Exam Two Flashcards
1
Q
What is accommodation?
A
increasing lens strength from 20-34D.
2
Q
Parasympathetic causes what in accommodation?
A
-contraction of ciliary muscle allowing relaxation of suspensory ligaments attached radially around lens, which becomes more convex, thus increasing refractive power.
3
Q
What is presbyopia?
A
- loss of elasticity of the lens with age
- this decreases accommodation.
4
Q
Types of errors of refraction?
A
- Emmetropia
- Hyperopia
- Myopia
- astigmatism
5
Q
What is emmetropia?
A
- normal vision
- ciliary muscle is relaxed in distant vision
6
Q
What is hyperopia?
A
- “far-sighted”
- focal point is behind the retina.
7
Q
What is myopia?
A
- “near-sighted”
- focal point in front of retina.
8
Q
What is astigmatism?
A
irregularly shaped
- cornea(more common), or
- lens(less common).
9
Q
Information the Snellen Eye Chart gives you
A
ratio of what that person can see compared to a person with normal vision.
10
Q
What is the fovea centralis?
A
area of greatest visual acuity.
11
Q
Outside the fovea centralis, visual acuity increases or decreases by how much and where?
A
decreases by more than 10 fold near periphery.
12
Q
What is Stereopsis?
A
binocular vision
13
Q
What happens in stereopsis?
A
- eyes are separated by 2 inches-slight difference in position of visual image on both retinas
- closer objects are more laterally placed.
14
Q
What is glaucoma?
A
- increased intraocular pressure by compression of optic nerve
- can lead to blindness.
15
Q
What is the function of the retina and what does it contain?
A
- Peripheral extension of CNS
- Processing of visual signal.
- Contains photoreceptors(rods, cones) and other cells(amacrine, ganglion, horizontal, bipolar)
16
Q
Examples of photoreceptors?
A
Rods and cones
17
Q
Light breaks down what?
A
Rhodopsin(rods) and cone pigments(cones)
18
Q
When stimulated by light, photoreceptors release less of?
A
glutamate
19
Q
What are bipolar cells?
A
cells that connect photoreceptors to either ganglion cells or amacrine cells.
20
Q
Two types of bipolar cells?
A
-“ON” or invaginating bipolars-hyperpolarized by glutamate -“OFF” or flat bipolars-depolarized by glutamate.
21
Q
What are ganglion cells?
A
- can be “ON” or “OFF” bipolar
- generate action potentials carried by optic nerve.
22
Q
Three types of ganglion cells
A
- x(p)
- y(m)
- w cells
23
Q
P(x) ganglion cells
A
- most numerous(55%)
- slower conduction velocity
- small receptive field
- responsible for color vision
- project to Parvocellular layer of lateral geniculate nucleus.
24
Q
M(y) ganglion cells
A
- receive input from amacrine cells
- 5% of ganglion cells
- larger receptive field
- fast conduction velocity
- more sensitive to brightness
- black and white images
- project to magnocellular lateral geniculate nucleus.
25
W ganglion cells
- smallest
- slowest conduction velocity
- 40% of all ganglion cells
- act as light intensity detectors
- broad receptive fields
- receive most of input from rods
- important for crude vision in dim light
26
Horizontal cells
- non-spiking inhibitory interneurons
- When depolarized, they inhibit photoreceptors.
- they make complex synaptic connections with photoreceptors.
27
What are amacrine cells?
cells that receive input from bipolar cells and project to ganglion cells. They release different neurotransmitters such as GABA, dopamine.
28
Center-Surround fields
receptive fields of bipolar and ganglion cells.
29
What is a Center Field?
Field mediated by all photoreceptors, synapsing directly onto the bipolar cell.
30
What is a Surround Field?
Field mediated by photoreceptors which gain indirect access to bipolar cells via horizontal cells.
31
Photoreceptor contribution to fields
photoreceptors contributing to center field of one bipolar cell contributes to surround field of other bipolar cells.
32
Simultaneous stimulation of light of both fields gives what?
no net response of either field.
