Lecture 6: Motor and Premotor Cortex

Question 1

what are the 3 sections of the motor cortex

Answer 1

Primary motor cortex (M1)

Premotor cortex

Supplementary motor
area

Question 2

which area of the motor cortex has somatotopic organization

Answer 2

the primary motor cortex (M1)

Question 3

which areas are enlarged in the primary motor cortex’s somatotopic organization?

Answer 3

motor maps for movements are requiring fine motor control are enlarged (fingerers, face, etc)

Question 4

what kind of movement is the primary motor cortex involved with

Answer 4

voluntary movements of contralateral body parts

Question 5

what about movement does the primary cortex encode

Answer 5

force, direction, distance, and speed of movement

Question 6

what is alien hand syndrome

Answer 6

only contralateral primary motor cortex is activated

involuntary uncontrollable movement of the upper extremity

Question 7

where is the premotor cortex

Answer 7

anterior to the M1 (primary motor cortex) in frontal lobe

Question 8

what is the function of the premotor cortex?

Answer 8

Motor planning - select the appropriate movement to perform

• Mirror neurons for action observation (watching something we want to learn)

Question 9

how does the premotor cortex influence motor behaviour

Answer 9

primarily via connections with M1

less commonly via axons projecting though the pyramidal tracts

Question 10

what do premotor cortex lesions cause

Answer 10

Impaired:
Speed and automaticity of
reaching/grasping

Sequential movements

Gait and posture

Question 11

what is the function of the Supplementary Motor Area (SMA)

Answer 11

Programming complex sequences and coordinating bilateral movements

• Selects movements based on previous experience
• Active during motor imagery practice (imagining doing an action)

Question 12

what does an unilateral lesion of the supplementary motor area cause

Answer 12

complete lack of contralateral movement and impaired ipsilateral movement

Antiphase movements can be affected (arms or legs doing different motions like typing or walking)

Question 13

what are the 3 inputs to the motor cortex to create movement?

Answer 13

intention - prefrontal cortex

planning - premotor cortex +SMA

programming and execution - primary motor cortex

Question 14

LMNs receive instructions from which 3 sources?

Answer 14

• Upper Motor Neurons
  – Descending pathways
• Local Circuit Neurons/Interneurons
• Sensory inputs

Question 15

how are LMNs organized in the anterior horn

Answer 15

▪ Medial = proximal muscles

▪ Lateral = distal muscles

Question 16

what are interneurons / local circuit neurons?

Answer 16

the “middle man” that branches locally to innervate other neurons

primarily inhibitory towards unwanted movement

Question 17

do interneurons / local circuit neurons project contra laterally or ipsilaterally?

Answer 17

both

Question 18

what are the two types of interneurons / local circuit neurons?

Answer 18

long distance

short distance

both link to anterior horn in spinal cord

Question 19

what are long distance interneurons?

Answer 19

activate medial aspect of anterior horn

span multiple levels of spinal cord and can cross sides

bilateral control of Proximal muscles for balance and postural control

Question 20

what are short distance interneurons?

Answer 20

Activate lateral aspect of anterior horn

Span few spinal levels and ipsilateral

Distal muscles for fine motor control

Question 21

what are the 2 kind of tracts of the descending motor pathways

Answer 21

Pyramidal tracts

Extrapyramidal tracts

Question 22

what are the pyramidal tracts responsible for

Answer 22

skilled, voluntary movements of the limbs

Question 23

where do extrapyramidal tracts originate

Answer 23

in the brainstem

Question 24

what are the extrapyramidal tracts responsible for

Answer 24

posture balance, gait

Question 25

what are the 3 pyramidal pathways

Answer 25

lateral corticospinal pathway anterior corticospinal pathway corticobubar pathway

Question 26

what are the 4 extrapyramidal pathways

Answer 26

* Vestibulospinal Tract * Reticulospinal Tract * Tectospinal Tract * RubrospinalTract

Question 27

where are the extrapyramidal pathways located?

Answer 27

most are in the medial part of spinal cord

Question 28

where does the lateral cortocospinal tract originate?

Answer 28

motor cortex, mostly M1

Question 29

where does 85% of the corticospinal tract cross

Answer 29

the pyramidal decussation

Question 30

what is the destination of the lateral corticospinal tract

Answer 30

lateral LMN of spinal cord or short distance interneurons

Question 31

what would a lesion on the lateral corticospinal tract cause

Answer 31

Impairments on contralateral side

Question 32

does the anterior corticospinal tract cross to the other side?

Answer 32

not at the medulla, but most of it crosses in the spinal cord

Question 33

what is the destination of the anterior corticospinal tract

Answer 33

Terminates bilaterally in spinal cord * via long distance interneuron networks

Question 34

what is the function of the anterior corticospinal tract

Answer 34

Gross control of proximal postural muscles

Question 35

what happens if there is a lesion on the anterior corticospinal tract

Answer 35

there is minimal clinical effect

Question 36

do most corticospinal fibers synapse directly with LMNs

Answer 36

some do that are involved with finer muscle control most synapse with spinal interneurons that in turn synapse with LMNs

Question 37

where does the corticobulbar tract originate?

Answer 37

motor cortex

Question 38

what is the function of the corticobulbar tract?

Answer 38

Controls efferent activation of cranial nerves

Question 38

what is the destination of the corticobulbar tract

Answer 38

Most terminate bilaterally on local circuit neurons in brainstem LMN nuclei of cranial nerves

Question 39

What region of the face is the primary motor cortex responsible for?

Answer 39

lower face (contralateral)

Question 40

what would an UMN injury (in the corticobublar tract) cause

Answer 40

Weakness in contralateral inferior facial muscles very concerning

Question 41

what would a LMN injury in the facial nerve cause

Answer 41

Weakness in ipsilateral superior and inferior facial muscles injury is outside of brain so less concerning

Question 42

If there is a lesion to the right facial nerve, where would you expect there to be weakness?

Answer 42

inferior and superior right side of face

Question 43

what happens with a transverse cord lesion

Answer 43

both sides of the level of spinal cord Bilateral loss of pain/temperature, vibration/position sense, and voluntary motor function at and below lesion

Question 43

What part of the brain would you expect to have a lesion if you have difficulty tapping your head and rubbing your belly at the same time?

Answer 43

Supplementary motor area

Question 44

what happens with a hemicord lesion (Brown-Sequard Syndrome)

Answer 44

damage to one half of spinal cord Ipsilateral loss of vibration/position sense and voluntary motor function Ipsilateral loss of pain and temperature over 1-2 segments near lesion Contralateral loss of pain and temperature

Question 45

what is the destination of the extrapyramidal pathways

Answer 45

Innervates bilateral local long interneuron circuits

Question 46

what is the function of the rubrospinal tract

Answer 46

Modulation of flexor muscle tone

Question 47

what is the function of the Vestibulospinal tract

Answer 47

posture and balance

Question 48

what is the function of the Reticulospinal tract

Answer 48

gait, posture, excites/inhibits muscle tone

Question 49

what is the function of the Tectospinal tract

Answer 49

Eye/head motion

Question 50

what are the 4 clinical presentations of extrapyramidal disorders?

Answer 50

Slowing or loss of voluntary and automatic movements Postural instability Abnormal movements Usually bilateral deficits

Question 51

which system controls volitional control

Answer 51

pyramidal tracts

Question 52

which system controls automatic control

Answer 52

extrapyramidal tracts

Question 53

do the pyramidal systems have more long or short local circuit neurons

Answer 53

Mostly short distance local circuit neurons (except anterior corticospinal tract)

Question 54

do the extrapyramidal systems have more long or short local circuit neurones

Answer 54

Long distance local circuit neurons

Question 55

What is the function of the Lateral Corticospinal Tract

Answer 55

Main voluntary motor pathway * Skilled, voluntary movements of the limbs

Question 56

Consider the lateral corticospinal tract originating from the left motor cortex. If this tract was injured below the pyramidal decussation, where would you expect to see motor deficits?

Answer 56

In the extremities on the right side of the body

Question 57

Which part of the brain is active while you watch Serena Williams hit a tennis serve?

Answer 57

Premotor cortex

Question 58

If there is damage to the primary motor cortex, which deficits might you observe? Difficulty swallowing Weakness in the contralateral hand Weakness in the lower face All of the listed answers are correct

Answer 58

All of the listed answers are correct

Question 59

Link the following descending pathway to the appropriate interneuron network Anterior Corticospinal Tract and short distance interneuron network Vestibulospinal Tract and long distance interneuron network Lateral Corticospinal Tract and long distance interneuron network Reticulospinal Tract and short distance interneuron network

Answer 59

Vestibulospinal Tract and long distance interneuron network

Question 60

Which part of the brain is active when you are imagining yourself performing a motor task?

Answer 60

Supplementary Motor Area

Question 61

what is the Cingulate Motor Area responsible for

Answer 61

the upper face, bilaterally

Question 62

_______ motor neuron injuries typically cause more wasting than ________ motor neuron injuries

Answer 62

Lower, Upper

Question 63

If there was damage to short distance local circuit neurons in the spinal cord, what would you expect to see?

Answer 63

Problems with fine motor control