Friday, January 18, 2008

Activities and Structures involved in Synaptic Transmission

By Sudipa Sarkar
Describe the major activities and structures involved in synaptic transmission. Address the role of action potential. Describe how some drugs may interfere with synaptic transmission and result in variations of consciousness.

Synaptic transmission refers to the transmission of nerve impulses from one nerve cell to another. This takes place at a specialized cellular structure known as the synapse. Synapse is a connection at which the axon of the presynaptic neuron ends at the same location upon the postsynaptic neuron.

Activities involved in Synaptic Transmission:

The neurotransmitter, created in the neuron, is stored in vesicles found at the axon terminal. When the action potential (a rapid shift in electrical potential traveling along cell membrane of a neuron) arrives at the axon terminal, it causes the vesicles to approach the cell membrane. There they fuse with the membrane and empty their contents, i.e., the neurotransmitter molecules into the synaptic cleft. These neurotransmitters then travel through the synaptic gap until they reach specialized receptor cell existed in other cell membrane. The specific neurotransmitters can deliver the signals to specific receptors and produce any of the two effects – excitatory or inhibitory. In excitatory effect, they cause to fire more neurons, whereas in inhibitory effect, they cause less likely that the neuron will fire. After the neurotransmitters cross one neuron to another, they either are taken back to reuse, process known as reuptake, or they are broken down into various enzymes.

Role of Action Potential

Action Potential is the most basic signal in the nervous system. It comprises of a rapidly moving wave of depolarization, that is, a shift in electrical potential), traveling along the cell membrane of the neuron and causes a disturbance along the membrane resulting communication information within neurons.

Influence of Drugs in Synaptic Transmission

In most of the cases, drugs affect our feelings or behaviour by altering the synaptic transmission. The synapse itself is so complex, that there is a variety of area where drugs can interfere with synaptic transmission. It is mainly because of the similarity of the chemical structure of drugs like neurotransmitter. Drugs can produce either of two effects: one is agonists, which is mimicking the effect of neurotransmitter, or antagonists, which is inhibiting the effect of neurotransmitter. While abusing drugs, it mainly produces increased amount of neurotransmitter dopamine, followed by increased amount of action potential. Drugs like alcohol, heroin, and nicotine causes increased level of action potential by exciting dopamine-containing neurons in Ventral Tegmental Area, whereas drugs like methamphetamine, crystal, crank result the release of dopamine from vesicles itself independent of the amount of action potential. But both of the types basically produce pleasure sensation and mood alteration.
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