Primary Somatosenory Cortex
- Embedded in the membrane of the postsynaptic neuron are receptors for the neurotransmitter, acetylcholine (or ACh).
- Two forms of ACh receptors occur in the central nervous system. The most common is called nicotinic type.
- The term nicotinic is applied to these receptors because they can be stimulated by the drug, nicotine. The second type of ACh receptor, the muscarine type, differs in structure and mechanism of action and will not be discussed.
- Nicotinic receptors are composed of five (5) polypeptide subunits, which together form a water-filled ion channel in the lipid bilayer.
- Normally, the gates are closed and ions are prevented from passing through the channel.
- Two of the receptor’s subunits have binding sites for ACh molecules. When ACh occupies both sites.
- The gated subunits change shape (conformation) and the channel opens.
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- Nicotinic ACh receptors are also known as chemical-gated or ligand-gated channels. Ligand is used because the term refers to one molecule binding to another (larger) molecule.
- While it is open, sodium (Na+ ) and potassium (K+ ) ions diffuse through the channel. The exchange of ions changes the membrane potential of postsynaptic neuron.
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