Classification, Receptors, Functions, and Clinical Significance
Molecular Categories: Blue border = Small molecules | Orange border = Large molecules | Teal border = Gaseous molecules
Advanced Concepts: Neurotransmission involves classical synaptic transmission, volume transmission (extrasynaptic diffusion), and glial cell modulation of synaptic activity
| Neurotransmitter | Type/Effect | Primary Locations | Receptors | Precursor | Primary Functions | Size |
|---|---|---|---|---|---|---|
| SMALL MOLECULES | ||||||
| Acetylcholine (ACh) | Excitatory | Neuromuscular junctions, CNS, Parasympathetic nervous system | Nicotinic, Muscarinic | Choline + Acetyl CoA | Muscle control, memory formation, parasympathetic response, skeletal muscle contraction | Small |
| Dopamine | Modulatory | Hypothalamus, Substantia nigra, Ventral tegmental area | D1, D2, D3, D4, D5 | Tyrosine | Reward pathways, motivation, motor control, cognition, voluntary motion | Small |
| Norepinephrine | Excitatory | Adrenal medulla, Locus coeruleus, Sympathetic nervous system | α and β adrenergic | Dopamine (via tyrosine) | Fight or flight response, arousal, attention, mood, increased heart rate and blood pressure | Small |
| Epinephrine | Excitatory | Adrenal medulla, Some CNS regions | α and β adrenergic | Norepinephrine | Sympathetic response, stress response, emergency situations | Small |
| Serotonin (5-HT) | Mixed | Gut (90%), CNS (Raphe nuclei), Platelets | 5HT₁, 5HT₂, 5HT₃, 5HT₄, 5HT₅, 5HT₆, 5HT₇ | Tryptophan | Mood regulation, appetite, sleep, anxiety, intestinal movement, muscle control | Small |
| Histamine | Excitatory | Hypothalamus, Mast cells, Basophils | H₁, H₂, H₃, H₄ | Histidine | Inflammatory response, wakefulness, arousal, allergic reactions | Small |
| Glutamate | Excitatory | CNS (widespread), Peripheral nervous system | NMDA, AMPA, Kainate, mGluR | Glutamine | Main excitatory neurotransmitter, long-term potentiation, memory, learning | Small |
| GABA | Inhibitory | Brain (widespread), Spinal cord | GABA_A, GABA_B | Glutamate | Main inhibitory neurotransmitter, muscle tone regulation, anxiety reduction | Small |
| Glycine | Inhibitory | Spinal cord, Brainstem, Retina | Glycine (GlyR), NMDA (co-agonist) | Serine | Main spinal cord inhibitory neurotransmitter, motor control, sensory processing | Small |
| L-DOPA | Precursor | Hypothalamus, Substantia nigra | N/A | Tyrosine | Precursor to dopamine, crosses blood-brain barrier | Small |
| Tryptophan | Precursor | Blood, Dietary sources | N/A | Essential amino acid | Precursor to serotonin, dietary essential | Small |
| Tyramine | Modulatory | CNS, Kidneys, Sympathetic terminals | TA1 (TAAR1) | Tyrosine | Blood pressure regulation, minor neurotransmitter | Small |
| LARGE MOLECULES (NEUROPEPTIDES) - Often act as neuromodulators with slower, longer-lasting effects | ||||||
| Endorphins | Mixed | Hypothalamus, Pituitary, Spinal cord | μ, κ, δ opioid receptors | Amino acids | Analgesia, euphoria, stress response, natural pain relief (slow neuromodulatory effects) | Large |
| Substance P | Excitatory | Spinal cord, Brain, Sensory neurons | Neurokinin (NK₁) | Amino acids | Pain transmission, inflammation, stress response (neuromodulatory action) | Large |
| ATP | Excitatory | Widespread CNS and PNS | P2X, P2Y purinergic | ADP | Cellular energy, neurotransmission, pain signaling | Large |
| GASEOUS MOLECULES | ||||||
| Nitric Oxide (NO) | Modulatory | Widespread CNS, Vascular endothelium | Soluble guanylate cyclase (sGC) | L-Arginine | Smooth muscle dilation, immune response, neurotransmitter modulation | Gas |