Lectures 15 & 16 - Eyes & Ears Flashcards
1
Q
Purpose of peripheral vision?
A
Detect movement
2
Q
Are there more false positives or false negatives for our peripheral to detect movement?
A
More false positives
3
Q
Where are the anterior and posterior chambers of the eye located?
A
Anterior: in front of iris
Posterior: behind iris and in front of lens
4
Q
What is the eye filled with?
A
Vitreous humor
5
Q
What is the sclera of the eye?
A
- Opaque connective tissue
- Posterior 5/6th of fibrous tunic
- Part of the eye commonly known as the “white”
6
Q
What is the choroid of the eye?
A
Posterior majority of vascular tunic made of vascularized connective tissue between the sclera and the retina
7
Q
What is the insertion point for the extraocular eye muscles?
A
Sclera
8
Q
How many intraocular muscles in the iris? What are they? What is each innervated by? What do they do?
A
- Sphincter (constrictor) muscle - Parasympathetic NS (CN III) -> constricts pupil
- Dilator muscle -Sympathetic NS -> dilates pupil
==> Control pupil size by pulling on the lens
9
Q
What is the pathway of light through the eye?
A
Light reflected from object => cornea => aqueous humor => pupil => lens => vitreous humor => retina photoreceptors and signal transduction => bipolar cells => ganglion cells
10
Q
What are the 3 important structures of the retina? Describe each.
A
- Optic disc: hole in posterior retina = highly vascularized exit/entry point of optic nerve
- Fovea: depression of outer-most cellular neuronal layer of retina that has improved acuity
- Macula: contains the fovea
11
Q
What constitutes the blind spot of the eye? What does it mean?
A
The optic disc of the retina
No photoreceptors in this spot
12
Q
Position of optic nerve/blind spot with regards to the macula?
A
Medial
13
Q
Position of blind spot image with regards to the macula?
A
Lateral
14
Q
Can the blind spots of each eye be in the same spot at the same time?
A
NOPE
15
Q
Describe the structure of the lens of the eye.
A
- Capsule: thick basement membrane containing collagen type IV and laminin
- Subcapsular epithelium: secretes the lens capsule
- Lens fibers (below the subcapsular epithelium): cells that have lost their nuclei and organelles, becoming thin, elongated, transparent structures
16
Q
What nourishes the cells of the lens of the eye?
A
Fluid from the posterior to the anterior chamber of the eye
17
Q
What can go wrong with the lens of the eye?
A
- Can become stiff
2. Can become cloudy
18
Q
What are the 2 types of photoreceptor cells?
A
- Rods: black and white
2. Cones: color
19
Q
In dim light are we primarily using rods or cones?
A
Rods
20
Q
What are the only retinal cells capable of firing APs?
A
Ganglion cells
21
Q
How many colors can you see? How many receptors/cone types do you have for each?
A
- Red: 1 or 2 (on X chromosome, so men only have 1)
- Blue: 2
- Green: 2
22
Q
Do men or women see colors better? Why?
A
Women because they have 6 color receptors instead of 5 in men (see red colors better)
23
Q
What is the dark current?
A
In the absence of light, photopigment proteins are inactive and therefore photoreceptors are depolarized and have current: cGMP opens cGMP gated cation channels (Na+ and Ca++ flow in)
24
Q
Describe the phototransduction pathway in rods.
A
Light hits retinal portion of rhodopsin => rhodopsin is now activated and facilitates the exchange of GDP for GTP on transducin => transducin dissociates into Tα-GTP and Tβγ => Tα-GTP activates cGMP phosphodiesterase (PDE) by binding and removing its inhibitory subunit (I) => PDE converts cGMP to 5’-GMP and reduces [cGMP] to below the level needed to keep cation channels open => cGMP gated cation channels close preventing Na+/Ca++ influx => hyperpolarization of membrane photoreceptor cell + Ca++ efflux through Na+/Ca++ exchanger => IPSP => inhibition of glutamate release => signal transmitted to brain
25
How does light affect retinal on rhodopsin exactly? Explain.
It bleaches it: photo absorption breaks the double bond between C11 and C12 which permits rotation and conversion from 11-cis-retinal to all-trans-retinal
26
What is the major mechanism of dark adaptation?