33
If center field is on, surround is?
off
34
In the Fovea, what is the ratio of cone:bipolar cell:ganglion cell?
(Can be as low as) 1 cone:1 bipolar cell: 1 ganglion cell
35
in peripheral retina, what's the ratio of rods:bipolar cell: ganglion cell
hundreds of rods can supply a single bipolar cell and many bipolar cells connected to 1 ganglion cell.
36
In dark adaptation, what adapts first?
cones then rods but rods adapt to a greater extent.
37
what happens in dark adaptation?
dilation of pupil, neural adaption, cone adaptation increases less than 100 fold, rod adaption increases more than 100 fold, and increase of retinal sensitivity 10,000 fold
38
3 types of cones
blue, green, and red sensitive
39
What is color blindness?
sex-linked trait carried on x chromosomes. Transmitted by the female, but occurs exclusively in males.
40
Most common color blindness
red-green. missing either red or green cones.
41
Loss of red cones is called what?
Protanope-decrease in overall visual spectrum.
42
Loss of green cones is called what?
Deuteranope-normal overall visual spectrum.
43
Ishihara chart
helps to distinguish between green, yellow, orange, and red problems.
44
Loss of blue cones
- rare
- may be under-represented
- "Blue Weakness"
45
List the visual pathway.
- optic nerve to optic chiasm
- optic chiasm to optic tract
- optic tract to lateral geniculate
- lateral geniculate to primary visual cortex (geniculocalcarine radiation)
46
Lesion at optic nerve?
blind in ipsilateral eye
47
Lesion at optic chiasm?
bitemporal hemianopia
48
Lesion in optic tract?
contralateral homonymous hemianopia
49
Additional visual pathways?
from optic tracts to:
- suprachiasmatic nucleus (biologic clock function)
- pretectal nuclei (reflex movement of eyes - focus on objects of importance)
- superior colliculus (rapid directional movement of both eyes -- orienting reactions)
50
Primary visual cortex
Brodman area 17 (VI) - two times neuronal density
51
BM 17 simple cells?
- respond to bar of light/dark
| - above and below layer IV
52
BM 17 complex cells?
- motion dependent
| - same orientation sensitivity as simple cells
53
BM 17 color blobs?
- rich in cytochrome oxidase in center of each occular dominance band
- starting point of cortical color processing
54
BM 17 vertical columns?
- input into layer IV
| - hypercolumn - functional unit, block through all cortical layers about 1mm squared
55
Visual association cortex
-visual signal is broken down and sent over parallel pathways
56
Visual analysis
- process along many paths in parallel
| - at least 30 cortical areas processing vision
57
Parvo-interblob
high resolution static form perception (black and white)
58
Blob
- color (V4)
| - Achromatopsia
59
Magno-interblob
- movement (MT)
| - Stereoscopic Depth
60
Old visual system
- old pathway projects to the superior colliculus
- locating objects in visual field, so you can orient to it (rotate head and eyes)
- subconscious
- blindsight
61
New visual system
- new pathway projects to the cortex
| - consciously recognizing objects
62
Blindsight
- patients who are effectively blind because of brain damage can carry out tasks which appear to be impossible unless they can see the object
- ie. reach out and grasp objects, post a letter through a narrow slot
63
Why can effectively blind people carry out tasks which appear to be impossible unless they can see the object?
- visual information travels along two pathways in the brain
- if the cortical pathway is damaged, a patient may lose the ability to consciously see an object but still be aware of its location and orientation via projections to the superior colliculus at a subconscious level
64
Cortical fixation areas - Voluntary fixation mechanism (anterior)
- person moves eyes voluntarily to fix on an object
| - controlled by cortical field bilaterally in premotor cortex
65
Cortical fixation areas - involuntary fixation mechanism (posterior)
- holds eyes firmly on object once it has been located
- controlled by secondary visual areas in occipital cortex located just in front of primary visual cortex
- works in conjunction with the superior colliculus (involuntary fixation is mostly lost when superior colliculus is destroyed)
66
Parasympathetic control of pupillary diameter?
causes decrease size of pupil - MIOSIS
67
Sympathetic control of pupillary diameter?
causes increase in size of pupil - MYDRIASIS
68
Pupillary light reflex pathway:
- optic nerve to
- pretectal nuclei to
- Edinger Westphal to
- ciliary ganglion to
- pupillary sphincter to
- cause constriction (parasympathetic)
69
What is Horner's Syndrome?
