Cortical Control of Movement Flashcards
There are 5 different components of the motor system including: spinal cord, association cortices, basal ganglia, cerebellum, and cortical motor areas. These 5 components have their own hierarchy. What is it?
Spinal cord
How do the lowest levels of the motor system differ from the upper levels of the motor system?
Lowest levels: accomplish the most automatic behaviors, like reflexes
Highest levels: complex planning and selection of movement
What is the path of a motor neuron from the primary motor cortex to the muscle?
- Primary motor cortex 2. Internal capsule 3. Crus Cerebri 4. Medullary pyramids 5. Decussation at the caudal medulla 6. Lateral corticospinal tract through the spinal cord 7. Synapse in the ventral white matter 8. Secondary neurons then go to the muscle
What is the difference between the lateral corticospinal tract and the ventral corticospinal tract?
Lateral corticospinal tract: in lateral white matter of spinal cord; innervates the distal muscles on the contralateral side and important in skilled movement
Ventral corticospinal tract: in the ventral white matter of the spinal cord; bilaterally innervates the axial muscles and important in posture/balance
There are two main categories of descending corticospinal terminations: direct and indirect. How are they different?
Direct: upper motor neurons descend down the corticospinal tract and synapse directly with the lower motor neurons which then go to the muscles
Indirect: upper motor neurons descend down the cortiocospinal tract and then synapse with an interneuron that then synapses with a lower motor neuron; important for proprioception
What are other names for local circuit neurons? What is their input? What is their function?
Can also be called interneurons or propriospinal neurons
Can receive input from either UMN (cortex/brainstem) or from local sensory (like in a simple reflex)
Fucntions to get
What is the difference between short distance local circuit neurons and long distance local circuit neurons?
Short distance: contain a cell body that can then project 1-2 segments up or down; activates/inhibits a small group of muscles; important for fine movement and located more lateral
Long distance: contain a cell body that can allow for projections to travel a great distance so that a large group of muscles can be activated/inhibited at the same time; important for posture and located more medial
There is a relationship between the number of alpha motor neuron terminations in the ventral horn and dexterity between species. What is this relationship?
Species that express more dexterity have more alpha motor neuron terminations
Why do babies exhibit a positive Babinski sign, like someone that has a spinal cord injury?
Full development of alpha motor neurons develops postnatally. So at first doesn’t have much dexterity
What are the four indirect motor pathways?
Cortio colliculo-spinal, corticorubrospinal, corticoreticulospinal, corticovestibulospinal
What are the two direct motor pathways?
Lateral corticospinal and anterior corticospinal
What is the vetibulospinal tract used for?
anti-gravity, important for changing position (acceleration/decceleration/ rotation)
What is the reticulospinal tract used for?
changing the strength of the muscle and central pattern generation
What is the colliculospinal tract used for?
Body orientation and response to auditory and visual cues
What is the rubrospinal tract used for?
Arm flexion
What are the cells called that are only found in the motor cortex? What happens to these cells as you move away from the primary motor cortex to other motor areas?
Betz cells
The amount of betz cells decreases as you move from the primary motor cortex into other association cortices
What are the 5 skeletomotor areas in the brain?
- Supplementary motor area
- Cingulate motor area
- Dorsal premotor area
- Ventral premotor area
- Primary motor cortex
What are the criteria that are needed to be considered a cortical motor area? (this is important!)
- Must project to motor neurons in the spinal cord (either directly to the ventral horn that then synapses with an alpha motor neuron or indirectly through an interneuron that then synapses with an alpha motor neuron)
- Needs to have projections to the primary motor cortex
- Needs to have betz cells
- When this area is stimulated a movement is produced
- A recording on EEG shows that during movement there is a change in activity in this area
Based on the criteria needed to be a cortical motor area are association areas such as the prefrontal cortex, pre-supplementary motor area, and the parietal and temporal lobe considered cortical motor areas?
No- but they are still involved in regulating motor function
In an experiment, monkey’s were trained to grab a grape and then gave these monkeys a lesion to their lateral corticospinal tract. The monkey was still able to reach out and grab the grape, although it took the monkey much longer to do so, meaning that the monkey was just grabbing the grape on chance. What was still intact allowing the monkey to grab the grape after the lesion?
Local Circuit Neurons that project past the lesions to bridge the area
The closer you get to the midline, means that the innervation of cranial nerves will likely be more bilateral or unilateral?
Bilateral
True or False: a given muscle is only represented on one portion of the cortex within the precentral gyrus?
False- there are multiple locations in the cortex that are used to represent the same muscle (an area in the primary motor, another in the supplemental etc)
These are arranged in columns
A single corticospinal neuron divides so that it can influence multiple motor neuron pools. What does this mean and how is related to function?
One motor neuron influences many different muscles (one UMN synapses with a bunch of LMN) This allows a group of different muscles to contract at the same time
By injecting rabies into motor neurons and watching retrograde transport, they were able to determine where corticospinal neurons arise from. Which layers of the cortex do the corticospinal neurons arise from?
Layers 3 and 4
What are three components of movement that a cortical motor neuron encodes?
- The specific muscle used
- Recruitment (force)
- Direction- certain motor cortical neurons fire to move your arm in one direction
True or False: all cortical muscle neurons change their activity with direction?
False
Some cortical neurons change their activity with direction while others remain unchanged. The changes that do occur do so in a predictable fashion and are important in prosthetics
What are the main functions of the primary motor, lateral premotor, medial premotor, pre-supplemental motor area, and prefrontal cortices?
Primary motor: simple movement
Lateral premotor: selection of motor responses based on sensory input
Medial premotor: execution of learned sequences
Pre-supplemental motor area: actual learning of sequences
Prefrontal: decision of action/working memory
What is the difference between decorticate and decerebrate postures?
Decorticate: arms flexed, legs extended, lesions above red nucleus
Decerebrate: extension of arms and legs, lesions below the red nucleus
