Final Material Prep Flashcards
(117 cards)
1
Q
What is systems neuroscience?
A
The science of networks or circuits of neurons having specific functions
2
Q
What does firing rate code for?
A
The firing rate codes for the strength of the sensory signal (rate code)
3
Q
Synchrony code is responsible for coordinated activity
A
4
Q
Electroencephalography (EEG) is a synchrony code **refer to lecture
A
5
Q
What does the amplitude of depolarization code for?
A
The amplitude of depolarization codes for the strength of the sensory signal
- The more depolarization, the more transmitter is released
6
Q
Central Pathway is responsible for:
A
Sensory signals transmitted from peripheral neurons to “central” neurons in the brain
7
Q
Sensory Receptor Cells:
A
- Modality specific
- Transduce energy of different forms to electrical activity so that can be passed onto other neurons
- Even within a single sensory system, different populations of neurons are specialized to detect different features of the same input
8
Q
Receptive field is….
A
The location in the environment (or the surface of the body) from which the appropriate stimulus will change that cell’s activity
9
Q
What is shown in a topographic map?
A
- Neurons positioned side by side in one region project neurons so they are positioned in the next region
- Orderly representation of the sensory space in the nervous system
10
Q
Why does light energy undergo phototransduction?
A
Light energy undergoes phototransduction to trigger neural activities
11
Q
Pupil
A
The opening that allows light to enter the eye
- Light goes into the retina
12
Q
Iris
A
Surrounds the pupil
- Responsible for eye color
- Contains muscles that can change the size of the pupil (controls the amount of light reaching the eye)
13
Q
Cornea
A
Covers the pupil and iris
- Responsible for light refraction
14
Q
Sclera
A
Continuous with the cornea
- “White of the eye”; is a tough outer wall
15
Q
Extraocular muscles
A
Move the eye
16
Q
Where does phototransduction occur?
A
In the retina
17
Q
What are the five major cell types in the retina?
A
- Retinal ganglion cells
- Amacrine cells
- Bipolar cells
- Horizontal cells
- Photoreceptor cells
18
Q
Retinal information processing
A
19
Q
What is the process of retinal information processing in the linear (direct) pathway?
A
Photoreceptor cells -> bipolar cells -> retinal ganglion cells -> brain
20
Q
Why are photoreceptor cells unique?
A
Photoreceptor cells are the only cell type directly affected by light
21
Q
Why are retinal ganglion cells unique?
A
Retinal ganglion cells are the retina’s only output cell type
22
Q
What is the process of retinal information processing in the lateral (indirect) pathway?
A
- Bipolar and photoreceptor cells target horizontal cells (and vice versa)
- Retinal ganglion cells and bipolar cells target amacrine cells (and vice versa)
23
Q
What are the two types of photoreceptor cells?
A
- Rods: ~120 million
- high sensitivity to light
- low acuity vision
- achromatic
- rare in fovea - Cones: ~ 6 million
- high acuity vision
- low sensitivity to light
- color sensitive (red, blue, green)
- concentrated in fovea
24
Q
Cones help detect light of specific wavelengths
A
25
Where is the fovea located?
The fovea is the center of the visual field
26
What is the process of light reaching photoreceptor cells?
Light directly reaches photoreceptor cells at the fovea
27
The fovea provides color & high resolution vision
28
Where are photoreceptor cells depolarized?
Photoreceptor cells are depolarized in the dark
29
What is the process of depolarizing a photoreceptor cell?
1. Intracellular cyclic guanosine monophosphate (cGMP) binds to cGMP gated Na+ channel
2. cGMP keeps the channel open and allows Na+ influx
3. Photoreceptor cell membrane is kept depolarized (-30 mV; DARK CURRENT)
4. Neuro transmitter glutamate is constantly released at the terminal
30
Where are photoreceptor cells hyperpolarized?
Photoreceptor cells are hyperpolarized in the light
31
How are photoreceptor cells hyperpolarized?
