A diagram of a leg stepping on a tack is indicated. The flow of signal is indicated by arrows. A diagram of the spinal cord with interneurons is indicated on the top. A diagram indicating the lifting the leg is indicated on the right. Reflex arc is explained in a sequence:
  1. Sensory receptors stimulate the sensory neurons.
  2. Sensory neurons transmit the impulse to interneurons in the spinal cord.
  3. The signal is then transferred to motor neuron.
  4. The motor neuron stimulates the muscle that lifts the leg.
The parts labeled in the diagram are:
  1. Sensory receptors
  2. Sensory neuron
  3. Interneuron
  4. Motor neuron
  5. Effector (responding muscle)
  6. Spinal cord