Direct and Indirect Motor System

Question 1

What is motor control highly dependent on

Answer 1

sensory information

Question 2

What is the main difference between direct and indirect motor systems

Answer 2

DMS = direct interaction with LMNs (can directly influence ongoing activity in LMNs)

LMNs = indirect interaction with LMNs (modulatory, have to act on the direct system to impact LMNs)

*summary: do they have the ability to directly synapse on lower motor neurons or not

Question 3

What is the primary motor cortex responsible for

Answer 3

movement execution (sending command to lower motor neurons)

Question 4

what is the premotor cortex responsible for

Answer 4

planning our motor actions (steps to complete a motor action)

Question 5

How does the direct motor system relate to the primary motor and premotor cortex

Answer 5

when we are talking about the DMS we are talking cell bodies in primary motor cortex and premotor cortex and the axons and tracts that leave the cell bodies to synapse on LMNs

Question 6

Corticospinal tract

Answer 6

originates in cortex and ends up in the spinal column

synapses on spinal nerves

Start in primary motor cortex → axons travel between the between the thalamus and the basal ganglia via a white matter region called the internal capsule → leaving cortex and entering the brainstem (midbrain, pons, medulla) → when medulla is reached, goes all the way down to the spinal column and and synapses on lower motor neurons that become spinal nerves

Question 7

Corticobulbar tract

Answer 7

originates in cortex and ends up in the brainstem

synapses on cranial nerves

Start in primary motor cortex → axons travel between the between the thalamus and the basal ganglia via a white matter region called the internal capsule → leaving cortex and entering the brainstem (midbrain, pons, medulla) → when medulla is reached, we reach the medullary pyramids → region in which region in which a majority of the corticospinal tract fibers cross over (decussation), becoming contralateral → reaches the level of the spinal column its responsible for and synapses on a lower motor neuron (or an interneuron that will synapse on a lower motor neuron eventually)

Question 8

what are corticospinal and corticobulbar tracts important for

Answer 8

skilled movement and voluntary action (most important for speech and voice production)

Question 9

What are the Brainstem UMN tracts

Answer 9

rubrospinal tract
vestibulospinal tract
reticulospinal tract
tectospinal tract

*all important for posture, balance and gait patterns

Question 10

What are the Cortical UMN tracts

Answer 10

M1
S1
SMA
PMA

Question 11

Do the vast majority of corticospinal tract neurons decussate

Answer 11

YES

this means in general, that movement on one side of the body is controlled by UMNs originating from the contralateral motor cortex

Question 12

Do the vast majority of corticobulbar neurons decussate

Answer 12

NO

some decussate, others synapse on both ipsilateral and contralateral cranial nerve nuclei (bilateral innervation)

Question 13

What is the organization of the Primary Motor Cortex?

Answer 13

somatotopic organization
clusters of cell bodies can be clustered with other cell bodies that all serve the same region of the body

Question 14

What is training-induced neuroplasticity

Answer 14

in response to really intense training, somatotopic organization of cortex can change to accommodate new skills

the amount of the cortex that is dedicated to this new skill will expand

important for rehabilitation

Question 15

What does damage of the UMNs from M1 cause

Answer 15

contralateral paralysis/paresis

hypertonia

overactive reflexes

reduction in skilled movement

Question 16

What will damage to the premotor area cause

Answer 16

apraxia (disruption in motor planning)

Question 17

What will damage to the LMNs cause

Answer 17

ipsilateral paralysis/paresis

hypotonia

flaccidity

decreased or absent reflexes

muscle denervation (atrophy, fasciculations)

Question 18

Is the basal ganglia part of the direct or indirect motor system

Answer 18

indirect motor system

means it does not directly synapse on LMNs

Question 19

What does the basal ganglia do

Answer 19

selects which movement will be performed and actively inhibits unwanted movments

allows us to interrupt an ongoing action

Question 20

What is the BG feedback loop

Answer 20

the BG receives input from cortex, processes this input, and returns it right back to where it started

Question 21

What happens in the presence of dopamine (loop 1)

Answer 21

direct pathway is dominant

initiate a behavior

Question 22

what happens in the absence of dopamine (loop 2)

Answer 22

indirect pathway is dominant

terminate a behavior

Question 23

what does tonic and phasic mean

Answer 23

tonic = happens all the time

phasic = happens as a result of something

Question 24

What is the cerebellum critical for

Answer 24

motor learning and coordination

compares intent of an action with its execution (integrates information from motor cortex with info from sensory cortex to correct and smooth movements)

Question 25

What does damage to the cerebellum cause

Answer 25

ataxia = abnormal rate and range of movement

intention tremor = increasing tremor during skilled movement

Dysdiadochokinesia = inability to produce rapidly changing/alternating movements

Dysmetria = inability to accurately judge the range of endpoint of a movement