Neuromodulators and Neurotransmitters
The brain’s nerves are not in direct contact with one another, and the synapse between each nerve regulates functioning through a burst of chemicals called neurotransmitters and neuromodulators, each of which has a specific task.
Neurotransmitters are similar to traffic lights that signal electrical impulses to stop (inhibit) or go (activate), controlling whether the impulses continue. Neurotransmitters allow the movement of information across the synapses, or gap, between a neuron and an adjacent neuron. A neurotransmitter functions similarly to a traffic light, or a driver putting their foot on either the accelerator or the brake in a car.
Neuromodulators are chemicals that do not directly activate or inhibit: rather, they are similar to police officers controlling traffic at busy intersections, overseeing a gradual flow of traffic in all directions. Neuromodulators work together with neurotransmitters, enhancing the excitatory (“go” or “go with caution”) or inhibitory (“stop” or “slow down”) responses of the receptors.
A neuromodulator is a messenger released from a neuron in the central nervous system, or in the periphery, that affects groups of neurons, or effector cells that have the appropriate receptors. Major Neuromodulators in the central nervous system include dopamine, serotonin, acetylcholine, histamine, and norepinephrine. Each has specific function.
Serotonin (Serotonin System)
Over 90% of the body’s serotonin is found in the gastrointestinal tract where it has a role in regulating bowel function and movements. It also plays a part in reducing the appetite while consuming a meal.
With this said, it is most well-known for its role in the brain where it plays a major part in mood, anxiety and happiness.
- Influences sustained arousal
- Not tied to sensory input
- Widespread effect on arousal, sensory perception, emotion and higher cognitive function
- Regulation of pain threshold
- Controls feelings of well-bring, not pleasure
- Affected by SSRI’s (Prozac-type antidepressants).
Dopamine (Dopamine System)
Dopamine is centrally involved in reward, approach behavior, exploration, and various aspects of cognition. Variations in this neuromodulator function appear to be associated with variations in personality. This results in changes in relatively stable patterns of behavior, motivation, emotion, and cognition that differ among individuals. No concrete evidence exists concerning its role in personality, and it has been implicated in traits ranging from extraversion to aggression to intelligence to schizotypy.
- Limited cortical and subcortical projections
- Projections to frontal cortex involved in control of direct attention
- Stronger projections to left hemisphere
- Mediates attention to important sensory input
- Projection to limbic system involved in experiencing pleasure
- Role in action of all addictive drugs
- Projections to basal ganglia involved in control of movement and motor readiness
- Internal control of sustained attention.
Norepinephrine is a neurotransmitter that is important for attentiveness, emotions, sleeping, dreaming, and learning. Norepinephrine is also released as a hormone into the blood, where it causes blood vessels to contract and heart rate to increase. Norepinephrine plays a role in mood disorders such as manic depression.
Released by Neurons it:
- Controls wakefulness, alertness, orienting to change and new stimuli
- Active startle response
- Enhances emotional memory storage
- Stronger projections to right hemisphere
- Phasic arousal, rapidly habituates
- Mediates external sensory attention and arousal
- Enhances emotional memory storage.
Internal and External Stressors
The Stress Response
An important phase of the body’s response to stressful stimuli takes place along the so-called HPA (hypothalamic-pituitary-adrenal) axis. The hypothalamus produces the hormone CRF, which stimulates the pituitary to release ACTH. This hormone in turn stimulates the adrenal glands, which sit atop the kidney, to release the stress hormone cortisol. When we’re reacting to a fight-or-flight situation, cortisol increases the body’s energy supply. It also acts in a complex feedback loop to the hypothalamus to regulate production of CRF. If the HPA axis is chronically active, the overproduction of stress hormones can produce illness and depression.