Final answer:
Muscle spindles are stretch receptors that detect muscle stretch and cause muscle contraction to maintain a constant length. Therefore, the correct option is 2.
Step-by-step explanation:
These specialised sensory receptors, known as muscle spindles, are found within skeletal muscles and are essential to the stretch reflex. They are made up of intrafusal muscle fibres, which are different from the extrafusal muscle fibres that cause muscle contraction.
Muscle spindles are sensitive to changes in muscle length, and when a muscle is stretched, they generate signals that are transmitted via sensory neurons to the spinal cord. This sets off a reflex response involving motor neurons, which causes the stretched muscle to contract, offering a quick and automatic means of maintaining posture and avoiding overstretching.
Therefore, the correct option is 2.
Your question is incomplete, most probably the complete question is:
stretch reflex receptors are called
multiple choice
- effectors.
- muscle spindles.
- sensory neurons.
- motor neurons.