Motor Systems Overview Flashcards
Big picture of motor systems
Desire for something -> idea of satisfying that desire -> coordination of various motor systems to achieve the necessary movement -> then actual movement -> interaction with real world
will give feedback to motor systems to adjust movement as necessary.
example of big picture of motor systems
Ex: I am feeling hungry. A cookie would be good. Let’s go get a cookie. walk to cookie jar and try to open Wow that cookie jar lid is really stuck on there. try harder to open cookie jar and/or grab hammer to bust up cookie jar and enjoy cookie goodness
feedforward mechanisms
anticipatory adjustments for movement
ex: I remember this door being hard to open, so I need to apply more force this time
feedback mechanisms
adjustments for movement based on external stimuli
ex: Welp, someone clearly fixed the door slow down there He-Man or you’ll break something
what does the concept of motor equivalence imply?
the nervous system can solve problems in many ways, and this flexibility is normal
the idea that different motor sets can achieve the same behavior
Therefore, if a pt loses both hands doing something crazy like cleaning brownie tins with chainsaws the pt can then adapt by learning to use their feet to write
alpha (lower) motor neuron
LMN’s are alpha motor neurons and their axons that directly innervate skeletal muscle
(extrafusal fibers), form part of motor units, form motor part of peripheral nerves
lower motor neuron syndrome
LMN syndrome is damage to those LMN’s, resulting in the following s/s:
- weakness (paresis)
- hypotonia
- hyporeflexia
- muscle atrophy
- fasciculations and fibrillations
effects of lower motor neuron syndrome
Affectation is ipsilateral and segmental (only in that segment or nerve), NOT in all below the lesion
ex) damage to R ventral horn at T4 will result in LMN s/s on R side in the muscles supplied by T4
motor unit
motor neuron (including its cell body/dendrites/axon) + ALL the muscle fibers (the muscle unit) it innervates
controlling/adjusting motor units to increase force
population coding - recruiting more motor units
frequency coding - each motor unit firing faster
lesions in which structures could give you “lower” motor neuron s/s?
Note that more laterally, the distal portion of the limb is represented. Medial to that is proximal portion of limb. Most medial is axial or trunk region.
location of alpha (lower) motor neurons
ventral horn of the SC at every segment and motor nuclei for cranial nerves in the brainstem
“upper” motor neurons
Neurons and their axons that directly or indirectly excite or inhibit “lower” motor neurons.
s/s associated with “upper” motor neuron lesions
weakness (paresis)
spasticity (usually)
no early atrophy (muscles may atrophy months later due to disuse)
abnormal reflex activity (Babinski reflex, clonus)
hyperreflexia
decreased coordination
abnormal muscle recruitment
loss of fractionation producing abnormal synergies
decreased muscle endurance
distribution of “upper” motor neuron lesions
- if the lesion is in the cortex: the area affected will be determined by the area of the homunculus that is affected
- if the lesion is in the SC: in corticospinal pathways, the lesion will affect all structures innervated below the level of the lesion
