Midterm 1 Flashcards
(177 cards)
1
Q
Where is the pain sensitivity within the skull restricted to
A
Pain sensitivity in the skull is restricted tot he intracranial meninges
2
Q
What are the three layers of the Meninges
A
Dura mater
Arachnoid mater
Pia Mater
3
Q
Describe the dura mater
A
Thickest, outermost layer, protective, impermeable
Made of two layers: Periosteal layer, Meningeal layer
4
Q
Describe the two layers of the Dura mater
A
Periosteal: attached to inner surface of skull, continuous with periosteum (outside) on outside of skull bones and cranial sutures
Meningeal layer: covering brain, penetrates spaces in cerebral hemispheres
5
Q
Describe the arachnoid mater
A
Middle layer, impermeable, adjoins dura (not tightly bound- potential subdural space) separated from Pia by Subarachnoid space that is filled with CSF
6
Q
Describe the Pia mater
A
Delicate, permeable, innermost, resting on the brain surface
vascular membrane that adheres closely to brain
7
Q
What are the two important partitions that arise from the meningeal layer
A
Falx cerebri, tentorium cerebelli
8
Q
Describe the Falx cerebri
A
Sickle-shaped fold separating the cerebral hemispheres. The superior convex border forms floor of superior sagittal sinus; inferior border houses inferior sagittal sinus
Restrict brain displacement
9
Q
Tentorium cerebelli
A
Fits between the cerebellum and the occipital lobes; separates the posterior cranial fossa from the rest of the cranial vault. Arches upward along median line to become continuous with falx cerebri to form straight venous sinus
Restrict Brain displacement
10
Q
What is the location, usual cause, and symptoms of an epidural hemorrhage
A
Location: tight potential space between the dura and the skull
Cause: rupture of the middle meningeal artery during head trauma
Symptoms: initially no symptoms (lucid interval), within hours the hematoma compresses the brain and increases ICP, which leads to herniation and death. (unless surgery)
11
Q
What is the location, usual cause, and symptoms of an subdural hemorrhage
A
Location: potential space between the dura and the loosely adherent arachnoid
Cause: rupture of bridging veins that pass through en route to dural sinuses (vulnerable to shear injury)
Same symptoms has epidural
12
Q
What are acute and chronic subdural hematomas/hemorrhages
A
Acute: can occur with high velocity impact
Chronic: seen in elderly where brain atrophy allows the brain to move freely (bridging veins susceptible to injury). Slow bleeding over weeks/ months allows brain to accommodate so symptoms often vague: headache, cognitive impairment, unsteady gait.
13
Q
What is the time frame each blood is seen in the brain: hyperdense, isodense, hypodense
A
hyperdense: More dense than surrounding brain tissue, acute/ recent injury
Isodense: 1-2 weeks
Hypodense: 3-4 weeks
14
Q
What separates the Pia from the Arachnoid mater
A
Subarachnoid space (CSF)
15
Q
Where are all cerebral arteries and veins (aneurysm site, may hemorrhage)
A
subarachnoid space, sending off branches that penetrate into the brain
16
Q
How is the Arachnoid connected to the Pia
A
Delicate threads called trabeculae
17
Q
What are arachnoid granulations
A
site where CSF diffuses into the venous sinuses
18
Q
What layer fuses with the ependyma to form the choroid plexus
A
Pia mater, arteries carry sheath of pia as they enter the parenchyma
19
Q
Where does pain from headaches come from
A
No pain receptors in brain, so pain comes from trigeminal and first three cervical nerves innervating the meninges and vasculature
Dura above the tentorium by the trigeminal ganglion
Dura below the tentorium by cervical nerves
20
Q
What innervates the dura above and below the tentorium
A
Above: trigeminal ganglion
below: cervical nerves (1-3)
21
Q
What do migraines depend on
A
depend on the activation of the trigeminal afferents that densely innervate the meninges
22
Q
Meningitis and meningiomas
A
Inflammation of the meninges and tumors in the meninges
23
Q
Effects of space-occupying lesions
A
Increased ICP and stretching of dura
24
Q
What is a cluster headache
A
Lancinating or boring periorbital pain. More sever than childbirth
25
How does a hangover affect the meninges
toxic effect on meninges
26
Where do immune cells reside? how does inflammation affect immune cells?
