The muscles of the back contract to straighten so that you sit at a more erect posture and subsequently the muscles are suddenly stretched as you nod off. Which of the following best represents the sequence of events when you start to nod off? (1) Muscles of the back are stretched.(2) The muscle spindle is stretched.(3) Action potentials in sensory neurons of the muscle spindles increase.(4) Action potentials in alpha motor neurons of skeletal muscle fibers increase.(5) Skeletal muscle of the back contract.Multiple Choice1, 2, 3, 4, 51, 5, 2, 3, 41, 5, 3, 2, 45, 2, 3, 4, 14, 5, 3, 2, 1

The correct sequence of events when you start to nod off is: 1, 2, 3, 4, 5.

Here's why:

1. Muscles of the back are stretched: This happens when you start to nod off and your posture changes, causing the muscles in your back to stretch.

2. The muscle spindle is stretched: Muscle spindles are sensory receptors within the belly of a muscle, which primarily detect changes in the length of this muscle. They convey length information to the central nervous system via sensory neurons. So, when the muscles of the back are stretched, the muscle spindle is also stretched.

3. Action potentials in sensory neurons of the muscle spindles increase: When the muscle spindle is stretched, it triggers an increase in action potentials in the sensory neurons of the muscle spindles.

4. Action potentials in alpha motor neurons of skeletal muscle fibers increase: The increased action potentials in the sensory neurons of the muscle spindles then cause an increase in action potentials in the alpha motor neurons of the skeletal muscle fibers.

5. Skeletal muscle of the back contract: Finally, the increased action potentials in the alpha motor neurons cause the skeletal muscles of the back to contract, which straightens the back and brings you back to a more erect posture.