22 – Motor Control I

Question 1

Lower motor neuron definition:

Answer 1

-motor neurons within CNS that have axons extending into PNS to innervate targets
>brainstem
>CN (except 1, 2, 8)
>SC

Question 2

LMN cell body and axon location:

Answer 2

-cell body: CNS
-axon: PNS

Question 3

Upper motor neuron definition:

Answer 3

-motor neurons that synapse on other UMNs or LMNs to control movements or functions, which are located in:
>cerebrum
>midbrain
>pons
>medulla

Question 4

UMN cell body and axon location:

Answer 4

-cell body: CNS
-axon: CNS

Question 5

What is the ultimate function of the NS?

Answer 5

-RESPOND to external stimuli
>initiates and completes motor movements

Question 6

UMN initiate:

Answer 6

-motor movements
>axon extend from brain through brain + SC to synapse with LMN in brainstem + SC
*damage=paresis and paralysis (loss of voluntary motor control)

Question 7

Brainstem UMNs:

Answer 7

-midbrain
-pons
-medulla

Question 8

What are the 3 nuclei that are important for UMN movements?

Answer 8

-red nucleus
-vestibular nucleus
-reticular nuclei

Question 9

Red nucleus ‘pathway’:

Answer 9

-midbrain
-brainstem
-SC (dorsal aspect of lateral funiculus)

Question 10

What is the name of the red nucleus spinal tracts?

Answer 10

-rubrospinal tracts
*dorsal aspect of lateral funiculus

Question 11

Red nucleus:

Answer 11

-located in midbrain
-paired structure
-axons decussate (crossover) immediately in midbrain
>have contralateral effects

Question 12

What are the rubrospinal tracts (red nucleus) involved in with regard to their motor neurons?

Answer 12

-activate FLEXOR muscles
-inhibit extensor muscles

Question 13

Vestibular nucleus:

Answer 13

-lives in medulla
*does NOT cross over
>ipsilateral effects

Question 14

What is the name of the vestibular nucleus spinal tracts?

Answer 14

-vestibulospinal tracts

Question 15

What are the vestibulospinal tracts (vestibular nucleus) involved in with regard to their motor neurons?

Answer 15

-inhibits the red nucleus
>activates extensors
>inhibits flexors

Question 16

Vestibular nucleus ‘pathway’:

Answer 16

-medulla
-brainstem
-SC (ventral aspect of lateral funiculus)

Question 17

Reticular nuclei:

Answer 17

-diffusely located in pons and medulla
-lateral and ventral funiculus
*bilateral innervation
>ventral=NOT crossed (ipsilateral)
>lateral=crossed

Question 18

What is the name of the reticular nucleus spinal tracts?

Answer 18

-reticulospinal tracts

Question 19

What are the reticulospinal tracts (reticular nucleus) involved in with regard to their motor neurons?

Answer 19

-activates extensors

Question 20

How do UMNs get activated?

Answer 20

-need to have input from MOTOR cortex (conscious part of brain)
*cortical UMNs give rise to corticospinal tract
>control motor nuclei in brainstem which then effect the motor movements

Question 21

Corticospinal tract:

Answer 21

-axons decussate (cross over) at caudal medulla (just before SC starts)
*in primates: primary motor pathway
*domestic species: doesn’t extend past the forelimbs, so must be other pathways (ex, brainstem nuclei that are activated by it)

Question 22

What are the 3 levels of control for motor movement (ex. locomotion) in animals?

Answer 22

-LMNs: involved in reflex arch
-UMNs in brainstem: synapse onto LMN
-UMNs in cortex: control brainstem nuclei

Question 23

Spinal cord contains circuitry that allows for:

Answer 23

-motor movement
>reflex arcs (patellar, withdrawal, cross-extensor)
*brainstem and motor cortex is what is controlling the VOLUNTARY movement of them