Neuro weeks 14-15 (5-10) Flashcards
(134 cards)
1
Q
Visual pathway ends retinotopically around the
A
calcarine sulcus of the primary visual cortex.
2
Q
Where axons from the Superior retinal (inferior visual) field end
A
The superior aspect of calcarine sulcus
3
Q
Where axons from the Inferior retinal (superior visual) field end.
A
cortex inferior to the calcarine sulcus
4
Q
Foveal area is represented most
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posterior
5
Q
Peripheral areas are represented more.
A
Rostral
6
Q
T / F- Some axons of the optic radiation bypass the primary visual cortex to terminate in the visual association cortex
A
True
7
Q
The visual Cortex is arranged in .
A
functional columns
8
Q
Principle LGN input into layer
A
IV.
9
Q
Matrix of different overlapping columns include: BOO
A
- Blobs
- Ocular dominance columns
- Orientation columns
10
Q
Cells in Ocular dominance columns respond with preference to .
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Right or left eye
11
Q
Cells in Ocular dominance are the
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Largest of column structures and are presented in the cortex with adjacent columns having alternating eye dominance
12
Q
Orientation columns contain
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Simple & complex cells and don’t respond to points of light but bars of light only in certain orientations with adjacent columns being related in position but different orientation
13
Q
Types of cells in the orientation columns
A
simple and complex
14
Q
Simple cells respond to
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Bars of light only in a certain orientation with inhibitory surround
15
Q
Since each LGN cell responds to a point of light with an opposing annulus, these simple cells represent a
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Convergence of many LGN cells onto a single simple cortical cell.
16
Q
Complex cells respond to
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Bars of light only in a certain orientation but do not have the inhibitory surround
17
Q
They are called complex cells because .
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They respond with movement of the bar of light in one direction
18
Q
Complex cells represent the
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convergence and summation of several simple cells
19
Q
Blob columns are located in
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Cortical layers II & III.
20
Q
Cortex is divided into
A
Blobs (for color processing) & interblob regions (form processing)
21
Q
The modular organization of the visual cortex
A
2x2 mm areas of 1° visual cortex which contains a complete 360° set of orientation columns. Set of left right ocular dominance columns and a set of 16 blobs & interblob regions for color and form discrimination. Each module is interconnected with adjacent modules and there is also binocular organization
22
Q
Binocular organization.
A
Layer IV cells of a single ocular dominance column are monocular but with the Interconnections between adjacent columns and layers produces binocular vision
23
Q
Visual Association Cortex is in Brodmann areas
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18 & 19
24
Q
Visual Association Cortex is divided into
A
Pre-striate cortex (V2) and Extra-striate (V3)
25
Pre-striate cortex V2
Brodmannn area 18- has a complete map of the visual world with more complex orientation spatial frequency, and color characteristics than seen
26
Pre-striate cortex is the area that responds to
Illusory contours.
27
Type of recognition associated with Pre-striate cortex?
Figure ground recognition - appears to also be part of visual attentional modulation
28
Extra-striate cortex – V3 Brodmann area
Gives a sense of more global motion and may also be part of dorsal & ventral visual streams
29
What is Figure-Ground relationships
Detection of objects from their background- It also gives a form of visual illusion.
30
Illusory contours
Dark circles with random lines drawn on them. When arranged in a certain way, image of box is seen -same process that gives us the “ability” to see duckies in the clouds and Jesus on a burnt tortilla
31
Dorsal Stream (Where pathway)
Cortical pathway projecing from area 18 visual association cortex to parieto-occipital cortex (posterior parietal cortex)
32
Function of Dorsal Stream (Where pathway) - MAN
* Manipulation of objects within the visual environment
* Analyzing motion and spatial orientation within the visual field
* Navigation around objects in the environment
33
Damage in the Dorsal stream (Where) pathway produces
Visual apraxia
34
Visual Apraxia signs & symptoms
Functional significance of objects is lost- can see and identify object but cannot use it. E,g can identify a comb by sight, but cannot use to comb hair
35
Ventral Stream (What pathway) projections
to occipito-temporal cortex and inferior temporal cortex
36
Function of the visual stream what pathway- IVm
Object Identification and further verbal manipulation.