Meningeal spaces
Inflammation = activation of immune cells. When immune cells are activated, they release things that lower the threshold of activation of pain fibres
27
Which arteries are responsible for posterior and anterior circulation
Anterior: internal carotid artery
Posterior: vertebral artery
28
Which arteries supply each cerebral hemisphere
carotid and vertebral arteries supply each cerebral hemisphere
29
What is the Circle of Willis? What is anastomosis
Anterior and posterior blood supply combines at the circle of Willis. Circle of WIllis provides overlapping blood supply and alternative routes for blood flow.
Anastomosis (circulatory connection between 2 blood vessels) protects the brain when part of vascular supply is blocked
30
Which cerebral arteries are important for anterior circulation and posterior circulation
Anterior: middle cerebral artery, anterior cerebral artery
Posterior: Posterior cerebral arteries
31
which cortical area does the MCA supply
most of the lateral convexity of the cortex (except the leg area of motor homunculus) and white matter, including the frontal, parietal, temporal, and occipital lobes of the insula
32
which cortical area does the ACA supply
The cortex and white matter of the medial frontal and parietal lobes and the anterior corpus callosum
A strip of cortex (1inch) wide on later surface
33
which cortical area does the PCA supply
The occipital lobes and portions of the medial and inferior temporal lobes and the posterior corpus callosum
34
How do deep structures receive blood
Deep structures receive blood directly from branches of the internal carotid artery and proximal portions of the cerebral arteries
35
what is the most common site of infarction/ ischemia
MCA
36
How does gray matter of the cerebral cortex and underlying white matter receive blood
supplied by branches of more distal cerebral arteries
37
What does in infarction in the MCA result in
Contralateral Hemiparesis and hemisensory loss (mainly in face and arm)
38
What is hemineglect? How does it happen?
Unawareness of space and the patient's own body contralateral to the lesion. Patients may seem unaware or deny the handicap. This may include unawareness of quite dramatic impairments such as blindness or paralysis. May not take care of the contralateral side of the body, deny own limbs, ignore objects in the contralateral visual field
Happens by an infarct in the right hemisphere MCA
Patients may experience anosognosia (denying or unaware of their handicap)
39
What is parietal neglect syndrome
- Failure to recognize side of body contralateral to injury
- May not bathe contralateral side of body or shave contralateral side of face
- Deny own limbs
- Objects in contralateral visual field ignored
40
What is Aphasia? What is the cause
Inability to comprehend or formulate language
Caused by infarct in left hemisphere MCA
41
What is Broca's aphasia
Difficulty producing speech, comprehension intact
42
What is Wernicke's aphasia
difficulty comprehending speech, speech fluent, well structured, grammar and syntax adequate by nonsensical.
43
What does an infarct in the ACA result in
Contralateral hemiparesis: paralysis or weakness of one side of the body
Hemisensory loss involving mainly the leg and foot
Personality changes (frontal lobe)
44
What does an infarct in the occipital region of the PCA result in
Hemianopsia or visual agnosia
45
What is hemianopsia
Loss of vision for one half of the visual field
46
What is visual agnosia
Inability to recognize or interpret objects in the visual field
47
What does an infarct in the temporal region of the PCA result in
memory impairment
48
What is prosopagnosia? What part of the cortex is damaged? what is the most common cause
Inability to identify facial characteristics or not able to recognize a face at all. Damage to the inferior temporal cortex. Most common cause is a PCA stroke
49
What is a stroke
death or dysfunction of brain tissue due to vascular disease
50
What is an infarction
neuronal death
51
What is ischemia
insufficiency of blood supply
52
what is anoxia
reduced oxygen supply
53
what is an embolus
Material carried from one point to lodge in another
(blood clot, air, or fat forms somewhere and travels to lodge somewhere else)
54
What is an embolism
Embolus becomes lodged in an artery and obstructs flow
55
describe hemorrhagic. what does it lead to
bleeding from a vessel (high chance if you have hypertension or aneurysm)
56
Describe occlusive and what does it lead to
Closure of a vessel
(high chance if you have Atherosclerosis or thrombosis
57
What is tissue plasminogen activator (tPA)
A protease enzyme that catalyzes the conversion of plasminogen to plasmin, the major enzyme responsible for clot breakdown
58
What does intraparenchymal hemorrhage mean
within the brain
59
What does extraparenchymal hemorrhage mean
at the brain surface
60
What is an intracranial aneurysm
Weakness in the wall of a cerebral vasculature causes a localized dilation or ballooning of the blood vessel
61
How could you fix a cerebral aneurysm
endovascular coiling or surgical clipping
62
What is endovascular coiling
A catheter is inserted in the artery and guided to the aneurysm, a stent is released to prevent the coil from blocking flow, the catheter is guided to the aneurysm to be filled with coil, the coil fills the aneurysm to prevent further growth and rupture
63
What is surgical clipping?
