Neurotransmitter Systems: Diffuse Projections and Peripheral

Glutamate: most common excitatory neurotransmitter; distributed widely throughout the nervous system.
GABA: gamma-aminobutyric acid; main inhibitory transmitter in the brain.
Glycine: main inhibitory transmitter in the spinal cord.

Some neuronal groups project diffusely to large areas of the cortex, releasing specific neurotransmitters widely.
Reticular activating system (glutamate): brainstem reticular formation and parts of the thalamus project diffusely to the cortex; essential for consciousness.
Acetylcholine (ACh): basalis nucleus and septal nuclei (frontal lobe) send diffuse cortical projections releasing ACh.
Histamine: hypothalamus sends histaminergic projections to the cortex.
Norepinephrine (NE): locus coeruleus in the pons projects diffusely to the cortex.
Serotonin (5-HT): raphe nuclei (brainstem) project to the cortex and other targets; higher raphe nuclei contribute cortical serotonin.
Dopamine (DA): ventral tegmental area (VTA) in the midbrain projects diffusely to the cortex.

Substantia nigra (midbrain, near VTA) projects dopamine to the striatum (nigrostriatal pathway); important for motor control; dysfunction linked to Parkinson’s disease.
Dopaminergic neurons in the hypothalamus project to the pituitary (tuberoinfundibular pathway) regulating pituitary hormone release.

Acetylcholine: main neurotransmitter at the neuromuscular junction (lower motor neurons) and in most autonomic nervous system (ANS) neurons.
Norepinephrine: used by a subset of ANS neurons (often sympathetic).

Broadly distributed transmitters support many functions; discrete diffuse projection systems modulate cortex and higher functions (cognition, emotion, consciousness).
Parkinsonian symptoms relate to dopaminergic loss in the nigrostriatal pathway; diffuse systems are common targets of psychoactive medications.
Autonomic nervous system relies largely on ACh (with some NE involvement) for peripheral control.