Motor Units

Question 1

Motor Pool

Answer 1

MNs coming out from spinal cord that activate a specific uscle

Question 2

5 Kinds of Neurons that Synapse Onto Lower Motor Neurons

Answer 2

Short and long distance local circuit neurons
Commissural Axons - (LD local circuits that decussate)
Input from UMNs (descending input from cortex)
Sensory input from muscle Rs

Question 3

Motor Unit

Answer 3

1 LMN and all of the muscle fibers it innervates. All are of same type and in a mosaic in the muscle

Question 4

Muscle Examples of Mostly Fast and Mostly Slow Fibers

Answer 4

Gastroc: fast
Soleus: slow

Question 5

3 Mechs of Graded Contraction

Answer 5

Increase firing rate

Recruit additional motor units and synergistic muscles

Question 6

2 Stronger Forces of Fast Motor Units

Answer 6

Fast Fibers produce more force each and there’s more of them in a motor unit

Question 7

Motor Unit Recruitment

Answer 7

Small diameter MNs are for slow and have few channels, and thus high resistance and so a stimulus causes a high V. Large diameters are for fast, so it requires more. So slow units recruited first, once they reach a certain point they recruit fast units. Fasts fatiguables activated last

Question 8

Acute Denervation and Reinnervation

Answer 8

Acute Denervation if a motor neuron dies/axon is injured, myofibers of its unit atrophy rapidly and so mosaic of normal and atrophied fibers. If healthy axons adjacent and it stays dead, healthy ones sprout w/in few weeks and reinnervate muscle fibers but will cause fiber type conversion so big blocks less well regulated, less graded, and have large fasciculations