Synaptic transmission and how drugs may modify this activity
Discuss the mechanism of synaptic transmission and how drugs may modify this activity.Synapses are crucial to the function of the nervous system. The majority of the synapses in the nervous system in vertebrates are chemical synapses, where chemicals are used to transmit information between cells; however there are also some electrical synapses (Carlson 2004, Sjaastad et al. 2003). The cells in smooth musculature and cardiac musculature are electrically connected through gap junctions which are exceptionally large protein channels forming membrane pores extending from cell to cell, enabling small molecules and ions to move freely between the cells (Sjaastad et al. 2003). But nevertheless, the majority of the synapses in vertebrates are chemical. Mechanism of chemical synaptic transmissionWhen a nerve impulse reaches a chemical synapse, neurotransmitters, which are signal molecules, are released from the nerve terminal and diffuse to the membrane of the target cell (Sjaastad et al. 2003). The target cell contains receptor molecules where th
In the direct method, the ion channel opens when the neurotransmitter attaches to it. The indirect method takes longer to begin, but lasts longer, and involves a chain of chemical events including a second messenger (Carlson 2004). In all of these ways, the drug acts as an agonist or an antagonist on one of the seven major steps of neurotransmission (See fig. Chemical synapses are crucial to the function of the nervous system, and are an important location for drug action. There are seven major steps in neurotransmission at a synapse, all of which potentially can be influenced by drugs: neurotransmitter synthesis, storage, release, receptor interaction, inactivation, reuptake and degradation (Kolb & Whishaw 2001). The opening of these channels can either excite or inhibit the electrical activity of the target cell, bringing the cell closer or further away from its threshold level for generation of an action potential (Bear et al. After use, the neurotransmitter is either destroyed or taken back up into the terminal from which it came for reuse, and the synapse also has mechanisms for degrading excess neurotransmitters and removing by-products from the synapse (Kolb & Whishaw 2001). In the pre-synaptic cell, you can find small vesicles containing the synthesized neurotransmitters, and the action potential will cause an influx of Ca2+ through voltage-gated calcium channels, fusing the vesicle membrane with the presynaptic membrane causing a release of the neurotransmitter into the synaptic cleft (Carlson 2004, Sjaastad et al. How drugs may affect the activity of chemical synaptic transmissionMost drugs with psychoactive effects influence the chemical reactions at synapses (Kolb & Whishaw 2001). The neurotransmitter will diffuse across the synaptic cleft, and when the neurotransmitters bind to the postsynaptic receptors, these receptors will open neurotransmitter-dependent ion channels (Sjaastad et al.
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