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.
Adrenaline is the original name for what we now call epinephrine. Stimulation of the adrenal medulla by the sympathetic nervous system causes the secretion of both epinephrine (E) (80%) and norepinephrine (NE)(20%) into circulation. Epinephrine is a hormone; norepinephrine is both a hormone and a neurotransmitter.lpha 2 Receptors. Alpha 2 receptors are located on secretory terminals of some postsynaptic adrenergic neurons. When these terminals secrete norepinephrine the neurotransmitter binds with these receptors as well as with adrenergic receptors on the other side of the synapse.