Question

multiple-choice question
what causes muscles to contract and relax?
signals from brain down the motor neurons
motor neurons attached to the spinal cord and muscles
sensory neurons from the brain
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Explanation:

To determine what causes muscles to contract and relax, we analyze each option:

• Option 1: Signals from the brain travel down motor neurons to muscles, triggering contraction/relaxation. This aligns with how the nervous system controls muscle movement.
• Option 2: Motor neurons' attachment to the spinal cord and muscles doesn't explain the cause of contraction/relaxation (it's about structure, not the triggering signal).
• Option 3: Sensory neurons transmit information to the brain (e.g., touch, pain), not from the brain to cause muscle movement (motor neurons do that).

Answer:

A. signals from brain down the motor neurons