Question

1. why doesnt the patellar reflex happen when your leg is straight? 3. how does the patellar reflex protect us?

Explanation:

For the first question, when the leg is straight, the muscle - tendon unit is already stretched. The patellar reflex is a stretch reflex, and when pre - stretched, the muscle spindles may not be able to detect additional stretch stimuli effectively. For the second question, the patellar reflex helps to quickly adjust muscle length and tension. When a sudden force tries to over - stretch the quadriceps muscle (e.g., tripping), the reflex contraction of the quadriceps helps to prevent excessive knee bending or falling, thus protecting the knee joint and maintaining balance.

Answer:

1. When the leg is straight, the muscle - tendon unit is pre - stretched and muscle spindles may not detect additional stretch for the reflex.
2. It helps maintain balance and protect the knee joint by quickly contracting the quadriceps in response to over - stretching stimuli.