Using a clip on the base of an aneurysm, preventing blood flow into the aneurysm
(very invasive, requires craniotomy)
64
Where do superficial veins, deep veins, and the superior sagittal sinus drain into
Superficial --> Super sagittal sinus and cavernous sinus
Deep --> Great vein of Galen
Superior sagittal sinus --> 2 transverse sinuses --> sigmoid sinus --> jugular vein
Venous blood drains into a system of valve channels called dural venous sinuses
65
Homeostasis of the the three fluid compartments are regulated by what?
Blood-brain and blood-CSF barriers
66
Describe the vasculature of the arachnoid mater
* The arachnoid mater is an epithelial layer that provides a barrier between the peripheral vasculature of the dura mater and the CSF present in the subarachnoid space through tight junctions and efflux pumps
67
Describe the vasculature of the dura matter
* The dura mater contains lymphatics and fenestrated blood vessels that lack tight junctions.
68
Describe the vasculature of the pia mater
* The pia mater meningeal blood vessels lack astrocytic ensheathment, but their endothelial cells are connected by tight junctions.
* The Pial arteries penetrating the brain are covered by a densely packed perivascular layer of astrocytic foot processes; Veins exiting the parenchyma have a perivascular space flanked by astrocytic foot processes as well as endothelial basement membranes (BMs). The pial BM is only present in the superficial (brain surface) portion of the veins.
69
What are the three intracranial fluid compartments
CSF compartment, interstitial compartment of the brain, intracellular compartment of the brain
70
What is the choroid plexus
Specialized capillary networks that secrete CSF
71
What are the cellular constituents of the choroid plexus? What constituent secretes CSF
Blood vessels and pia form the core and the choroid epithelium secretes CSF
72
What is the total CSF production (mL/ day)? what is the total volume? how many times does it turn over per day
500mL/day (~0.5mL/min)
73
What is the total CSF production (mL/ day)? what is the total volume? how many times does it turn over per day
500mL/day (~0.5mL/min)
~150 mL
3 times
74
What junctions bind choroid epithelial cells to each other
tight junctions
75
What are the two sequential stages of CSF formation?
1: ultrafiltration of plasma across the fenestrated capillary into the ECF beneath the basolateral membrane of the choroid epithelial cell
2: Choroid epithelial cells secrete fluid into the ventricle
76
CSF occurs with a net transfer of _____ and ______ that drives water movement _______
NaCl, NaHCO3, Isosmotically
77
describe the two step process of the net secretion of Na from plasma to CSF
1: Na-K pump in choroid plexus epithelia apical membrane moves Na+ out of the cell into the CSF
2: Active movement of Na+ out of cell generates an inward Na+ gradient across the basolateral membrane, energizing basolateral Na+ entry through the Na-H exchange and Na+- coupled HCO-
78
What is the route of cerebrospinal fluid circulation
Lateral ventricle --> foramina of Monro --> third ventricle --> cerebral aqueduct --> fourth ventricle --> Foramina of Magendie and Luschka --> subarachnoid space, over brain
79
How is CSF absorbed
absorbed by dural venous sinuses through arachnoid granulations
80
How do the granulations function?
Granulations appear to function as pressure-sensitive, one-way valve that allow CSF to go to venous blood
81
At what pressure does CSF formation and absorption change
CSF formation is insensitive to changes in the pressure of the CSF
Absorption of CSF increases steeply at presures around 70 mmH20
82
What happens when absorption exceeds formation
Lower CSF volume decreases intracranial pressure
83
how can small and large intracranial masses be compensated for?
* Small intracranial masses can be compensated for by reductions in intracranial CSF and blood volume without causing much rise in intracranial pressure (flat part of curve).
