Basic Building Blocks of Neurobiology: Neurons
Foundational components of the nervous system are neurons, or nerve cells that differ in forms. Each neuron has a cell body and its dendrites, which are bushy and branching extensions that receive information and conduct impulses toward the cell body. From there, the axon extension passes the messages away from the cell body to other neurons, while being encased in a layer of fatty tissue–myelin sheath–for insulation and speed. The transmission of information by neurons happens when triggered by sensory or chemical signals and causes the firing of a neural impulse called action potential, an electrical charge going down the axon. There is a threshold, or a level of stimulation required to trigger a neural impulse, and the neuron either fires or doesn’t fire at all according to the all-or-none response. The meeting point between neurons is called a synapse, and it presents a junction with a gap referred to as the synaptic gap.
Neurotransmitters in Action
When action potentials travel down a neuron’s axon until reaching the synapse where the terminal of the axon is present, it stimulates the release of neurotransmitter molecules. These molecules are chemical messengers that cross the synaptic gap and bind to receptor sites on the receiving neuron, allowing ions to enter the receiving neuron and excite or inhibit a new action potential. Afterwards, the process of reuptake occurs when the sending neuron reabsorbs excess neurotransmitters. So how do neurotransmitters influence us? They have phenomenal impacts on people’s hunger, thinking, depression, euphoria, addictions, and therapy.
Well-known Neurotransmitters:
- Acetylcholine (ACh)
- Dopamine
- Serotonin
- Norepinephrine
- GABA (gamma-aminobutyric acid)
- Glutamate
Out of these well-understood neurotransmitters, Serotonin and Norepinephrine have strong links to the onset of depressive behaviors when they lack in supply. Serotonin affects mood, hunger, sleep, and arousal, and Norepinephrine helps control alertness and arousal.
Causes of Depression
Stressful events related to work, marriage, and close relationships can often precede depression. If stress-related anxiety is a “crackling, menacing bushfire,” according to biologist Robert Sapolsky (2003), then depression is a “suffocating blanket thrown on top of it.” Sadness is a powerful factor, which can cause one to lose motivation, abandon unattainable goals, and even provoke ideations of self-harm and suicide. Statistics have reported suicide as the second leading cause of death for young people ages 15 to 24 (Burrell, 2020). The causes of depression are typically approached from a biological, psychological, and social lens. About one in four people diagnosed with depression is debilitated by traumatic social issues like experiencing a significant loss of a relative or unemployment. Individuals hit by depression can also hold genetic dispositions as the core onset of depression.
Antidepressants and their restorative chemical properties
Drugs and other chemicals can greatly affect brain chemistry at synapses, typically by either exciting or inhibiting neurons’ firing. Agonist molecules stimulate a response through binding to a receptor site, mimicking a neurotransmitter’s actions. Some opiate drugs fall into the agonist category, and produce temporary euphoria and pleasure by increasing normal sensations of arousal. Antagonists, on the other hand, inhibit a response when they bind to a receptor site. Antidepressants are mainly antagonists. For example, Serotonin antagonist and reuptake inhibitors (SARIs) are a class of drugs used mainly as antidepressants, but also as anxiolytics and hypnotics. They act by antagonizing serotonin receptors such as 5-HT2A and inhibiting the reuptake of serotonin, norepinephrine, and/or dopamine.
Works Cited:
The Chemistry of Depression:
Causes of Depression:
Antidepressants:
Onset of depression more complex than a brain chemical imbalance:
Neurobiology of mental illness:
Myers Psychology textbook for AP, second edition (pg 120)