L39 Corticospinal and Corticobulbar Fibers

Question 1

what cortex does motor planning?

Answer 1

prefrontal and limbic cortex

Question 2

what cortex does production of motor programs?

Answer 2

premotor cortex (BA 6)

Question 3

what cortex executes motor activity?

Answer 3

primary motor cortex (BA 4)

Question 4

what do the premotor cortex pyramidal layer 5 cells that project via? what does it do?

Answer 4

corticospinal tract

excite motor neurons

Question 5

what does the medial aspect of the premotor cortex contain?

Answer 5

the supplemental motor area

Question 6

what do the layer 5 pyramidal cells of the primary motor cortex make excitatory synapses to?

Answer 6

LMN’s in the spinal cord both directly and indirectly via interneurons

Question 7

what has a distinct somatotropic map?

Answer 7

primary motor cortex

Question 8

where does the motor cortex receive input from?

Answer 8

• primary somatosensory (BA 3,1,2)
• post. parietal areas (BA 5,7) = integrates sensory info for motor planning
• basal ganglia (via thalamus and premotor area)
• cerebellum (via thalamus)
• visual center
• auditory center
• limbic and prefrontal areas

Question 9

where does the premotor cortex receive input from?

Answer 9

• post. parietal area
• basal ganglia (via thalamus)
• cerebellum (via thalamus)

Question 10

what does simple finger movement activate?

Answer 10

• motor cortex

- somatosensory

Question 11

what does complex finger movements activate?

Answer 11

• premotor cortex

- supplemental motor cortex

Question 12

what does rehearsed finger movements activate?

Answer 12

-supplemental cortex (programmed from rehearsal)

Question 13

what is the predominant role of the lateral corticospinal tract?

Answer 13

voluntary contraction of distal flexor muscles of the limbs - reaching and walking

Question 14

sensory input from the lateral corticospinal tract is constantly processed by the ____ and modified by the ___ and ____

Answer 14

cortex
BG
cerebellum

Question 15

where does the corticospinal tract start?

Answer 15

pyramidal cells layer 5 of preCG

Question 16

where does the corticospinal tract end?

Answer 16

contralateral anterior horn (gray matter) of the spinal cord where the UMN synapse on alpha-gamma LMNs

Question 17

what is the route of the corticospinal tract?

Answer 17

• corona radiata
• internal capsule
• crus cerebri
• basilar pons
• pyramid (medulla)
• pyramidal decussation (causal medulla)
• (lateral) corticospinal tracts in spinal cord
• alpha/gamma LMNs

Question 18

what do LMN lesions result in?

Answer 18

• paralysis/paresis
• areflexia/hyporeflexia
• atrophy/wasting
• faciculations due to denervation which show on EMG as fibrillations

Question 19

what side, in relation to the damage, do LMN symptoms occur?

Answer 19

ipsilateral (same)

Question 20

what are examples of LMN syndromes?

Answer 20

• ALS (Lou Gehrig’s disease)

- peripheral nerve damage (traumatic)

Question 21

what do UMN lesions result in?

Answer 21

initially - flaccifity and arefleia due to spinal shock
after weeks - spinal cord circuits regain function and motor sx/sx emerge to include
-spastic paralysis (increase muscle tone)
-postitive babinski reflex
-hyperreflexia

Question 22

in UMN lesions, above the lesion which side is affected?

Answer 22

contralateral to side of lesion

Question 23

in UMN lesions, below the lesion, which side is affected?

Answer 23

ipsilateral to side of lesion

Question 24

what are the symptoms of paraplegia?

Answer 24

• flaccid paralysis below lesion (spinal shock) then spasticity
• increase deep tendon reflex and clonus
• +Babinski reflex
• urine retention,
• painless bladder distension + overflow
• decrease flexor spasms
• loss of all somatosensory below

Question 25

the lateral corticospinal and corticobulbar tracts are the most important motor pathways that arise in the primary motor cortex and overlap with what?

Answer 25

- precentral gyrus (lateral) | - anterior paracentral lobule (medial)

Question 26

how do the thalamus permit regulation of the motor cortex?

Answer 26

by BG and cerebellum *BG and cerebellum does not control LMN, they talk to motor centers, so they can INDIRECTLY regulate LMN

Question 27

what is the medial premotor (supplementary) area involved in?

Answer 27

planned sequences

Question 28

what is the lateral premotor areas involved in?

Answer 28

sensory-guided movements

Question 29

axons forming these two are the same - if you damage one, you will get degenerations of the other.

Answer 29

crus cerebri | pyramids

Question 30

the continuous axons from crus cerebri to pyramid are not visible on the ventral surface of the pons, given the presence of _____ which form the middle cerebellar peduncles.

Answer 30

superficial transverse pontine fibers

Question 31

which part of the internal capsule do the corticospinal and corticobulbar fibers run?

Answer 31

posterior limb of internal capsule

Question 32

A minority of corticospinal fibers (typically arising from parietal areas) will terminate in the _____ presumably to regulate sensory inputs.

Answer 32

dorsal spinal gray matter

Question 33

The upper motor neurons commonly release glutamate onto AMPA receptors, either directly or indirectly activating ______

Answer 33

alpha / gamma LMN

Question 34

when does paraplegia occur?

Answer 34

after spinal cord injury