Changes

Although NO is a neurotransmitter, it's characteristics differ from those discussed above. NO relies on calcium ion activation of the enzyme '''nitric oxide synthase (NOS)''' which is found throughout the nervous system and is the enzyme that is responsible for catalysing NO from the amino acid '''L-arginine'''. NO has a very short half life and is highly reactive. It is able to pass easily through lipid membranes. What makes NO differ from the SMTs above is that is can be released in all directions rather than pre-synaptically as per the classical SMTs. Therefore NO is able to act as a signalling pathway for the post-synaptic neuron to affect the pre-synpatic neuron.  

Although NO is a neurotransmitter, it's characteristics differ from those discussed above. NO relies on calcium ion activation of the enzyme '''nitric oxide synthase (NOS)''' which is found throughout the nervous system and is the enzyme that is responsible for catalysing NO from the amino acid '''L-arginine'''. NO has a very short half life and is highly reactive. It is able to pass easily through lipid membranes. What makes NO differ from the SMTs above is that is can be released in all directions rather than pre-synaptically as per the classical SMTs. Therefore NO is able to act as a signalling pathway for the post-synaptic neuron to affect the pre-synpatic neuron.  

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===Neuropeptides===

===Neuropeptides===

The neuropeptide group of neurotransmitters contain a wide range of molecules of which only the major transmitters are included below. These include; '''enkephalin''', '''subtance P''', '''LHRH''', '''Vasopressin''', '''cholecystokinin/CKK''', '''Vasoactive Intesinal Peptide (VIP)''', '''endorphin''', '''neurotensin''', '''TRH''', '''angiotensin-II''', '''somatostatin''' and '''oxytocin'''. These neuropeptides have a wide range of effects throughout the nervous system. Many of these neuropeptides are released from nerve terminals but also as hormones from endocrine cells. Cholecystokinin is an example of a neuropeptide that acts as both a neuropeptide but also as a hormone.

The neuropeptide group of neurotransmitters contain a wide range of molecules of which only the major transmitters are included below. These include; '''enkephalin''', '''subtance P''', '''LHRH''', '''Vasopressin''', '''cholecystokinin/CKK''', '''Vasoactive Intesinal Peptide (VIP)''', '''endorphin''', '''neurotensin''', '''TRH''', '''angiotensin-II''', '''somatostatin''' and '''oxytocin'''. These neuropeptides have a wide range of effects throughout the nervous system. Many of these neuropeptides are released from nerve terminals but also as hormones from endocrine cells. Cholecystokinin is an example of a neuropeptide that acts as both a neuropeptide but also as a hormone.