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Motor Systems/LMNs
| Question | Answer |
|---|---|
| What structure is said to be involved in "gating of volitional movements?" | basal ganglia |
| What is the relation of flexor to extensor motoneuron pools? | flexors are more dorsal within the ventral horn |
| What is the relation of proximal to distal muscle motoneuron pools? | proximal muscles are medial to distal muscles within ventral horn |
| Would one expect muscles of the medial rectus to have a high or low muscle fiber:motor unit ratio? | low (10 fibers per unit) |
| Would one expect muscles of the vastus lateralis to have a high or low muscle fiber:motor unit ratio? | high (1000 fibers per unit) |
| What type of neurons innervate intrafusal fibers? | gamma motoneurons |
| How much synaptic current is required to intiate repetitive firing of a motoneuron? | 1.5x the amount needed to recruit the neuron |
| Which type of muscle maximally contracts at higher frequencies (relative to the other muscle types)? | fast fatigable |
| Explain the concept of motor unit plasticity. | persistent changes in motor neuron activity can over time induce changes in muscle fiber type |
| How might an experimenter achieve more force from the muscles in the cats he is testing? | increase the firing rate of active units and recruit more units |
| Which type of muscle's nerve fibers will have the lowest threshold? | small motoneurons |
| If a firing rate of 20 Hz is needed to fully recruit all motor units of the soleus muscle, will a lower or higher frequency be needed to fully recruit a lateral rectus muscle? | lower freq |
| Explain the size principle of motoneurons. | Small motoneurons have a larger input resistance and thus a smaller current can is needed to successfully initiate a depolarization. Large motoneurons require more current to depolarize due to their small effective resistance |
| A 25 yr old pt with spinal muscular atrophy, a LMN disorder, should have what characteristic findings on exam? | focal atrophy or diffuse muscle wasting, fasciculations, muscle weakness, decreased DTRs |
Created by:
sirprakes
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