Regeneration of unbleached retinal
27
Describe the mechanism of decrease in intracellular Ca++ during light adaptation/recovery?
Light => decreases Ca++ conductance => less Ca++ in cells to inhibit the GC => GC activated => more [cGMP] to dark levels => cGMP gated channels open => returning RMP to prestimulus level => rhodopsin kinase phosphorylates bleached rhodopsin (stimulated by low Ca++ and recoverin) => arrestin binds phosphorylated carboxyl terminal to inactivate rhodopsin => slowly arrestin dissociates, rhodopsin is dephosphorylated and all-trans-retinal is replaced with 11-cis-retinal => rhodhopsin ready for another phototransduction cycle
28
What kind of receptor is transducin?
Inhibitory GPCR
29
What causes glare?
Light scatters on the retina when it is very bright
30
Why doesn't light exit back out of the pupil? What to note?
Because pigments in the epithelium of the retina absorbs it
This also prevents light scattering and glare
31
What is ocular cutaneous albinism?
Defect in pigment producing enzyme in the retina epithelium, causing:
1. Pink eyes because the light reflects from the blood vessels in the back of the eye
2. Poor vision due to glare that is not prevented by the pigment in the retina epithelium
32
Why does the fovea have improved acuity?
1. Because the depression allows for the light to directly reach the photoreceptors
2. Because it has a higher density of photoreceptor
33
What is the central visual pathway?
Retina => optic nerves => optic chiasm => optic tracts => synapse in lateral geniculate nuclei of thalamus (LGN) => optic radiations => visual cortex of occipital lobe
34
Result of optic chiasm lesion? 2 names
Bitemporal blindness = bitemporal hemianopia
35
Result of right optic radiations lesion?
Blindness in right nasal and left temporal visual fields
36
Purpose of optic chiasm?
Allows for 2 neurons receiving signals from the same part of the visual field but receiving signals from each the left or the right eye to be next to each other in the same cerebral hemisphere
37
Result of lesion of right optic nerve?
Right eye blindness
38
Result of left optic tract lesion?
Bilateral right hemianopia
39
What could cause a lesion at the optic chiasm?
Pituitary tumor
40
6 extrinsic muscles of the eye?
1. Superior rectus
2. Medial rectus
3. Superior oblique
4. Levator palpebrae superioris
5. Lateral rectus
6. Inferior oblique
41
What 3 cranial nerves control the extrinsic muscles of the eye?
Cranial nerve III: oculomotor => superior oblique
Cranial nerve IV: trochlear => lateral rectus
Cranial nerve VI: abducens => all other extrinsic muscles of the eye
42
Function of oblique muscles of the eye (superior and inferior)?
Prevents eye ball rotation and depression
43
What is strabismus? What does it cause?
Failure of eyes to converge on a same point => causes diplopia
44
What is diplopia?
Cross-eyed causing double vision
45
What is amblyopia? What is it due to?
Lazy eye
When the two neurons receiving signals from the same part of the visual field receive conflicting information, the brain will shut-off one of the eyes (or ignore input from that eye) => one of the eyes will become blind
46
What is nystagmus? What to note?
Alternating smooth and jerky eye movements
Note: can be normal or pathological; if pathological, usually caused by problem with vestibular system
47
Treatment for amblyopia?
Patch over the stronger of the two eyes to strengthen the other
48
What do balance issues result in visual issues?
Because the eyes try to stay in the same location despite head movement so if the vestibular senses imaginary movement the eyes will drift off
49
What is myopia?
Near sightedness = parallel rays of light are brought to a focus in front of the retina
50
What is hyperopia?
Far sightedness = parallel rays of light come to a focus behind the retina in the unaccommodative eye
51
What is simple myopic astigmatism?
1. Vertical bundle of rays is focused on the retina
2. Horizontal bundle of rays are focused in front of the retina
=> all vision is out of focus
52
What is presbyopia? Cause?
Loss of near vision due to a loss of accommodation causing the eyes to be "stuck" in distance vision (aka neutral vision)
Due to stiffening of the lens with age
53
Why do smart people end up being myopic?
Because as children they focus a lot on near objects and their eyes develop preferentially for near sight
54
What are the 4 leading causes of blindness in the US? Describe each. List in order.
