Topic 3: Cortical Sensorimotor systems Flashcards
- What is the cortex?
- How is the cerebral cortex organised?
- The cortex forms the outer surface of the forebrain (grey matter)
- Organised into 6 layers (“laminae”)
How many areas does the cerebral cortex have?
Cytoarchitectural differences define 52 functionally relevant areas
Betz cells within the primary motor cortex (M1) originate from which laminae layer?
Layer 5
What are Betz cells and where do they project from?
Large pyramidal cells that project from the motor cortex
Where do they project to?
5% project to motor neurons
95% project to spinal interneurons
They also project to brain-stem
What do Betz cells control, and how?
- Initiate, regulate, control, conscious VOLENTARY skilled movements of skeletal muscles
- By innervating alpha and gamma motor neurons in the spinal cord
What happens when you electrically stimulate the motor cortex briefly, and for prolonged time?
Brief: simple movements / contractions of contralateral muscles
Prolonged: complex, goal-directed actions
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?
- Frontal lobe
- Area in the brain that contains Betz cells
- Precision, fine motor control rather than size of body part
- Unclear, but individual muscles and complex actions can be ‘stimulated’
- Permanent loss of fine motor control
What are the 3 secondary motor / association areas called?
- Supplementary motor area (SMA) - SMA proper and Pre-SMA
- Pre-motor cortex (PMC) - Dorsal (PMd) and Ventral (PMv)
- Posterior parietal cortex (PPC)
What is the role of the Supplementary Motor Area
SMA proper (learning)
Pre-SMA (execution)
- Postural stability
Planning and executing complex sequential movements
- initiation of internally generated movements (rather than stimulus driven)
What is the dorsal and ventral pre motor for?
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
What is the posterior parietal cortex used for?
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.
What are mirror neurons?
Where are they located?
Learning through observation
Located in the premotor ventral
What is neuroplasticity?
Where can it occur?
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
What can cause neuroplasticity/sensory remapping?
- Training (expands map)
- Denervation/amputation (reduces map)
- Co activation (fuses the map)
How do learning- based neural changes affect synapse efficacy?
1. Pre synaptic
2. Synaptic cleft
3. Post synaptic
4. Growth
- increase vesicle volume, availability, release probability
- Reduce re uptake mechanisms, gap dimensions
- Increase receptor density and area
- Make new synapses
What is long-term potentiation?
What is long-term depression?
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.
How does associative LTP induction work?
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
What are three key principles of LTP?
- Cooperatively: LTP requires simultaneous activation of large number of axons (due to large depolarisation).
- Associative: When weak synaptic input is paired with strong, then large depolarisation can propagate and cause LTP at synapse with weak input.
- Synapse specific: If particular synapse is not activated then LTP will not occur even with strong post synaptic depolarisation.
How is each principle important to memory and learning?
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.
Where was LTD first identified?
What does it involve?
It NMDA dependent?
Hippocampus
Decrease in AMPA receptors
NOT NMDA-dependent
