Descending motor pathways

Question 1

levels of motor hierarchy

Answer 1

the highest level - precommand level
middle level - projection level
lowest level - segmental level

Question 2

precommand level

Answer 2

involves the premotor cortex, basal ganglia and cerebellum

Question 3

what is the premotor cortex role at the precommand level?

Answer 3

responsible for initiating a plan for the next intended movement

Question 4

what is the role of the basal ganglia at the precommand level?

Answer 4

release brake to start a specific movement

Question 5

what is the role of the cerebellum at the precommand level?

Answer 5

precisely calculates the best way to achieve coordinates synergistic across multiple limb joints, as well as monitoring muscle tone and balance

Question 6

projection level

Answer 6

involves the primary motor cortex and the brainstem

Question 7

what is the role and location of upper motor neurons?

Answer 7

directly control the spinal cord. they are located in the primary cortical motor areas and brainstem

Question 8

what is the role and location of the pyramidal tracts?

Answer 8

they originate from the primary motor cortex, synapse either with interneurons or with ventral horn motor neurons in the spinal cord. they are concerned with voluntary, discrete, skilled movements

Question 9

what is the role and location of the command neurons?

Answer 9

they are located in the brainstem nuclei. they function to start, stop or modify the basic rhythm of CPGs of the spinal cord through the indirect pathways.

Question 10

segmental level

Answer 10

the spinal cord

Question 11

reflex arcs

Answer 11

are composed of afferent axons, which synapse onto interneurons in the spinal cord, which relay the information back to efferent neurons. these axons go onto effector organs to initiate a command

Question 12

What is the role of lower motor neurons?

Answer 12

their axons synapse onto the skeletal muscles, creating motor units

Question 13

central pattern generators (CPGs)

Answer 13

the segmental circuits in the spinal cord that control locomotion and other specific and often-repeated motor activity. it consists of a network of neurons, on both sides of the spinal cord, that work together to generate a rhythmic pattern of motor activity. CPGs are initiated and generated by brainstem command neurons.

Question 14

the direct (pyramidal) system

Answer 14

origin in from the primary motor cortex. axons go down via the internal capsule, and decussate at the pyramid. axons largely cross over, but not all together. 90% decussate at the lateral corticospinal tract. 8% cross over at the anterior corticospinal tract. 2% are uncrossed and pass through the corticospinal tract.

Question 15

stroke at the internal capsule

Answer 15

the face, upper extremity, trunk and lower extremity all sit at the internal capsule. stroke can result in paralysis in any of these regions

Question 16

the corticospinal (pyramidal) tract (function)

Answer 16

involved with regulating fast and skilled movements, and controlling reflex motor output and modifying sensory input.

Question 17

the lateral corticospinal tract

Answer 17

crosses over at the lateral part of the pyramid

Question 18

the anterior corticospinal tract

Answer 18

crosses over at the anterior part of the pyramid

Question 19

damage to the corticospinal tract

Answer 19

leads to paralysis of the target muscles.
if the lesion is above pyramidal decussation, paralysis occurs on the opposite side to the lesion in upper and lower limb muscles.
if the lesion is below pyramidal decussation in the lateral T10, paralysis is on the same side lower limb muscles.

Question 20

the corticobulbar tracts

Answer 20

part of the direct system. the have bilateral synapses, but are mainly contralateral.
the tract goes from the cortex → brainstem → cranial nerve nuclei

Question 21

the indirect (extrapyramidal) system

Answer 21

motor axons arise from several brainstem nuclei

Question 22

what are the four major tracts of the indirect system?

Answer 22

1. tectospinal tracts
2. rubrospinal tracts
3. reticulospinal tracts
4. vestibulospinal tracts

Question 23

tectospinal tracts

Answer 23

move the head and back, and provide visual input. are formed by the superior colliculus on the tectum or roof of the midbrain

Question 24

rubrospinal tracts

Answer 24

maintains muscle tone. formed by the red nucleus in the midbrain

Question 25

reticulospinal tracts

Answer 25

initiate CPGs in the spinal cord. formed by the reticular formation in the pons and medulla

Question 26

vestibulospinal tracts

Answer 26

maintain balance. formed by the vestibular nuclei in the medulla