1. Light stimulation reduces cGMP
2. Na+ channel closes which allows membrane hyperpolarization (-65 mV)
3. Glutame release stops at the terminal
32
What is used by light to decrease cGMP?
Light decreases cGMP through transducin (g-protein)
33
Light intensity gradually changes membrane potential and glutamate release **
Glutamate release increases the darker it is
34
How is a visual image mapped onto the retina?
Cells in different locations in the retina have receptive fields in different locations in the visual field
35
The photoreceptor receptive field:
1. Is circular
2. The receptive field of a given photoreceptor is determined by its location in the retina
3. Photoreceptors respond to changes of light intensity in its receptive field
36
What is a receptive field?
In the visual system, a neuron's receptive field is the location in the visual field (sensory space) from which light changes the cell's activity
- All cells in the visual system have receptive fields
37
What types of cells are activated by signals from photoreceptor cells?
- Retinal ganglion cells (RGCs)
- Amacrine cells
- Bipolar cells
- Horizontal cells
38
Receptive field size differences in distinct RGC types:
- RGCs in peripheral: convergence of synaptic input = large receptive field= M (magno) type
- RGCs in central: no or less convergence of synaptic input = small receptive field= P (parvo) type
39
Divergence of single photoreceptor cells onto multiple RGCs leads to...?
Overlapping receptive fields
40
Neighboring RG cells have overlapping receptive fields
41
What are the 2 different glutamate receptors in bipolar cells?
- Inhibitory
- Excitatory
42
What is the process of using an inhibitory glutamate receptor process?
1. Glutamate release from pre-synapse in PR cell
2. Received by inhibitory receptor at post-synapse in BP cell
3. Decrease membrane potential in BP cell
4. No neurotransmitter release
43
In what order do the cells show up in retinal structures?
Retinal ganglion cells, bipolar cells, photoreceptor cells
44
In the visual system, what is the difference between a neuron's receptive and visual fields?
A neuron's receptive field is the location inside of the visual field (sensory space in which light changes the cell's activity
45
Light on in an ON center RG cell... Light on in an OFF center RG cell...
Increases APs; decreases APs
46
The receptive field is comprised of the center + surround
47
What is the mechanism of BP cell response to the receptive field surround?
HC depolarization -> PR cell inhibition + BP cell excitation
48
Center PR cell
Potential = depolarized + inhibition by HC
49
ON-center BP
Potential = hyperpolarized + excitation by HC
50
Light on surround = large decrease of AP
51
Light on center = large increase of AP
52
Visual perception is not dependent on illumination level
53
Why do we see advertisements for bright and dark environments?
Contrasts in light intensity are more informative than the overall illumination
- So our perceptions of what we see are not dramatically affected by the level of ambient illumination
54
The retina consists of 3 structures:
- Lateral geniculate nucleus (LGN)
- Superior colliculus (SC)
- Suprachiasmatic nucleus (SCN)
55
Suprachiasmatic Nucleus (SCN)
- Receives inputs from intrinsically photosensitive RGC (ipRGC)
56
What is circadian rhythm?
24 hour fluctuations of biological processes in the suprachiasmatic nucleus
57
Axons from RGCs in both eyes that are activated by the same object in the visual field converge onto the same neurons in the SC
58
Sensory neurons directly synapse onto motor neurons to control movements, such as gaze and saccades
59
The SC has a layered structure
60
What is the pathway for the LGN?
LGN is required to consciously perceive objects
61
In blindsight...
- LGN not functioning
- SC can track/avoid objects subconsciously
- SCN responsible for circadian rhythm intact
62
Magno type cells are...
Achromatic; 5%
63
Parvo type cells are...
Color sensitive, carry detailed information; 90%
64
LGN duties/responsibilities:
- Receive synaptic inputs from RGCs
- LGN neurons project to the primary visual cortex
65
There are 6 distinct layers in the LGN:
- Lyers 1 & 2 contain larger cells
->Magnocellular LGN layer
- Layers 3-6 contain smaller cells
-> Parvocellular LGN layer
66
What are the extra layers of LGNs?