37
Damage to ventral stream what pathway causes
Visual agnosia – inability to name an object even though it is seen.
38
Monocular visual loss
Damage to the optic nerve which causes loss of all axons from one retina (eye)
39
Contralateral homomynous hemianopsia
Complete lesion of optic tract fibers causes loss of half of visual field – contralateral to damage
40
Macular sparing
Vascular lesions of the cortex (occipital lobe) causes loss of vision because of damage to the optic cortex. However, since both MCA and PCA supply the cortical area representing the macula, macular sparing is obtained.
41
Signs of Macular Sparing- OSV
One of the first signs of MS is visual disturbances which include :
* Optic neuritis
* Scotoma and
* Visual field defects dependent upon the nature of the optic nerve/tract demyelination.
42
Lesions of the parieto-occipital lobe (where pathway) or Balint’s syndrome produces: SOO
* Simultagnosia
* Optic ataxia
* Ocular apraxia
43
Role of the Inferior temporal cortex in the visual stream pathway
Identification of complex stimuli such as faces.
44
Damage to the inferior temporal complex produces
Posopagnosia, the inability to identify people by their faces
45
Optic neuritis - MS
An Inflammatory demyelinating disorder often related to multiple sclerosis.
46
Which labyrinth preserves the basic form of the osseous labyrinth
The Membranous labyrinth
47
Characteristics of optic neuritis **DIE**
* Decreased acuity
* Impaired color vision.
* Eye pain
* Recovery is common
48
Papilledema
Optic disc swelling associated with elevated intracranial pressure
49
T / F -Damage to optic nerve/ chiasm and tract can lead to similar patterns of vision loss
False very different patterns
50
Monocular visual loss
Damage to the optic nerve causing loss of all axons from one retina (eye)
51
What is released when intracellular Ca++ increase and depolarization of hair cell occurs?
Glutamate to activate auditory primary afferent axons- slight K+ current all the time so regular depolarization of hair cell and low frequency firing of primary afferent neurons.
52
Contralateral homomynous hemianopsia
Complete lesion of optic tract fibers causing loss of half of visual field – contralateral to damage
53
Function of the Auditory system
To detect and analyze sounds from the environment
54
Conduction of the auditory vibrations are controlled by
Tensor tympani innervated by CN V which controls the movement of the tympanic membrane and the stapedius which is innervated by CN VII and controls the movement of the stapes. These two muscles reflexively contract to lessen movement & sound conduction.
55
Scotoma
An area of partial alteration in the field of vision consisting of a partially diminished or entirely degenerated visual acuity that is surrounded by a field of normal – or relatively well-preserved – vision.
56
Prodromal phase of classic migraine involves
Visual cortex. 1/3 of migraine sufferers experience a visual aura – described as fireworks – lights, colors, flashing. About 10% of people with migraine experience a
57
Scintillating scotoma
A fixed or expanding spot of flickering light near or in the center of the visual field
58
Simultagnosia
Can see only small parts of the visual field at a time – difficulty comprehending large visual areas and objects – see only the trunk of an elephant so cannot recognize the whole structure
59
Optic ataxia
Impaired ability to point to or reach for an object
60
Ocular apraxia
Difficulty directing gaze toward an object in peripheral field
61
Cause of cortical blindness
Bilateral lesion of primary visual cortex.
62
How are inner hair cells depolarized
By movement of endolymph in inner spiral sulcus which pivot their stereocilia
63
Blindsight
Cortical blindness, but preserved ability to use some visual information Sparing of pulvinar to posterior parietal area projections
64
Two main divisions of both the bony & membranous Labyrinth- VC
Cochlear Vestibular
65
A series of bony cavities and channels within the petrous part of the temporal bone is known as
Osseous or bony labyrinth
66
A series of fluid filled communicating ducts & sacs within the bony labyrinth secured to bony labyrinth by fibrous bands.
