Other Motor Pathways 3

Question 1

Describe alpha-gamma co-activation

Answer 1

Alpha motor neurons – innervate extrafusal muscle fibers

• Gamma motor neurons – innervate intrafusal muscle fibers
• Alpha and gamma motor neurons are activated by higher centers so that the sensitivity of muscle spindles to stretch is maintained

Question 2

Describe muscle contraction & alpha gamma co-activation

Answer 2

• Activated alpha. Motor. Neuron
• When extrafusal fibers contract the intrafusal fibers become less tense (slack)

• In this state the fibers are unable to measure subsequent changes in the muscle

Question 3

What does the gamma motor neuron do?

Answer 3

The gamma motor neuron gives innervation to the contractile poles of the intrafusal fibers

• When they fire they cause the intrafusal fibers to shorten, thus shortening the muscle spindle
• In this state the muscle spindle is able to detect muscular stretch

Question 4

What is the gamma loop?

Answer 4

Intrafusal fibers of the muscle spindle play a role in proprioception.

Alpha motor neuron innervates the extra- fusal fibers

Gamma motor neurons innervate the intrafusal fibers

Descending pathways influence these lower motor neurons.

Question 5

What is the purpose co-activation?

Answer 5

Somepathwaysco-activatethealphaand gamma motor neurons (e.g. corticospinal)

• Somepathwayspredominantlyexciteeither alpha or gamma motor neurons and therefore must cooperate with other pathways to accomplish co-activation the two lower motor neurons.
• Purpose of co-activation: To ensure that contraction of the intrafusal fibers is tuned to allow the neuromuscular spindle