The Voluntary Control of Movement

Question 1

What neurodevelopment of movement occurs at 1-5 months and where?

Answer 1

• Pons (1-5 months)
  o Crawling on tummy – attention and motivation
  o Hands out integrating grasp reflex
  o Vital tactile information received

See diagram in notes for location

Question 2

What neurodevelopment of movement occurs at 4-13 months and where?

Answer 2

• Midbrain (4-13 months)
  o Crawling on hands and knees
  o Hands open and close
  o Connects vestibular, proprioception and visual systems

See diagram in notes for location

Question 3

What neurodevelopment of movement occurs at 8-96 months and where?

Answer 3

• Cortex (8-96 months)
  o Upright walk and cross pattern
  o Cortical opposition of both hands working together but independently

See diagram in notes for location

Question 4

What neurodevelopment of movement occurs at up to 25 years and where?

Answer 4

• Prefrontal cortex (up to 25 years)
  o Refined skills for performance
  o Executive functions
  o Planning, organisation

See diagram in notes for location

Question 5

What is voluntary/conscious movement and where do these thoughts form? Where and how are motor plans then formed and perfected? - Why is this important and what part does the proprioceptive information play in the formation of the motor plan?

Answer 5

• You have a itch on your forehead, how do you go about scratching it?
• The thought of having to scratch that itch forms in prefrontal cortex
• Signals to appropriate cortex to begin composing motor plans
• From cortex to basal ganglia nuclei
  o Perfects motor plan
• Back to cerebral cortex before execution of the action impulse in the PNS
  o Cerebral cortex to cerebellum
   Motor plan plus proprioception information
• Why is this important and what part does the proprioceptive information play in the formation of the motor plan?
  o With proprioceptive information, your brain is able to develop a more accurate motor plan since it will be aware of the original positioning of your body. For instance, if you wanted to scratch the itch on your eyebrow, but your arm was buried under a duvet, your motor plan would be to free your arm from the duvet, lift your arm, and scratch.
  o If your arm was already near your head, the motor plan would only entail the movement of your hand to the left or the right to reach the itchy spot. In consideration of the proprioceptive information, the final motor plan is sent back up to the cerebrum from the basal ganglia to be distributed to the peripheral nervous system through the spinal cord.

See flowchart in notes

Question 6

What type of muscular contractions are required for voluntary movement and how are they orchestrated? What is the hierarchy of the 4 systems to do this?

Answer 6

• Requires co-ordinated and graded patterns of muscular contractions orchestrated by motorneurons of the spinal cord and brainstem
• Requires 4 distinct but interactive systems that are organised hierarchically
  o Simplest movement = stretch reflex
  o Lower motorneurons (LMN)
  o Upper motorneurons (UMN)
  o Cerebellum
  o Basal ganglia

See diagram in notes

Question 7

What are the functions of the LMN, UMN, cerebellum and basal ganglia? How are these components organised?

Answer 7

• LMN – produce muscle contractions via activation of motor neurons that synpase on a group of muscle fibres = motor units
  o Strength of contraction dependent on number of active motor units
• UMN – produce voluntary movements
• Cerebellum
  o Co-ordinate muscle movement
  o Select correct sequences
• Basal ganglia
  o Initiation and maintenance of movements
  o Contains motor programs
• All somatopically organised (so that you know exactly how to carry out each movement)

See spinal diagram in notes

Question 8

Where are lower motor neurons located? How are they involved voluntary movement? What can damage to LMN cause?

Answer 8

• Located in anterior (ventral) horn of spinal cord and in cranial nerve nuclei in brainstem
• All voluntary movements rely on direct innervation from a motor neuron
• Damage
  o Flaccid paralysis
  o Hypotonia
  o Fasciculations
  o Absent deep tendon reflexes
  o Muscle atrophy

Question 9

Do upper motor neurons innervate muscle directly? How are they involved in voluntary movement? Where do they synapse? Where are their cell bodies located? Which 3 motor pathways do they contribute to and what is the function of each?

Answer 9

• UMN do not innervate muscle directly
• Carry voluntary motor commands to the LMNs
• UMNs synapse directly or indirectly onto the LMNs
• UMN cell bodies mostly in primary motor cortex
• UMNs contribute to 3 functionally distinct motor pathways
  o Corticospinal tract (corticobulbar tract)
   Precise movements
  o Rubrospinal tract
   Gross movements (large muscles)
   Facilitates flexor movement
  o Vestibulospinal and reticulospinal tracts
   Posture and balance
   Muscle tone
   Position of head and limbs

See diagram in notes (and for organisation and location of UMN pathways)

Question 10

What is the corticospinal tract, what is its function and where does it terminate? What connections does it have in the brain and how are these maintained?

Answer 10

• Corticospinal tract (corticobulbar tract)
  o Highest order of motor functions
  o Most directs control of fine, digital movements
  o Many of the tracts fibres terminate on interneurons of the spinal cord
   55% terminate at the cervical levels
   20% terminate at the thoracic level
   25% at the lumbosacral levels
  o Lateral CST controls distal musculature
  o Ventral (anterior) CST controls axial musculature
• The corticospinal tract maintains connections with multiple regions of the cerebrum, primarily the motor cortex. The motor cortex is recognized to have three main components, the primary motor cortex, premotor cortex, and the supplementary motor area – each of these maintain their own unique connections and methods of communication with the corticospinal tract.

See diagram in notes for pathway

Question 11

What is the rubrospinal tract, where does it begin and where does it receive input from? What is its function (what does it inhibit/facilitate)?

Answer 11

• Rubrospinal tract
  o Starts in red nucleus and terminates by synapsing on interneurons in spinal cord
  o Red nucleus receives input from cerebral cortex and cerebellum
  o Tract modulates motor tone so that when flexors contract extensors relax and vice versa
  o Red nucleus receives input from reticular formation and inhibits the activity of extensors and facilitate activity in flexors
  o Facilitates reflex activity (withdrawal reflex) and inhibits contraction of anti-gravity muscles
   Prevents decerebrate posture (all body parts extended and stretched due to unregulated activity in extensors and antigravity muscles

Question 12

What are the descending tracts?

Answer 12

Corticospinal tract
Rubrospinal tract
Vestibulospinal and reticulospinal tracts

Question 13

What are the vestibulospinal tract, where do they start, what is their function and what is the effect of damage to them? What is the reticulospinal tract, where is it located and what is its function?

Answer 13

o Vestibulospinal starts vestibular nuclei to spinal cord
 Head eye coordination
 Maintaining balance and upright posture
 Vestibulospinal reflex
o Damage results in
 Ataxia especially when eyes closed falls to damaged side
o Reticulospinal
 Reticular formation to spinal cord
 Has both excitatory and inhibitory activity
• Assists the CST
 Also controls ANS outflow

Question 14

What knowledge is required for voluntary movement? How is this knowledge held? What are the functions of the UMNs in voluntary movement?

Answer 14

• Voluntary movements require knowledge of where the body is in space, where it intends to go, and the selection of a plan of how to get there
• When plan is selected it must be held in memory until it is required
• Functions of the UMNs
  o Excitation
  o Inhibition
  o Reflex modulation
  o Efference copy (for smooth movements)
  o Activation of other brainstem UMNs
   Reticular formation and red nucleus)

Question 15

Where do around half of axons in the corticospinal tract originate? Where do the other axons originate from?

Answer 15

Approx 1/2 of the axons in the corticospinal tract originate in the primary motor cortex (Brodmann’s area 4).
Most of the other axons originate from area 6: mainly from the supplementary motor cortex and a smaller portion from the (lateral) premotor cortex.
Parietal cortex (area 5) and somatosensory areas (3, 2 and 1) contributes a small number of axons to the corticospinal tract.

Question 16

What is efference? How can efference copy signals reduce cognitive load? What does this mean?

Answer 16

• Motor signal from the CNS to the periphery = efference
  o An internal copy of an efferent movement producing signal
  o Can be then be compared to the sensory input that results
• Efference copy signals reduce cognitive load by:
  o Decreasing sensory processing of reafferent information
• We cannot tickle ourselves as we have generated an efference copy (the efference copies tell us we are touching ourselves). Whereas for other people tickling us we don’t have the efference copies of the movements that touch us

See diagram in notes

Question 17

Which cortical regions are involved in motor control?

Answer 17

• A = prefrontal cortex
• B = frontal eye fields
• C = pre-motor cortex
  o Lateral and supplementary (medial) cortex
• D = primary motor cortex
• Basically the more anterior you go the more complex or abstract the role is in movement

See diagram in notes

Question 18

In the motor cortex, what region gets your ready for movement? Which get you steady for movement? What initiates movement (go)?

Answer 18

• Ready:
  o Posterior parietal cortex (Brodmann 5&7)
   Decision to move and functional consequences of action
• Steady:
  o Association motor cortex (Brodmann 6)
   Pre-motor – external cues
   Supplementary motor – internal cues
   Plans to move are stored until required
• Go:
  o Primary motor cortex (Brodmann 4)
   Instruction to move – activation of descending pathways

See diagram in notes

Question 19

What does the cerebellum do, where does it receive input from and what are the effects of damage to it?

Answer 19

• Co-ordinates complicated multi joint movements
• Acts as comparator or predictor of movement
• Receives direct input from muscles and compares it with the intended signal for movement
• Damage results in un-coordinated movements

See diagrams/MRIs in notes

• Vestibulocerebellum = flocculus and nodulus
• Spinocerebellum = vermis and adjacent intermediate zone
• Cerebrocerebellum = lateral zone

Question 20

What are the functions of each region of the cerebellum and what are the effects of damage to these regions?

Answer 20

• Vestibulo-cerebellum
  o Balance and posture
  o Co-ordinates eye and head movements
  o Damage impairs ability to stand up, maintain posture
  o Cerebellar nystagmus
• Spino-cerebellum
  o Locomotion
  o Voluntary movements of arms and legs
  o Damage = overshoot and intention tremor, impaired gait
• Cerebro-cerebellum
  o Skilled motor tasks
  o Speech, hand-eye co-ordination and cognitive eye movements
  o Damage = ataxia failure of smooth progression

Question 21

What is an intention tremor and what causes this?

Answer 21

• Intention tremor = involuntary tremor during an intentional movement
• Spinocerebellar lateral (intermediate) movement of distal muscle central portion (vermis) movement of proximal muscles

Question 22

What are the features of the basal ganglia and what is its function, what is the brake theory, and what is the effect of basal ganglia damage?

Answer 22

• Five nuclei
  o Caudate, putamen, globus pallidus, substantia nigra and subthalamic nuclei
  o Concerned with initiation and maintenance of motor actions
   Decision making about what we are going to do next
• Unlike cerebellum they do not directly regulate the execution of movements
• In conjunction with the motor association cortex they scale the strength of the response and organise correct sequence of activity
• Brake theory
  o To keep still you must put the brakes on all movements except those reflexes that maintain an upright posture
  o To move you must apply a brake to some postural reflexes and release the brake on voluntary movement
• Damage
  o Tremors
  o Involuntary muscle movements
  o Abnormal increase in muscle tone
  o Difficulty initiating movement
  o Abnormal posture
  o Parkinson disease

See diagrams and flowchart in notes

Question 23

What is muscle tone, what is it dependent on, how is it maintained, how is it regulated and how is tension detected in the tendons?

Answer 23

• Tension in the muscle due to a partial state of contraction in some fibres
• Muscle tone is dependent on the integrity of the monosynaptic reflex
• Tone is maintained reflexively (by stretch & reflexes & gamma motoneurons) and adjusted to the needs of posture and movement
• Tone is also regulated by descending motor pathways
• Golgi tendon organs detects tension in the tendon
  o Spinocerebellar tract and interneuron in SC
  o Inhibition of alpha motor neurons causes muscle relaxation relieving tension in the muscle

Question 24

Where is most of your body weight distributed? Which muscles are important in maintaining posture? How is postured maintained and what input is required to do so? How is it maintained at the lower and higher levels? What phenomenon does this cause?

Answer 24

• Most of bodyweight is anterior to vertebral column
• Deep muscles of back are important in maintaining postural stance
• Antigravity muscles are more developed & have greater tone (& stretch reflexes)
• In a given stance, to maintain posture, muscle tone is constantly finely adjusted (unconsciously) by muscle fibres contracting in relays.
• Requires input from higher levels of the nervous system
• At the lowest level, the spinal level, local reflexes act to maintain tone within muscles while at a higher, bulbar level, nuclei in the medulla and pons act to enhance the tone of muscles that are involved in keeping the you upright, or the antigravity muscles. An person that has had a transection of the brain stem at the level of the pons will therefore be able to “stand upright” due to this phenomenon, but not in any functional way.

Question 25

What are the differences between upper and lower motor neuron lesions?

Answer 25

UMN Lesion

• Paralysis affect movement rather than muscles
• Muscle wasting is only from disuse, therefore slight. Occasionally marked in chronic severe lesions.
• Spasticity of ‘clasp-knife’ type. Muscles hypertonic.

LMN Lesion

• Individual muscle or group of muscles are affected.
• Wasting pronounced.
• Flaccidity. Muscles hypotonic.

Question 26

What is the hierarchical organisation of movement?

Answer 26

See flowchart in notes

Question 27

Summarise this lecture in 4 sentences.

Answer 27

• Association Motor cortex & BG – strategy – planning & selecting programmes to produce desired movements
• Primary motor cortex & CB – tactics – sequences of muscle contractions over time to produce smooth accurate movements
• Brainstem & Spinal cord – execution of voluntary movement and any necessary postural adjustment.
• Lesions produce distinct clinical signs.