Children have 1,000 trillion synapses. By the time somebody is 30 years old, though, only 100-500 trillion of their synapses remain. This means that in just 7,000 days, as much as 90% of a person’s synapses disappear. Fortunately, though, this decline is not completely disastrous; many studies indicate that 30 year olds are not catatonic. Synapses are specialized neuronal junctions in which neurons, muscles, or glands can communicate with each other. Over time, synapses strengthen, die, and move based on the activities of the individual. Psychoactive drugs affect synapses either directly or indirectly, and can give the patient artificial happiness or emptiness. Synapses are constantly changing to accommodate activities, interact with chemicals, form memories, and encourage development.
Neurons communicate with each other, muscles, and glands via the synapses, which change with age. A synapse is a junction where the presynaptic neuron releases a neurotransmitter, and the postsynaptic cell undergoes transformations in response. As a result, synapses are crucial to thought, perception, mobility, and homeostasis. Humans initially have 1,000 trillion synapses. However, this number declines dramatically in babies as they eliminate excess synapses. This is done by programmed cell death, which makes sure that the growing brain does not get too big. Adolescents undergo further synaptic pruning; very little programmed cell death occurs, however. This makes sure that synapses are made more efficient; more neurotransmitter is available for the synapses, which are necessary. Unnecessary synapses, which impede efficiency, are eliminated. After adolescence, the body remains at a peak for several years. After this peak, though, the body quickly deteriorates in a process called aging. As people continue to get old, the human brain declines in function despite its changes in gene expression. It tries desperately to down-regulate synaptic plasticity genes and synaptic vesicle release. It focuses more on neuronal maintenance by up regulating genes associated with stress, DNA damage, and antioxidant attack. As the synapses become increasingly static and the neurons lose their youth, the effects of senescence take effect and the brain eventually becomes necrotized. This process begins around the age of 25.
To avoid this depressing reality, many people become addicted to drugs which function at the synapse. Agonists, such as nicotine, mimic neurotransmitters to activate receptors. Antagonists, such as atropine, bind to receptors and block their activation. Overexposure to a neurotransmitter results in the disappearance of its receptors. This is a response mechanism to too much neurotransmitter, resulting in drug tolerance. To avoid reality, then, druggies will need to take increasingly high drug doses to try to get their first high. Therefore, overexposure results in decreased synaptic efficacy. There are three primary mechanisms by which these psychoactive drugs take effect. The first is that psychoactive drugs can prevent an action potential from starting, thereby preventing any related synaptic activity. Examples include lidocaine, which binds to voltage-gated sodium channels. The second mechanism is that a drug can alter neurotransmitter synthesis, resulting in no, reduced, or overproduction of a neurotransmitter. A third mechanism is interference with neurotransmitter release. Black Widow Spider toxin increases release of a neurotransmitter, thereby heightening synaptic efficacy momentarily. Botulism and tetanus decrease neurotransmitter release.
When new memories are formed, synaptic changes occur. An extremely basic example of this is shown by Hebb’s Rule. According to Hebb’s Rule, a synapse that is repeatedly activated in conjunction with the firing of a postsynaptic neuron will be strengthened by structural and chemical changes. For example, many people associate UCLA with bears. The synapses between the UCLA neuron and the bear neuron will therefore strengthen. This strengthening occurs by release of more neurotransmitter, removal of excess synapses, and the presence of more receptors. As people age, though, the genes related to synaptic plasticity are down regulated. As a result, old people have a harder time forming new memories.
In conclusion, the brain is constantly changing. As people approach their third decade on this planet, they are losing hundreds of trillions of synapses. Fortunately, though, this is necessary to remove excess synapses (excess synapses reduce neuronal efficiency). As people get old and lose synapses, their minds also undergo tremendous morphological transformations.