* Larger masses overcome compensatory mechanisms and lead to a steep rise in intracranial pressure, causing reduced cerebral perfusion and, ultimately, herniation and death (right-most part of the curve)
84
what is the equation for cerebral perfusion pressure
CPP= MAP - ICP
85
What is a lumbar puncture (spinal tap)
A needle is inserted between the fourth and fifth lumbar vertebrae and into the subarachnoid space. CSF flows through the needle which attached to a manometer and the fluid is allowed to rise
86
What is the normal intracranial pressure
65-195 mm CSF (H20)
3-15 mm Hg
87
What is papilledema
Optic disc swelling caused by increased intracranial pressure
elevated ICP is transmitted to the optic nerve sheath, obstructing axonal transport and venous return in the optic nerve.
Pressure on the optic nerve head forces it inward
88
What is hydrocephalus? What are the three things it can result from
excess CSF in the intracranial cavity
1: excess CSF production (rare)
2: obstruction of flow at any point in the ventricles or subarachnoid space
3: decrease in reabsorption when granulations are damaged or clogged
89
Communicating hydrocephalus vs noncommunicating hydrocephalus (common)
Communicating: Caused by impaired CSF reabsorption in the arachnoid granulations, obstruction of flow in the subarachnoid space, or rarely by excess CSF production
Noncommunicating: Caused by obstruction in ventricular system
90
What is the treatment for hydrocephalus
involves a procedure that allows CSF to bypass the obstruction and drain the ventricles.
A more permanent treatment is a shunt, in which the tubing passes from the lateral ventricle and is then tunneled under the skin to drain into the peritoneal cavity. A valve prevents backflow
91
Where are the three main barrier sites? What is the physical barrier caused by?
1: brain endothelium forming the blood-brain barrier
2: Arachnoid epithelium forming the middle layer of the meninges
3: Choroid plexus epithelium which secretes CSF
Physical barrier caused by tight junctoins
92
What are the three proteins in the tight junctions of the BBB? which molecules do they let pass
Claudins, occludings, and junctional adhesion molecules
Non-water soluble
93
What are the three ways entry into the brain is achieved
1: Diffusion of lipid soluble substances
2: Facilitative and energy-dependent receptor-mediated transport
3: Ion channels and exchanger
94
What is anosmia? how can it be acquired
Loss of the ability to detect one or more odors
congenital, sinus infection or inflammation, head injury, toxins, aging, neurodegenerative conditions, chemotherapy, eating disorders, diabetes,
95
Describe the olfactory epithelium
Layer of olfactory receptor cells, supporting cells, and basal cells.
Odorants dissolve in the mucus layer and contact the cilia of the olfactory cells. Axons of the olfactory cells penetrate the bony cribiform plate on way to CNS
96
what is the molecular mechanism of odorant transduction
Odorant receptor --> activates Golf (G-protein) --> activates Adenylyl cyclase, which converts ATP to cAMP --> activates Na/Ca channel --> activates Cl- channel and Na/Ca exchanger
97
Describe the 3 steps of transduction in olfactory receptor neurons
1: odorants generate a slow receptor potential in the cilia
2: receptor potential propagates along the dendrite and triggers a series of action potentials in the soma
3: action potentials propagate along the nerve axon
98
how do ~950 functional receptor proteins discriminate tens of thousands of odors given that each receptor allows for the binding of different odors more or less readily?