- interruption of SNS supply to an eye
| - from cervical sympathetic chain
70
What are symptoms of Horner's syndrome?
- constricted pupil compared to unaffected eye
- drooping of eyelid normally held open in part by SNS innervated by smooth muscle
- dilated blood vessels
- lack of sweating on that side of face
71
What are the functions of the medial and lateral recti (extraoccular muscles)?
-medial rectus of one eye works with the lateral rectus of the other eye as a yoked pair to produce lateral eye movements
72
What are the functions of the superior and inferior recti (extraoccular muscles)?
- elevate and depress the eye respectively
| - most effective when the eye is abducted
73
What is the function of the superior oblique muscles?
-lowers the eye when it is adducted
74
What is the function of the inferior oblique muscles?
-elevates the eye when it is adducted
75
What is the innervation of the extraoccular muscles?
- CN III: rest of the muscles
- CN IV: superior oblique only
- CN VI: lateral rectus only
76
**Summary of extraoccular muscles**
See page 7 of notes for chart
77
What is the unit of sound?
decibel (dB)
78
Decibel = ?
1/10 log [ 1 (measured sound)/1 (standard sound) ]
79
What is the reference pressure for standard sound?
0.02 x 10^-2 dynes/cm squared
80
Sound
-energy is proportional to the square of pressure
81
A 10 fold increase in sound energy equals?
1 bel
82
One dB represents an actual increase in sound energy of?
about 1.26 X
83
Ears can barely detect a change of how many decibels?
1 dB
84
How many decibels is a whisper?
20 dB
85
How many decibels is a normal conversation?
60 dB
86
How many decibels is a symphony?
100 dB
87
How many decibels is a threshold of discomfort?
130 dB
88
How many decibels is a threshold of pain?
160 dB
89
What is the frequency of audible sound in a young adult?
20-20 000 Hz
| -decreases with age
90
What is the greatest acuity for the frequency of an audible sound?
1000-4000 Hz
91
In tympanic membrane and ossicles, what is impedance matching?
it occurs between sound waves in air and sound vibrations generated in the cochlear fluid
92
What percentage is perfect for sound frequency of 300-3000 Hz?
50-75%
93
Ossicular system
- reduces amplitude by 1/4
- increases pressure against oval window 22 X (increased force 1.3, decreased area from TM to oval window 17)
- non functional ossicles or ossicles absent
- decrease in loudness about 15-20 dB
- medium voice now sounds like a whisper
94
Ossicular system: Attentuation of sound by contraction of?
- Stapedius muscle - pulls stapes outward
| - Tensor tympani - pull malleous inward
95
What causes contraction of stapedius and tensor tympani muscles?
CNS reflex
96
What is the attenuation of sound activated by?
- loud sound
| - speech
97
What is the latency period of the attenuation of sound?
40-80 msec
98
The attenuation of sound is most effective at frequencies of?
< 1000 Hz
99
Attenuation of sound:
creation of rigid ossicular system which reduces ossicular conduction
100
What is the function of attenuation of sound?
- protect cochlea from very loud noises
| - makes low frequency sounds in loud environments
101
The cochlea is a system of 3 coiled tubes which are:
- scala vestibuli
- scala media
- scala tympani
102
Scale Vestibuli
- separated from the scala media by Reissner's membrane
- associated with the oval window
- filled with perilymph (similar to CSF)
103
Scala Media
- separated from scala tympani by basilar membrane
- filled with endolymph secreted by stria vascularis which actively transports K+
- top of hair cells bathed by endolymph
104
Scala Tympani
- associated with the round window
| - filled with perilyph which bathes lower bodies of hair cells
105
What is Endocochlear potential?
-electrical potential of +80mV exists between endolymph and perilymph due to active transport of K+ into endolymph
106
What is the purpose of the endocochlear potential?
