During anesthesiology class, we always talk about how the drug goes into the CNS, thereby produce pharmacological effect on the brain by reducing some of the neurotransmitter receptor in order to function. Then I started to think, animal and humans have a lot of neurotransmitters which play many important roles maintaining body system, and who are they??
Ps: Just a basic physiology nervous system revision
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NEUROTRANSMITTER
Neurotransmitters are the chemicals responsible for signal transmission between the individual neurons. Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies. 50 or more neurotransmitters have been identified. It is classified by chemical structure and by function.
Criteria to Classify a Biochemical Substance as Neurotransmitter:
- Substance must be present in the pre-synaptic nerve terminal and packaged into synaptic vesicles ·
- The substance must be released from the nerve terminal upon arrival of action potential or depolarization of presynaptic membrane ·
- Specific receptors must be present on the post synaptic membrane for the substance
Life cycle of a neurotransmitter
1.Synthesis of the transmitter
2.Packaging and storage in Synaptic vesicles
3.If necessary, transport from the site of synthesis to the site of release from the nerve terminal 4.Release in response to an action potential
5. Binding to postsynaptic receptor proteins
6.Termination of action by diffusion, destruction, or reuptake into cells.
Chemical classification of neurotransmitter
1. Acetylcholine
2. Biogenic amine
- Catecholamine: Dopamine, noreprinephrine (NE), and epinephrine (Epi)
- Indolamines
- Serotonin and dopamine
3. Amino acid
- GABA- Gammbaaminobutyric acid
- Glycine
- Aspartate
- Glutamate
4.Neuropeptidase
- Substance P
- Endorphines
- Somatostatin, gastrin, cholecystokinin, oxytoxin, vasopressin, leutanizing hormone releasing hormone
5. Purines
- Adenosine
- ATP
6. Gases and Lipid
- Nitric oxide
- Carbon monoxide
- Cannabinoids
Functional classification of neurotransmitter
1. Excitatory neurotransmitter
2.Inhibitory neurotransmitter
Below are some examples of neurotransmitter
Acetycholine
Acetylcholine (Ach) was the first neurotransmitter to be identified It is the most abundant neurotransmitter in the brain. Released at neuromuscular junctions and some ANS neurons Synthesized by enzyme choline acetyltransferaseDegraded by the enzyme acetylcholinesterase (AChE)
Formation and degradation of Ach
Acetylcholine has many functions: It is responsible for much of the stimulation of muscles, including the muscles of the gastro-intestinal system. It is also found in sensory neurons and in the autonomic nervous system (parasympathetic), and has a part in scheduling REM (dream) sleep.
Catecholamine
Catecholamines-Dopamine, norepinephrine (NE), and epinephrine are synthesized from Tyrosines involved in reward-pleasure and learning. Dopamine is the principle neurotransmitter involved in Addiction pathway
1. Norephrineprine
Norepinephrine is strongly associated with bringing nervous systems into "high alert." It is prevalent in the sympathetic nervous system, and it increases our heart rate and our blood pressure. Adrenal glands release it into the blood stream, along with its close relative epinephrine (adrenalin). It is also important for forming memories.Stress tends to deplete our store of adrenalin, while exercise tends to increase it. Amphetamines ("speed") work by causing the release of norepinephrine, as well as other neurotransmitters called dopamine and seratonin.
2. Dopamine
Dopamine has many functions in the brain, including important roles in behavior and cognition, voluntary movement, motivation, punishment and reward, inhibition of prolactin production (involved in lactation and sexual gratification), sleep, mood, attention, working memory, and learning.
3. Serotonin
Serotonin is an inhibitory neurotransmitter that has been found to be intimately involved in emotion and mood. Too little serotonin has been shown to lead to depression, problems with anger control, obsessive-compulsive disorder, and suicide. Too little also leads to an increased appetite for carbohydrates (starchy foods) and trouble sleeping, which are also associated with depression and other emotional disorders. It has also been tied to migraines, irritable bowel syndrome, and fibromyalgia.
Broadly distributed in the brain, derived from Tryptophan involved in sleep, dreaming, hunger and arousal. Play roles in emotional behaviors and the biological clock. Depletion of serotonin in brain leads to depression.
4. GABA
GABA—Gamma-aminobutyric acid is the major inhibitory neurotransmitter in CNS synthesized from decarboxylation of Glutamate involved in regulating anxiety may be related to eating or sleep disorders
GABA acts like a brake to the excitatory neurotransmitters that lead to anxiety. People with too little GABA tend to suffer from anxiety disorders, and drugs like Valium work by enhancing the effects of GABA. Lots of other drugs influence GABA receptors, including alcohol and barbituates. If GABA is lacking in certain parts of the brain, epilepsy results.
5. Endorphins, Enkephalins and Substance P
Substance P is the mediator of pain signals. Endorphins and Enkephalins act as natural opiates; reduce pain perception. They also depress physical functions like breathing and may produce physical dependence.
Endorphin is short for "endogenous morphine." It is structurally very similar to the opioids (opium, morphine, heroin, etc.) and has similar functions: Inhibitory, it is involved in pain reduction and pleasure, and the opioid drugs work by attaching to endorphin's receptor sites. It is also the neurotransmitter that allows bears and other animals to hibernate.
6. Endocannabinoids
Endocannabinoids are lipid soluble; synthesized on demand from membrane lipids. Bind with G protein–coupled receptors in the brain. Involved in learning and memory.
7. Glutamate
Glutamate is an excitatory relative of GABA. It is the most common neurotransmitter in the central nervous system - as much as half of all neurons in the brain - and is especially important in regards to memory. Curiously, glutamate is actually toxic to neurons, and an excess will kill them. Sometimes brain damage or a stroke will lead to an excess and end with many more brain cells dying than from the original trauma. ALS, more commonly known as Lou Gehrig's disease, results from excessive glutamate production. Many believe it may also be responsible for quite a variety of diseases of the nervous system, and are looking for ways to minimize its effects
Neurotransmitter effects may be excitatory (depolarizing) and/or inhibitory (hyperpolarizing). Determined by the receptor type of the postsynaptic neuron.
- GABA and glycine are usually inhibitory.
- Glutamate is usually excitatory
- Acetylcholine-Excitatory at neuromuscular junctions in skeletal muscle
Neurotransmitter Actions
1. Direct action
- Neurotransmitter binds to channel-linked receptor and opens ion channels
- Promotes rapid responses
- Examples: ACh and amino acids
- Neurotransmitter binds to a G protein-linked receptor and acts through an intracellular second messenger
- Promotes long-lasting effects
- Examples: biogenic amines, neuropeptides, and dissolved gases
1. Channel-linked receptors
2. G protein-linked receptors
Channel-Linked (Ionotropic) Receptors
Ligand-gated ion channels. Action is immediate and brief. Excitatory receptors are channels for small cation. Na+ influx contributes most to depolarization. Inhibitory receptors allow Cl– influx or K+ efflux that causes hyperpolarization.
G Protein-Linked (Metabotropic) Receptors
Transmembrane protein complexes. Responses are indirect, slow, complex, and often prolonged and widespread. Examples: muscarinic ACh receptors and those that bind biogenic amines and neuropeptides
Sources: General psychology Dr C George Boeree
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