Sandbox Reserved 475: Difference between revisions

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Acetylcholine receptor proteins are present in the peripheral nervous system (PNS) as well as the central nervous system (CNS) in humans and many organisms, including invertebrates. The function of the receptor follows a general mechanism to which it is applied to almost any organism with a nervous system, that relies on the firing action potentials of the neurons. The structure depicted to the right is a redering of the the nicotinic acetylcholine receptor extracted from [http://en.wikipedia.org/wiki/Marbled_electric_ray Torpedo marmorata], more commonly known as the Marbled Electric Ray. Specifically, it is extracted from the electric organ's tissue from within the organism.

Acetylcholine receptor proteins are present in the peripheral nervous system (PNS) as well as the central nervous system (CNS) in humans and many organisms, including invertebrates. The function of the receptor follows a general mechanism to which it is applied to almost any organism with a nervous system, that relies on the firing action potentials of the neurons. The structure depicted to the right is a redering of the the nicotinic acetylcholine receptor extracted from [http://en.wikipedia.org/wiki/Marbled_electric_ray Torpedo marmorata], more commonly known as the Marbled Electric Ray. Specifically, it is extracted from the electric organ's tissue from within the organism.<ref>Unwin N. (March 4, 2005). "Refined structure of the nicotinic acetylcholine receptor at 4A resolution". Journal of Molecular Biology 346 (4): 967–89. doi:10.1016/j.jmb.2004.12.031. PMID 15701510.</ref>

== '''Mechanism''' ==

The neurotransmitter acetylcholine binds ~~specifically~~ to the α-subunits in the ~~homeric receptor example~~.

The neuromuscular junction is the location where the neuron activates muscle to contract. This is a step in the '''excitation-contraction coupling''' of skeletal muscle.

#Action potential travels down the axon of the activated presynaptic neuron.

#Upon the arrival of an action potential at the presynaptic neuron terminal, voltage-gated calcium channels open and Ca2+ ions flow from the extracellular fluid into the presynaptic neuron's cytosol.

#This influx of Ca2+ causes neurotransmitter-containing vesicles to dock and fuse to the presynaptic neuron's cell membrane through '''SNARE''' proteins.

#Fusion of the vesicular membrane with the presynaptic cell membrane results in the emptying of the vesicle's contents ('''acetylcholine''') into the synaptic cleft, a process known as exocytosis.

#Acetylcholine diffuses into the synaptic cleft and binds to the '''nicotinic acetylcholine receptors''' bound to the motor end plate.

#These receptors are ligand-gated ion channels, and when they bind acetylcholine at the two specific subunits, it causes a conformational change to open and form the pore-like structure for the ion exchange to occur.

#Because of the differences in electrochemical gradients across the plasma membrane, more sodium moves in than potassium out, producing a local depolarization of the motor end plate known as an end-plate potential.

#This depolarization spreads across the surface of the muscle fiber and continues the excitation-contraction coupling to contract the muscle.

#The action of acetylcholine is terminated when the enzyme acetylcholinesterase degrades part of the neurotransmitter (producing choline and an acetate group) and the rest of it diffuses away.

#The choline produced by the action of acetylcholinesterase is recycled — it is transported, through reuptake, back into the presynaptic terminal, where it is used to synthesize new acetylcholine molecules.<ref>Dale Purves, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White (2008). Neuroscience. 4th ed.. Sinauer Associates. pp. 121–2. ISBN 978-0-87893-697-7.</ref>

Sandbox Reserved 475: Difference between revisions

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 <span style="font-size:110%">
-Acetylcholine receptor proteins are present in the peripheral nervous system (PNS) as well as the central nervous system (CNS) in humans and many organisms, including invertebrates. The function of the receptor follows a general mechanism to which it is applied to almost any organism with a nervous system, that relies on the firing action potentials of the neurons. The structure depicted to the right is a redering of the the nicotinic acetylcholine receptor extracted from [http://en.wikipedia.org/wiki/Marbled_electric_ray Torpedo marmorata], more commonly known as the Marbled Electric Ray. Specifically, it is extracted from the electric organ's tissue from within the organism.
+Acetylcholine receptor proteins are present in the peripheral nervous system (PNS) as well as the central nervous system (CNS) in humans and many organisms, including invertebrates. The function of the receptor follows a general mechanism to which it is applied to almost any organism with a nervous system, that relies on the firing action potentials of the neurons. The structure depicted to the right is a redering of the the nicotinic acetylcholine receptor extracted from [http://en.wikipedia.org/wiki/Marbled_electric_ray Torpedo marmorata], more commonly known as the Marbled Electric Ray. Specifically, it is extracted from the electric organ's tissue from within the organism.<ref>Unwin N. (March 4, 2005). "Refined structure of the nicotinic acetylcholine receptor at 4A resolution". Journal of Molecular Biology 346 (4): 967–89. doi:10.1016/j.jmb.2004.12.031. PMID 15701510.</ref>
 </span>
 == '''Mechanism''' ==
 <span style="font-size:110%">
-The neurotransmitter acetylcholine binds specifically to the α-subunits in the homeric receptor example.
+The neuromuscular junction is the location where the neuron activates muscle to contract. This is a step in the '''excitation-contraction coupling''' of skeletal muscle.
+#Action potential travels down the axon of the activated presynaptic neuron.
+#Upon the arrival of an action potential at the presynaptic neuron terminal, voltage-gated calcium channels open and Ca<sup>2+</sup> ions flow from the extracellular fluid into the presynaptic neuron's cytosol.
+#This influx of Ca<sup>2+</sup> causes neurotransmitter-containing vesicles to dock and fuse to the presynaptic neuron's cell membrane through '''SNARE''' proteins.
+#Fusion of the vesicular membrane with the presynaptic cell membrane results in the emptying of the vesicle's contents ('''acetylcholine''') into the synaptic cleft, a process known as exocytosis.
+#Acetylcholine diffuses into the synaptic cleft and binds to the '''nicotinic acetylcholine receptors''' bound to the motor end plate.
+#These receptors are ligand-gated ion channels, and when they bind acetylcholine at the two specific subunits, it causes a conformational change to open and form the pore-like structure for the ion exchange to occur.
+#Because of the differences in electrochemical gradients across the plasma membrane, more sodium moves in than potassium out, producing a local depolarization of the motor end plate known as an end-plate potential.
+#This depolarization spreads across the surface of the muscle fiber and continues the excitation-contraction coupling to contract the muscle.
+#The action of acetylcholine is terminated when the enzyme acetylcholinesterase degrades part of the neurotransmitter (producing choline and an acetate group) and the rest of it diffuses away.
+#The choline produced by the action of acetylcholinesterase is recycled  — it is transported, through reuptake, back into the presynaptic terminal, where it is used to synthesize new acetylcholine molecules.<ref>Dale Purves, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White (2008). Neuroscience. 4th ed.. Sinauer Associates. pp. 121–2. ISBN 978-0-87893-697-7.</ref>
 </span>