Neurotransmitters

Neurotransmitters

molecules synthesized by a neuron, released when a nerve

signal reaches an axon terminal, have a specific effect on physiology

Acetylcholine (ACh)

Neuromuscular junctions, most synapses of autonomic nervous system, retina, and many parts of the brain; excites skeletal muscle, inhibits cardiac muscle, and has excitatory or inhibitory effects on smooth muscle and glands depending on location

Glutamate (AA)

cerebral cortex and brainstem; accounts for about 75% of all excitatory synaptic transmission in the brain; involved in learning and memory

Aspartate (AA)

spinal cord; effects similar to those of glutamate

Glycine (AA)

inhibitory neurons of the brain, spinal cord, and retina; most common inhibitory neurotransmitter in the spinal cord

GABA (AA)

thalamus, hypothalamus, cerebellum, occipital lobes of cerebrum, and retina; the most common inhibitory neurotransmitter in the brain

Norepinephrine (monoamines)

sympathetic nervous system, cerebral cortex, hypothalamus, brainstem, cerebellum, and spinal cord; involved in dreaming, waking, and mood; excites cardiac muscle; can excite or inhibit smooth muscle and glands depending on location

Epinephrine (monoamines)

hypothalamus, thalamus, spinal cord, and adrenal medulla; effects similar to those of norepinephrine

Dopamine (monoamines)

hypothalamus, limbic system, cerebral cortex, and retina; highly concentrated in substantia nigra of midbrain; involved in elevation of mood and control of skeletal muscle

Serotonin (monoamines)

hypothalamus, limbic system, cerebellum, retina, and spinal cord; also secreted by blood platelets and intestinal cells; involved in sleepiness, alertness, thermoregulation, mood, and behavior; over 95% of the body’s serotonin is made by intestinal bacteria

Histamine (monoamines)

hypothalamus; also a potent vasodilator released by mast cells of connective tissue and basophils of the blood

Substance P (neuropeptides)

basal nuclei, midbrain, hypothalamus, cerebral cortex, small intestine, and pain receptor neurons; mediates pain transmission

Enkephalins (neuropeptides)

hypothalamus, limbic system, pituitary, pain pathways of spinal cord, and nerve endings of digestive tract; act as analgesics (pain relievers) by inhibiting substance P; inhibit intestinal motility; modulate immune responses

B-endophins (neuropeptides)

digestive tract, spinal cord, and many parts of the brain; also secreted as a hormone by the pituitary gland; suppresses pain; secretion rises sharply during labor and delivery in response to other situations

Cholecystokinin (neuropeptides)

cerebral cortex and small intestine; suppresses appetite