pathway that travels along either side to the thoracic segments of the spinal cord. This pathway helps to integrate head mvmts with eye mvmts
Descending fibers from the medial vestibular nuclei form the medial vestibulospinal pathway that travels along either side to the thoracic segments of the spinal cord. This pathway helps to integrate head mvmts with eye mvmts
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What is the importance of spinothalamic pathway (anterolateral system)?
pain and temperature information from the body
think "hot spine"
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Where does the spinothalamic pathway decussate?
at the neck, causes a contralateral lesion
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What is the pathway of the spinothalamic pathway?
Nerve endings in the periphery synapse at the substantia gelatinosa within the dorsal horn of the spina cord
fibers that leave the substantia gelatinosa cross the midline and become lateral spinothalamic pathway
The fibers remain contralateral until they terminate in the ventral posterior thalamus
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What is the importance of the trigeminothalamic pathway?
carries pain and temperature information from the face
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Where does the trigeminal pathway decussate?
medulla
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What is the pathway of the trigeminothalamic pathway?
originates in the trigeminal ganglion cells, as well as facial pain and temp receptors that extend into the brain stem at the level of pons
axons descend into the medulla (forming the spinal tract of CN 5), where they synapse onto 2nd order neurons in one of 2 sub-regions of the trigeminal complex of the spinal cord
Axons from neurons within the trigeminal complex then cross the spinal column in the medulla and ascend contralaterally until they terminate in the thalamus
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What happens if there is a lesion in the trigeminal pathway above the cross over?
loss of pain or temp on the contralateral side of the face
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What is the importance of the medial lemniscus pathway?
carries info about touch, pressure and vibration
lemniscus think limbus
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Where does the medial lemnisucus cross?
medulla
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What is the pathway of the medial lemniscus?
Cuneate tract - receives info from mechanoreceptors from the upper body and travels along the cuneate tract
Gracilis tract - receives info from the lower body and travels along the gracilis tract
These tract enter the cervical and lumbar regions of the spinal cord and ascend into the cuneatus and gracilis nuclei in the caudal medulla
axons from 2nd neurons in this region cross the midline at the level of the medulla and become the internal arcuate fibers. These fibers travel contralaterally until they terminate at the VPL
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What happens if there is a lesion at the medial lemniscus pathway below the crossover?
affects ipsilateral side, while lesions above the crossover point affects the contralateral side
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What is the importance of ANS?
control input to the visceral organs, secretory glands, and smooth muscle of the cardiovascular, digestive, excretory and thermoregulatory systems of the body
NOT voluntary and helps maintain homeostasis
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What is the ANS composed of?
2 neurons between CNS and the target tissue.
preganglionic is located in the brainstem or spinal cord
postganglionic is located in the autonomic ganglion in the periphery (outside CNS)
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The ANS is separated into what 2 divisions?
sympathetic and parasympathetic
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What is the sympathetic nervous system responsible for?
fight or flight response
increases heart rate, dilates bronchioles, vasodilation within skeletal muscle, increases blood glucose levels, and decrease GI motility and blood flow
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Where are preganglionic neurons for sympathetic located?
thoracic and lumbar sections of the spinal cord in the lateral horn of the gray matter
Their axons ascend the spinal cord to enter sympathetic chain of ganglia located on the vertebral column
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What does pre-ganglionic sympathetic fibers release?
Ach
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What does post ganglionic sympathetic fiber release?
NE
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Which is the only gland innervated directly by the pre-ganglionic sympathetic fiber?
adrenal
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What is the parasympathetic nervous system responsible for?
"rest and digest " response
decreases heart rate, constricts bronchioles, increase salivary and lacrimal glands secretions, incr GImotility and causes pupil constriction and accommodation
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Where are pre-ganglionic neurons located for the parasympathetic nervous system?
CN nuclei of the brain stem or in the 2nd-4th sacral segements of the spinal cord
the brainstem parasypathetic innervates head, thorax, and abdomen
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What does the pre- and post- ganglion of the parasympathetic fibers release?
ach
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What are CT scans used for?
emergent situations (faster than MRI)
bone and calcification
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How does a CT scan work?
compares calcium density of neighboring tissues
as tissues undergo apoptosis, calcium enters cells and increase density of the tissue
the denser tissue appears whiter on CT scans
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If a pt has an orbital fracture which scan would you recommend?
CT scan
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How do PET scans work? What are they used for?
analyze the metabolic activity of tissues by comparing glucose uptake of neighboring tissues
often used in conjunction with CT scans to monitor metastasis in cancer
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What are MRI used for? How does it work?
scan soft tissue
diseased tissue has higher water content than healthy tissue and will have more free protons
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What should you avoid with MRI scans?
claustrophobia pts and magnetically activated iimplanted devices (pacemakers, defibrillators, cochlear implants)
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Pt has psuedotumor cerebri, what tests would you recommend?
lumbar puncture * MRI
MRI before lumbar puncture
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Where does the axons of retinal ganglion terminate?