Membranous labyrinth
67
What preserves the basic form of the osseous labyrinth
The Membranous labyrinth
68
The primary afferent axons of primary afferent bipolar neurons end on the
dorsal & ventral cochlear nuclei. These relay nuclei are tonotopically map with high frequencies dorsal & low frequencies ventral
69
Fluid that separates the osseous & membranous labyrinth- Contiguous with CSF of subarachnoid space via peri-lymphatic duct.
Perilymph
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Fluid within membranous labyrinth that has the same ionic composition as intracelluar fluid.
Endoilymph
71
Axons from 3° neurons of the inferior colliculus ascend to
Thalamus as brachium of inf colliculus. Some of these fibers decussate and some rise ipsilaterally. Note- this is another point that contributes to the bilateral nature of the ascending auditory pathways. Tonotopic mapping continues in the inferior colliculus with high frequencies more ventral & low more dorsal
72
Endoilymph is formed by
Specialized secretory cells of the membranous labyrinth
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The Primary Auditory cortex transverses
Temporal gyrus & adjacent planum temporale.
74
How is endolymph removed?
By specialized cells of endolymphatic sac
75
Larger representation of the primary auditory cortex is on which side?
Left than right in most individuals. It appear to parallel the distribution of the speech centers because of the strong linkage between audition and speech
76
How are receptor cells of vestibular & auditory systems similar?
Both when activated secrete neurotransmitters to excite terminal endings of vestibulocochlear nerve (CN VIII).
77
Hair cells are
Receptor units or first order sensory cell not a nerve cell.
78
Structure of hair cells
Polar with a very large single kinocilium and 60-100 smaller stereocilia arranged away from the kinocilium by decreasing height. The Kinocilium degenerates during development in cochlear receptor surface but is retained in the vestibular system
79
What happens when hair cells are adequately stimulated? Function
Stimulus causes mechanical “bending” of cilia or hairs. Although referred to as bending, pivoting better term. Actin myofilament holds cilia stiff so cilium pivots at flexible base where it connects to hair cell. The Cilia bundle is displaced as a unit- held by top links.
80
Pivoting of cilia on hair cell causes
Depolarization of hair cell. Endolymph rich in K+ & poor in Na+ & positively charged compared to negative intra-cellular environment. Pivoting of cilia produces increased influx K+ into cell and the depolarization resulting from this influx of K+ produces cell depolarization- opens voltage-gated Ca++ channels
81
What is released when intracellular Ca++ increased and depolarization of hair cell occurs?
Glutamate to activate auditory primary afferent axons. There are actually slight K+ current all the time so regular depolarization of hair cell and low frequency firing of primary afferent neurons. So activation of the hair cell increases the spontaneous firing of these hair cells.
82
Activation of the hair cell causes
Increases in the spontaneous firing of these hair cells.
83
Hair cell polarity plays an important role in
Vestibular function.
84
Pivoting of the Stereocilia away from kinocilium
Decreased spontaneous firing rate of the vestibular nerve primary afferent
85
Function of the Auditory system
To detect and analyzes sounds from the environment
86
Outer ear consists of
Pinna & external auditory meatus and is designed to collect sound and transfer it to the middle ear.
87
What separates outer and middle ear
Tympanic membrane
88
Middle ear
An air-filled cavity within the temporal bone that contains 3 ear ossicles: malleus, incus, and stapes 2 muscles – tensor tympani & stepedius
89
In the Middle ear, vibrations of tympanic membrane is conducted by
Ear ossicles to vibrate oval window. There is a 25 fold increase in pressure on oval window compared to tympanic membrane due to both the difference in the sizes of the two membranes and the mechanical advantage ear ossicles
90
Conduction of the vibrations are controlled by
Tensor tympani innervated by CN V which controls the movement of the tympanic membrane and the stapedius which is innervated by CN VII and controls the movement of the stapes. These two muscles reflexively contract to lessen movement & sound conduction.
