why is D. wrong and B. right?? 1 point) which of the following is a TRUE stateme

Question

why is D. wrong and B. right??

1 point) which of the following is a TRUE statement? A A given neuron may release both glutamate and GABA from its presynaptic terminals and have both glutamate and GABA at postsynaptic sites. B. A given neuron may release either or GAB e but not bath from its presynaptic terminals and have both glutamate and GABA receptors at postsynaptic sites. c. fa given neuron releases glutamate from its presvnaptic nals, it expresses glutamate but not GABA receptors at postsynaptic sites. DA given neurotransmitter can bind to either G-protein coupled receptors or receptors that are -e EABAergie neurons are neurons thetewPress GABA-Feeepwow 3. (1 point) some density nicotinicacetylcholine (AChlreceptors autoimmune disorders reduce the of

Explanation / Answer

Based on their structural and functional characteristics, the neurotransmitter receptor can be classified into two broad categories: metabotropic and ionotropic receptors. Ionotropic receptors form an ion channel pore. In contrast, metabotropic receptors are indirectly linked with ion channels on the plasma membrane of the cell through signal transduction mechanisms, often G proteins. Hence, G protein-coupled receptors are inherently metabotropic. Other examples of metabotropic receptors include tyrosine kinases and guanylyl cyclase receptors.

Both receptor types are activated by specific neurotransmitters. When an ionotropic receptor is activated, it opens a channel that allows ions such as Na+, K+, or Cl to flow. In contrast, when a metabotropic receptor is activated, a series of intracellular events are triggered that can also result in ion channels opening but must involve a range of second messenger chemicals.

Metabotropic receptors have neurotransmitters as ligands, which, when bound to the receptors, initiate cascades that can lead to channel-opening or other cellular effects. When a ligand (the neurotransmitter) binds to the receptor (the transducer) the latter activates a primary effector via the G-protein, which can go on to activate secondary messengers or have other effects. Since opening channels by metabotropic receptors involves activating a number of molecules in turn, channels associated with these receptors take longer to open than ionotropic receptors do, and they are thus not involved in mechanisms that require quick responses. However, metabotropic receptors also remain open from seconds to minutes. Thus they have a much longer-lasting effect than ionotropic receptors, which open quickly but only remain open for a few milliseconds. While ionotropic channels have an effect only in the immediate region of the receptor, the effects of metabotropic receptors can be more widespread through the cell.

Metabotropic receptors can either open or close channels in the cell membrane. They can make a membrane more excitable by closing K+ channels, retaining positive charge within the cell and thus reducing the amount of current necessary to cause an action potential. Metabotropic receptors on the presynaptic membrane can inhibit or, more rarely, facilitate neurotransmitter release from the presynaptic neuron.

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