LGN and are thought to be " drivers" for LGN output
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Axons that leave the LGN are called?
optic radiations
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LGN receives input from which part of the brain?
axons of retinal ganglion cells, superior colliculus and feedback from the visual cortex regarding visual signal (aka modulators for LGN output)
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Where is LGN located?
dorsal thalamus
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What is the LGNs purpose?
process visual info from retina, filtrates the information to V1
size, direction, and orientation
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LGN has how many layers? Describe the layers
6
1,2 magnocellular layers (ventral)
3,4,5,6 parvocellular layers (dorsal)
koniocellular layers are located between each of the 6 layers
each layer receives input from only one eye
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Which layers of the LGN is contralateral?
1,4,6
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Which layers of the LGN is ipsilateral?
2,3,5
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Where does the macula project to in the LGN?
dorsal wedge that makes up 2/3 of the LGN
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What is the first location for binocular processing?
V1
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Review: Which cells have center-surround receptive field?
ganglion
bipolar
Magno and Parvo (LGN)
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What are parvo cells important for?
red-green, fine details, slow motion, slow speed of transmission of visual signals
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What are magno cells important for?
monochromatic, fast mvmts, large details, higher speed of transmission due to large axons (compared to parvo)
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What are Konio cells important for?
blue-yellow contrast
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What are some other names for V1?
Striate cortex, brodmann area 17 or V1
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V1 has how many layers?
6 (similar to LGN)
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Where is V1 located? Where is LGN located
V1 = occipital lobe
LGN = thalamus
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Where does V1 receive input from?
LGN via optic radiations
other cortical areas
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What is V1 important for?
Binocular processing and evaluation of binocular disparity
evaluates input based on size, orientation, and direction
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Which layer of V1 receives input from the LGN?
Layer 4
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What does layer 4 of V1 consist of?
Non-oriented cells (receive input from LGN)
Simple cells (orientation, edges, colors depth)
ex. P cells (parvocellular system)
have elongated center surround
Complex cells (direction and orientation)
ex. M cells (magnocellular system)
does NOT have center-surround
End-stopped cells (lines with a specific length) hyper complex cell
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Which layers of V1 are processing layers and send axons to other cortical layers
2 and 3
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Which layers send axons to subcortical areas and provide direct feedback to the LGN
layer 6
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What is the extrastriate cortex?
V2-V5, located on the lateral aspect of occipital cortex. Important for complex processing of info.
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The visual input travels to what 2 locations within the extrastriate cortex? What is important about these 2 locations?
Inferotemporal (IT) cortex; Identifies the object ("what"), object recognition, visual attention, object constancy
Middle temporal (MT) cortex:
identifies spatial relationship of the object ("where"). Involves direction, velocity, motion integration, figure ground segregation
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Where does superior colliculus and FEF receive information from?
V1
SC = controls saccades, visual orientation, foveation
FEF = located in the frontal lobe and is important for pupillary response to near objects, activates during initiation of voluntary and reflex eye mvmts
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What are voluntary saccades initiated by?
input from FEF and superior colliculus
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Which input makes up a large percentage of the visual cortex?
fovea
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What does EOG measure? What does it help diagnose?
the difference in electrical charge between the front and back of the eye
health of the RPE
helps diagnose for Best disease, Stargardts, advanced drusen, and patterned RPE anomalies
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What is the arden ratio equation? What is considered normal
Arden ratio = light rise/dark trough
>1.8 is normal
1.65-1.80 subnormal
<1.65 very abnormal
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What does ERG measure? What does it help diagnose?
ERG records graded potential in the retina in response to light
checks health of PR
helps diagnose RP
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The ERG is composed of 3 waves, what do they each represent?
A wave: PR
B wave: Bipolar and mueller
C wave: RPE (Rarely used, EOG analyzes RPE function)
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What is characterized in an electronegative ERG?
loss of B wave
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What does a pattern ERG target?
ganglion cells
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What does a multifocal ERG target?
localization of retinal disease
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What are serial ERGs used for?
track intraocular foreign bodies
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What is Retinitis Pigmentosa characterized by?
vessel attenuation, bone spicule pigmentation, waxy optic disc pallor, PSC cataracts, CME, disc drusen
early cases, scotopic (rod) ERG is abnormal
late stages, ERG is completely extinguished due to poor function of rods and cone
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What are visual evoked potentials used for (VEP)?
analyzes the electrical response (latency) of brain activity to a visual stimulus
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What does a normal VEP look like? What does an abnormal test look like?
large positive wave that peaks at 90-110 msec after the initial representation
waves that peak after 110 msec are abnormal
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What does the VEP help diagnose
optic neuritis, optic nerve, tumors, retinal disorders, demyelinating disease (MS)
VEP can detect an anomaly between the fovea and V1 but cannot localize the defect
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What is Argyll-Robertsonal pupil characterized by?
light-near response due to damage of the tectotegmental tract
associated with neurosyphilis
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What is the importance of the Edinger Westphal (EW) nucleus?
miosis and accommodation
288
Describe the pathway of the afferent pupillary fibers of the light response.
