L5 UMNs Flashcards
Medial Ventral horn
Most UMNs that project to the medial part also project to the intermediate zone, innervating the LMNs responsible for posture, balance, proximal muscles.
Pathways travel through the anteromedial white matter, they receive input from both sides of the brainstem
Lateral ventral horn
Most UMNs come from the motor cortex and travel in the lateral white matter and terminate in the lateral ventral horn
distal limbs, precise movements
Corticobulbar Axons
terminate bilaterally and contralaterally
ensures that loss in one side does not significantly impact the other side
terminate in the reticular formation before reaching the LMNs, meaning motor commands are refined before being created
Exceptions for Bilateral Innervation
- Hypoglossal nucleus: controls tongue muscles
- Trigeminal Motor Nucleus: chewing
- Facial Motor Nucleus: facial expressions
Primary Motor Cortex Organization
- Neurons located near each other are connected by local circuits. Allows for organization of movements. Instead of one action, a grouping/pattern can be completed
- Less specific then the somatosensory cortex, allows the M1 to be dynamic and flexible
Role of premotor cortex
- Indirectly: through connections with M1
- Directly: through axons projecting to corticobulbar and corticospinal pathways (over 30 %)
- Significant role in motor control
- Encode action goals oriented toward extrapersonal space/objects that are farther away
When do neurons in the preomotor cortex fire?
fire at the appearance of the cue, before we actually received a signal to make a movement
Ventrolateral subdivision of premotor cortex
active when individual prepares to perform specific movement but also when observing someone else doing a similar action
mirror motor neurons play out this mechanism, particularly when action involves a specific goal
plays a crucial role in understanding, encoding, imitating actions performed by others
Frontal lobe damage
patients have difficulty learning to select a movement in response to a visual cue
Medial Division of premotor cortex
- mediates selection of movements, specialized for initiating movements by internal cues
- Region is active when individual performs something from memory
- Example is the frontal eye fields, cingulate gyrus
- Damage reduces the amount of self initiated movements
Brainstem motor circuitry
contain circuits of UMNs
organize axial musculature of trunk and limbs
helps with balance, posture, visual gaze
can direct motor activities w/out higher motor centers in cortex
include vestibulospinal, medial vestibulospinal, tectospinal, pontine reticulospinal, and medullary reticulospinal tracts
Feedforward Control
create a motor plan to move body of limb from current location to its ultimate location
cannot adjust for unexpected events
works well in case feedback is delayed
reticular formation initiate, when they are inactive, you see a lack of postural responses
Feedback control
using information from environment to adjust the motor plan
works well when we need to be sensitive to change
does not work well when our feedback is slow or there are errors
uses muscle spindles and vestibular nuclei
What are S/S you would expect w/UMN involvement?
hyperflexia
sensory input is there, unable to create appropriate motor plan
upregulation
spasticity, clonus
fine motor impairment
Upper motor neuron syndrome
damage to internal capsule typically results in flaccid presentation to contralateral side
hypotonia = called spinal shock, due to decreased activity of spinal circuits. Resolves in a few days
Babinskis sign and clonus
more widespread distribution of impariment in body regions
mild or no atrophy develops