- K1-K6 (before layer 1) ventral to each principal layer
- NonM-nonP type
-> Koniocellular
67
CICIIC
C: Contralateral
I: Ipsilateral
68
Each layer in the right LGN contains a complete disproportionate representation of the left visual field
69
Primary Vision Cortex (V1)
Topographic map in V1 is inherited from retina
- 1/2 of the neurons in V1 code for the fovea region
70
What are pyramidal cells?
- Single thick apical dendrite that branches towards the end
- Multiple basal dendrites
- Axon descending from the soma
- Long- rage axonal projections
71
What are spiny stellate cells?
- Small neurons
- Multiple dendrites that radiate from the soma
- Most of the axons make local connections
72
What are the different types of inhibitory neurons?
PYR: pyramidal neuron
PV+: parvalbumin interneuron
SST+: somatostatin interneuron
VIP+: vasointestinal peptide-expressing interneuron
73
What are the stripe like structures in V1?
- Ocular dominance columns
- indicate recent metabolically active areas
74
What are blobs?
Spots in V1 as a result of K layer inputs from LGN
- Blob neurons only respond to color
75
What does the cortical module: hypercolumn entail?
- same receptive field
- complete coverage of all orientations (multiple orientation columns)
- input from both eyes
- multiple blobs
- repeating modules throughout V1
76
Orientation columns responsibility:
- 36 orientation columns in each cortical module
- Observed in all layers except layer IVC
- Neurons in orientation columns analyze the shape, form, or motion of an object
77
Ocular dominance columns responsibility:
- All the neurons in a column preferentially have input from a single eye
- 0.5 mm wide stripes
- Each cortical module has 4 ocular dominance columns
- Neurons in layer IV have exclusive input from one eye
- Neurons in layer II, III, V, VI have dominant input from one eye, but also have input from both eyes
78
Blobs responsibility:
- Cytochrome oxidase rich neurons
- Observed in layer II,II, V, VI
- Arranged in rows (each blob is centered on an ocular dominance stripe in layer IV)
- Each cortical module has 16 blobs
- Neurons in blobs are color sensitive, but insensitive to shape
79
What are the 3 parallel pathways of visual information?
- V5: dorsal stream for motion and direction
- V4: ventral stream for color
- V4/IT: ventral stream for shape
80
What is the inferotemporal (IT) cortex?
- IT cortex has subsets of neurons that respond selectively to highly complex visual stimuli (hands, face, food)
-> involved in object recognition
- A wide variety of colors and abstract shapes are good stimuli for neurons in the IT cortex
81
Order for the receptive field in the central visual pathway:
Photoreceptor -> RGC -> LGN -> V1 -> Higher order areas (IT)
82
What are the 3 modalities of somatosensation?
1. Exteroception
2. Proprioception
3. Interoception
83
Exteroception:
- Mechanoreception: discriminative touch, social/affective touch
- Thermoreception: warm/cool
- Nociception: pain (mechanical, thermal, chemical), itch
84
Proprioception:
- Joint position
- Muscle length, force
- Skin stretch
85
Different afferent fibers have different ending structures
With end organs = hairy skin
Without end organs = bare skin
86
What is the function of the 4 classes of afferent fibers?
Convey signals from body/organ surface to CNS
87
The sense of touch
- Mechanoreception
- Myelinated fibers: Aalpha, Abeta, Adelta
- All have end organs, triggered by physical deformation
- Cell bodies in dorsal root ganglion and trigeminal ganglion
- Topographic mapping
88
The microneurographic technqiue
Thin electrode contacts an afferent nerve fiber and impulses from the cutaneous sense organ respond to touch
89
Depth of end organ determines size of receptive field which determines amount of response properties
90
Receptor density -> sensitivity
91
2 Point Discrimination
The ability to discriminate that two close-by points touching the body surface are truly separated
92
Thermoreceptors
1. Cold receptors:
- Adelta bare nerve endings
- 100 x more sensitive to sudden cooling than to gradual skin cooling
2. Warm receptors:
- C bare nerve endings
- Equally sensitive to rapid and slow warming
- Stop firing at 45 C
93
What does the primary somatosensory cortex (S1) entail?
