NEUROTRANSMITERS

There are billions of neurons in our brain. Neurons do not touch, even if they are very close to each other. This gap between two neurons is called a synapse. Therefore, the number of synapses in our brain reaches trillions. This gap is of great importance because synapses allow two nerve cells to transmit signals between them. This transmission proceeds from the axon of one neuron in the direction of the dendrite of the other neuron.
Chemicals called neurotransmitters are of great importance in the transmission of information between neurons. These chemicals provide communication with signals between neurons or between neurons and cells. They are released from the nucleus called Medial Septal Nucleus in the brain stem. Each neurotransmitter travels in a unique way and reaches its own receptor. In order for a released neurotransmitter to do its job, it must bind to protein receptors on the receiving neuron. At this point, if the receptor is a lock, the neurotransmitter is the key to this lock.
Neurotransmitters are either excitatory or inhibitory.

THERE ARE 4 CRITERIA FOR A CHEMICAL TO BE A NEUROTRANSMITTER:
1. It must be synthesized or contained within the neuron.
2. When the neuron becomes active, it should be released from the neuron and create an action and response in the opposite neuron.
3. The response it creates in the opposite neuron should be proven in the experimental field.
4. There must be a mechanism to ensure that it is retrieved after its mission is over.

SMALL MOLECULAR NEUROTRANSMITTERS
Acetylcholine (ACh)
Amines
catecholamines

      Dopamine (DA) Noradrenaline (NA) Adreanline
- Serotonin (5-HT)

Amino Acids
- Glutamate (Glu)
- Gamma-Aminobutyric Acid (GABA)

Acetylcholine (ACh)
• It is the first neurotransmitter found. It is considered on its own as it does not fit into other structural classifications. It plays a key role for the neuromuscular junction and some synapses. It is important for both the central and peripheral nervous systems. memory and learning in the central nervous system; In the peripheral nervous system, it is effective in sending messages to the muscles and glands.
• Linked to Alzheimer's disease.
• Like serotonin and dopamine, it is not transported back into the cell. After use, it is broken down and recycled by the enzyme Acetylcholinesterase.
• Some toxins, such as Botulinum Toxin, prevent the acetylcholinesterase enzyme from working. Failure of acetylcholinesterase to work causes muscle problems. Therefore, Botulinum Toxin has effects such as paralysis, cessation of breathing, cardiac arrest and tremor.
• Acetylcholine has 2 types of receptors. These receptors get their name from their Agonists, which perform the same function.
1. Muscarinic Receptors
- It is found in a mushroom.
- It affects the intracellular signaling mechanism.
- Depending on its type, it sends a warning and stop signal to the cell.

2. Nicotinic Receptor
- It is found in tobacco.
- Ligand-gated ion channel. When acetylcholine binds to this channel, sodium, potassium and calcium ions enter the cell.
- Found in neurons and muscles.

• Cholinergic System and Cognition
- There are 2 types of systems:
1. Sympathetic Nervous System: "Fight or Flight"
2. Parasympathetic Nervous System: “Nutrition and Urea” – “Rest and Digest”
- Cholinergic system is another name for Parasympathetic Nervous System. The main precursor of this system is Acetylcholine. It uses Acetylcholine while preparing the body to feed, rest, reproduce and digest.

Amines

• Dopamine (DA)
- It is necessary for basal ganglia to process.
- Produces intense feelings of pleasure. Excess secretion may cause Schizophrenia, under secretion may cause Parkinson's Disease.
- It is the main neurotransmitter of the Mesocorticolimbic System, which is an important part of the reward system and related to addiction.
- It is produced in two places:
1. Substantia Nigra (SN)
It is in the midbrain.
Responsible for reward and movement.
It is an important location for Parkinson's Disease.
It has a darker structure due to the amount of Melanin hormone in its structure.
2. Ventral Tegmental Area (VTA)
It is in the midbrain.
It produces neurons with cognitive function.
It has to do with pleasure, learning, motivation and drug addiction.

• Noradrenaline (NA)
- It is produced in the brain stem.
- A decrease or increase in its level affects the mental state. For example, low levels of noradrenaline can lead to depression.

• Adrenaline
- Produced by the adrenal glands.
- Prepares the organism for immediate action.

• Serotonin (5-HT)
- Affects mental state and social behavior.
- Antidepressants prevent Serotonin reuptake and keep Serotonin in the synapses.

• Catecholamines and Serotonin
- Catecholamines are produced by nervous tissue, brain and adrenal glands. They give the message of "Fight or Flight", which is the message of the Sympathetic Nervous System.

- There are 3 catecholamines:
1. Dopamine (DA)
2. Noradrenaline (NA)
3. Adrenaline

- Although these three catecholamines are produced in the same place, they differ as a result of biosynthesis.

- Biosynthesis
It is the reason for the main difference of catecholamines.
It ensures the survival, growth and development of the organism.
Its raw material is Tyrosine. The first place where Tyrosine emerges as an amino acid is the liver. It is important for healthy brain development.
In catecholamine biosynthesis, tyrosine is first sent to the brain. As a result of biosynthesis, Tyrosine is converted to Dopamine, Dopamine to Noradrenaline, and Noradreanline to Adrenaline.

Amino Acids
• Glutamate (Glu)
- It's a warning. It depolarizes the neuron from which it is released.
- Affects learning and memory.
- Disruption in transmission can lead to Schizophrenia.

• Gamma-Aminobutyric Acid (GABA)
- It is an important neurotransmitter with inhibitory effect.
- Benzodiazepine and similar antidepressant drugs have a calming effect thanks to the inhibition of GABA.
- Picrotoxin drug causes convulsions by closing GABA receptors.