W5 - Cerebral Cortex Flashcards
1
Q
What is the cerebral cortex?
A
It is the outermost layer of the forebrain made of grey matter and is involved in high-level brain functions.
2
Q
How many layers does the cerebral cortex have?
A
It has six distinct layers (laminae), each with different cell types and functions.
3
Q
What is found in Lamina I of the cerebral cortex?
A
Dendrites.
4
Q
What is Lamina II known as?
A
The external granular layer.
5
Q
What types of cells are found in Lamina III?
A
Pyramidal neurons, including Betz cells.
6
Q
What is the function of Lamina IV?
A
It is the internal granular layer and serves as the major sensory input layer.
7
Q
What characterizes Lamina V?
A
It contains large pyramidal cells (Betz cells) and acts as a key output structure.
8
Q
What is the role of Lamina VI?
A
It is also an internal granular layer and functions as a key output structure.
9
Q
What are Betz cells and why are they important?
A
Betz cells are large pyramidal neurons in Lamina V critical for the execution of voluntary movement.
10
Q
What subcortical structures are covered by the cerebral cortex?
A
The thalamus, brainstem, and spinal cord.
11
Q
Are inputs and outputs to the cortex random or specific?
A
They are layer-specific.
12
Q
What are the hierarchical stages in sensory-motor organization for movement?
A
- Planning – Basal Ganglia, Pre-motor areas
- Programming – Motor Cortex
- Integration – Cerebellum, Brainstem
- Execution – Spinal Column → Muscles
13
Q
What role does the cerebellum play in the motor system?
A
It integrates and fine-tunes motor commands before they are sent to the spinal cord.
14
Q
How does the motor system use sensory feedback?
A
Sensory systems provide input that is continuously integrated to guide and adjust movements.
15
Q
What is the focus of the motor control system related to the cortex?
A
Planning and programming of action, primarily involving pre-motor areas and motor cortex.
16
Q
Which cortical regions are involved in motor planning and programming?
A
• Premotor cortex
• Supplementary motor area
• Primary motor cortex
• Posterior parietal cortex
• Dorsolateral prefrontal cortex
17
Q
What does “cytoarchitectonics” refer to in the cerebral cortex?
A
The study of different areas of the cortex based on their distinct cellular structures.
18
Q
Who identified distinct cortical areas based on cytoarchitectonics?
A
Korbinian Brodmann (1868–1918).
19
Q
How many cortical areas did Brodmann identify?
A
52 cortical areas.
20
Q
Why are Brodmann areas important beyond anatomy?
A
Because the anatomical distinctions have functional relevance in brain activity and specialization.
21
Q
Which Brodmann area corresponds to the Primary Motor Cortex (M1)?
A
Brodmann Area 4 (BA4).
22
Q
What key type of neuron is found in Layer V of BA4?
A
Betz cells, which are large pyramidal neurons crucial for motor output.
23
Q
What is the corticospinal tract?
A
A major descending pathway that transmits voluntary motor commands from the motor cortex to the spinal cord.
24
Q
What is the origin of corticospinal tract projections?
A
The motor cortex (particularly M1).
25
Where do neurons of the corticospinal tract project to?
From the motor cortex to the spinal cord (and also to the brainstem).
26
What are Betz cells and where are they located?
Large pyramidal neurons found in Layer V of the primary motor cortex (M1).
27
Where do Betz cells project?
To the spinal cord and brainstem.
28
What proportion of Betz cells project directly to motor neurons?
Only 5%, but they play a crucial role in volitional motor control.
29
Where do the remaining Betz cell projections go?
To spinal interneurons, which indirectly influence movement.
30
What is the function of Betz cells in motor control?
They initiate, regulate, and control voluntary skilled movements by innervating alpha and gamma motor neurons in the spinal cord.
31
What does the corticospinal tract provide control over?
Conscious, voluntary control of skeletal muscles.
32
What does contralateral motor control mean?
Each hemisphere of the brain controls the opposite side of the body.
33
Where does the corticospinal tract cross over to the contralateral side?
At the medulla (a part of the brainstem).
34
Which side of the body does the left motor cortex control?
The right side of the body.
35
Which side of the body does the right motor cortex control?
The left side of the body.
36
What did Fritsch & Hitzig (1870) discover through electrical stimulation in dogs?
They mapped somatotopic motor representation, showing that different parts of the motor cortex control specific body parts.
37
What did Penfield (1940) discover about the motor cortex through work with epilepsy patients?
He found a somatotopic organization—stimulation caused simple movements in specific body parts.
38
What is a cortical motor map?
A representation in the motor cortex showing specialized areas for controlling different effectors like limbs, hands, and fingers.
39
How are sensory and motor maps related?
There is a close relationship; motor maps often mirror the organization of sensory maps.
40
Why is the "motor homunculus" considered an oversimplification?
Real motor maps show more dynamic and overlapping representations than the simplified homunculus suggests.
41
What might overlapping motor representations indicate?
That different body parts must work together in coordinated, ecologically relevant movements.
42
What is a key concept challenging the classical somatotopic view of the motor cortex?
The motor cortex may encode movements or action goals, not just individual body parts.
43
What are effector-specific maps interspersed with in the motor cortex?
Inter-effector regions with distinct connectivity, structure, and function.
44
What are inter-effector regions connected to?
Each other and the cingulo-opercular network.
45
What role do inter-effector regions seem to play?
Action planning, rather than movement execution.
46
Do inter-effector regions show effector specificity?
No—they are not tied to specific body parts.
47
What does this suggest about motor cortex organization?
It may be organized into an alternating somato-cognitive action network, not just strict somatotopy.
48
What does brief electrical stimulation (50 ms) of the motor cortex elicit?
Simple movements or muscle contractions on the contralateral side of the body.
49
What does prolonged stimulation of the motor cortex produce?
Complex, goal-directed actions.
50
What is a precision grip and how is it represented in the motor cortex?
A precise, coordinated grip using two fingers; it activates more motor cortex neurons than a power grip.
51
What’s the difference between a power grip and a precision grip in terms of brain activation?
Precision grip causes more motor cortex activity due to higher dexterity needs.
52
Does force or precision determine motor cortex activation?
Precision and dexterity—not force—drive higher cortical activity.
53
Where is the primary motor cortex (M1) located?
In the frontal lobe, anterior to the central sulcus.
54
What is the main function of M1?
To send movement signals to muscles—it's the final output for voluntary motor commands.
55
What defines the structure of M1?
The presence of Betz cells, large pyramidal motor neurons.
56
Where do Betz cells project?
They have long axons that connect to alpha motor neurons in the spinal cord.
57
How is M1 somatotopically organized?
It shows a contralateral organization—each hemisphere controls the opposite side of the body.
58
What determines the size of regions in M1?
The level of fine motor control—areas like the hands and face have larger representations.
59
Is the coding of movement in M1 fully understood?
No—M1 can activate individual muscles and complex movements, but its precise coding is still under research.
60
What is the clinical importance of M1?
Damage, such as from stroke, can cause permanent loss of fine motor control.
61
How do secondary motor areas contribute to movement?
They work with M1 to plan and coordinate actions, often activating even before movement begins.
62
What happens in brain imaging when a person imagines movement?
Secondary motor areas like SMA and PMC are activated—even if no movement occurs.
63
What is the function of the SMA proper?
It helps in learning and initiating internally generated movements.
64
What is the role of the pre-SMA?
It is involved in executing complex, sequential movements.
65
What else activates the SMA?
Tasks involving response inhibition and movement organization.
66
What does the dorsal premotor cortex (PMd) do?
It is involved in movement preparation and learning conditional actions in response to external cues.
67
What is the role of the ventral premotor cortex (PMv)?
It supports sensory-guided movement, especially visuomotor control during grasping.
68
What are mirror neurons and where are they found?
Neurons in PMv that fire both when performing and observing a goal-directed action.
69
Why are mirror neurons important?
They support learning through observation and understanding others' intentions.
70
What area in humans has mirror-like activity and is associated with object interaction?
Broca’s Area (BA44/45).
71
What is the main function of the PPC?
To link sensory input with motor plans for goal-directed behavior.
72
What information does the PPC receive?
Sensory input from the visual, somatosensory, and sensorimotor cortex.
73
How does the PPC work with the frontal cortex?
The frontal cortex decides which action to take; the PPC helps plan the appropriate movement.
74
What happens when the PPC is damaged?
The person may still be able to move but struggles to know what actions are appropriate for interacting with the environment.
75
What do the Frontal Eye Fields (FEF) control?
Eye movement and visual attention.
