Question

You are walking and hear a loud noise. You turn to see a large tree branch falling on your neighbor’s dog.

i. You run over and try as hard as possible to lift the branch but after barely lifting it your arms give out under the weight. Provide a detailed description of the role that tendon organs played to prevent you from lifting the branch. Why is it beneficial to you?

ii. You try again and slowly get the branch up just enough for the dog to escape. Provide a detailed description of the role that muscle spindles played allowing you to lift the branch. Your response must include a detailed description of alpha-gamma coactivation.

Answer 1

Ans i) The tendon organs prevent from lifting the branch and is important or beneficial as it helps in reducing the muscle tension. It is basically a proprioceptive sensory receptor organ which upon lifting heavy weight sense changes within the muscle tension and hence prevents the hand from lifting which reduces stress. While lifting the heavy weight, there is force generated in the muscle and this leads to also compression of the sensory terminals. This tends to stress the whole of the muscle force and fire nerve impulse and hence in order to prevent any injury tendon organ prevents the lifting. Upon activation or stimulation of the Golgi tendon organ, it causes the muscle associated with it to relax and does so by interrupting with contraction. As the muscle is inhibited by the tendon organ, it causes autogenic inhibition and hence opposes muscle contraction that prevents the lifting of the branch of the tree.

Ans b) Slowly it enables the lifting and leads to the activation of the muscle spindles which are stretch receptors. They are present within the muscle and hence they help in detecting changes in the muscle length. As soon as the lifting of the branch starts, the muscle spindle are activated and hence it enables contraction allowing the upward movement and removal of the branch. This also is due to the alpha gamma co-activation which helps in maintaining the muscle spindle tension upon muscle shortening and hence the stretch does not impact the muscle much. The muscle spindle being the stretch receptor helps in detecting changes within the muscle and with the alpha gamma co-activation, there is parallel activation of alpha motoneurons with the gamma ones and hence it helps in stabilizing and maintaining the spindle tension when the extrafusal muscle shortens. This helps in enabling the lifting of the muscle enough for allowing the dog to escape.