The structural unit of a nerve fiber is a neuron cell, which has fascinating anatomy. A neuron has a body and two types of branches, namely dendrites and axons. The main body of the neuron contains all cellular structures packed in the cytoplasm — from this point of view, the neuron is similar to other cells. What makes it distinctive is the presence of short outgrowths, the dendrites, and one long outgrowth, the axon, covered by a myelin sheath (Woodruff, 2019). A nerve impulse through a particular neuron takes its origin from a synapse, the contact of two neurons, where excitation occurs because of a change in the electrochemical potential; the impulse through the dendritic terminals passes through the entire cell and is released at the axon terminals, thereby transmitting the impulse to the next neuron.
The brain is a complex, multi-component system, and one of its layers is the subcortical structures. As the name suggests, the structures of this area are located between the cerebral cortices of the large hemispheres; the structures are immersed deep into the hemispheres. They include the optic tuberosities, the limbic system, the hypothalamus, the basal nerve nodes, the thalamus, and the reticular formation of the brainstem (Vasković, 2022). The limbic system includes the hippocampus, a physical section of the subcortical layer that is responsible for processing spatial information. The hippocampus is thought to allow emotions to form and to activate short- and long-term memory.
In addition, the dopamine neurotransmitter is critical in the subcortical structure of the brain. There are many hypotheses surrounding this mediator regarding its involvement in processes such as learning, pleasure generation, addiction development, and even its connection to schizophrenic disorders. It is correct to say that the fundamental functions of dopamine are still not fully understood, so the idea of its considerable significance cannot be dismissed. In the brain, dopamine has four pathways of synthesis, and among them, we can single out the nigrostriatal pathway, which controls movements. There is also an area called black substance, which is where the main processes of dopamine synthesis take place. There are two types of neurotransmitters in this zone, namely the pars compacta (SNpc), which is formed by dopaminergic neurons, and the pars reticulata (SNpr), which contains gamma-aminobutyric acid inhibitor (Sonne et al., 2019). The functionality of the substantia nigra depends on the efficient functioning of both mediators.
It would be erroneous to assume that nerve fiber cells are composed entirely of neurons; on the contrary, there are also non-neuronal structures in the nerve tissue that are not capable of conducting an electrical impulse. Such cells are generically referred to as glia or neuroglia, and their presence in the brain is critical. For example, glial cells have a protective function since microglia are capable of phagocytosis, an insulating function; since glial cells are non-excitable, they create the myelin sheath of the axon, and they can also provide nutrition to neurons. In other words, glia is in many ways auxiliary to the primary fiber neurons, but their role in the functioning of the brain system is integral.
As mentioned above, the interaction of neurons takes place in the synaptic area, literally the void between two neurons. In this area, the axon terminals of the first neuron connect to the dendrites of the second neuron, creating a space for the exchange of ions. The axon of the first neuron can initiate the release of neurotransmitters into the synaptic cleft, which are absorbed by dendritic receptors. This creates a concentration gradient that has a chemical potential — an electrical impulse is transmitted to the second neuron, after which the conduction function is activated to conduct the impulse along with the fiber.
Finally, in terms of cognitive experience, the human brain is characterized by the property of neuroplasticity. Neuroplasticity should be understood as the ability to adapt under the influence of external changes through structural and functional rearrangements. One meaning of this restructuring is the brain’s response to critical damage in which some brain function has been lost, for example, after a stroke. In terms of specific changes, examples are the structural transformation of the synaptic cleft, the number of dendrite receptors, and the number of axon terminals increases. As a general consequence, neuroplasticity means that the brain is an open system, not segmented in function.
Sonne, J., Reddy, V., & Beato, M. R. (2019). Neuroanatomy, substantia nigra [PDF document]. Web.
Vasković, J. (2022). Subcortical structures. KENHUB. Web.
Woodruff, A. (2019). What is a neuron? The University of Queensland. Web.