Motor Control

Question 1

Outline the broad principles of motor control

Answer 1

Hierarchical organisation
- higher order areas - involved in more complex tasks, e.g. planning movement
- lower order areas - involved in lower level tasks, e.g. execution of movement

Functional segregation
- Different areas control different aspects of movement

Question 2

What are the pyramidal tracts?

Answer 2

Corticospinal
Corticobulbar
- Pass through pyramids of the medulla

Question 3

What are the extrapyramidal tracts?

Answer 3

Vestibulospinal
Tectospinal
Reticulospinal
Rubrospinal
- Do not pass through pyramids of the medulla

Question 4

Outline the route of the pyramidal tracts and their function

Answer 4

Motor cortex to spinal cord or cranial nerve nuclei in brainstem
Voluntary movements of body and face

Question 5

Outline the route of the extrapyramidal tracts and their function

Answer 5

Brainstem nuclei to spinal cord
Involuntary (automatic) movements for balance, posture and locomotion

Question 6

Where is the primary motor cortex and what is its function?

Answer 6

Precentral gyrus
Controls fine, discrete, precise voluntary movements
Provides descending signals to execute movements

Question 7

Where is the premotor area and what is its function?

Answer 7

Anterior to primary motor cortex
Involved in planning movements
Regulates externally cued movements, e.g. seeing an apple and reaching for it

Question 8

Where is the supplementary motor area and what is its function?

Answer 8

Located anterior and medial to primary motor cortex
Involved in planning complex movements (e.g. internally cued, speech)
Becomes active prior to voluntary movement

Question 9

Describe the route of the corticospinal tract

Answer 9

Question 10

Outline the somatotopic representation of the motor and sensory cortices

Answer 10

Question 11

What is the function of the corticobulbar tract?

Answer 11

Principal motor pathway for voluntary movements of the face (and neck)

Question 12

What is the function of the vestibulospinal tract?

Answer 12

Stabilise head during body movements, or as head moves
Coordinate head movements with eye movements
Mediate postural adjustments

Question 13

What is the function of the reticulospinal tract?

Answer 13

Most primitive descending tract - from medulla and pons
Changes in muscles tone associated with voluntary movement
Postural stability

Question 14

What is the function of the tectospinal tract?

Answer 14

From superior colliculus of midbrain
Orientation of the head and neck during eye movements

Question 15

What is the function of the rubrospinal tract?

Answer 15

From red nucleus of midbrain
In humans mainly taken over by corticospinal tract
Innervate lower motor neurons of flexors of the upper limb

Question 16

What are the negative sign(s) of upper motor neuron lesion?

Answer 16

Loss of voluntary motor function

Question 17

What is the different between ‘paresis’ and ‘plegia’?

Answer 17

Paresis: graded weakness of movements
Paralysis (plegia): complete loss of voluntary muscle activity

Question 18

What are the positive signs of upper motor neuron lesion?

Answer 18

Increased abnormal motor function due to loss of inhibitory descending inputs
Spasticity: increased muscle tone
Hyper-reflexia: exaggerated reflexes
Clonus (twitching/jerking): abnormal oscillatory muscle contraction
Babinski’s sign

Question 19

What is apraxia?

Answer 19

A disorder of skilled movement. Patients are not paretic (don’t have paresis) but have lost information about how to perform skilled movements

Question 20

What can cause apraxia?

Answer 20

Lesion of inferior parietal lobe
Lesion of the frontal lobe (premotor cortex, supplementary motor area - SMA)
Most common - stroke and dementia

Question 21

What are the characteristics of a lower motor neuron lesion?

Answer 21

Weakness
Hypotonia (reduced muscle tone)
Hyporeflexia (reduced reflexes)
Muscle atrophy
Fasciculations: damaged motor units produce spontaneous action potentials, resulting in a visible twitch
Fibrillations: spontaneous twitching of individual muscle fibres; recorded during needle electromyography examination

Question 22

What is motor neuron disease?

