Lecture 11: Spinal Cord, Brainstem, Cortex Control of Motor Function II

Question 1

Pyramidal tracts

Answer 1

Include corticospinal and corticobulbar tracts; pass through medullary pyramids

Question 2

Upper motor neurons

Answer 2

Originate in motor cortices; 75-85% decussate in pyramids and form lateral corticospinal tract

Question 3

Medial activation system

Answer 3

Upper motor neurons innervate postural and girdle muscles

Question 4

Lateral activation system

Answer 4

Associated with distally located muscles used for fine movements

Question 5

Nonspecific activating system

Answer 5

facilitates local reflex arcs

Question 6

Corticospinal tract

Answer 6

Origin: primary motor cortex/premotor cortex/somatosensory area
Pathway: Origin, internal capsule, medullary pyramids, decussate in lower medulla, lateral column of spinal cord (or continue ipsilaterally in anterior tract)

Question 7

Lateral corticospinal tract

Answer 7

Made up of corticospinal fibers that have crossed in the medulla - supply ALL levels of the spinal cord

Question 8

Anterior corticospinal tract

Answer 8

Made up of uncrossed corticospinal fibers that cross near level of synapse with LMNs - supply neck/upper limbs

Question 9

Giant pyramidal cells

Answer 9

Large cells/fibers, rapid transmission, located in motor cortex; send collaterals back to cortex

Question 10

Functions of corticospinal tract

Answer 10

Adds speed/agility to conscious movement; provides high degree of motor control

Question 11

Results of corticospinal tract lesions

Answer 11

Reduced muscle tone, clumsiness, weakness, incomplete paralysis

Question 12

Corticobulbar tract

Answer 12

Innervates head; most fibers terminate in reticular formation near CN nuclei; association neurons leave reticular formation and synapse with lower motor neurons

Question 13

Red nucleus

Answer 13

Gives rise to rubrospinal tract; magnocellular region contains somatotopic representation of all muscles in the body; stimulation results in stimulation of flexors, inhibition of extensors

Question 14

Rubrospinal tract

Answer 14

Motor cortex, red nucleus, spinal cord

Question 15

Extrapyramidal system

Answer 15

Includes descending motor tracts that do not pass thorugh medullary pyramids or corticobulbar tracts

Question 16

Rubrospinal tract

Answer 16

Originates in red nucleus, decussates in midbrain, descends in lateral funiculus

Question 17

Results of rubrospinal tract lesions

Answer 17

Impairment of distal arm/hand movement; intention tremors

Question 18

Vestibulospinal tract

Answer 18

Originates in vestibular nuclei, descends in anterior funiculus, synapses with LMNs to extensors

Question 19

What constitutes the major input to the vestibulospinal tract?

Answer 19

Vestibular nerve (CN VIII)

Question 20

What is the primary purpose of the vestibulospinal tract?

Answer 20

Maintenance of upright posture

Question 21

Reticulospinal tract

Answer 21

Originates in reticular formation, descends in anterior portion of lateral funiculus

Question 22

What is the proposed purpose of the reticulospinal tract?

Answer 22

Mediates larger movements of trunk and limbs that does not require balance or fine movement of upper limbs

Question 23

Pontine reticular nuclei

Answer 23

Fibers make up reticulospinal tract; stimulatory effect on extensors and flexors

Question 24

Medullary reticular nuclei

Answer 24

Fibers make up medullary reticulospinal tract; inhibitory effect on extensors and flexors

Question 25

Utricle macula

Answer 25

Located on horizontal plane

Involved in determining orientation of head when upright

Question 26

Saccule macula

Answer 26

Located in vertical plane

Signals head orientation when person is lying down

Question 27

Relationship between statoconia and cilia

Answer 27

Weight of statoconia bends cilia in direction of gravitational pull

Question 28

How does depolarization/excitation of hair cells occur?

Answer 28

Bending of stereocilia toward kinocilium causes opening of cation channels

Question 29

How does hyperpolarization of hair cells occur?

Answer 29

Bending of stereocilia in opposite direction of kinocilium causes closure of cation channels

Question 30

What occurs in the semicircular canals when the head is bent forward 30 degrees

Answer 30

Lateral ducts are horizontal, anterior ducts are in vertical planes projecting forward 45 degrees, and posterior ducts are in vertical planes projecting backward 45 degrees