Descending Motor Tracts: Pyramidal System

Question 1

What are the two tracts in the Pyramidal System?

Answer 1

Lateral Corticospinal Tract
Ventral Corticospinal Tract

Question 2

What type of information (Sensory, Motor, Mixed) does the Lateral Corticospinal Tract have?

Answer 2

Motor

Question 3

What motor information does the Lateral Corticospinal Tract provide?

Answer 3

Flexor and Extensor activity especially of the distal limbs, also urinary bladder function

Question 4

What type of information (Sensory, Motor, Mixed) does the Ventral Corticospinal Tract have?

Answer 4

Motor

Question 5

What motor information does the Ventral Corticospinal Tract provide?

Answer 5

Facilitation of voluntary movement in the neck and trunk

Question 6

What type of motor function is the Lateral and Ventral Corticospinal Tract transmitting?

Answer 6

Somatic

Question 7

Describe the somatic motor function involving the movements of the Lateral Corticospinal Tract?

Answer 7

Skilled, learned, voluntary, fine, distal, complex, and coordinated

Question 8

Describe the somatic motor function involving the movements of the Ventral Corticospinal Tract?

Answer 8

Unskilled, non-learned, involuntary, crude, proximal, simple, and coordinated

(Extensor or “anti-gravity” form of CST)

Question 9

What are the components of the CST?

Answer 9

• Corticospinal Cells
• Spinal Interneurons
• Spinal Motor Neurons
• Skeletal Muscle Cells

Question 10

What is another name for the corticospinal cells?

Answer 10

Upper motor neurons

Question 11

What is another name for the spinal motor neurons?

Answer 11

Lower motor neurons

Question 12

Describe “Crossed” CST Fibers

Answer 12

• Cross midline
• Contralateral to their motor cortex origin
• > 90% are crossed
• Predominantly the lateral CST
• Gives rise to the classic voluntary motor control
• Often involves skilled somatic motor control of the extremities

Question 13

Describe “Uncrossed” CST Fibers

Answer 13

• < 10% are uncrossed
• Ipsilateral to their motor cortex origin
• Predominantly ventral CST
• Gives rise to involuntary motor control
• Involves unskilled somatic motor control of the trunk

Question 14

How do homotropic regions connect to each other?

Answer 14

Corpus callosum

Question 15

What do we mean when we refer to homotropic?

Answer 15

Structures that are a match (or mirror) each other on both sides of the body and have similar functions

Question 16

What allows for coordinated movements on both sides of the body?

Answer 16

Interhemispheric connections

Question 17

What does UMNs release to activate LMNs?

Answer 17

Glutamate

Question 18

What does LMNs release to activate skeletal muscle?

Answer 18

Acetylcholine

Question 19

True or False: Somatic motor requires coordinated skeletal muscle contraction and relaxation of antagonistic muscle pairs

Answer 19

True

Question 20

True or False: There is little to no diversity in spinal motor neurons

Answer 20

False, there is remarkable diversity

Question 21

What are some areas of diversity we can see in spinal motor neurons?

Answer 21

• Location
• Input
• Output
• Neurochemical released
• Molecular signature

Question 22

What neurochemicals are considered excitatory?

Answer 22

Cholinergic and Glutamatergic

Question 23

What neurochemicals are considered inhibitory?

Answer 23

Glycinergic and GABAergic

Question 24

What do alpha LMNs innervate?

Answer 24

Skeletal muscle fibers to signal bulk muscle fiber contraction

Question 25

What do gamma LMNs innervate?

Answer 25

Skeletal muscle spindles to signal muscle fiber contraction on the spindle themselves (adjust length)

Question 26

What is the "RAT" breakdown when having UMN disease

Answer 26

Reflexes: Normal to increased Atrophy: Disuse, mild, generalized Tone: Normal to increased

Question 27

What is the "RAT" breakdown when having LMN disease

Answer 27

Reflexes: Decreased to absent Atrophy: Neurogenic, severe, specific muscles Tone: Decreased to absent

Question 28

How is the motor cortex organized?

Answer 28

Somatotopically

Question 29

What is the effect of a stroke or acquired brain injury when the brain is the site of the injury?

Answer 29

- Deficits on contralateral side of body - Only a small number of related movements are dysfunctional because it typically only affects one location of the motor cortex

Question 30

What is the effect of a stroke or acquired brain injury when UMN axon bundles are the site of injury?

Answer 30

- Greater number of movement dysfunction - Deficits will present on contralateral side of body - If lesion is after pyramidal decussation, deficits present on ipsilateral side of body

Question 31

What is the effect of an injury to the LMNs and LMN axon bundles?

Answer 31

- Deficits will present on ipsilateral side of body - Injury to LMN: Widespread deficits in spinal reflexes and descending motor pathways - Injury to LMN axon bundles: Deficits more focal and located more distal