Action 2: Structure

43 important questions on Action 2: Structure

Connections from cortex to brainstem go to the nuclei of?

- Nuclei of extrapyramidal tracts
- Nuclei of cranial nerves (head & eye movements)

What do de-efferented animals do? What is an example of this in humans?

- Action without guidance from the brain
- Reflexes remain
- In humans: locked in syndrome

What do de-afferented animals do?

- No proprioception
- Still accurate actions
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What does the Central Pattern Generator do?

- Generates regular movement patterns
- Completely autonomous in the spinal cord.

What information does the Central Pattern Generator receive?

Gait command: Basal Ganglia (Top-Down)
Proprioceptive feedback (Bottom-Up)

What can a de-cerebrated cat still do?

Autonomous walking (Central Pattern Generator)

What connection in the spinal cord are reflexes?

A straight connection between Dorsal/Afferent (Feeling) to Ventral/Efferent (Action)

How does the Golgi Tendon Reflex work?

Neuron from Golgi tendon organ fires --> Motor Neuron is inhibited --> Muscle relaxes --> Load is dropped

How does the Withdrawal reflex work?

Pain receptor in the skin fires --> Connects to efferent neuron throuh interneuron --> Muscle contracts the point of pain away

How does the Knee reflex work?

- Contraction of the Agonist muscle
- Also inhibition of antagonist muscle

What is the crossed extensor reflex?

- Step on pin with left leg: Left extensor relaxes, Flexor contracts
- Right leg does the other way (to straighten leg: Right extensor contracts, Flexor relaxes

What is the final stage in the spinal cord?

Alpha Motorneurons

When are Alpha motorneurons involved in action?

Always in action.
- Irrespective of signal source
- Irrespective of signal target

How to Alpha Motorneurons work?

Alpha motor neuron excrete Acetylcholine into muscle fibre --> Leads to contraction of muscle fiber --> Same for tendon, joint

What types of muscles are there (function)?

Extensor/Flexor
Agonist/Antagonist

How is M1 organised?

Somatotopic: Every body part has it's own area

Lateral Corticospinal tracts control

- Distal skeletal muscles (Precision, Effectors)

Medial Corticospinal Tracts control:

- Proximal Skeletal muscles
- Posture, Balance, Tonus

What are corticospinal tracts also called & why?

Pyramidal tracts: In the medulla thick bands of motor neuron output looks like pyramids

Where do axons of M1 go? And dendrites?

Axons: Spinal Cord
Dendrites: Lower Motor Neurons

What goal does M1 serve?

- Voluntary control of skeletal muscles
- Goal-directed behaviour

How do neurons in M1 encode for a specific direction?

- Every motor neuron is sensitive for a certain direction
- Ensembles of motor neurons encode for desired direction
- Populations of neurons have their own preferential direction

How can motor neurons in M1 be used in prosthetics?

M1 populations already fire in preparation of movement direction --> Anticipatory vector can be read out to 'see' predicted movement direction

What is the role of the cerebellum in motor action? Where does it connect to?

Modulation in
- Interneurons in the spinal cord
- Brainstem nuclei
- Motor / Premotor cortex (cortico-subcortical loop)

What are the 3 cerebellar systems and their functions?

- Vestibulocerebellar: Control of balance & Eye body movement coördination (Vestibulo-Ocular Reflex)
- Spinocerebellum: Fine-tuning (precise & flexible control of limbs/effectors)
- Neocerebellum: Planning of movements (Finger-to-nose)

What is the role of Basal Ganglia in motor control?

Possible responses  --> Response with most activation
- Selection
- Initiation
- Prevention of action

What does the Basal Ganglia output to?

BG (dis)inhibits:
- Thalamus
- Motor cortex

What does the direct route (D1) of the basal ganglia do?

Direct = Disinhibition of action

What are modulators in the basal ganglia?

- Globus Pallidus pars Externa (GPe)
- Subthalamic Nucleus (STN)

What is the Hyperdirect route in the Basal Ganglia? What does it do?

Emergency brake on action (quick stop)
PFC --> STN --> GPi --> Thalamus --> Inhibition of action

What (besides anatomy) is the difference between supplementary motor complex (SMC) and premotor cortex (PMC)?

SMC: Organisation of internally guided action
PMC: Organisation of externally guided action

Supplementary Motor Complex (SMC)  gets input from?

- Prefrontal cortex (PFC)
- Basal Ganglia (BG)

What do the different area's of the Supplementary Motor Complex (SMC) output to?

- Supplementary Eye Field (SEF): outputs to: Caudatus (occulomotor)
- pre(SMA):  outputs to: M1, Basal Ganglia, Spinal Cord

Premotor Cortex gets input from? And outputs to?

Input from: Posterior Parietal Cortex (PPC) & Cerebellum
Output to: M1, Basal Ganglia (BG) & Spinal Cord

What does the Premotor Cortex have in common with M1?

- Both have populations of neurons encode for direction of movement
- Both also fire in anticipation of movement

PMC: Encodes for multiple actions untill a selection has to be made

What role does the (medial) Posterior Parietal Cortex (PPC) play in motor control?

Action memory: What to do with an object & Translating cue's and information into action plans

Posterior Parietal Cortex (PPC) gets input from? And output to?

Input: Diffuse; Perceptual systems & PFC
Output: Premotor Cortex (PMC) & Spinal Cord

What is special about the activation of Posterior Parietal Cortex's position?

It's always left lateralised, no matter where the movement is.

What role does the Dorsolateral Prefrontal Cortex (DLPFC) play in motor control?

Action goal: What do I want to do?
- Prioritising actions
- Focus: action goals in mind
- Flexibility: Switching between action goals

What role does the Inferior Frontal Gyrus play in action control?

What do I not want to do (opposite of dlPFC)
- Action inhibition: selectively suppressing unwanted/inappropriate actions

Inferior Frontal Gyrus: What input? What output?

Input: Everywhere
Output: DLPFC,  M1, Basal Ganglia (NOODREM; striatum & STN)

What is the role of Anterior Cingulate Cortex (ACC) in motor control?

- Using action outcomes (reward, feedback, error) to guide voluntary action: Costs/Benefit analysis of action
- What action leads to reinforcement?
- Is an action worth the effort given the expected reward?

Anterior Cingulate Cortex (ACC): Output & Input?

Input: Everywhere
Output:  Everywhere

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