The finger had been pricked by a thorn which is the stimulus.
Pain receptors in the person's hand are stimulated releasing impulses
Impulses travel along the sensory neurone to the Central Nervous System (brain / spinal cord)
Impulses are passed along a relay neurone (which is in the CNS), via a synapse. information crosses this gap using neurotransmitters rather than electrical impulses. one neurone releases neurotransmitters into the synapse. these then diffuse across the gap and make the other neurone transmit an electrical impulse
Impulses travel along a motor neurone via a synpase which carries the impulses to the effector
When impulses reach effector muscles they contract and carry out the response of moving finger from thorn. Many factors can affect the rate of impulse movement such as: - the strength of the myelin sheath - diameter of the axon (the larger the axon the faster the movement) - temperature (the higher the temperature the faster the rate)