CNS

I. Central Nervous System (CNS) Neurotransmitters

These are primarily found in the brain and spinal cord.

Neurotransmitter	Main Locations	Functions	Notes / Disorders
Glutamate	Cerebral cortex, hippocampus, spinal cord	Major excitatory neurotransmitter in CNS	Too much → seizures, excitotoxicity
GABA (γ-aminobutyric acid)	Cerebral cortex, cerebellum, spinal cord	Major inhibitory neurotransmitter in CNS	Too little → anxiety, seizures
Glycine	Brainstem, spinal cord	Inhibitory in spinal cord	Blocked by strychnine → convulsions
Dopamine (DA)	Substantia nigra, ventral tegmental area (VTA), hypothalamus	Reward, movement, motivation	Deficiency → Parkinson’s; excess → schizophrenia
Serotonin (5-HT)	Raphe nuclei (brainstem) → projects widely to cortex, limbic system, spinal cord	Mood, sleep, pain, appetite	Low → depression; high → serotonin syndrome
Norepinephrine (NE)	Locus coeruleus (pons) → cortex, limbic system, spinal cord	Alertness, attention, mood	Deficiency → depression; excess → anxiety, hypertension
Epinephrine (adrenaline)	Medulla (small amount in CNS)	Fight or flight (CNS and periphery)	Often acts as hormone more than neurotransmitter
Acetylcholine (ACh)	Basal forebrain (nucleus basalis), brainstem, neuromuscular junction	Learning, memory, muscle contraction	Low → Alzheimer’s; blocked in myasthenia gravis
Histamine	Tuberomammillary nucleus (hypothalamus)	Arousal, wakefulness, appetite	Blocked by antihistamines → drowsiness
Endorphins / Enkephalins / Dynorphins	Hypothalamus, pituitary, limbic system	Natural opioids → pain relief, euphoria	Act on opioid receptors
Substance P	Spinal cord, hypothalamus	Pain transmission	Blocked by some analgesics

II. Peripheral Nervous System (PNS) Neurotransmitters

A. Somatic Nervous System

• Acetylcholine (ACh) → at neuromuscular junctions (motor neurons → skeletal muscle)

  • Causes muscle contraction.

B. Autonomic Nervous System (ANS)

Division	Preganglionic NT	Postganglionic NT	Receptors / Effectors
Sympathetic (SNS)	Acetylcholine	Norepinephrine (mainly)	Adrenergic receptors (α, β) → fight-or-flight
	Acetylcholine	Acetylcholine (in sweat glands)	Muscarinic receptors
Parasympathetic (PSNS)	Acetylcholine	Acetylcholine	Muscarinic receptors (M1–M5) → rest-and-digest
Adrenal medulla	Acetylcholine (preganglionic)	Epinephrine & Norepinephrine released into blood	Acts like sympathetic ganglion

III. Other / Modulatory Neurotransmitters

Neurotransmitter	Main Source / Area	Main Function
Nitric oxide (NO)	Diffuses from neurons	Vasodilation, learning, memory
Carbon monoxide (CO)	Brain, smooth muscle	Modulatory gas neurotransmitter
ATP / Adenosine	CNS and PNS	Energy signaling, sleep regulation
Cannabinoids (anandamide, 2-AG)	Widespread in brain	Appetite, pain modulation, memory

Summary by Function

Category	Examples	Effect
Excitatory	Glutamate, Acetylcholine	Stimulate neurons
Inhibitory	GABA, Glycine	Reduce neuron activity
Modulatory (neuromodulators)	Dopamine, Serotonin, NE, Histamine	Fine-tune brain activity
Neuropeptides	Endorphins, Substance P	Long-lasting effects