The stretch reflex is also known as a ______.

• A. Polysynaptic reflex
• B. Monosynaptic reflex
• C. Reciprocal reflex
• D. Disynaptic reflex

Answer: (B)

The stretch reflex is defined by a direct, one-synapse pathway in the spinal cord. When a muscle is stretched, sensory nerve fibers from the muscle spindle (Ia afferents) send a signal straight to the same muscle’s alpha motor neurons in the spinal cord, causing a quick contraction to resist the stretch. This single synapse between the sensory neuron and the motor neuron is what makes it monosynaptic, producing a rapid, automatic response without the involvement of interneurons. A knee-jerk is the classic example of this reflex. Other patterns require additional synapses or interneuronal relays—polysynaptic reflexes have multiple synapses, disynaptic would involve one interneuron, and reciprocal mechanisms relate to coordinated actions of opposing muscles but don’t define the stretch reflex itself.