Topic 3: Cortical Sensorimotor systems

Question 1

1. What is the cortex?
2. How is the cerebral cortex organised?

Answer 1

1. The cortex forms the outer surface of the forebrain (grey matter)
2. Organised into 6 layers (“laminae”)

Question 2

How many areas does the cerebral cortex have?

Answer 2

Cytoarchitectural differences define 52 functionally relevant areas

Question 3

Betz cells within the primary motor cortex (M1) originate from which laminae layer?

Answer 3

Layer 5

Question 4

What are Betz cells and where do they project from?

Answer 4

Large pyramidal cells that project from the motor cortex

Question 5

Where do they project to?

Answer 5

5% project to motor neurons
95% project to spinal interneurons
They also project to brain-stem

Question 6

What do Betz cells control, and how?

Answer 6

• Initiate, regulate, control, conscious VOLENTARY skilled movements of skeletal muscles
• By innervating alpha and gamma motor neurons in the spinal cord

Question 7

What happens when you electrically stimulate the motor cortex briefly, and for prolonged time?

Answer 7

Brief: simple movements / contractions of contralateral muscles
Prolonged: complex, goal-directed actions

Question 8

The primary motor cortex:
1. Where is it located in the brain?
2. How is it anatomically defined?
3. What is size based on?
4. What does it code for?
5. What happens if you have a stroke in your motor cortex?

Answer 8

1. Frontal lobe
2. Area in the brain that contains Betz cells
3. Precision, fine motor control rather than size of body part
4. Unclear, but individual muscles and complex actions can be ‘stimulated’
5. Permanent loss of fine motor control

Question 9

What are the 3 secondary motor / association areas called?

Answer 9

1. Supplementary motor area (SMA) - SMA proper and Pre-SMA
2. Pre-motor cortex (PMC) - Dorsal (PMd) and Ventral (PMv)
3. Posterior parietal cortex (PPC)

Question 10

What is the role of the Supplementary Motor Area

Answer 10

SMA proper (learning)
Pre-SMA (execution)
- Postural stability
Planning and executing complex sequential movements
- initiation of internally generated movements (rather than stimulus driven)

Question 11

What is the dorsal and ventral pre motor for?

Answer 11

Dorsal: preparation of movement and learning conditional actions (response to cues e.g. traffic lights)
Ventral: sensory guidance of movement (responds to tactile, visual, auditory stimuli), visuomotor control during grasping, mirror neurons

Question 12

What is the posterior parietal cortex used for?

Answer 12

Links frontal cortex (decision-making) with premotor (planning) areas
Receives information from sensory regions (visual cortex, sensorimotor cortex etc).
Determining potential actions/goals given the environment (pick up coffee, pick up sandwich, continue working).
The frontal cortex then decides which action to perform, and secondary areas develop plan for that action.

Question 13

What are mirror neurons?
Where are they located?

Answer 13

Learning through observation
Located in the premotor ventral

Question 14

What is neuroplasticity?
Where can it occur?

Answer 14

The ability of the brain to form and reorganize synaptic connections, especially in response to learning or experience or following injury
Occurs anywhere in the brain

Question 15

What can cause neuroplasticity/sensory remapping?

Answer 15

1. Training (expands map)
2. Denervation/amputation (reduces map)
3. Co activation (fuses the map)

Question 16

How do learning- based neural changes affect synapse efficacy?
1. Pre synaptic
2. Synaptic cleft
3. Post synaptic
4. Growth

Answer 16

1. increase vesicle volume, availability, release probability
2. Reduce re uptake mechanisms, gap dimensions
3. Increase receptor density and area
4. Make new synapses

Question 17

What is long-term potentiation?
What is long-term depression?

Answer 17

LTP: activity-dependent persistent strengthening of synapses. These produce along-lasting increase in signal transmission between two neurons.
LTD: activity-dependent reduction in the efficacy of neuronal synapses. These produce along-lasting decreases in signal transmission between two neurons.

Question 18

How does associative LTP induction work?

Answer 18

NMDA channels blocked by Mg2+

Glutamate binds to NMDA and AMPA receptors

Causes change in shape, opening channels

Ca2+ enters, triggering cascade

Migration of AMPA receptors from inside cell to cell membrane

Synthesis of more AMPA receptors

Question 19

What are three key principles of LTP?

Answer 19

1. Cooperatively: LTP requires simultaneous activation of large number of axons (due to large depolarisation).
2. Associative: When weak synaptic input is paired with strong, then large depolarisation can propagate and cause LTP at synapse with weak input.
3. Synapse specific: If particular synapse is not activated then LTP will not occur even with strong post synaptic depolarisation.

Question 20

How is each principle important to memory and learning?

Answer 20

Cooperatively: ensures that only events of a high degree of significance (that active sufficient inputs) will result in memory storage.
Associative: allows an event with little significance (CS) to be endowed with a higher degree of meaning, if associated with a significant event (US).
Synapse specific: Inputs that convey info not related to a particular event will not be strengthened to participate in a given memory.

Question 21

Where was LTD first identified?
What does it involve?
It NMDA dependent?

Answer 21

Hippocampus
Decrease in AMPA receptors
NOT NMDA-dependent