- Modality segregation
- Somatotopy
- Column Structure
94
What is somatotopy?
Orderly representation of the body surface area in the somatosensory cortex
95
Columnar structure in S1:
- Column: neurons spanning vertically across multiple layers sharing similar response properties
- Same receptive field
- Respond to a certain type of tactile feature
96
Recording in humans (microneurographic technique) is limited in revealing central mechanisms...
Animal models of whiskers are used instead
97
Rodent whisker system advantages
- The neural circuits from periphery to CNS is relatively simple (only 3 synapses from whisker to cortex)
- Exquisite somatotopy (each whisker represented in S1 by distinct group of neurons)
- Genetic accessibility (mouse)
- Powerful recording techniques during behavior
98
Bottom-up sensory pathway (whiskers)
Whiskers - brainstem - VPM thalamus - S1 cortex
99
Calcium pacing allows for monitoring the activity of hundreds of neurons simultaneously
100
Optogenetics
Genetically encoded light activated ion channels
- Allows changing neuronal activity at fine timescales
101
Tactile detection of head fixed mice
Head-fixed mice are trained to report the perception of a single whisker deflection by licking toward a water port. They are also trained to withhold licking in the absence of whisker deflection. Neuronal recording and perturbations can be performed simultaneously during task performance.
102
Different types of motor control
- Reflexive: triggered by external events
- Rhythmic: walking, chewing, whisking
- Voluntary: self initiated, goal directed
103
Spinal cord: reflex, rhythmic
Innervate muscle
104
Brainstem: reflex, rhythmic
Innervate spinal cord and muscle
105
Forebrain: voluntary
Does not directly innervate muscle
106
What is the importance of the brain stem?
- Signals from the periphery go through brainstem to the rest of the brain
- Controls vitals such as blood pressure and respiration
107
What is the importance of the basal ganglia and cerebellum?
- Interconnected with cortex
- Controls smooth movement and posture
- Don't directly project to spinal cord or motor neurons
108
Each fiber in the muscle is innervated by a single axon branch from the CNS
109
1 motor neuron = multiple fibers; 1 muscle fiber = 1 neuron
110
Alpha motor neuron
- Directly triggers the generation of muscle force
- A single alpha motor neuron innervates multiple muscle fibers
111
Flexor vs. Extensor
- Extension: contraction of the extensor pulls the left end of the bone upward causing the right end to pivot downward
- Flexion: contractions of the flexors pull the right end of the bone upward
112
Locomotion cat experiment
- Cat is paralyzed and can't consciously move its lower body. It's supported on a sling and its legs are placed on a treadmill. The cat can't initiation locomotion by itself, but it can be made to walk with perfect coordination on 4 limbs if we stimulate the brainstem or turn on the treadmill
113
Neuronal mechanisms for locomotion
- central pattern generators
- command neurons
- sensory inputs
- coordinating fibers
114
Central Pattern Generator (CPG)
- A network of neurons that produces rhythmic output based on intrinsic properties of individual neurons
- can generate complex patterned output even if the CPG is isolated from the brain and sensory inputs
115
Command neurons for locomotion are located in the mesencephalic locomotor region (MLR)
116
Stretching of the muscle spindle induces depolarization of the sensory axon
Sensory feedback activates CPG
117
Complex movement occurs in 3 stages (picking up a cup)
1. Spatial assessment: analyze where you are with respect to the cup
- Posterior parietal cortex
2. Planning strategy: plan for picking up cup
- Premotor cortex
3. Detailed execution: control which muscles contracted in what order and strength
- Primary motor cortex
