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.
Like the postganglionic neurons of the sympathetic ganglia, cells in the adrenal medulla release norepinephrine (but they also release epinephrine). In this case, epinephrine and norepinephrine are considered hormones because they are released to the circulation.However they both bind to adrenergic receptors, and thus have much the same physiological effects as sympathetic neural stimulation.n this case, epinephrine and norepinephrine are considered hormones because they are released to the circulation. However they both bind to adrenergic receptors, and thus have much the same physiological effects as sympathetic neural stimulation.