76
Where are the FEF located?
In the frontal lobe, anterior to the motor cortex.
77
What areas are the FEF connected to?
The visual cortex in the occipital lobe and the prefrontal cortex.
78
What is the ultimate output structure for eye movements?
The superior colliculus, which receives FEF input and initiates eye muscle contractions.
79
Do the FEF show somatotopic organization?
Yes—they show a mapped representation of eye movement control.
80
What is neuroplasticity?
The brain's ability to form and reorganize synaptic connections in response to learning, experience, or injury.
81
When is neuroplasticity most pronounced?
During childhood, and it declines with age.
82
What is somatotopic map plasticity?
The reorganization of motor/sensory cortex maps due training, injury, or co-activation.
83
How does training affect cortical maps?
Training (e.g., playing piano) expands cortical representations.
84
What effect does array or injury have on cortical maps?
It leads to shrinkage or loss of cortical representation (denervation).
85
What happens when two fingers are surgically fused?
Their cortical representations become merged due to co-activation.
86
What did Kolasinski et al. (2016) show using high-resolution scanners?
Rapid reorganization of motor maps, with significant changes in adjacent finger areas after just 24h of finger fusion.
87
What did Muret et al. (2022) find about hand amputation and brain mapping?
Recent amputees had mappings similar to controls; only congenital one-handers showed invasion or retreat of nearby regions.
88
What did Ziv & Ahissar (2009) show about learning and synaptic remodeling?
Synaptic growth and pruning occur within hours or days, with neurons competing for space.
89
What did Schone et al. (2023) find about cortical maps after arm amputation?
No changes in cortical maps were found, despite expectations of reorganization.
90
What textbook discusses motor systems and sensorimotor learning?
Tresilian.
91
What role do synapses play in neuroplasticity?
They enable communication between neurons and can strengthen or weaken based on experience.
92
What are three types of synaptic changes that improve communication?
1. Pre-synaptic changes (more vesicles, higher release probability)
2. Cleft changes (less re-uptake, smaller gap)
3. Post-synaptic changes (more receptors)
93
What structural change also improves learning and memory?
The growth of new synapses to form stronger pathways.
94
What is Long-Term Potentiation (LTP)?
A persistent strengthening of synapses that boosts signal transmission between neurons, crucial for learning and memory.
95
How is the NMDA channel involved in LTP?
Normally blocked by Mg²⁺ ions; it becomes active when glutamate binds to AMPA receptors and depolarizes the cell.
96
What happens when NMDA receptors are activated?
Calcium enters the neuron, triggering signaling cascades that enhance synaptic strength.
97
What intracellular processes does calcium entry initiate during LTP?
Migration of AMPA receptors to the membrane and synthesis of new ones.
98
What are the 3 principles of LTP?
1. Cooperativity – requires strong synaptic input
2. Associativity – weak inputs paired with strong can gain LTP
3. Synapse Specificity – only stimulated synapses show LTP
99
What is Long-Term Depression (LTD)?
A persistent weakening of synapses, reducing signal strength between neurons.
100
What role does LTD play in the brain?
It’s essential for motor learning, particularly in the cerebellum.
101
Is cerebellar LTD NMDA-dependent?
No, cerebellar LTD is not NMDA-dependent.
102
What does cerebellar LTD involve?
A decrease in AMPA receptors and reduced synaptic efficacy.
103
What is Transcranial Magnetic Stimulation (TMS)?
A non-invasive method to map motor areas and study plasticity in the brain.
104
How is TMS used to study neuroplasticity?
It can simulate LTP/LTD-like changes and measure cortical excitability over time.
105
What happens to LTP in the presence of NMDA antagonists in TMS studies?
LTP is blocked.
106
What happens to LTD in the presence of NMDA antagonists in TMS studies?
LTD is not blocked.
107
What did Schone et al. (2023) study?
Changes in cortical body maps before and after arm amputation.
108
How many participants were involved in Schone et al.’s study?
Two patients, followed longitudinally before and after surgery.
109
What did Schone et al. assess post-surgery?
Kinaesthetic vividness, phantom pain, and imagined motor control of the amputated limb.
110
What was the unexpected finding in Schone et al. (2023)?
No cortical reorganization occurred, despite loss of limb and increased imagined control.
111
Why is this finding significant?
It challenges the traditional view that motor maps undergo reorganization after limb loss.