91
Inner ear is separated from the middle ear by
oval & round windows.
92
Inner ear is comprised of
Cochlea- the spiral bony container with the modulus wound around central core of the spiral. Bipolar cells of spiral ganglion in modulus. The spiral ganglia is where the cell bodies of the auditory primary afferent axons sit.
93
The inner ear is fluid filled with
Perilymph between bony & membranous labyrinth. Endolymph in the several membranous structures form the cochlear duct.
94
3 chambers within the inner ear:
Scala vestibuli & scala tympani – filled with perilymph Scala media or cochear duct formed by vestibular & basilar membranes which is filled with Endolymph
95
Vibrations in perilymph are produced by
Vibration of oval window and are carried down the scala vestibuli & around the heliotrema into the scala tympani. Here these vibrations vibrates the basilar membrane.
96
The Basilar membrane varies in width and stiffness from base to apex of cochlea. The basilar membrane is thinner & more compliant near the ------------ where it is vibrated by higher frequency vibrations of \_\_\_\_\_\_\_\_\_\_\_
oval window, perilymph
97
Basilar membrane is thicker & stiffer toward which apex?
cochlear apex – vibrated by lower frequency vibrations of perilymph.
98
With tonotopic mapping of cochlea the highest frequencies are received at the \_\_\_\_\_\_\_\_and the Lowest frequencies sensed at the
base, apex
99
where does auditory transduction occurs
In hair cells of the organ of Corti in the cochlear duct.
100
Basic structure of the organ of Corti
Outer & inner rows of hair cells rest on basilar membrane. Above these hair cells is the tectorial membrane. The tectorial membrane is gelatinous shelf resting on stereocilia of the outer hair cells
101
Peripheral processes of the bipolar cells of the spiral ganglion surround
Base of hair cells and are held in place with supporting cells
102
where are hair cells found / located?
Within the endolymph-filled scala media. There are approximately 3500 flask-shaped inner hair cells and \>15,000 cylindrical outer hair cells
103
Inner hair cells sit on the \_\_\_\_\_\_\_\_\_portion of basilar membrane while the outer hair cells are on the\_\_\_\_\_\_ .
least flexible, most flexible portion
104
T / F- Inner hair cells do not touch tectorial membrane but the tectorial membrane rest on the stereocilia of the the outer hair cells
True
105
How are outer hair cells depolarized
By pivoting hair cells against tectorial membrane
106
How are inner hair cells depolarized?
By movement of endolymph in inner spiral sulcus which pivot their stereocilia
107
What % of afferent axons in cochlear nerve receive their input from inner hair cells
95%
108
what % of afferent axons in cochlear nerve receive their input from outer hair cells?
5%
109
Primary sensory element of the organ of Corti
Inner hair cells
110
Outer hair cells have motor proteins activated by
Depolarization of hair cell. These proteins shortens outer hair cell which amplifies movement of basilar membrane up to 100 fold producing a much greater depolarization of the inner hair cells. So it appears that the outer hair cells regulate the excitability of the organ of Corti by regulating the movement of the basilar membrane.
111
Cell bodies of the primary afferent bipolar neurons reside in
Spiral ganglion
112
Axons of cell bodies of the primary afferent bipolar neurons enter the brainstem
Lateral and slightly caudal to vestibular 1° afferents as part of CN VIII – Vestibulocochlear nerve.
113
The primary afferent axons of primary afferent bipolar neurons end on the
dorsal & ventral cochlear nuclei. These relay nuclei are tonotopically map with high frequencies dorsal & low frequencies ventral
114
Cochlear Nuclei are
2° or relay auditory neurons.
