The human brain is a complex chemical environment, containing various types of neurons and neurotransmitters which stimulate electrical activity within cells and allow these cells to communicate with one another (Ankrom, 2019), which is what allows us to have thoughts, feelings and behaviour. Neurons and neurotransmitters have their own roles and work together to allow this communication; however, the transmissions can only occur when using unique cell structures – receptors, which help the transmission of these chemical messages (Sukel, 2019). Neurotransmitters are essentially chemical messengers which can either be excitatory and stimulate the electrical activity of the cell or they can be inhibitory which would do the opposite and calm the activity of the brain cell. Neuron activity is determined by the balance between the two (Cherry, 2019) and neurotransmissions are responsible for activating receptors. The brain has two types of communication modes, ionotropic and metabotropic communication.
Ionotropic communciations accounts for 99 per cent of communication within the brain and is responsible for how we think and feel. Ionotropic communication is when receptors bound to the membrane allow ions to flow into a cell either increasing or decreasing the action potential of the neuron to fire (Dingman, 2020). Ionotropic receptors tell the cell whether to open the cell, to help continuing the transmission of a signal to another cell, or to close the cell altogether allowing the transmission to slow down or eventually stop (Sukel, 2019).
Metabotropic receptors are different. Communication is slower and more complex, as it involves a second messenger pathway, which adds extra steps to the signalling but is also responsible for how the brain regulates itself and keeps itself healthy (O’Connor, 2018). By changing the chemistry of the cell, it can also change the DNA expression through metabotropic binding, which is when a neurotransmitter binds with a metabotropic receptor via the G-protein, activating the second messenger pathway by causing a sudden activity surge within the cell (Sukel, 2019). If a neuron is expecting a particular input, it will have the specific receptors for it. Metabotropic receptors can retain positive charge by closing the potassium channels and reducing the amount of energy needed to transmit the signal, thus slowing it down or stopping it (Hammond, 2015).
Metabotropic neurotransmitters like serotonin and dopamine are what keep our brain cells healthy. They are known as monoamine neurotransmitters, as they only contain one amino group. G-protein coupled receptors (GPCR) have specific roles within the regulation of our behaviour and mood, so for example when we display low levels of 5-hydroxytryptamine (5-HT), also known as serotonin (Alberts et al., 2019), it has been linked to anxiety and depression.
Serotonin is produced in the intestines and the brain and cannot cross the blood-brain barrier. This means that any serotonin used by the brain, has to be produced by it. The most effective way of increasing serotonin levels is by undertaking vigorous exercise, which studies have shown increases the production of serotonin (McIntosh, 2018). When following an omega-3 fatty acids deficient diet, it can lower serotonin levels in the brain (University of Bristol, n.d.) and lead to symptoms of depression (Sukel, 2019). A common form of antidepressants, called selective serotonin reuptake inhibitors (SSRIs), can lead to higher levels of serotonin in the synapses, thus regulating behaviour and mood (Sukel, 2019). Increasing SSRIs means increasing the level of serotonin in the brain, decreasing anxiety and inhibiting panic attacks (Ankrom, 2019).
For our brains to be healthy, neurotransmitters have to be in balance whilst remaining interconnected to one another, as this will allow them to function properly. For example, for the neurotransmitters that induce the feeling of relaxation to function, they need considerable amounts of serotonin (Ankrom, 2019). The last 50 years have seen key theories develop that an imbalance of neurotransmitters in the body is what causes depression, although low levels of serotonin have been linked with depression, it is still unclear if depression is actually caused by the low levels, or if it causes the low levels in the first place (McIntosh, 2018). What we do know, is that when people are depressed, it is down to a problem with this intracellular functioning, which shows that the impact of metabotropic neurotransmission is quite profound.
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