Question

#3

of to as to of In Panel A the muscle is passively beched by adding a load at the arrow marked "PULL". Why does the latest Sher from the degan increase its action potential discharge when the food is added stimulating ONLY the mo o n and the caused the muscle to short What causes the latteren for decrease discharge when t he motoneuronne mulated? c. In Panel of the arrow labeled on the muscles are contracted by simulating them AND m ely motornare stimulated contracting the intraus s Why does the latenter's discharge we not change when both pha and garma motorneurons are coactivated? d. Considering the overall previous page] → Which Panel A rci most to what happens in normal person when they voluntarily contract their skeletal muscles, and why is this poem of activation physiologically advantageous? EXPLAIN the advantage . During your physical exam a doctor tape your right partendon to trigger motati reflex. If your reflex is NORMAL, the flowing should occur in the innervation to your right quadriceps muscle: → AP Discharge in your la terenis briefly Choog increases, decreases, stays the same) AP Discharge in your alpha motomeurons briefly Choo ame) Increases, decreases, stays the AP Discharge in your gamma motomeurons briefly Choo increases, decreases, stays the

Answer 1

a.)The muscle spindle is a Length Receptor that senses changes in the length of the muscle. In particular stretch causes an increased rate of firing of action potentials (A)

Muscle spindles comprise of sensor receptors

• Sensor receptors include nuclear bag fibres and nuclear chain fibres
• nuclear bag fibres sense ounset of stretch
• nuclear chain fibres sense sustained stretch

• Sensor receptors associated with Afferent sensory neurons convey muscle spindle information to Central Nervous system
• Firing rate of afferent neurons is proportional to muscle spindle length
• Sensory neurons synapse with Gamma motor neurons at the spinal cord

b.)The muscle spindle is unloaded (i.e. shortens and has a reduced tension) during contraction of the extrafusal fibres (B)

Gamma motor neurons

• innervate intrafusal muscle fibres
• carry efferent information from Central Nervous System to muscle fibr

c.) The slack in the spindle (low tension) can be returned to normal by the gamma efferent innervation of the intrafusal fibres (C).

Alpha motor neurons:

• innervate extrafusal muscle fiibers
• responsible for contraction of extrafusal muscle fibres

Gamma motor neurons adjust the stretch sensitivity of the muscle spindle, so that the spindle is active even when the muscle shortens.

d.) Alpha Gamma Coactivation causes the tension on the muscle spindles to be maintained as the muscle shortens; thus sensitivity to stretch is maintained.

e.)

1. remains the same
2. increases
3. decreases