THE FIRST MIDTERM Flashcards
What is another name for cell body?
Perikaryon
What is the definition of a direct action of neurotransmitters?
The neurotransmitter binds to and opens ion channels, which promotes rapid responses by altering the membrane potential.
What is the definition of an indirect action of neurotransmitters?
The neurotransmitter acts through intracellular second messengers, usually G-protein pathways, which ends up having broader and longer-lasting effects.
How does a voltage-gated channel work?
A channel that opens and closes in response to voltage changes across the membrane, or changes in the membrane potential in the cell. An example is a voltage -gated sodium channel, lidocaine.
How does a ligand-gated ion channel work? And what is another name for these types of channels?
A hormone, drug, or transmitter binds to the protein and the channel opens up. Action is immediate and brief, some are excitatory and open channels for small cations, some are inhibitory and allow Cl- influx or K+ efflux to cause hyperpolarization. Examples include glutamate (AMPA) and nicotinic ACh receptors and GABA-A. They are also called Ionotropic.
How do Metabotropic receptors work?
These are seven-transmembrane G protein-coupled receptors. The binding of neurotransmitter to this type of receptor does not result in the direct gating of a channel. Rather, binding to the receptor engages a G protein, which results in the production of second messengers that modulate voltage-gated channels and change the excitability of the neuron, thus they are not directly linked to ion channels. Metabotropic receptors initiate biochemical processes that mediate more long-term effects (tens of seconds to minutes) and modify the responsiveness of the neuron.
What are the two types of Metabotropic receptors?
Membrane-delimited and Diffusible second messengers
With which type of Metabotropic receptor does the G-protein subunit interact direct with the voltage-gated ion channel?
Membrane-delimited
Which two types of voltage-gated ion channels are the targets of Membrane-delimited signaling?
Calcium channels and potassium channels
With membrane-delimited receptors, what happens when G-proteins interact with calcium channels?
They inhibit channel function. This mechanism accounts for the presynaptic inhibition that occurs when presynaptic metabotropic receptors are activated.
With membrane-delimited receptors, what happens when G-proteins interact with potassium channels?
They activate channel function and with potassium, they will be postsynaptic, resulting in a slow postsynaptic inhibition.
How does a diffusible second messenger metabotropic receptor work?
A classic example of this type of action is provided by the β adrenoceptor, which generates cAMP via the activation of adenylyl cyclase. Whereas membrane-delimited actions occur within microdomains in the membrane, second messenger-mediated effects can occur over considerable distances.
What is the definition of an autoreceptor?
It is a receptor on an axon terminal through which the neuron’s own neurotransmitter can influence the function of the terminal, and this is almost always inhibitory. The D2 receptor is an example.
What is the definition of a heteroreceptor?
It is a receptor on an axon terminal through which neurotransmitters from other neuronal types can influence the function of the terminal, and they are almost always inhibitory.
What are the three main catecholamines?
Dopamine, Norepinephrine, and Epinephrine
What is name of the neurotransmitter that looks very similar to catecholamines, but isn’t?
Amphetamine. A lot of times the way drugs exert their effect is by mimicking the neurotransmitter, and if the structure is similar, it is easier.
What is the precursor amino acid for catecholamines?
Tyrosine
What are the four main monoamine neurotransmitters?
Dopamine, Epinephrine, Norepinephrine, and Serotonin. Histamine is also a monoamine. But remember, serotonin is not a catecholamine like the first three are.
What are the two main classes of fibers/receptors of the autonomic nervous system?
Cholinergic (Muscarinic and Nicotinic) and Adrenergic
What is the process of Dopamine entering at the adrenergic junction?
Tyrosine is transported into the noradrenergic ending or varicosity by a sodium-dependent carrier. Tyrosine is converted to DOPA (Dihydroxyphenylalanine) by tyrosine hydroxylase, and dopa is converted to dopamine by aromatic amino acid decarboxylase, and transported into the vesicle by the vesicular monoamine transporter (VMAT). Physiologic release of transmitter occurs when an action potential opens voltage-sensitive calcium channels and increases intracellular calcium. Fusion of vesicles with the surface membrane results in expulsion and dopamine can enter the synaptic cleft and do one of the following three things: 1) Bind to a post-synaptic receptor (there are 5, D1-D5), 2) Bind to the D2 autoreceptor (which would shut down tyrosine hydroxylase, so dopamine cannot be made nor released, and 3) Re-enter the neuron through a dopamine transporter. Once it does so, dopamine can be metabolized by MAO, Monoamine Oxidase, which converts dopamine into DOPAC.
What is the process of NE entering the synaptic cleft of an adrenergic junction and when does it happen?
For this to happen, it all starts with Tyrosine again, which is converted to Dopamine and Dopamine’s same process takes place but once it enters the synaptic vesicle via VMAT, Dopamine is then converted to NE by Dopamine Beta Hydroxylase, DBH. NE can then enter the synaptic cleft and have the same three options as Dopamine does. However, instead of binding to D1-D5 post-synaptic receptors, NE binds to alpha and beta receptors. And there is no D2 pre-synaptic receptor, it is an alpha-2 receptor.
Where is Epinephrine usually found? And what converts NE to Epinephrine?
It is mainly found in adrenal medullary cells, although it is also found in some CNS neurons. It is converted from NE by PNMT, phenylethanolamine-N-methyltransferase.
What is another name for Serotonin?
5-HT, 5-hydroxytryptamine. It is associated with sleep, depression, and migraines.
What is the amino acid precursor for Serotonin?
Tryptophan