Answer 22

Progressive neurodegenerative disorder of the motor system
Spectrum of disorders - upper and lower motor neuron symptoms
Also known as Amyotrophic Lateral Sclerosis (ALS)

Question 23

What are the upper motor neuron signs of motor neuron disease?

Answer 23

Spasticity (increased tone of limbs and tongue)
Brisk limbs and jaw reflexes
Babinski’s sign
Loss of dexterity
Dysarthria (difficulty speaking)
Dysphagia (difficulty swallowing)

Question 24

What are the lower motor neuron signs of motor neuron disease?

Answer 24

Weakness
Muscle wasting
Tongue fasciculations and wasting
Nasal speech
Dysphagia

Question 25

What structures make up the basal ganglia?

Answer 25

Caudate nucleus
Lentiform nucleus (putamen + external globus pallidus) – together caudate and putamen are known as the striatum
Nucleus accumbens
Subthalamic nuclei
Substantia nigra (midbrain)
Ventral pallidum, claustrum, nucleus basalis (of Meynert)

Question 26

What are the functions of the basal ganglia?

Answer 26

• Decision to move
• Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions
• Moderating and coordinating movement (suppressing unwanted movements)
• Performing movements in order

Helps us perform fluid movements

Question 27

What is Parkinson’s Disease?

Answer 27

A condition caused by the degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum

Question 28

What are the symptoms of Parkinson’s Disease?

Answer 28

Bradykinesia - slowness of (small) movements (doing up buttons, handling a knife)
Hypomimic face - expressionless, mask-like (absence of movements that normally animate the face)
Akinesia - difficulty in the initiation of movements because cannot initiate movements internally
Rigidity - muscle tone increase, causing resistance to externally imposed joint movements
Tremor at rest - 4-7 Hz, starts in one hand (“pill-rolling tremor”); with time spreads to other parts of the body

Question 29

What is Huntington’s Disease?

Answer 29

Condition caused by degeneration of GABAergic neurons in the striatum, caudate and then putamen

Question 30

What are the symptoms of Huntington’s Disease?

Answer 30

Choreic movements (chorea - dance) - rapid jerky involuntary movements of the body; hands and face affected first; then legs and rest of body
Speech impairment
Difficulty swallowing
Unsteady gait
Later stages, cognitive decline and dementia

Question 31

What causes Huntington’s Disease?

Answer 31

Genetic neurodegenerative disorder
Chromosome 4
Autosomal dominant
CAG repeat

Question 32

What is ballism and what is it usually caused by?

Answer 32

Sudden uncontrolled flinging of the extremities
Usually from stroke affecting the subthalamic nucleus
Symptoms occur contralaterally

Question 33

Where is the cerebellum and what is its function?

Answer 33

Located in posterior cranial fossa
Separated from cerebrum above by tentorium cerebelli
Coordinator and predictor of movement - compares what is happening with what should be happening and makes fine adjustments

Question 34

What is the function of the vestibulocerebellum?

Answer 34

Regulation of gait, posture and equilibrium
Coordination of head movements with eye movements

Question 35

What happens when the vestibulocerebellum is damaged?

Answer 35

Damage usually due to a tumour
Causes a syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient is sitting and eyes open)

Question 36

What is the function of the spinocerebellum?

Answer 36

Coordination of speech
Adjustment of muscle tone
Coordination of limb movements

Question 37

What happens when the spinocerebellum is damaged?

Answer 37

Damage usually due to degeneration and atrophy associated with chronic alcoholism
Affects mainly legs - causes abnormal gait and stance (wide-based)

Question 38

What is the function of the cerebrocerebellum?

Answer 38

Coordination of skilled movements
Cognitive function, attention, processing of language
Emotional control

Question 39

What are the main signs of cerebellar dysfunction?

Answer 39

Ataxia: General impairments in movement coordination and accuracy. Disturbances of posture or gait: wide-based, staggering (“drunken”) gait
Dysmetria: Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)
Intention tremor: Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)
Dysdiadochokinesia: Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)
Scanning speech: Staccato, due to impaired coordination of speech muscles