1. Cataracts: clouding of the lens which impairs light traveling through it
2. Glaucoma: increased pressure in the anterior chamber of the eye => increased pressure in eye ball => increased pressure in optic canal => damage to the optic nerve
3. Macula degeneration: causes central blindness
4. Diabetic retinopathy: increased vascular permeability and angiogenesis destroys the retina => blurriness/vision loss in the whole visual field
55
In what patients are cataracts more common?
DM patients
56
Treatment for cataracts?
Replacement of cloudy lens with superficial one
57
How to test for glaucoma?
Puff of air on high and measure velocity of air bouncing off of the lens to measure the pressure in the anterior chamber of the eye (high in glaucoma)
58
Complication of glaucoma?
Possible complete blindness
59
Treatment for glaucoma?
Drugs to increase rate of fluid drainage from the anterior chamber of the eye
60
Leading preventable cause of blindness?
Glaucoma
61
One of the best ways to look at the health of the heart is to...
Look at health of retinal blood vessels (some would argue this)
62
What are the 3 major components of the gross anatomy of the ear? Describe each.
1. Outer ear = auditory canal + pinna
2. Middle ear = tympanic membrane + ossicles
3. Inner ear = oval and round windows + cochlea + semicircular canals + auditory-vestibular nerve + otolith organs
63
Other name for auditory canal?
External auditory meatus
64
What attaches to the middle ear? Role?
Eustachian tube
Equalizes pressure
65
What are the 3 bones of the middle ear? What are they called?
Ossicles:
1. Stapes
2. Incus
3. Malleus
66
What can each ossicle be compared to?
1. Stapes: stirrup
2. Incus: anvil
3. Malleus: hammer
67
What are the 2 otolith organs of the inner ear?
1. Saccule (vertical acceleration)
| 2. Utricle (horizontal acceleration)
68
What does the fusion of the vestibular and auditory nerves
| give rise to? 2 names.
CN VIII = acoustic nerve = vestibular-cochlear nerve
69
To what structure are both the oval and round window attached to?
Cochlea
70
To what structure are the vibrations that cause undulation of the ear drum transmitted? How?
The oval window:
ear drum => malleus => incus => stapes => oval window
71
What are the 3 parts of the cochlea? In which one does signal transduction occur?
1. Scala vestibuli
2. Scala media***
3. Scala tympani
72
Describe the signal transduction pathway inside the cochlea.
1. A vibration is transmitted and amplified to the oval window
2. Reverberations are sent through fluid in the vestibular canal of the cochlea (scala vestibuli) to the apex, and then back through the tympanic canal (scala tympani)
3. This increase in pressure causes the round window to bulge out
4. This displacement pulls the tectorial membrane, producing a shearing force
5. Hair cells are embedded in the basilar membrane, and this shearing force causes them to shift
6. The stereocilia of hair cells are all joined at the top by actin (tip-links), so when one moves they all move
7. This shifting will open mechanically-gated potassium channels located in stereocilia
8. Because the concentration of K+ is high in the scala media, it will flood in and depolarize the cell
9. Voltage-gated calcium channels will open, allowing neurotransmitter-filled vesicles to dock and release glutamate to the nearby afferent nerves in spiral ganglion
73
Describe the movement of the oval and round windows in relationship to one another?
Will always be moving in opposite directions
74
What does the vestibular labyrinth consist of? What does each convey?
- 3 semicircular canals: rotational accelerations of the head
- 2 otolith organs: horizontal and linear accelerations of the head
- cochlea
75
Describe the composition of both otolith organs.
Hair cells are found in the macula of both organs and contain stereocilia, which project into a gelatinous cap above the hair cells.
On top of the gelatinous cap is the otolith layer called the otoconia, which is a layer of calcium carbonate crystals.
76
How do the otolith organs work? What to note?
During movement, the gelatinous membrane is responsible for the shearing force between the otolithic membrane and macula needed to bend the stereocilia in the direction opposite from that of the head and causing increased firing of the hair cells
77
Describe excitation and inhibition of hair cells.
- Inhibition of hair cells: stereocilia move away from kinocilium = hyperpolarization => decreased firing rate
- Excitation of hair cells stereocilia move toward kinocilium = depolarization => increased firing rate
78
Do hair cells hyperpolarize or depolarize when you are moving at a constant velocity?
Neither, they will exhibit resting activity
79
What is found within the otolith organs? Where? Purpose?
