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Neurotransmitters - Anatomy & Physiology (view source)
Revision as of 16:02, 11 November 2011
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===Other SMTs===
Other common SMTs include acetylcholine, ATP and nitric oxide.
Other common SMTs include acetylcholine, ATP and nitric oxide.
'''Acetylcholine (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 & Physiology#Neurogenic Contraction|neuromuscular junction]]. When ACh is released, it facilitates the opening of sodium channels within the post-synaptic membrane allowing sodium ions to enter the membrane and causing depolarisation. Therefore ACh makes it easier for the cell to reach its depolarisation threshold and generate an action potential. ACh has an effect on the post-synaptic membrane in skeletal muscle via '''nicotinic receptors''', which are ionotropic (see below). ACh also exerts an effect on smooth muscle via the parasympathetic nervous system via '''muscarinic receptors''', which are metabotropic (see below).
'''Acetylcholine (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 & Physiology#Neurogenic Contraction|neuromuscular junction]]. When ACh is released, it facilitates the opening of sodium channels within the post-synaptic membrane allowing sodium ions to enter the membrane and causing depolarisation. Therefore ACh makes it easier for the cell to reach its depolarisation threshold and generate an action potential. ACh has an effect on the post-synaptic membrane in skeletal muscle via '''nicotinic receptors''', which are ionotropic (see below). ACh also exerts an effect on smooth muscle via the parasympathetic nervous system via '''muscarinic receptors''', which are metabotropic (see below).
Ach is primarily involved in skeletal muscle movement within the sympathetic nervous system and visceral movements as part of the parasympathetic nervous system. When binding to '''muscarinic''' receptors, ACh can have a number of different effects dependant on the type of receptor.
:If an '''M2''' receptor is bound this will result in hyperpolarisation of the cell and a slowing of the rate of spontaneous contraction of the heart.
:If an '''M3''' or an '''M5''' receptor is bound this will result in depolarisation of the cell and contraction of smooth muscle within glands.
'''Adenosine triphosphate (ATP)''', as well as having many important '''intracellular functions''', is an important neurotransmitter and also has an '''autocrine''' and '''paracrine''' function. ATP belongs to the '''purines''' SMT group. 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 its own right if the post-synaptic 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. Other SMTs within the purine group include '''Guanosine triphosphate (GTP)''' and their derivatives.
'''Adenosine triphosphate (ATP)''', as well as having many important '''intracellular functions''', is an important neurotransmitter and also has an '''autocrine''' and '''paracrine''' function. ATP belongs to the '''purines''' SMT group. 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 its own right if the post-synaptic 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. Other SMTs within the purine group include '''Guanosine triphosphate (GTP)''' and their derivatives.
Although '''nitric oxide (NO)''' is a neurotransmitter, its 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 '''nitric oxide (NO)''' is a neurotransmitter, its 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. Nitrous oxide is involved in enlargement of the genital organs leading to erection.
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