Mind and Brain

The brain is the control center for many actions that occur in the body. Its ability to conduct complex processes is due to the interconnecting of its 100 billion neurons. Neurons are able to communicate with each other through the neurotransmitters that are released at specialized junctions called synapses. These synapses are found in two locations where the pre-synaptic terminal is found at the tip of an axon and the post-synaptic terminal is on the dendrite. These two membranes line up against each other separated by a small gap about 20nm wide. The narrowness of the gap allows the neurotransmitters to pass quickly from one another. The release of neurotransmitter from the pre-synaptic nerve terminal is caused by the appearance of an action potential. When an action potential arrives at the synapse, it results in the calcium ion channels to open. The movement of the calcium triggers the release of neurotransmitters through a process known as exocytosis. The neurotransmitters then disperse across the synaptic cleft to bind to receptors. Two effects can happen when the neurotransmitters bind to the receptor: excitatory, where the membrane is brought closer to the threshold of an action potential production or inhibitory, where the membrane becomes stable near its resting place. If the result of the neurotransmitters is excitatory, it leads to the opening of the ion channels once more causing another production of an action potential, which will travel from the dendrite through the axon eventually arriving at another pre-synaptic nerve terminal. This process will continue until the chemical signal arrives at its desired location. Through these progressions, cells are allowed to communicate with one another.

The ability of the synapses between two neurons to change in strength allows the brain to achieve plasticity. Achieving synaptic plasticity can occur in various ways such as changing the ways cells respond to neurotransmitters or even changing the amount of neurotransmitters released into the synapse. The effectiveness of synapses can be changed with the presence of a psychoactive drug. These drugs work by affecting the neurons either pre-synaptically or post-synaptically. For example, Prozac is a reuptake inhibitor for serotonin that causes it to enhance its effect along with cocaine, where it blocks the reuptake of dopamine, leaving the neurotransmitters in the synaptic gap for a longer amount of time. Psychoactive drugs like these causes an imbalance of neurotransmitters

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