Guyton:
Norepinephrine is secreted by the terminals of many
neurons whose cell bodies are located in the brain stem
and hypothalamus. Specifically, norepinephrine-secreting
neurons located in the locus ceruleus in the pons send
nerve fibers to widespread areas of the brain to help
control overall activity and mood of the mind, such as increasing the level of wakefulness. In most of these areas,
norepinephrine probably activates excitatory receptors,
but in a few areas, it activates inhibitory receptors instead.
Norepinephrine is also secreted by most postganglionic
neurons of the sympathetic nervous system, where it
excites some organs but inhibits others.
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Origins:
Norepinephrine is synthesized and secreted by adrenergic neurons.
These neurons have their cell bodies primarily in two regions:
Brain Stem: Specifically, in the locus ceruleus (LC), which is part of the pons.
Hypothalamus: The hypothalamus orchestrates various physiological processes, including stress responses and autonomic functions.
Functions of Norepinephrine:
Fight-or-Flight Response: Norepinephrine is a key player in the sympathetic nervous system. When faced with stress or danger, it prepares the body for action:
Increases heart rate and blood pressure.
Dilates pupils.
Mood Regulation: Norepinephrine is involved in mood modulation. Imbalances are associated with conditions like depression and anxiety.
Attention and Focus: Norepinephrine helps regulate attention and focus. It’s like the brain’s spotlight, directing cognitive resources where needed.
Memory Formation: Norepinephrine influences memory consolidation, especially during emotionally charged events.
Wakefulness and Arousal: LC neurons fire more actively during wakefulness and less during sleep.