- sensitizes hair cells
| - inside of hair cells (-70mv vs -150mv)
107
What is the function of cochlea?
- change mechanical vibrations in fluid into action potentials in CN 8
- causes movement of the basilar membrane
- increased displacement - increased neuronal firing resulting in an increase in sound intensity (some hair cells only activated at high intensity)
108
What causes movement of the basilar membrane?
sound vibrations created in the fluid of cochlea
109
What is the Place Principle?
- different sound frequencies displace different areas of the basilar membrane
- natural resonant frequency
110
Hair cells near oval window (base):
- short and thick
| - respond best to higher frequencies (>4500Hz)
111
Hair cells near helicotrema (apex):
- long and slender
| - respond best to lower frequencies (<200Hz)
112
What is the Fourier analysis by the cochlea
any complex wave can be broken down into its component sine waves with differing phases, frequencies and amplitudes
113
The cochlea behaves like a Fourier analyser by:
- acts as a kind of auditory prism
| - sorting out vibrations of different frequencies into different positions along the membrane
114
Central Auditory Pathway
- organ of corti to ventral and dorsal cochlear nuclei in upper medulla
- cochlear nucleus to superior olivary nucleus (most fibers pass contralateral, some stay ipsilateral)
- superior olivary nucleus to nucleus of lateral lemniscus
- nucleus of lateral lemniscus to inferior colliculus (via lateral lemniscus)
- inferior colliculus to medial geniculate nucleus
- medial geniculate nucleus to primary auditory cortex
115
Where is the primary auditory cortex located?
in the superior gyrus of temporal lobe
116
What does the primary auditory cortex do?
tonotopic organization
- high frequency sounds: posterior
- low frequency sounds: anterior
117
What is S.Q.U.I.D?
Super Quantum Interference Device
| -detects changes in central sensitivities in the primary auditory cortex
118
What does the air conduction pathway involve?
- external ear canal
- middle ear
- inner ear
119
What does the bone conduction pathway involve?
direct stimulation of cochlea through the vibration of the skull as the cochlea is imbedded in the petrous portion of the temporal bone
120
Reduced hearing may involve?
- ossicles (air conduction)
| - cochlea or associated neural pathway (sensory neural loss)
121
If there is a known bad ear, how can we differentiate a hearing loss?
- Weber test (512 Hz) - tuning fork placed on midline of the skull
- if sounds louder in bad ear: conduction loss in bad ear (external canal or ossicles involved)
- if sounds louder in good ear: sensory neural loss in bad ear
122
What test confirms the results of the Weber test?
Rinne test
- air conduction > bone: sensory neural
- bone conduction > air: air conduction loss
123
What two principal mechanisms determine the horizontal direction from which sound originates from?
1. Time lag between ears
- functions best at frequencies <3000 Hz
- involves medial superior olivary nucleus (neurons that are time lag specific)
2. Difference in intensities of sounds in both ears
- involves lateral superior olivary nucleus
124
Exteroceptive chemosenses?
- taste
| - olfaction (smell)
125
Taste works together with?
smell
126
What are the 6 categories of primary tastes?
- sweet
- salt
- sour
- bitter (lowest threshold - protective mechanism)
- Umami (savory/pungent)
- Fatty (some evidence supports this as a 6th taste)
127
Olfaction (smell)
primary odors (100-1000 different receptors)
128
Taste receptors:
- may have preference for stimuli
| - influenced by past history
129
How are taste receptors influenced by past history?
- recent past: adaptation
| - long standing: memory and conditioning-association
130
Sour taste
caused by acids (H ion concentration)
131
Salty taste
caused by ionized salts (primarily Na+)
132
Sweet taste
- most are organic chemicals (ie. sugars, esters, glycols, alcohols, aldehydes, ketones, amides, amino acids)
- inorganic salts of lead (Pb) and beryllium (Be)
133
Bitter taste
no one class of compounds but:
- long chain organic compounds with N
- alkaloids (quinine, strychnine, caffeine, nicotine)
134
Umami/Savory taste
- flavor associated with MSG
| - receptor responds to amino acids
135
Taste sensations are generated by?