3 Hypotheses
Olfactory population coding
Olfactory spatial maps
Olfactory temporal coding
99
What is olfactory population coding
Each receptor cell expresses a single receptor protein. Each one responds to many odors with differing preferences. Brain distinguishes between odors using a combination of responses
100
describe the central olfactory pathway
Olfactory receptor neurons send axons into the two olfactory bulbs, each bulb contains 2000 glomeruli. 25, 000 olfactory axons converge on the dendrites of about 25-100 olfactory neurons within each glomerulus
101
What is olfactory spatial maps
Receptor neurons expressing a particular receptor gene all send their axons to the same glomeruli extremely accurately. So the glomeruli within each bulb is an orderly map of the receptor cells in the epithelium expressing a particular receptor protein. the smell of an odor is converted into a specific map within the bulb
102
What is olfactory temporal coding
odor information encoded by the detailed timing of spikes within cells and between groups of cells as well as number, pattern, rhythm, and synchronicity of spikes
103
what are the two ways mitral cells can be tuned
Only care about the about the position of side chains
Only care about the type of side chain
104
What is lateral inhibition
Using inhibitory interneurons to enhance contrast
105
why can individuals mitral cells become more sharply tuned
Mitral cells synapse with granule cells that can enhance the contrast between strongly activated and faintly activated glomeruli
106
Is the segregation of information in the olfactory bulb maintained in the olfactory cortex
no
107
Why don't humans have a blind spot
Brain fills in blindspot based on given info, brain fills in image
108
T/F we don't just passively perceive the world, we actively generate it
true
109
what are the 5 classes of neurons
Rods, cones, horizontal cells, bipolar cells, amacrine cells
110
What is the most direct route for transmitting visual information
Photoreceptor, bipolar cell, and ganglion cell
111
What are horizontal and amacrine cells used for
Mediates lateral interactions in the inner and outer layers respectively
112
Rods vs Cones
Rods: 1000x more sensitive to light. Contains more disks that make vision possible in low light. Produce a reliable response to a single photon. 100 million. low spatial resolution. Only rods are illuminated at low lighting
Cones: Responsible for color, contains one of 3 photopigments. Cones enable us to see in daylight.~5 million
113
Peripheral retina vs Central retina
Peripheral: much higher ratio of rod to cones, higher ratio of photoreceptors to ganglion cells, peripheral retina are much more sensitive to low light
Central: Cones only, low ratio of photoreceptors to ganglion cells, specialized for high resolution resolution
114
What is the fovea? why is there no image blur
area of the retina responsible for high visual acuity in the center of the macula
Lateral displacement of cells above photoreceptors reduces scattered light
115
Are rods or cones more densely present in the fovea
Cones
116
What is protanopia and deuteranopia
both have difficulties in red and green
Protanopia: impairment in perception of long wavelength(red)
Deuteranopia: impairment in the perception of medium wavelengths(green)
117
What are the three uses for melanin
1: reduces photo-oxidative stress
2: primary nourishment
3: increased visual acuity
118
Describe the removal of photoreceptor disks by the pigment epithelium
The tips of photoreceptors are in the pigment epithelium. Disks move from the inner segment to outer segments over a 12 day period. Expended disks are shed from the outer segment and phagocytosed. Photopigment from the disks are then cycled back to newborn photoreceptor disks
119
What is retinitis pigmentosa? what are the hall marks? cause and cure?
Progressive vision loss due to gradual degeneration of photoreceptors.
Hallmarks: night blindness, loss of peripheral vision, dark clumps of pigment within the retina. Visual defects begin in the periphery and enlarge leading to tunnel vision and can progress to blindness
Unknown cause and no cure
120
What is macular degeneration
Progressive loss of central vision
121
How does light affect a cone cell (hyper or depolarization)
hyperpolarization
122
Describe the depolarization of cells in the dark,
How does light affect it
cGMP in the outer segment are high, it binds to Na channels keeping them open and allowing sodium to enter, depolarizing the cell.
Absorption of photons leads to a decrease in cGMP, closing the channels and resulting in hyperpolarization
123
describe the retinoid cycle
Following photoisomerization, all-trans-retinal is converted to all-trans retinol --> all-trans retinyl ester --> 11-cis retinol --> 11-cis retinal --> transported back to outer segment where it recombines with opsin
124
What molecule is responsible for photoreceptor light adaptation. How does it modulate it
Calcium, calcium-mediated inhibition
Calcium channels close in the light, leading to a reduction in calcium. As a result photoreceptor's sensitive to photon capture is reduced
125
What is the Calcium light adaptation pathway
Ca/Na channel brings calcium into the cell which inhibits rhodopsin kinase and guanylate cyclase and reduces the affinity of cGMP for their gated channels
Preventing GTP --> cGMP
Preventing phosphorylation of Rh
126
Which cells make up the outer nuclear layer, the inner nuclear layer, and the ganglion layer
Outer: rods and cones
Inner: bipolar and horizontal
Ganglion: ganglion
127
What molecules do photreceptor, ipolar and horizontal cells release
Photoreceptor and bipolar cells release glutamate
Horizontal cells release GABA
128
Which retinal processing cell fires APS
ganglion cells
129
What are the two classes of bipolar cells
mGluR6 and AMPA
130
Are mGluR6 and AMPA cells OFF or ON
mGluR6- ON, depolarized when light is on
AMPA- OFF, depolarized when light is off
131
What is a receptive field and how is it located
The receptive field is a location on the retina which causes spiking in the ganglion cell's firing rate.
