The Upper Motor Neurons

Question 1

The corticospinal tract originates from 3 different regions of the cortex. Name them and their percentages:

Answer 1

• 30% from precentral gyrus (area 4, Primary Motor Cortex)
• 40% from postcentral gyrus (areas 3,1,2, Primary somatosensory cortex)
• remaining 30% from supplemental motor area (area 6, SMA) and the premotor cortex (PMC)

Question 2

Explain the somatotopism of the precentral gyrus (primary motor cortex, area 4)

Answer 2

• dorsal and medial aspects control lower limb
• more lateral aspects control upper limb
• far lateral aspect control face and tongue

Question 3

The corticospinal tracts arise from what cell layer in the cortex? (Name and Roman numeral)

Answer 3

Internal pyramidal cell layer (V)

Question 4

Corticospinal fibers are located in the ____ limb of the internal capsule

Answer 4

Posterior

Question 5

Corticobulbar fibers are located within the _____ limb of the internal capsule

Answer 5

Genu

Question 6

Explain the location of the corticospinal and corticobulbar fibers in the crus cerebri of the midbrain:

Answer 6

Located in middle 3/5 of crus cerebri.
Corticospinal are more lateral (lower limb most lateral, upper limb medial to them) and finally, corticobulbar (head region) are more medial

Question 7

What % of corticospinal tract fibers NEVER cross the midline

Answer 7

2% (considered lateral corticospinal tract fibers)

Question 8

Fibers from the cerebellum that project to the primary motor cortex (area 4) do so via a relay in the ____ nucleus of the thalamus

Answer 8

Ventrolateral (VL)

Question 9

The fibers of the primary motor cortex project to the ____ horn at all levels of the spinal cord, but most predominantly the cervical and lumbar levels

Answer 9

Ventral

Question 10

The key inputs to the primary somatosensory cortex are from the ____ nucleus of the thalamus

Answer 10

Ventral posterolateral (VPL)

Question 11

Descending pyramidal tract fibers originating in the somatosensory cortex project to cells of the ____ horn of the spinal cord

Answer 11

Dorsal

Question 12

The actions of area 6 neurons can only occur if they receive integrated somatosensory and visual signals from the ____

Answer 12

Posterior Parietal Cortex (PPC, areas 5 and 7)

Question 13

Area 6 consists of what two secondary motor regions (of the cortex)?

Answer 13

Supplemental Motor Area (SMA)
Premotor Cortex (PMC)

Question 14

A small localized area of dead tissue resulting from failure of blood supply

Answer 14

Infarct

Question 15

The corticobulbar tracts arise from the lateral most aspect of the _____

Answer 15

Primary motor cortex (M1)

Question 16

The corticobulbar fibers innervate cranial nerve nuclei mostly bilaterally. The exceptions are CN’s ___ and ___, which are only innervated contralaterally

Answer 16

VII (Facial - lower face)

XII (Hypoglossal - genioglossus muscle)

Question 17

Approximately what % of the pyramidal fibers cross the midline to become the LCST?

Answer 17

85-90%

Question 18

The precentral gyrus (primary motor cortex) is in the ____ lobe, while the post central gyrus (primary somatosensory cortex) is in the ____ lobe

Answer 18

Frontal, parietal

Question 19

The basal nuclei input to the various motor areas of the cortex travels through the _____ nucleus in the thalamus, mainly

Answer 19

Ventral Anterior (VA)

Question 20

Lesions of the supplemental motor area (SMA) result in _____, the inability to initiate specific, purposeful movements

Answer 20

Apraxia

Question 21

The inability to execute a movement upon request is called _____ apraxia. An example would be the inability to brush one’s hair or tie one’s shoe laces.

Answer 21

Ideomotor

Question 22

____ apraxia is the inability to conceptualize the movements, and the patient is unable to identify the sequences of movements that are necessary for carrying out the response in question. Example: the patient would have a hard time when asked to do different things with both arms simultaneously.

Answer 22

Ideational

Question 23

The posterior parietal cortex (PPC, areas 5 and 7) is mainly concerned with relaying _____ and _____ signals to area 6

Answer 23

Vestibular, visual

Question 24

Lesions of the RIGHT PPC will result in ____-sided apraxia or “sensory neglect”

Answer 24

Left

Question 25

These motor fibers project to the DWC and dorsal horn of the spinal cord, and function in “sensory filtering”: only the pieces of information that are necessary to the present movement are allowed, others are filtered out

Answer 25

Somatosensory cortex fibers (areas 3, 1, 2)

Question 26

Fibers from the ____ tract supply mainly the neurons that innervate distal flexor musculature

Answer 26

Rubrospinal

Question 27

The reticulospinal tract arising from the Pons is the ____ reticulospinal tract, while the one arising from the Medulla is the _____ reticulospinal tract

Answer 27

Medial, lateral

Question 28

The primary motor function of the ____ tract is to facilitate voluntary or cortical induced movements and to increase muscle tone

Answer 28

Medial reticulospinal

Question 29

The actions of this pathway inhibit voluntary movements and cortically induced movements, and reduce muscle tone

Answer 29

Lateral reticulospinal tract

Question 30

This tract arises from the medial vestibular nucleus and projects as the descending component of the medial longitudinal fasciculus (MLF) to reach cervical levels of the cord bilaterally

Answer 30

Medial vestibulospinal tract

Question 31

The vestibular nuclei (medial and lateral) are first found in the ____

Answer 31

Pons (middle)

Question 32

This tract arises from the lateral vestibular nucleus and projects to all levels of the spinal cord. It’s major function is to stimulate the neurons that innervate extensor muscles, mainly of the lower limb.

Answer 32

Lateral vestibulospinal tract

Question 33

The medial vestibulospinal tract fibers activate LMNs associated with CN __. This activation can cause rotation and lifting of the head as well as scapular rotation. This helps orient the individual in response to forces that can cause changes in posture and balance.

Answer 33

XI, Spinal Accessory

Question 34

The ____ tract arises from the red nucleus (motor tract)

Answer 34

Rubrospinal tract

Question 35

Do rubrospinal tract fibers cross?

Answer 35

Yes - via ventral tegmental decussation

Question 36

The ____ tract arises from the superior colliculus in the superior midbrain and soon crosses over via the dorsal tegmental decussation

Answer 36

Tectospinal tract

Question 37

Where does the tectospinal tract terminate?

Answer 37

Cervical levels of the cord

Question 38

Little is known about this tract, but it is believed to produce postural changes in response to visual stimuli

Answer 38

Tectospinal tract

Question 39

Motor fibers from this part of the cortex are involved in the planning of response. They provide muscle contraction of individual muscles

Answer 39

Primary motor cortex (area 4)