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Autonomic Neurotransmitters and Receptors

Autonomic Neurotransmitters and Receptors - alpha types are...

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Autonomic Neurotransmitters and Receptors The different effects of the ANS depend upon 1) the neurotransmitters released by the neurons and 2) the receptors expressed by the target organ. Neurotransmitters The two major neurotransmitters used by the autonomic nervous system are acetylcholine and norepinephrine . All preganglionic neurons release ACh onto the postganglionic dendrites and cell bodies. However, the sympathetic nervous system primarily releases NE from the postganglionic neuron onto the target organ while the parasympathetic postganglionic neurons release ACh. Receptors While there are only two neurotransmitters used by the ANS, there are several types of receptors for each NT, resulting in lots of different effects on the targets. Norepinephrine binds two main types of receptors known as the alpha adrenergic receptor and the beta adrenergic receptor. Within these two classes are several subtypes: alpha-1, alpha-2, beta-1, and beta-2. Generally, the
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Unformatted text preview: alpha types are excitatory while the beta subtypes are inhibitory. In the autonomic nervous system, acetylcholine also binds two types of receptors, the nicotinic acetylcholine receptors and the muscarinic acetylcholine receptors . The nAChR are the familiar type of ACh receptors that are also sodium ion channels and are found on all of the neuronal cell bodies and dendrites in the autonomic ganglia (and at neuromuscular junctions in skeletal muscle). When ACh binds to nAChRs, Na + enters the cell and causes an excitatory depolarization. Thus, nAChRs are excitatory in nature and cause the postganglionic cell to fire an action potential and release NT from its terminal (onto the target). The second type of ACh receptors, the muscarinic receptors, have several subtypes and can be either excitatory or inhibitory. These receptors are found on the glands, smooth muscles and cardiac muscle cells that receives cholinergic innervation....
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