A small spot of light is projected onto various parts of the retina, and detecting the changes in firing rate
132
What is the direct pathway from photoreceptor to bipolar cells
Bipolar cell receives direct synaptic input from a cluster of photoreceptors, constituting the receptive field center.
133
What is the indirect pathway from photoreceptor to bipolar cells
Light hits the surrounding receptive field causing the the surround photoreceptors to hyperpolarize. This causes hyperpolarization of horizontal cells to release GABA on the bipolar cell which hyperpolarizes the bipolar cell.
134
What determines whether a ganglion cell is ON or OFF?
Determined by the bipolar cell
On bipolar = On ganglion
135
What are mach bands? explain them
Our system exaggerating the borders so we can see borders
Certain cells will have their whole surround in the lighter region but when part of it is in the darker region it will have less inhibition and will have higher firing rates. (For ON ganglion)
136
What is the function of the hypothalamus
Regulation of circadian rhythms
137
What is the function of the pretectum
reflex control of pupil and lens
138
What is the function of the superior colliculus
Orienting the movement of head and eyes
139
______ receives a selective input from the retina that is necessary and sufficient for photic entrainment of circadian rhythms
Suprachiasmatic nucleus receives a selective input from the retina that is necessary and sufficient for photic entrainment of circadian rhythms
140
T/F retinal photoreceptors are require for circadian photoreception
false, ganglion cells send signals to the suprachiasmatic nucleus
141
What opsin-like pigment is expressed in photosensitive ganglion cells
melanopsin
142
Do ganglion cells respond slow or fast
slow with a big barrage of action potentials
143
Describe the pupillary light reflex pathway
When light is shone in one eye, it will have a direct response and the opposite eye will have a consensual response. This is because the resopnse is mediated by the parasympathetic innervation of the iris. The signal travels down an afferent pathway back to the nuclei which talk to the other nuclei through a bilateral effect causing a reaction in both eyes.
144
Would the defect be in the afferent or efferent pathway if:
1. There was a failure to elicit a response (either direct or indirect) to stimulation of the right eye if both eyes respond normally to stimulation of the left eye.
2. There is a direct response in the left eye without a consensual response in the right eye.
1. Afferent pupillary defect
2: Efferent pupillary effect
145
retinal signals converge on the _____
tectum
146
what is the optokinetic response
combination of a slow-phase and fast-phase eye movements. Initial slow phases in the direction of the stimulus, followed by fast, correctve phases (return saccade)
147
What is a saccade
Fast eye movements that present various parts of the visual scene to the fovea (foveation)
Line up or fovea at all time
148
describe the sensorimotor integration in the superior colliculus
Neurons in a particular region of the superior colliculus are activated by specific visual stimuli in a limited region of visual space. Which leads to the generation of a saccade by activating upper motor neurons that move the eye enough to align the foveae
149
what is blindsight
blindness in the visual cortex, completely perceptually blind
150
P-type vs M-type ganglion cells
(population, size of receptive field, conduction velocity, type of firing, color?, Type of resolution, what aspects are it good for)
P-type: 90% population, small receptive fields, slow conduction velocity, sustained firing to the presentation of visual stimuli, can transmit information about colour. Important for high spatial resolution vision and detailed analysis of the shape, size and colour of object
M-type: 5% population, large receptive field, fast conduction, transient bursts of action potentials to the presentation of visual stimuli, cannot transmit information about colour. High temporal resolution, such as evaluating the location, speed and direction of rapidly moving objects
151
Which hemisphere does the right visual field project to
left hemisphere
152
how are images from the pupil projected on to the retina
inverted and left-right reversed
153
Which axons of ganglion cells in the retina cross in the optic chiasm
nasal retina axons
154
Which ganglion correspond to which layer of the LGN
M-type: --> magnocellular (1,2)
P-type --> Parvocellular (3-6)
155
visuotopic organization of the striate cortex is found in the ______ _______ _______
right occipital lobe
156
describe the layers of the striate cortex
6 principle layers
layer 4 has several subdivisions ABC
157
Which layer is dominated by spiny stellate neurons? Which layer to lateral geniculate axons terminate most heavily in? Where do neurons in layer 4C terminate? where do axons of layer 2/3 terminate? 6? Connections with extrastriate cortex arise primarily from neurons in layers ___ and ____? Descending projections to the lateral geniculate nucleus arise from layer ___ neurons, while those projecting to the superior colliculus reside in layer __?
