4.1 Cortical Motor Function

Question 1

What are the 4 levels of motor system hierachy?

Answer 1

1. Spinal cord (site of lower motor neurones → execution of lower level commands)
2. Brainstem
3. Motor cortex (includes primary motor cortex, premotor cortex, supplementary motor area)
4. Association cortex (selection and accuracy of movements)

Question 2

The motor system hierarchy consists of 4 levels as shown below:
- The lower levels of the hierarchy take care of basic functions ( _______________ to enable adaptive movements):
• Higher levels process information related to the _______________, __________________ and coordination of all body movements
• Higher centres do not have to account for precise details of each contraction (already taken care of by the lower levels) The 2 side loops of the motor system (_________& _________) interact with the main hierarchy through connections via the thalamus.

Answer 2

generation of proper force on individual muscles and muscle groups;

planning of movements; construction of sequences of movements;

basal ganglia and cerebellum

Question 3

Pyramidal: Originates in brain with upper motor neurones via the _________ and ____________
• Synapse with lower motor neurones in the _____________ → lower neurones terminate in skeletal muscles

Answer 3

corticobulbar (face); corticospinal tracts;

anterior horn of the spinal cord

Question 4

Extra-pyramidal: Basal ganglia and cerebellum; do not innervate lower motor neurones, but ________________:
• Involved in monitoring and coordinating movements

Answer 4

sample motor cortex output and modify the motor cortex programme

Question 5

What are the 3 motor cortex areas in the frontal lobe (anterior to central sulcus) and what are they in charge of?

Answer 5

• Brodmann’s area 4 (Primary motor cortex M1): Control of fine, discrete, and precise movements
• Brodmann’s area 6 (Premotor cortex): Planning and assembling of movements into coordinated actions
• Brodmann’s area 6 (Supplementary motor area): Involved in planning complex and internally driven voluntary movements (e.g. speech)

Question 6

What are the lateral descending pathways? what do they do?

Answer 6

• lateral corticospinal
• rubrospinal
• control of proximal and distal muscles
• Voluntary movements of limbs

Question 7

What are the medial descending pathways? what do they do?

Answer 7

• Anterior corticospinal
• Vestibulospinal, reticulospinal, tectospinal
• Control of axial muscles
• Balance and posture

Question 8

Lateral corticospinal tract: Originates in the _____________ (90% of the axons → crossing over to the contralateral side at the ____________________):
• Controls mainly the muscles of the upper and lower limbs, especially the _________________
• Motor command from the left motor cortex travels in the lateral tract, then ends up in the right side of the body (e.g. writing with right hand)

Answer 8

motor cortex;

pyramidal decussation in the medulla;

distal musculature (e.g. fingers)

Question 9

Rubrospinal tract: Originates in the __________________, serving as an alternative pathway for voluntary motor commands to travel to the spinal cord:
• Involved in movement velocity (lesions cause _________________)
• Red nucleus receives some input from the motor cortex → important pathway for recovery of __________________ after corticospinal damage

Answer 9

red nucleus of the midbrain;

temporary slowness;

some voluntary motor function

Question 10

Vestibulospinal tracts: Originate in the brainstem from the __________________ respectively:
• Mediate postural adjustments, ____________

Answer 10

lateral and medial vestibular nuclei;

head and eye movements

Question 11

Reticulospinal tracts: Both pontine and medullary tracts originate in the brainstem reticular formation (large diffused collection of neurones in the _______________):
• Involved in _________________

Answer 11

pons and medulla;

complex actions (e.g. orienting, stretching, maintaining complex postures)

Question 12

Tectospinal tract: Originates in the deep layers of ____________:
• Function not well known (likely reflex turning of head to orient to visual stimuli)

Answer 12

superior colliculus (midbrain)

Question 13

Anterior corticospinal tract: Originates in the_____________ (10% of the axons → do not cross over to contralateral side):
• Controls the ________________

Answer 13

motor cortex;

proximal musculature

Question 14

The premotor cortex (Brodmann’s area 6) is also found in the frontal lobe (anterior to the primary motor cortex ____________):
• Involved in planning and associated with assembly of movements into coordinated actions → movements involving ________________
• Sends axons to the PMC and to the spinal cord directly
• Performs more complex task-related processing than the PMC and selects appropriate motor plans for voluntary movements
• Neurones are involved in preparation of movement, ____________ of a particular movement (intention), and correct and incorrect actions to modify them