Afferent pupillary fibers travel with the ganglion until the posterior 1/3 of the optic tract > exit and travel to the brachium of the superior colliculus > synapse at the pretectal nucleus (midbrain) > ipsilateral and contralateral EW nuclei forming the tectotegmental tract
pre-ganglionic parasympathetic fibers leave EW and travel to the CG
postganglionic parasympathetic fibers project from CG to iris sphincter and ciliary muscle
**Efferent parasympathetic are responsible for miosis and accommodation, remember anisocoria is always due to efferent pathology**
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What is the near reflex triad?
convergence, accommodation, miosis
290
In the near response, what is pupillary constriction mediated by?
FEF
FEF activates EW nucleus, which projects to the ciliary ganglion and then onto the sphincter muscle and ciliary muscle
**the light and near pupillary response both utilize EW nuclei and CG as the efferent pathway for pupillary constriction**
291
What inhibits EW nuclei?
sympathetic nervous system via supranuclear control (during waking hours) = normal pupils
when uninhibited, EW neurons continuously fire action potentials to the sphincter muscle (during sleep or anesthesia) = miosis
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What is Goldmann tonometry based on?
Imbert-Fick Law, assumes that force that the force from the surface tension of the tear film cancels the elasticty of the cornea
293
Goldmann's method assumes that all have the same average of what thickness?
520um
this assumption causes us to over estimate IOP in thicker corneas and underestimate in thinner corneas
294
What is the avg corneal thickness?
555
295
How does noncontact tonometry (NCT) work?
a form of indentation tonometry that utilizes an airstream of unknown force to flatten a circular area of the cornea
less predictable than goldmann
296
How does a PASCAL tonometry work?
the tip is contoured and resembles a shape of a cornea when the pressure on both sides of the probe is equal
the contoured tips help minimize the unique characteristics of a pts cornea on IOP measurement
297
What is the average IOP?
15.5 mmHg
298
When is IOP the highest?
morning 12:00-6:00 AM, peak IOP at 330-530AM
299
Which medications can decrease aqueous production?
B-blockers
apha 2 agonist
CAI
Cardiac glycoside
Hyperosmotics
Significant decline of BP
Uveitis (inflamed/sick CB)
300
corneoscleral outflow vs uveoscleral outflow
corneoscleral = 80% outflow (pressure dependent), drains thru schlemms canal
Uveoscleral = 20% outflow
(pressure independent), drains through ciliary stroma
301
What is the equation for aqueous outflow?
F out = corneoscleral (IOP-EVP) + Uveoscleral)
F out = aqueous outflow
EVP = Episcleral venous pressure
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What is the total amount of aqueous outflow?
2.5 ul/min
303
What is the total volume of the aqueous humor? when is it replaced?
250 ul/min, replaced every 100 mins
2.5 uL of aqueous is produced and 2.5 uL of aqueous is drained every min in healthy eyes
304
What can cause an increase in EVP?
compression of the external juglaur vein = incr EVP = incr IOP
Sturge weber
arteriovenous fistulas
compression of external jugular vein (tight necktie)
305
What other factors can increase IOP?
supine position
thicker corneas (false high readings)
blinking, squeeze, straining eyes
caffeine (transient incr in IOP)
306
What factors can decrease IOP
exercise
307
what are the main functions of the aqueous humor?
maintains pressure and shape of the eye
provides nutrition for the cornea, lens, anterior vitreous and TM
collection bin for metabolic waste of surrounding tissue and clears out inflammatory products and blood from the globe
308
What produces aqueous humor
NPCE , involves diffusion, ultrafiltration and active secretion
309
What are the key parts of active secretion?
Na+/K+ ATPase pump (Na+ out)
Carbonic anhydrase
Active transport - facilitates the mvmt of sodium, chloride and bicarb to create a gradient for water mvmt and aqueous humor production
310
Factors that can cause "covering" of the TM
Diabetes - neo causing obstruction and acute angle closure 2' to PAS formation
Uveitis - inflammation cells can cause clogging. Posterior and peripheral anterior synechiae can cause angle closure
Hyphema - blood accumulates in the anterior chamber and impede aqueous flow
311
What factors can cause injury to the TM?
Fuchs heterochromic iritis
Glaucomatocyclitic crisis
Angle recession glaucoma (wide CBB)
312
Which factors can occlude the TM?
pseudoexfoliative glaucoma
pigment dispersion glaucoma
313
Aqueous humor vs plasma
AH has less protein than plasma but more amino acids than plasma
AH has vit C 20x than plasma
AH has more lactate than plasma but less bicarb ions (AH is more acidic)
314
What is the pH of the AH
7.2
315
BAB consists of tight junctions located in what 3 places?
Schlemms canal
NPCE
iris vessels
