Motor Control

Question 1

What are the 2 broad principles of motor control and explain them?

Answer 1

Hierarchical organisation - higher order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity).

Functional segregation - Different areas that control particular aspects of movements.

Question 2

The brainstem passes motor commands from the cortex to where?

Answer 2

Spinal cord

Question 3

The motor cortex receives information from other cortical areas and sends commands to where?

Answer 3

Thalamus and brainstem

Question 4

What structures adjust commands received from other parts of the motor control system?

Answer 4

Cerebellum and basal ganglia

Question 5

Whats the difference between a pyramidal descending and extrapyramidal descending tract?

Answer 5

Pyramidal tracts pass through the pyramids of the medulla whereas extrapyramidal tract don’t.

Question 6

List the major descending pyramidal tracts and the major descending extrapyramidal tracts.

Answer 6

Pyramidal:
Corticospinal + corticobulbar

Extrapyramidal: vestibulospinal, tectospinal, reticulospinal, rubrospinal

Question 7

Where does the primary motor cortex reside?

Answer 7

Precentral gyrus anterior to the central sulcus.

Question 8

What is the function of the primary motor cortex?

Answer 8

Controls fine, discrete, precise voluntary movements.

Provides descending signals to execute movements.

Question 9

Where is the premotor cortex relative to the primary motor cortex?

Answer 9

Anterior to the primary motor cortex.

Question 10

What is the function of the premotor area?

Answer 10

Concerned with movement planning and regulates externally cued movements (e.g. seeing an apple and reaching out for it).

Question 11

Where is the supplementary motor area located relative to the primary motor cortex?

Answer 11

Located anterior and medial to the primary motor cortex.

Question 12

What is the function of the supplementary motor area?

Answer 12

Involved in planning complex movements (internally cued, speech). Becomes active prior to voluntary movement.

Question 13

What percentage of motor descending fibres of the corticospinal tract decussate at the medulla?

Answer 13

80-85% > form the lateral corticospinal tract > innervate the limb muscles

Question 14

What does the anterior corticospinal tract supply motor innervation to?

Answer 14

Innervate the axial musculature (trunk muscles)

Question 15

Explain the function of the corticobulbar tract.

Answer 15

The corticobulbar tract is responsible for providing voluntary movements for the face and neck.
UMNs synapse with brainstem cranial nuclei:
- Oculomotor, trochlear and abducens - Movements of the extra-ocular muscles
- Trigeminal - Muscles of mastication
- Facial - Muscles of the face
- Hypoglossal - Tongue

Question 16

What is the function of the vestibulospinal tract?

Answer 16

Stabilise head during body movements, or as head moves.
Coordinates head movements with eye movements.
Mediates postural adjustments.

Question 17

What is the function of the reticulospinal tract?

Answer 17

Changes in muscle tone associated with voluntary movement.

Postural stability.

Question 18

What is the most primitive descending tract from the medulla and pons?

Answer 18

Reticulospinal

Question 19

Where does the tectospinal tract arise from?

Answer 19

Superior colliculus of midbrain.

Question 20

What is the function of the tectospinal tract?

Answer 20

Orientation of the head and neck during eye movements.

Question 21

What is the origin of the rubrospinal tract?

Answer 21

From red nucleus of the midbrain.

Question 22

What is the function of the rubrospinal tract?

Answer 22

Innervate LMNs of flexors of the upper limb.

(In humans this function is mainly taken over by the corticospinal tract. The rubrospinal tract only comes into play when there are lesions in the CNS).

Question 23

List the negative signs a patient would present with if they had an UMN lesion.

Answer 23

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

Question 24

List the positive signs a patient with an UMN lesion would present with.

Answer 24

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

Question 25

What is apraxia?

Answer 25

A disorder of skilled movement, patients are not paretic however have lost information regarding how to perform skilled movements.

Question 26

Lesions or any disease to which areas of the cerebral cortex may lead to a patient developing apraxia?

Answer 26

Inferior parietal lobe, frontal lobe (premotor cortex, supplementary motor area -SMA)

Question 27

What are the most common causes of apraxia?

Answer 27

Stroke and dementia

Question 28

Where do LMN lesions occur?

Answer 28

Cranial nerve nuclei to corticobulbar tracts or within the spinal cord for innervating limb muscles.

Question 29

List the symptoms a patient with a LMN may present with.

Answer 29

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 electromyography examination.