Within the membranous sacs of the otolith organs is the fluid endolymph = fluid medium that can flow in either direction in the semicircular canals to register movement
80
How do the semicircular canals work?
The endolymph from the otolith organs moves in them and disturbs the cupula in which there are hair cells (surrounded by support cells). These hair cells synapse with afferents of the vestibular nerve
81
What are the 3 rotational accelerations of the head sensed by the semicircular canals? Explain each and note the axis it corresponds to.
1. Roll (head tilt left and right): y axis
2. Pitch (head up and down): z axis
3. Yaw (head turn left and right): x axis
82
2 types of vertigo? Describe each.
1. Peripheral: problem with the vestibular system
| 2. Central: problem with the brain’s “balance” centers
83
4 symptoms of vertigo?
1. Feeling of spinning while at rest, dizziness
2. Motion sickness potentially with nausea and vomiting
3. Loss of balance
4. Visual difficulties: trouble focusing, nystagmus
84
Incidence and prevalence of vertigo?
~5% of people report vertigo in a given year
>7% lifetime incidence
85
What patients are more likely to report vertigo?
Women ~3 times more likely to report vertigo
86
Describe the pitch code of the auditory system. What is this called?
TONOTOPY
If you unwind the cochlea, the basilar membrane is narrow and stiff at the base, and wide and floppy at the apex and different hair cells respond to different frequencies according to their location along the basilar membrane:
- Hair cells closer to the base of basilar membrane are more sensitive to higher frequency sounds
- Hair cells closer to the apex have greater sensitivity to lower frequencies
87
What is the human audible range?
60 to 20,000 Hz
88
What audible range is lost with age?
Higher frequency sounds
89
Differences in audible ranges between men and women? Why?
Women can hear a higher frequency range because they have a smaller cochlea than men
90
Measure of sound intensity?
Decible (db)
91
Threshold of hearing?
0 db
92
Sound intensity of speech?
20-60 db
93
Difference in males and females for hearing crying babies?
Males have a deficit for hearing crying babies
94
2 types of hearing loss? Describe each.
1. Conductive hearing loss: problem with conduction of sound
| 2. Sensoneural hearing loss: problem with detection of sound or brain
95
How to tell the severity of the hearing loss?
1. 25 – 40 dB = mild (20 – 40 dB for children)
2. 41 – 55 dB = moderate
3. 56 – 70 dB = moderately severe
4. 71 – 90 dB = severe
5. > 90 dB = profound = deafness
96
4 causes of hearing loss?
1. Exposure to loud noises
2. Diseases, particularly ear infections
3. Numerous drugs and other chemicals
4. Genetic diseases
97
Incidence and prevalence of hearing loss?
~1 per 1000 people in USA became deaf before 18 yo
~4 per 1000 lifetime prevalence of deafness
>10% lifetime incidence of “hard of hearing” (=moderate hearing loss), mostly > 65 yo
98
Frequency range of speech?
300 – 2800 Hz
99
Why do children get many ear infections?
Because their Eustachian tube does not drain properly because their heads are tilted slightly backwards
100
Test to check for hearing loss?
Audiogram
101
What is presbyacusis? To what is it due?
Sloping high frequency hearing loss with age due to both neural and conductive hearing loss
102
What is low frequency hearing loss?
< 1000 Hz
103
What is mild frequency hearing loss?
1000 – 2000 Hz
104
What is high frequency hearing loss?
> 2000 Hz
105
What determines what frequencies are lost when it is due to loud noises?
Loose frequencies of the loud noises that are causing the hearing loss
106
How have hearing aids gotten much better?
They can amplify speech and filter out noise
107
What is a hearing aid made of? What issue does this cause?
Microphone + speaker = feedback because the microphone hears the sound coming out of the speaker
108
When are larger hearing aids required?
Required for greater gain in order to prevent feedback
109
What are the 3 tissue layers of the eye?
1. Fibrous tunic
2. Vascular tunic
3. Retina
110
What are the 2 parts of the fibrous tunic of the eye? What does each constitute?
1. Sclera (posterior 2/3rds)
| 2. Cornea (anterior 1/3rd)
111
What are the 3 parts of the vascular tunic of the eye?
1. Iris
2. Ciliary body
3. Choroid
