The head of a Roman snail, four tentacles well visible. [RN] Observing a snail crawling around, the view is immediately attracted by its head, orienting itself in its surroundings using the tentacles. The snail feels its environment, touches an obstacle and withdraws the tentacle.
Norepinephrine is a neurotransmitter secreted by neurons in the sympathetic nervous system. This chemical is secreted in response to stress, which triggers the 'fight or flight response.' The release of norepinephrine causes several changes that help our body to work more efficiently.
Epinephrine vs Norepinephrine. Both Epinephrine and Norepinephrine are similar chemical messengers released by adrenal medulla. Both of these messengers belong to the chemical class of catecholamine, which are derived from an amino acid called tyrosine.