4C
4C and 4A
4B and 2/3
5
4C
2/3 and 4B
6, 5
158
Which layers of the lGN does the contralateral eye project to? which layers do the ipsilateral eye project to?
Contralateral projects to 1, 4, 6
Ipsilateral: 2, 3, 5
159
Which sublayer do parvocellular layers project to in the primary visual cortex? Magnocellular?
Parvocellular: 4CB
Magnocellular: 4CA
160
Which layer is responsible for receiving segregated inputs from the eyes, and then sending their neurons to more superficial layers to synapse on those layers
Layer 4
161
Where does the mixing of pathways from the two eyes first occur
in the striate cortex, in layer 4
162
Which layers are binocular
4/3
163
What is the head bob called by pigeons which is prompted by seeing the surrounding environment moving relative to the bird
motion parallax
164
How is a net magnetic field created that changes in time and gives rise to an electric current that is ultimately measured in MRI (3 steps)
1: water protons spin around their axes, creating individual random magnetic fields
2: vertical magnetic field is applied, protons align to create a net magnetic field that is small and vertical
3: a radio frequency pulse is applied in the horizontal direction to make the protons wobble around the vertical axes
165
How do MRI measurements work (3 steps)
Place subject in vertical magnetic field, then a horizontal radio frequency pulse is applied so that they rotate in the horizontal plane in phase with one another
2: the horizontal is turned off and the protons begin to move out of phase leading to a decay in the measured current
3: after the withdrawal of the horizontal pulse, the protons will realign with the vertical magnetic field
Different tissues will have different rates of decay T2 (~30ms)
166
What is an fMRA based on? What does it measure?
BOLD effect: blood oxygen level dependent signal
Measures blood flow
167
The BOLD signal reflects changes in the ratio of ___ to ___
ratio of oxyhemoglobin to deoxyhemoglobin
168
is deoxyhemoglobin or oxyhemoglobin paramagnetic
deoxyhemoglobin
169
what is the ratio of oxyhemoglobin in a resting neuron and an activated neuron?
Resting: even ratio
Activated: more oxyhemoglobin
170
How would an increase in neuronal activity affect dephasing? What would an fMRI reveal?
Increase in neuronal activity = increased oxygenated blood
This decreases deoxyhemoglobin concentration, causing dephasing to occur more slowly and hence slowing down the decay of the measured electric current.
This results in an fMRI image of the location of metabolic activity as revealed by the changes in deoxyhemoglobin concentration
171
How would increased deoxyhemoglobin affect dephasing
Increased deoxyhemoglobin = increased dephasing
172
What is neurovascular coupling
the active process linking local neuronal activity to orchestrated increase in blood flow
173
fMRI bold signals are sensitive to which type of hemoglobin
deoxyhemglobin
174
What is the vascular evolution (pathway) of stimulus-evoked functional hyperemia
First capillaries respond and dilate to increase total Hb
Then arterioles will dilate
Then venous outflow will increase (increasing blood flow)
Deoxyhemoglobin decreases next
175
What happens in the following times of stimulus-evoked functional hyperemia?
t < 1, t< 2s, 2s < t< 6s, t>6s, t>10s
t < 1 = stimulus?
t < 2 s = arterioles dilate, venous flow speed increases
2-6s = venous outflow is seen as an increase in HbO and decrease in HbR. Veins do not notably dilate
t>6= for prolonged stimulation, pial arteries return to baseline. Parenchymal hyperemia remains
t>10 = Reponse returns to baseline
176
what are the mechanisms for blood flow change?
4 ways
1: direct action of neuronally derived substances such as glutamate and nitric oxide on the vasculature
2: cellular mediators of neurovascular coupling, such as astrocytes, interneurons, and pericytes
3: afferents from the basal forebrain via acetylcholine release
Vsoactive substance by cortical interneurons including VIP and NO
177
What mediates the rapidly propagated retrograde vasodilation mechanism during functional hyperemia
endothelial hyperpolarization