- complex transactions among chemicals and receptors in taste buds
- subsequent activities occurring along the taste pathways
136
What contributes to gustatory experiences?
- sensory processing
- centrifugal control
- convergence
- global integration among related systems
137
What consists of taste buds distributed over the tongue, pharynx and larynx?
taste neuroepithelium
138
Taste buds are aggregated in relation to 3 kinds of papillae which are?
1. fungiform: blunt pegs 1-5 buds/top
2. foliate: submerged pegs in serous fluid with 1000's of taste buds on side
3. circumvallate: stout central stalks in serous filled moats with tastes buds on sides in fluid
139
What are taste buds?
40-50 modified epithelial cells group in barrel shaped aggregate beneath a small pore which opens onto epithelial surface
140
Innervation of taste buds:
- each taste nerve arborizes and innervates several buds (convergence in 1st order)
- receptor cells activate nerve endings which synapse to base of receptor cell
- individual cells in each bud differentiate, function and degenerate on a weekly basis
141
Taste nerves:
- continually remodel synapses on newly generated receptor cells
- provides trophic influences essential for regeneration of receptors and buds
142
Adaptation of taste:
- rapid: within minutes
- taste buds account for 1/2 of adaptation
- rest of adaptation occurs higher in CNS
143
What is the CNS pathway of taste for the anterior 2/3 of the tongue?
- lingual nerve to
- chorda tympani to
- facial nerve (CN VII)
144
What is the CNS pathway of taste for the posterior 1/3 of the tongue?
-CN IX (petrosal ganglion)
145
What is the CNS pathway of taste for the base of the tongue and palate?
-CN X
146
Where do the 3 CNS pathways of taste all terminate?
-nucleus tractus solitarius (NTS)
147
What happens from the nucleus tractus solitarius?
- goes to the VPM of thalamus via central tegmental tract (ipsilateral) which is just behind the medial lemniscus)
- goes from the thalamus to the lower tip of the post-central gyrus in parietal cortext and adjacent opercular insular area in sylvian fissure
148
What are the two taste receptors?
- G protein linked receptors
| - Ion channels
149
What tastes are the G protein linked receptors responsible for?
- bitter
- sweet
- umami
150
What tastes are the ion channels responsible for?
- sour
| - salty
151
Olfaction is the least understood because:
- smell is subjective
- hard to study in animals
- rudimentary in humans (humans are microsmatic - poorly developed sense of smell)
152
How many conchae does the nose have?
3 conchae bilaterally
153
What are the conchae?
highly vascularized organs covered with erectile tissue
154
What are the functions of the conchae?
- moisten and warm incoming air
| - limit loss of heat and water in expired air
155
What happens to the conchae when you have a cold?
- becomes engorged with blood
- blocks air from reaching olfactory receptors
- partial loss of smell
156
What is found at the top of the conchae?
olfactory cleft made of olfactory epithelium
157
What is the olfactory cleft/epithelium associated with?
olfactory receptors
158
How much air reaches the olfactory cleft?
- normally only a small portion
| - sniffing increases the percentage by creating turbulence around the conchae
159
What is another name for the vomeronasal organ?
Jacobson's organ
160
Where is the vomeronasal/Jacobson's organ located?
medially on septum in lower part of nasal cavity
161
What is the function of the vomeronasal/Jacobson's organ?
appears to contribute to olfaction
| -probably more receptive than olfactory epithelium to pheromones which have profound effects on behavior
162
Where is the olfactory membrane located?
superior part of nostril
163
What are olfactory cells?
- bipolar nerve cells
- 100 million in olfactory epithelium
- 6-12 olfactory hairs/cells project in mucus
- react to odors and stimulate cells
- connect to olfactory bulb via cribriform plate
164
What are the 3 cells in the olfactory membrane?
- olfactory cells
- cells which make up Bowman's glands (secrete mucus)
- Sustenacular cells (supporting cells)
165
What are the characteristics of odorants?
