1d Motor 1&2 Gamma MNs + Decerebrate Rigidity

Question 1

What do Gamma Motor Neurons do?

Answer 1

prevent muscle spindle (1a) from unloading/becoming too loose that it collapses on itself. (think of muscle spindle as a rubber band, if there is no tension on it, then it will collapse and not give precise reading of muscle length; therefore, gamma motor neurons keep tension on muscle spindle to ensure proportional length-tension)

Question 2

What does Ia fiber regulate?

Answer 2

muscle length

Question 3

How does a patient with Decerebrate Rigidity present?

Answer 3

extension of all 4 limbs

Question 4

Where do Gamma Motor Neurons exit the spinal cord?

Answer 4

dorsal root

Question 5

What tracts are damaged in Decerebrate rigidity?

Answer 5

corticospinal + rubrospinal

Question 6

What tracts are active in Decerebrate rigidity?

Answer 6

vesitbulospinal + reticulospinal (which both have a preference for extensors)

Question 7

How does Decerebrate Rigidity work?

Answer 7

vestibulospinal + reticulospinals are nailing Gamma Motor Neurons, which nail extensors over flexors (firing of gamma motor neurons causes muscle spindle to make alpha motor neurons contract)

Question 8

How can Decerebrate Rigidity be alleviated?

Answer 8

cutting of dorsal (Sensory) roots since 1a fibers are sensory.

Question 9

What is Gamma Bias?

Answer 9

UMNs control myotactic reflex through Gamma Motor Neurons, which are constantly firing to set muscle tone. (increase activity of extensors/flexors - think of how jittery you get when about to run a race)