2. What is receptor? What is neurotransmitter? Where is neurotransmitter stored,

Question

2. What is receptor? What is neurotransmitter? Where is neurotransmitter stored, and how does it function? How is it destroyed?? Name several well-known neurotransmitters. 3. Propranolol is one kind of B receptor blocker which is widely used in clinic against hypertension. Propranolol can bind with B receptor and do not have effect. We have known that if Norepinephrine(NA) bind with B receptor, NA can increase heartbeat, cardiac output and cardiac contractility What will be the main pharmacological actions of propranolol? Why?

Explanation / Answer

2. A receptor is specialized for receiving signal. A receptor is a protein molecule that receives chemical signals from outside a cell. When such chemical signals bind to a receptor, they cause some form of cellular/tissue response, e.g. a change in the electrical activity of a cell. All of these responses are transmitted within the cell. Neurotransmitters are any of several chemical substances, such as epinephrine or acetylcholine, that transmit nerve impulses across a synapse to a postsynaptic element (another nerve, muscle, or gland).

Once they are synthesized, neurotransmitters, both small molecules and neuropeptides, are stored in vesicles within the axon terminal until an action potential arrives and they are released. Most small-molecule neurotransmitters are stored in small vesicles that range from 40 to 60 nm in diameter and, the vesicles that store neuropeptides are larger, ranging from 90 to 250 nm in diameter. Calcium enters the axon terminal during an action potential, causing release of the neurotransmitter into the synaptic cleft.

After its release, the transmitter binds to and activates a receptor in the postsynaptic membrane. In response to a threshold action potential or graded electrical potential, a neurotransmitter is released at the presynaptic terminal. The released neurotransmitter may then move across the synapse to be detected by and bind with receptors in the postsynaptic neuron. Binding of neurotransmitters may influence the postsynaptic neuron in either an inhibitory or excitatory way. The binding of neurotransmitters to receptors in the postsynaptic neuron can trigger either short term changes, such as changes in the membrane potential called postsynaptic potentials, or longer term changes by the activation of signaling cascades.

The neurotransmitter is either destroyed enzymatically, or taken back into the terminal from which it came, where it can be reused, or degraded and removed. The names of the main neurotransmitter are-

3. Propranolol leads to a reduction of the heart rate and of the cardiac output; initially the hypotensive effect is delayed because of peripheral vasoconstriction. The AV nodal conduction time and the AV refractoriness are prolonged. Blood flow decreases in most vascular territories. Propranolol also increases plasma renin activity and suppresses lipolysis. In the plasma the triglycerides increase, whereas the HDL cholesterol decreases slightly. The bond between propranolol and ß2-receptors causes an increase of the airway resistance and the inhibition of glycogenolysis and gluconeogenesis.

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