- volatile
- slightly water soluble (for mucus)
- slightly lipid soluble (for membrane of cilia)
166
What is the threshold for smell?
-very low
167
Methyl mercaptan:
- 1/25 billion of mg/ml of air can be detected
| - mixed with natural gas so gas leaks can be detected
168
Stimulation of olfactory cells:
- odorant binds to receptor protein
- inside of protein is couple to a G-protein (3 subunits)
- G-protein activates adenyl cyclase
- adenyl cyclase converts ATP to cAMP which causes protein gated Na+ channels to open
- Ca++ enters as well which opens chloride channels
- high Cl- concentration inside olfactory receptors (ununsual)
- efflux of Cl- prolongs depolarization
- at every step the effect is amplified
169
Is there such thing as a primary odor?
no
- there is no objective, physical way of classifying smells systematically like color or tone
- no classification enables one to predict the result of making mixtures (like color triangle)
170
Primary sensations of smell:
-significant aspect of the brain's analysis of odor is carried out by receptors in the olfactory membrane
171
What is anosmia?
- odor blindness
- has been described for more than 60 different substances
- may involve lack of a specific receptor protein
172
What is the resting membrane potential for an olfactory receptor when not activated?
- 55mv
| - 1 impulse/20 sec to 2-3 impulses/sec
173
What is the activated membrane potential for an olfactory receptor?
- 30mv
| - 20 impulses/sec
174
Prolongation of response in response to positive charge:
- Na+ and Ca++ influx during depolarization
- Ca++ influx binds to and opens Cl- channel protein
- high Cl- therefore have Cl- efflux therefore prolong depolarization
175
How many glomeruli in an olfactory bulb?
several thousand per bulb
176
What are glomerulus in olfactory bulb?
-connections between olfactory cells and cells of the olfactory tract
177
What are the functions of the glomerulus in olfactory bulb?
- receive axons from olfactory cells (25, 000)
| - receive dendrites from large mitral cells (25) and smaller tufted cells (6)
178
What are the four cells in the olfactory bulb?
-mitral cells
-tufted cells
granule cells
-periglomerular cells
179
What do the mitral cells do?
- continually active
| - send axons into CNS via olfactory tract
180
What do the tufted cells do?
- continually active
| - send axons into CNS via olfactory tract
181
What do granule cells do?
- inhibitory cell which can decrease neural traffic in olfactory tracts
- receive input from centrifugal nerve fibers
182
What do periglomerular cells do?
-inhibitory cells between glomerulus
183
What does the very old CNS pathway for olfaction do?
- medial olfactory area
- feeds into hypothalamus and primitive areas of the limbic system (from medial pathway)
- basic olfactory reflexes
184
What does the less old CNS pathway for olfaction do?
- lateral olfactory area
- prepyriform and pyriform cortex - only sensory pathway to cortex that doesn't relay via thalamus (from lateral pathway)
- learned control/adversion
185
What does the newer CNS pathway for olfaction do?
- passes through the thalamus to orbitofrontal cortex (from lateral pathway)
- conscious analysis of odor
186
What forms the medial and lateral pathways?
-2nd order neurons form the olfactory tract and project to primary olfactory paleocortical areas
187
What are the four primary olfactory paleocortical areas?
- anterior olfactory nucleus
- amygdala and olfactory tubercle
- pyriform and periamygdaloid cortex
- rostral entorhinal cortex
188
What does the anterior olfactory nucleus do?
modulates information processiong in the olfactory bulbs
189
What do the amygdala and olfactory tubercle do?
important in emotional, endocrine and visceral responses of odors
190
What do the pyriform and periamygdaloid cortex do?
olfactory perception
191
What does the rostral entorhinal cortex do?
olfactory memories
192
Psychological links between olfactory of limbic function:
- in humans odors can evoke recollection of past experience
- not just the experience but also the mood or emotion that was felt at the time
- sometimes very intensely which is seldom duplicated by either auditory or visual stimulation memory recall
193
What is the psychological link between olfactory and limbic function thought to be due to?
direct penetration of the emotional areas of the limbic system by olfactory fibers
