Brain Control of movement

Question 1

Describe the origin and function of the lateral pathways

Answer 1

Lateral pathways = corticospinal tract (CST) & rubrospinal tract (RST)
origins: CST = motor cortex (through internal capsule -> midbrain -> medullary pyramid (decussation) -> lateral column -> ventral horn)
RST = red nucleus (through medulla (decussation) -> lateral column -> ventral horn)

Function: fine control of distal motor units, inc individual finger movements

Question 2

Describe the effects of lateral pathway lesions

Answer 2

CST lesions cause deficity in precision grip (ie opposing thumb).
is RST is unaffected, recovery possible.
Stroke in CST = contralateral paralysis.

Question 3

Describe the origin and function of the ventromedial pathways.

Answer 3

All originate in the brainstem & synapse onto interneurons.
Comprised of:
1. vestibulospinal tract - from vestibular nucleus to cervical spinal cord for posture of head and neck
2. tectospinal tract - from tectum (superior colliculi) for orientation of head in response to visual stimuli
3. reticulospinal tracts - from reticular formation for control of posture of limbs & trunk. pontine reticulospinal enhances antigracity reflexes, medullary reticulospinal releases antigravity reflexes.

Question 4

List all the areas of the cerebral cortex that are directly involved in the planning and execution of a voluntary movement.

Answer 4

Frontal Lobe:
* Area 4 - primary motor - M1
* Area 6 - premotor & supplementary motor (PMA & SMA)
* Area 8 - frontal eye fields
* Areas 24 & 32 - cingulate cortex
* Areas 9, 46, 12, 11, 13 - prefrontal cortex

Parietal Lobe:
* Areas 1, 2, 3 - primary somatosensory - S1
* Areas 5 & 7 - posterior parietal

Question 5

Discuss the role of the posterior parietal, prefrontal and premotor areas in the planning of a movement.

Answer 5

posterior parietal (5 & 7): integration of somatosensory, proprioceptive and visual inputs. attentional processing. sense of self.

Prefrontal: working memory (holding the goal in mind), decision making, selecting motor response on basis of their success

Premotor (6): planning & sequencing of movement.

Question 6

Describe the basic anatomy of the basal ganglia, including major inputs and outputs.

Answer 6

• BG comprised of sorpus striatum, subthalamic nucleus & substantia nigra
• major input from cortex
• cortex to striatum, striatum to globus pallidus (sometimes via subthalamic nucleus), substantia nigra into striatum
• output to thalamus

Question 7

Describe the major symptoms of basal ganglia disease, and discuss the implications for function of the basal ganglia in motor control.

Answer 7

Parkinsons symptoms: hypokinesia, bradykinesia, rigidity, tremors in hand/jaw.
caused by degeneration of dopaminergic substantia nigra.
Function of dopaminergic substantia nigra: modulating direct & indirect loop to facilitation necessary movement and suppress unwanted movement

Huntingtons symptoms: chorea, hyperkinesia, dementia.
caused by degeneration of indirect pathway.
Function of indirect pathway: decreasing motor thalamus activity to prevent unwanted movement.

Question 8

Describe the major inputs and outputs of the primary motor cortex

Answer 8

• cortical inputs & thalamic inputs - both into the Betz cells (layer 5 pyramidal)
• outputs to corticospinal tract

Question 9

discuss the role of population coding in the primary motor area in the execution of motor tasks.

Answer 9

Population coding is summation of population vectors of neurons using their spike frequencies.

Each neuron has an optimal direction that will give greatest spike frequency response. Each neuron has a “vote”. Net vote result of a cortical area determines the direction of movement.

Question 10

Describe the motor cortical loop

Answer 10

From cortex to basal ganglia to thalamus (ventrolateral) then back as major input to cortex Area 6 (premotor)

Question 11

Describe the motor loop through the cerebellum

Answer 11

Cortex to Pons to cerebellum back to Area 4 (M1). Area 4 then drives lateral & ventromedial pathways.

Question 12

discuss the role of cerebellar corticothalamic feedback loop in the planning and execution of voluntary movement.

Answer 12

analyses & corrects motor output.

Plan comes in - cerebellum fine tunes the movement based on sensory info (real time & long term), correct the motor output and returns it to cortex

Question 13

What is the function of direct and indirect loops

Answer 13

Direct - stimulates facilitation of movement
Indirect - reduces activity & suppresses movement

Question 14

What are the general steps involved in brain controlled movement?

Answer 14

1. Where is the body in space rn?
2. Where do we want to go?
3. What’s the plan to get there?
4. remember the plan
5. issue instructions