3.18.14 34 Motor Systems I (Organization and projection fibers)

Question 1

Axial and proximal musculature is typically (tonical/phasic)
This is in control of (discrete movement/posture)

Answer 1

Tonic - posture

Question 2

Distal musculature is typically (tonical/phasic)

This is in control of (discrete movement/posture)

Answer 2

Phasic - discrete movement

Question 3

Tonically controlled muscles are typically (flexors/extensors)

Answer 3

Extensors - used for posture

Question 4

Phasically controlled muscles are typically (flexors/extensors)

Answer 4

Flexors - used for controlled, discrete movements

Question 5

Motoneurons and interneurons of the final common pathway are organized such that those innervating 1. ____ are located medially and those innervating 2. ____ are located laterally.

Answer 5

1. axial and proximal musculature (posture)

2. distal musculature (discrete movements)

Question 6

Within the organization of the ventral horn, 1. ____ are located ventrally and 2. ____ are located dorsally.

Answer 6

1. Extensors (posture)

2. Flexors (movement)

Question 7

Describe the image of the arm within the ventral horn. Describe what constitutes the ventral and dorsal portions. Describe what constitutes the medial and lateral portions.

Answer 7

Ventral = extensors
Dorsal = flexors
Medial = axial/proximal muscles
Lateral = distal muscles

Question 8

Where does the somatosensory input to the cortical columns originate? Is this dependent upon the postcentral gyrus (primary sensory cortex)?

Answer 8

Arises in the VA and VL nuclei of the thalamus.

This is independent of the input to the primary sensory cortex.

Question 9

From what “areas” do corticospinal tract projections originate?

Answer 9

4 (precentral gyrus)
6 (premotor cortex)
8 (frontal eye fields)
3, 1, 2 (postcentral gyrus)

Question 10

From what area do projections destined for distal musculature primarily originate?

Answer 10

Area 4 (precentral gyrus)

Question 11

From what area do projections destined for proximal and axial musculature primarily originate?

Answer 11

Area 6 (premotor)

Question 12

From what area do projections destined to terminate on the dorsal column nuclei and dorsal horn originate?

Answer 12

Areas 3, 1, and 2 (postcentral gyrus)

Question 13

Describe the pathway of corticospinal projections from the cortex to the lateral/anterior corticospinal tracts

Answer 13

Cortex –> corona radiata –> internal capsule –> cerebral peduncle –> basis pontis –> pyramids –> (pyramidal decussation –> LCST) or (ACST without decussation)

Question 14

Describe the three main terminations of the lateral corticospinal tract

Answer 14

1. Dorsal column nuclei and dorsal horn (collaterals; modulation of afferent information)
2. Dorsal interneuron pools in the ventral horn (primarily flexors)
3. Alpha motor neurons in the dorsolateral ventral horn (10% of LCST fibers)

Question 15

Describe the primary termination of the anterior corticospinal tract

Answer 15

Medial and ventral interneuron pools (proximal/axial muscles; extensors)

Question 16

Describe the path of corticorubral fibers

Answer 16

Precentral areas –> posterior limb of the internal capsule –> red nucleus (midbrain) - rubrospinal system

Question 17

Describe the path of corticopontine fibers

Answer 17

Frontal –> ANTERIOR limb of internal capsule –> pontine nuclei
OR
Parietal/Occipital/Temporal –> POSTERIOR limb of internal capsule –> pontine nuclei

Question 18

Describe the path of corticobulbar fibers

Answer 18

Pre- and postcentral cortex –> genu of internal capsule –> reticular formation, motorneurons of cranial nerve nuclei, sensory relay nuclei

Question 19

What exists in the anterior limb of the internal capsule?

Answer 19

Corticopontine fibers (from frontal cortex)

Question 20

What exists in the genu of the internal capusle?

Answer 20

Corticobulbar fibers (pre and postcentral cortex)

Question 21

What exists in the posterior limb of the internal capsule?

Answer 21

Corticospinal fibers
Sensory fibers
Corticorubral fibers
Corticopontine fibers (from parietal, occipital, and temporal cortices)

Question 22

Describe corticobulbar projections to cranial nerve nuclei (i.e. which are bilateral or contralateral)

Answer 22

5 and 7 (upper face only) are bilateral

7 (lower face only), 12, and ambiguus are contralateral

Question 23

Motoneurons and interneuron pool organization:
Where are flexors?
Extensors?
Axial/Proximal musculature?
Distal musculature?

Answer 23

Flexors = dorsal
Extensors = ventral
Axial/proximal = medial
Distal = lateral