Answer 14

laterally;

several joints and/or bilateral (complex, sequential);

various behavioural aspects

Question 15

SUPPLEMENTARY MOTOR AREA
The supplementary motor area (Brodmann’s area 6) is also found in the frontal lobe (anterior to the primary motor cortex medially):
• Involved in ________________
• Programmes complex sequences and coordinates bilateral movements
• Responds to _________________
• Transforms kinematic ( _____________ defining particular movement in space) to dynamic (____________ needed) information

Answer 15

planning and internally driven voluntary movements (e.g. speech);

sequences of movements and mental rehearsals of sequences ;

distance and angles;

amount of force

Question 16

What is the function of the posterior parietal cortex?

Answer 16

Ensures movements are targeted accurately to objects in external space

Question 17

What is the function of the prefrontal cortex?

Answer 17

Involved in selection of appropriate actions for a particular course of action

Question 18

In summary, the cortical motor function is carried by the various cortical areas:

• Primary motor cortex: Execution of ________________
• Premotor cortex: Selection of appropriate motor plans for voluntary movement based on ______________
• Supplementary motor area: Selection of movements based on _______________
• Association cortex: Ensures movements are adaptive to the needs of the organism and appropriate to the behavioural context

Answer 18

voluntary movements ;

visual stimuli or abstract association ;

remembered sequences;

Question 19

A lesion in the descending pathway can occur at any level:
• Upper motor neurones: affected higher up in the _______________ or in the __________________
• Lower motor neurones: affected at the ____________, at the _________________, or at the ___________________

Answer 19

brain (e.g. during stroke);

spinal cord (e.g. during spinal cord injury) ;

root level; peripheral nerve; neuromuscular junction

Question 20

Meaning of paresis (see in upper motor neuron lesion)

Answer 20

graded weakness of movements

Question 21

Meaning of paralysis (see in upper motor neuron lesion)

Answer 21

complete loss of muscle activity)

Question 22

Meaning of spasticity (see in upper motor neuron lesion)

Answer 22

increased motor tone

Question 23

Meaning of hyperreflexia (see in upper motor neuron lesion)

Answer 23

exaggerated reflexes)

Question 24

Meaning of clonus (see in upper motor neuron lesion)

Answer 24

abnormal oscillatory muscle contraction → due to decreased AP threshold (repeated firing)

Question 25

Apraxia: disorder of skilled movement not caused by weakness, abnormal tone or posture, movement disorders (tremors/chorea), intellectual deterioration or poor comprehension

• Patients are not paretic , but ____________
• Due to lesion of the ___________ lobule , frontal lobes (especially ________________)
• Caused by any disease affecting these areas (most commonly stroke and dementia

Answer 25

lost information about how to perform skilled movements;

inferior parietal ;

premotor cortex, supplementary motor area and convexity

Question 26

why is there weakness in lower motor neuron lesion?

Answer 26

Alpha motor neurone damage → atrophy → profound weakness

Question 27

why is there hypotonia in lower motor neuron lesion?

Answer 27

Reduced muscle tone (alpha motor neurones are the only way to stimulate extrafusal muscle fibres)

Question 28

why is there hyporeflexia in lower motor neuron lesion?

Answer 28

Reduced/absent reflexes (alpha motor neurones causing contraction are damaged)

Question 29

why is there muscle atrophy in lower motor neuron lesion?

Answer 29

Muscles are deprived of necessary trophic factors

Question 30

why is there fasciculations in lower motor neuron lesion?

Answer 30

Damaged motor units produce spontaneous APs → visible twitch

Question 31

why is there fibrillations in lower motor neuron lesion?

Answer 31

Spontaneous twitching of individual muscle fibres (recorded by EMG)

Question 32

Motor neurone disease (amyotrophic lateral sclerosis/Lou Gehrig’s disease): unique combination of upper & lower motor neurone signs –> progressive neurodegenerative disorder

• Upper : increased muscle tone (spasticity of _______________), brisk limbs and jaw reflexes, Babinski’s sign, loss of dexterity, ________ (slurred/slow speech), dysphagia
• Lower : weakness, muscle wasting, tongue fasciculations and wasting (CN XII innervates ____________), nasal speech, dysphagia

Answer 32

limbs and tongue;

dysarthria;

genioglossus muscle