Is Acetylcholine Excitatory or Inhibitory?
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Synapse is a structure that enables the neuron to pass electrical or chemical signal to another neuron or other cells like muscle cell. Synapse is a tiny gap or cleft that can be found between the presynaptic membrane that send information and postsynaptic membrane that receive the information. There are different types of synapses such as axodendritic, axosomatic, axoaxonal and dendrodendritic. Basically, these synapses can be classified into electrical and chemical synapses. Electrical synapse transfers the current through an intercellular channel, the gap junction. The structure of gap junction allows passive transfer of the current whereby the action potential is generated due to the fluctuations in postsynaptic potential. The chemical synapse involves the release of neurotransmitter from the presynaptic membrane to postsynaptic cell as the space between the pre- and post-synaptic neurons is much bigger than that for electrical synapse. The transfer of synapse is recognized as one way conduction in which the synapse impulse only pass through the presynaptic membrane toward the postsynaptic membrane and it will never happen in the reverse direction as the receptor of neurotransmitter can only be found on the postsynaptic membrane. Unlike the other synapses, non-channel synapses comprise of membrane-bound enzymes instead of channel to be the neuroreceptor. When the neurotransmitters bind to the receptor, a series of chemical reaction will be triggered inside the cell. These synapses are usually involved in slow and long-lasting responses. Neuromuscular junctions are the synapses the found between motor neurons and muscle cells connecting the nervous system to muscular system.
Here we identify actions of cholinergic signaling on cellular and synaptic properties of neurons in several brain areas and discuss the consequences of this signaling on behaviors related to drug abuse, attention, food intake, and affect. The diverse effects of acetylcholine depend on the site of release, the receptor subtypes, and the target neuronal population, however, a common theme is that acetylcholine potentiates behaviors that are adaptive to environmental stimuli and decreases responses to ongoing stimuli that do not require immediate action. The ability of acetylcholine to coordinate the response of neuronal networks in many brain areas makes cholinergic modulation an essential mechanism underlying complex behaviors.Acetylcholine (ACh) is a fast-acting, point-to-point neurotransmitter at the neuromuscular junction and in the autonomic ganglia; however, there are fewer demonstrations of similar actions in the brain (Changeux, 2010). Instead, central cholinergic neurotransmission predominantly changes neuronal excitability, alters presynaptic release of neurotransmitters, and coordinates the firing of groups of neurons (Kawai et al., 2007).
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