5.1.2 Central Motor Systems I

Question 1

Describe the Spindle load compensation mechanism.

Answer 1

Question 2

What is the importance of Laminas VIII and IX? How are they arranged from medial to lateral?

Answer 2

• motor neuron groups in medial and lateral portions of the ventral gray
• Medial: LMNs for axial and proximal musculature
• Lateral: LMNs for distal muscles of arm/leg

Question 3

What are the results of a transection of the spinal cord?

Answer 3

Paraplegia: loss of voluntary movement below level of lesions

• Results from interruption of descending pathways from motor centers in brain stem and higher centers

Loss of conscious sensation from below level of lesions

Initial loss of reflexes due to spinal shock

• Loss of excitation to alpha and gamma motor neurons
• Limbs flaccid, reflexes absent
• Partial recovery over time

Question 4

What are the characteristics of the Tectospinal tract?

Answer 4

• Originates from superior colliculus in the midbrain
• Travels in the ventral column, primarily crossed and terminates on interneurons and motoneurons in cervical spinal cord
• Plays role in reflexive control of neck muscles in response to visual stimuli
• More developed in other animals

Question 5

Transection above the level of the red nucleus will result in?

Answer 5

-Decorticate posturing and intact tonic neck reflexes

Question 6

What are the 4 tracts in the ventral column of the white matter of the spinal cord? What do they control?

Answer 6

Vestibulospinal tract, Ventral reticulospinal tract, ventral corticospinal tract, and tectospinal tract

-Adjustment of proximal muscles and posture

Question 7

What is the origin of the Reticulospinal tract?

Answer 7

Originates from reticular formation of medulla and pons

Question 8

What are the characteristics of the Rubrospinal tract?

Answer 8

• Originates in red nucleus
• -Receives input from the contralateral deep cerebellar nuclei and motor cortex bilaterally
• Travels in lateral column to terminate on interneurons in spinal cord

-Largely crossed

-Controls distal limb muscles

• -Stimulates flexors
• -Inhibits extensors

Question 9

Lesion in the Rubrospinal tract will lead to?

Answer 9

Little or no deficit

Question 10

Compare Decerebrate and Decorticate postures.

Answer 10

Question 11

Lesions in the Reticulospinal tract will lead to?

Answer 11

Severe impairment of axial/proximal muscles, loss of righting reflexes

Question 12

What is the motor component of the corticospinal system?

Answer 12

Motor: motor cortex (precentral gyrus) ⇒ ventral gray of the spinal cord

-Acts on alpha and gamma motorneurons

Question 13

What are the characteristics of the vestibulospinal tract?

Answer 13

Originates from vestibular nuclei

Primarily lateral vestibular nucleus (Dieters’ nucleus)

Terminates mainly on interneurons and motorneurons in anterior horn, mainly on ispilateral side

Plays role in facilitating anti-gravity muscles in order to maintain an erect posture

Question 14

Somatic motor activity depends on and what does it integrate?

Answer 14

depends on pattern and rate of discharge of spinal motor neurons and homologous neurons in the motor nuclei of cranial nerves

Integrates activity of multiple inputs to regulate posture of body and make coordinated movements possible

Question 15

What are the characteristics of UMN lesions?

Answer 15

reduced strength, hyperactive (spastic) reflexes, hypertonic (spastic, claspknife) tone, withdrawal spasms, abnormal reflexes

Question 16

Lesion in the lateral corticospinal tract will lead to?

Answer 16

-Loss of fine motor control

Question 17

What is the role of the corticobulbar tract?

Answer 17

face region of sensorimotor cortex ⇒ cranial nerve nuclei thru posterior limb of IC and middle portion of crus cerebri

Question 18

Compare the Ventral vs Lateral Reticulospinal Tract.

Answer 18

Ventral - Fibers from pontine reticular formation and travel in ventral column

Lateral - Fibers from medullary reticular formaiton and travel in lateral column

Question 19

What is the importance of coactivation of Gamma Motorneurons with alpha MNs?

Answer 19

• Coactivation increases spindle afferent activity which in turn further excites alpha motoneurons, assisting with the movement
• Coactivation also makes spindle system sensitive to changes in length resulting from external load perturbations

-Changes compensate for changes in external load

Question 20

What is the sensory component of the Corticospinal System what are the characteristics?

Answer 20

primary somatosensory cortex (postcentral gyrus) ⇒ dorsal column nuclei

• Excite or inhibit dorsal horn and dorsal column neurons
• Modulates activity in the ascending systems and may allow screening out of routine stimulation of skin (aka adaptation)
• May also enable heightened sensation of interesting stimuli

Question 21

What are the characteristics of LMN lesions?

Answer 21

reduced strength, muscle atrophy, hypoactive reflexes, hypotonic (flaccid), fasciculations but not abnormal reflexes

Question 22

Both ventral and lateral reticulospinal tracts do what?

Answer 22

• Both tracts act primarily on extensors to modulate spinal reflex activity
• Pontine: stimulates
• Medullary: inhibits

Question 23

Transection above the level of the lateral vestibular nucleus will result in?

Answer 23

-Decerebrate rigidity due to removal of central inhibition

Question 24

Transection above the level of the pontine reticular formation will result in?

Answer 24

-Decerebrate rigidity

Question 25

Lesions in the Vestibulospinal tract will lead to?

Answer 25

Severe impairment of axial/proximal muscles, loss of righting reflexes

Question 26

What is included in the pyramidal tracts (3)?

Answer 26

corticobulbar

lateral corticospinal

ventral cortical spinal

Question 27

What are the excitatory and inhibitory roles of the descending fibers of the spinal cord?

Answer 27

Excitation:

• -Descending fibers make direct, excitatory monosynaptic connections with both alpha and gamma motorneurons
• -Descending fibers can synapse with interneurons to excite spinal reflex pathways

Inhibition:

• -Descending fibers can synapse with interneurons to inhibit spinal reflex pathways

Question 28

What are the 3 tracts in the lateral column of the white matter of the spinal cord? What do they control?

Answer 28

lateral corticospinal tract, rubrospinal tract, and lateral reticulospinal tract

-Skilled voluntary movements

Question 29

Fill in this chart for corticospinal (pyramidal) and extrapyramidal syndromes

Answer 29