115
Axons of cochlear nuclei can take one of three paths:
Ventral acoustic stria (trapezoid body) – runs ventrally thru caudal pontine tegmentum Dorsal & intermediate acoustic stria (runs more dorsally through caudal pons) or Ascend contralaterally as lateral lemniscus. some ascend in ipsilateral lateral lemniscus, and some synapse on a variety of nuclei in pons – most prominent is superior olivary nucleus. But even at this point the auditory ascending system is bilateral.
116
The Lateral lemniscus have Axons from
2° auditory neurons & few 3° from superior olivary nucleus. Some fibers ascend ipsilaterally and some ascending contralaterally. The lateral lemniscus ascends just lateral to the STT. Some of the axons in the lateral lemniscus synapse in nucleus of lateral lemniscus but most ascend to inferior colliculus
117
Most 2° auditory neurons end on neurons in
Inferior colliculus but a few will continue to ascend to the meidal geniculate body of the thalamus.
118
Axons from 3° neurons of the inferior colliculus ascend to
Thalamus as brachium of inf colliculus. Some of these fibers decussate and some rise ipsilaterally. Note- this is another point that contributes to the bilateral nature of the ascending auditory pathways. Tonotopic mapping continues in the inferior colliculus with high frequencies more ventral & low more dorsal
119
Mostly 3° axons end on 4° in
Medial geniculate nucleus of thalamus (however some of the fibers that synpase here are already 4° fibers in the pathway and some are only 2° fibers.
120
Medial Geniculate Nucleus Axons give rise to
Auditory radiations to 1° auditory cortex. There continues to be tonotopic mapping in the Medial Geniculate nucleus with high frequencies medial & low frequencies lateral
121
Much of the primary auditory cortex lies within the
Insular side of the superior temporal gyrus.
122
Larger representation of the primary auditory cortex is on which side?
Left than right in most individuals. It appear to parallel the distribution of the speech centers because of the strong linkage between audition and speech
123
2° axons from cochlear nuclei decussate in 1 of 3 locations
Axons of superior olivary nucleus also decussate in the trapezoid body (inferior acoustic stria) Commissural connections between the inferior colliculi
124
Bilaterality of acoustic projections at each point of decessation and decussation of already decussated pathway means that
Loss of one central pathway or loss of auditory cortex does not produce deafness in one ear but issues related to sound localization & identification
125
Two peripheral mechanisms that contribute to the ability to localize sounds: ITD & IID
Difference in timing between sound arriving at one ear versus the other (interaural time difference - ITD) Difference in sound intensity between the two ears (interaural intensity difference - IID)
126
Time difference is best at determining
Direction of low frequencies
127
Intensity difference best at distinguishing
Direction of high frequencies. This may be true since the head is a greater sound barrier to high frequencies than it is to low freqeuncies, so high frequencies may be attenuated to a greater degree and therefore be more localizable using this mechanism.
128
The Pinnae of the ear assists in
Sounds to the front, back and above which would not be distinguishable otherwise. But sounds immediately to the front, back or just above the head are still the hardest to localize. That is why we will often move our head to one side or the other to localize a sound.
129
Neural mechanisms involve
Superior olivary nucleus.
130
Lateral superior olivary nucleus is specialized for
High frequencies and cells measure interaural intensity difference by integrating ipsilateral excitatory and contralateral inhibitory inputs
131
Medial superior olive is specialized for
Low frequencies and measures interaural time differences using excitatory inputs from both sides
132
Tensor tympani/stapedius reflex- Afferent (sensory) limb of reflex:
A few fibers from the auditory nuclei terminate in the nuclei of the facial and trigeminal motor nuclei
133
Tensor tympani/stapedius reflex- Efferent (motor) limb of reflex:
Branch of facial nerve to stapedius and a Branch of trigeminal nerve to tensor tympani
134
Function of the tensor tympani / stapedius reflex
To limit amplitude of loud and high-frequency sounds and to filter out noise arising from the head itself
