Motor Cortical Control

Question 1

What is hierarchical organisation?

Answer 1

High order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity)
Low order areas of hierarchy are involved in lower level tasks (execution of movement)

Question 2

What is functional segragation?

Answer 2

Motor system organised in a number of different areas that control different aspects of movement

Question 3

Describe the motor system hierarchy

Answer 3

The primary motor cortex and non-primary motor cortex receives info from other cortical areas and sends commands to thalamus and brainstem. These commands can be direct or are adjusted by the basal ganglia or cerebellum which is then passes to thalamus and back to primary motor cortex. Finally, impulses sent to brainstem and spinal cord.

Question 4

What are the 2 major pyramidal descending tracts?

Answer 4

Corticospinal and corticobulbar. They pass through the pyramids of the medulla with upper motor neurons projecting from motor cortex to spinal cord or cranial nerve nuclei in brainstem. They control the voluntary movements of body and face.

Question 5

What are the 4 major extrapyramidal descending tracts?

Answer 5

Vestibulospinal, Tectospinal, Reticulospinal and Rubrospinal. These do not pass through thepyramidsof the medulla. Tracts project from brainstem nuclei to spinal cord. Control involuntary (automatic) movements for balance, posture and locomotion.

Question 6

Where is the primary motor cortex and what are its roles?

Answer 6

Located in the pre-central gyrus, anterior to central sulcus. Controls fine, discrete, precise voluntary movements. Provides descending signals to execute movements.

Question 7

Where is the premotor area located and what are its functions?

Answer 7

Is located anterior to primary motor cortex. Is involved in planning movements and regulates externally cued movements.

Question 8

What is the supplementary motor area and what are its functions?

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 path of the corticospinal tract

Answer 9

Upper motor neurons project down as a major part of the internal capsule, passing through the cerebral peduncles as white matter tracts to the medulla. Decussation occurs in the pyramids of the lower medulla. 85-90% of fibres decussate and form the lateral corticospinal tract supplying the muscles of the limbs. 10-15% do not decussate and form the anterior corticospinal tract supplying the muscles of the trunk.

Question 10

What is the corticobulbar tract?

Answer 10

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

Question 11

Describe pathway of corticobulbar tract

Answer 11

Upper motor neurons of the cranial nerves originate from the precentral gyrus and descend as corticobulbar tract to the midbrain. Neurons branch off to synapse with Oculomotor nucles, Trochlear nucleus and Abducens nucleus. The tract then carries on through cerebral peduncles in midbrain to pons where neurons synapse with motor trigeminal nucleus, and facial nucleus. In medulla oblongata, neurons synapse with glossopharyngeal nucleus, vagal nucleus, accessory nucleus and hypoglossal nucleus. All these nuclei contain neurons that innervate structures in the head, face, tongue, or neck (pharynx and larynx). Neurons to lower half of face have contralateral control while neurons to upper half have bilateral control.

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 rubrospinal 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 reticulospinal 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 negative signs of an upper motor neuron lesion?

Answer 16

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

Question 17

What are positive signs of an upper motor neuron lesions?

Answer 17

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

Question 18

Define apraxia

Answer 18

A disorder of skilled movement. Patients are not paretic but have lost information about how to perform skilled movements.

Question 19

What causes apraxia?

Answer 19

Lesion of inferior parietal lobe, the frontal lobe (premotor cortex, supplementary motor area - SMA). Any disease of these areas can cause apraxia, although stroke and dementia are the most common causes.

Question 20

What are the symptoms of a lower motor neurone lesion?

Answer 20

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

Question 21

What is motor neuron disease?

Answer 21

Progressive neurodegenerative disorder of the motor system and includes a spectrum of disorders. Can affect upper motor neurons, lower motor neurons projecting from brainstem, voluntary contraction of the tongue, upper lim/lower limb muscles and eventual death due to loss of respiratory control as intercostal muscles are no longer controlled.

Question 22

What are UMN signs of motor neuron disease?

Answer 22

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 23

What are LMN signs of motor neuron disease?

Answer 23

Weakness
Muscle wasting
Tongue fasciculations and wasting
Nasal speech
Dysphagia

Question 24

Describe the structure of the basal ganglia

Answer 24

Contains caudate nucleus, putamen and external globus pallidus. Caudate + Putamen known as Striatum while Putamen + EGP are known as lentiform nucleus. Also contains nucleus accumbens, subthalamic nucleus, substantia nigra (midbrain), Ventral pallidum, claustrum, nucleus basalis (of Meynert).

Question 25

What are the 4 functions of the basal ganglia?

Answer 25

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

Question 26

What parts of the basal ganglia circuitry do certain diseases affect?

Answer 26

Parkinson’s disease affects communication between rostral substantia nigra and striatum. Ballism affects communication between subthalamic nucleus and external globus pallidus. Huntington’s disease interferes with the sending of messages from the striatum to the internal globus pallidus.

Question 27

What is Parkinson’s disease?

Answer 27

Degeneration of the dopaminergic neurons that originate in the substantia nigra and project to the striatum.

Question 28

Describe the symptoms of Parkinson’s

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 causes Huntington’s disease?

Answer 29

Degeneration of GABAergic neurons in the striatum, caudate and then putamen. Is a genetic neurodegenerative disorder caused by CAG repeat in Chromosome 4, autosomal dominant.

Question 30

What are the symptoms of Huntington’s

Answer 30

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

Question 31

What is ballism?

Answer 31

Caused usually by a stroke affecting the subthalamic nucleus. Sudden uncontrolled flinging of the extremities. Symptoms occur contralaterally.

Question 32

Describe the location and function of the cerebellum

Answer 32

Located in posterior cranial fossa. Separated from cerebrum above by tentorium cerebelli. Coordinator and predictor of movement.

Question 33

What is the role of the vestibulocerebellum?

Answer 33

1. Regulation of gait, posture and equilibrium

2. Coordination of head movements with eye movements

Question 34

What happens when there is a tumour in the vestibulocerebellum?

Answer 34

Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia and tendency to fall (even when patient sitting and eyes open)

Question 35

What is the role of the spinocerebellum?

Answer 35

1. Coordination of speech
2. Adjustment of muscle tone
3. Coordination of limb movements

Question 36

What happens when there is damage to the spinocerebellum?

Answer 36

Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)

Question 37

What is the role of the cerebrocerebellum?

Answer 37

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

Question 38

What happens when there is damage to the cerebrocerebellum?

Answer 38

Damage affects mainly arms/skilled coordinated movements (tremor) and speech

Question 39

What are the 5 main signs of cerebellar dysfunction?

Answer 39

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