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==Types of neurotransmitter==

==Types of neurotransmitter==

===Small-molecule Neurotransmitters===

===Small-molecule Neurotransmitters===

There are two major sub-groups of SMTs; '''amino acids''' and '''biogenic amines'''.  

There are two major sub-groups of SMTs; '''amino acids''' and '''biogenic amines'''. All SMTs play an important role within the central nervous system with the exception of acetylcholine and norepinephrine which both are important within the peripheral nervous system.

====Amino Acids===

====Amino Acids====

'''Amino acid glutamate''' is the most common excitatory SMT in the [[Nervous_and_Special_Senses_-_Anatomy_%26_Physiology#Central_Nervous_System_.28CNS.29|central nervous system]] whilst '''gamma-aminobutyric acid (GABA)''' is the most common inhibitory SMT. Other amino acid SMTs include '''aspartate''' and '''glycine'''.

'''Amino acid glutamate''' is the most common excitatory SMT in the [[Nervous_and_Special_Senses_-_Anatomy_%26_Physiology#Central_Nervous_System_.28CNS.29|central nervous system]] whilst '''gamma-aminobutyric acid (GABA)''' is the most common inhibitory SMT. Other amino acid SMTs include '''aspartate''' and '''glycine'''.

====Biogenic Amines====

====Biogenic Amines====

Biogenic amines are synthesised from only several types of amino acids and dependant on which amino acids are used in their formation depends on their classification. Biogenic amines that are derived from the amino acid tyrosine are classified as '''catecholamines''' and include the SMTs '''norepinephrine''' (noradrenaline), '''epinephrine''' (adrenaline) and '''dopamine'''. The biogenic amines that is dervied from the amino acid '''tryptophane''' is called '''serotonin (5-HT)''' whilst the SMT derived from '''histidine''' is called '''histamine'''.  

Biogenic amines are synthesised from only several types of amino acids and dependant on which amino acids are used in their formation depends on their classification. Biogenic amines that are derived from the amino acid tyrosine are classified as '''catecholamines''' and include the SMTs '''norepinephrine''' (noradrenaline), '''epinephrine''' (adrenaline) and '''dopamine'''. Adrenergic neurons release norepinephrine. The biogenic amines that is dervied from the amino acid '''tryptophane''' is called '''serotonin (5-HT)''' whilst the SMT derived from '''histidine''' is called '''histamine'''. Serotonergic neurons release serotonin. Whilst these SMTs are primarily of importance in the central nervous system, norepinephrine is predominantly found in the peripheral nervous system. 

====Other SMTs====

====Other SMTs====

Other common SMTs include '''acetylcholine''' (ACh) and '''nitric oxide'''. Ach is the most common excitatory neurotransmitter in the peripheral nervous system.

Other common SMTs include '''acetylcholine (ACh)''', '''ATP''' and '''nitric oxide'''. Ach is the most common excitatory neurotransmitter in the peripheral nervous system. Cholinergic neurons release ACh and for example, are found in the [[Muscles_-_Anatomy_%26_Physiology#Neurogenic_Contraction|neuromuscular junction]]. ATP, as well as having many important intracellular functions, is an important neurotransmitter and also has an autocrine and paracrine function. All synaptic vesicles released by the terminal membrane of a nerve contain ATP as well as other neurotransmitters, although ATP can only function as a neurotransmitter in it's own right if the post-synpatic terminal membrane contains ATP receptors. These ATP receptors are referred to as '''purinergic receptors'''. A pre-synaptic nerve terminal or terminal membrane never releases multiple types of SMT in addition to ATP, although it is common that neuropeptides are released in addition to ATP and SMTs.  

These include:

These include: