Direct and Indirect Motor System Flashcards
What is motor control highly dependent on
sensory information
What is the main difference between direct and indirect motor systems
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
What is the primary motor cortex responsible for
movement execution (sending command to lower motor neurons)
what is the premotor cortex responsible for
planning our motor actions (steps to complete a motor action)
How does the direct motor system relate to the primary motor and premotor cortex
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
Corticospinal tract
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
Corticobulbar tract
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)
what are corticospinal and corticobulbar tracts important for
skilled movement and voluntary action (most important for speech and voice production)
What are the Brainstem UMN tracts
rubrospinal tract
vestibulospinal tract
reticulospinal tract
tectospinal tract
*all important for posture, balance and gait patterns
What are the Cortical UMN tracts
M1
S1
SMA
PMA
Do the vast majority of corticospinal tract neurons decussate
YES
this means in general, that movement on one side of the body is controlled by UMNs originating from the contralateral motor cortex
Do the vast majority of corticobulbar neurons decussate
NO
some decussate, others synapse on both ipsilateral and contralateral cranial nerve nuclei (bilateral innervation)
What is the organization of the Primary Motor Cortex?
somatotopic organization
clusters of cell bodies can be clustered with other cell bodies that all serve the same region of the body
What is training-induced neuroplasticity
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
What does damage of the UMNs from M1 cause
contralateral paralysis/paresis
hypertonia
overactive reflexes
reduction in skilled movement
What will damage to the premotor area cause
apraxia (disruption in motor planning)
What will damage to the LMNs cause
ipsilateral paralysis/paresis
hypotonia
flaccidity
decreased or absent reflexes
muscle denervation (atrophy, fasciculations)
Is the basal ganglia part of the direct or indirect motor system
indirect motor system
means it does not directly synapse on LMNs
What does the basal ganglia do
selects which movement will be performed and actively inhibits unwanted movments
allows us to interrupt an ongoing action
What is the BG feedback loop
the BG receives input from cortex, processes this input, and returns it right back to where it started
What happens in the presence of dopamine (loop 1)
direct pathway is dominant
initiate a behavior
what happens in the absence of dopamine (loop 2)
indirect pathway is dominant
terminate a behavior
what does tonic and phasic mean
tonic = happens all the time
phasic = happens as a result of something
What is the cerebellum critical for
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)
