NURS 4430 Week 1: Introduction to Neuroanatomy
The neuron entails three major parts: the cell body or the soma, the axon, and the dendrites (Vergnolle & Cirillo, 2018). The cell body entails the various organelles of the cell body and assists in maintaining the function of the neuron. The soma also secretes proteins required by other parts of the neuron. The soma has projections known as dendrites. Dendrites receive electrical impulses from other neurons. On the other hand, the axon is a cylindrical structure that transmits electrical impulses from the cell body to its axon terminal and finally to another neuron's dendrites. An electric impulse is generated when a stimulus in a cell membrane is depolarized, disrupting the balance of Na+ and K+ in the cell, thus generating an action potential. The impulse later travels through the axon via voltage-gated ion channels and finally reaches the axon terminal, which stimulates other neurons at its dendrites. Notably, impulse conduction is faster along myelinated axons since the electrical impulse can "jump" from one node of Ranvier to another. The "jumping" is also referred to as saltatory conduction (Vergnolle & Cirillo, 2018). A good example of impulse conduction happens when one touches a hot object. Once the impulse touches the object, the neurons or free nerve-endings at the skin get stimulated. The neural impulses are later transmitted from the sensory receptors to the spinal cord, particularly to the dorsal root ganglion that transmits sensory inputs. From this point, an interneuron gets stimulated, and this is the neuron that connects the sensory pathway with the motor pathway of the spinal cord. The interneuron transmits the impulses to an alpha motor neuron of the ventral horn of the spinal cord, whose function is to send impulses to the effector muscles. Once the effector's muscles get stimulated, a reflex withdrawal of the hand happens.
The subcortical structures comprise major components such as the diencephalon, pituitary gland, certain limbic structures, and the basal ganglia (Bidelman, 2018). These neurons lie deep within the brain or below the cortex and have complex functions. The limbic system is the component involved in learning, memory, and addiction, and its subcortical portion involves the olfactory bulb, dorsomedial nuclei of the thalamus, septal nuclei, amygdala, and hypothalamus. The hippocampus is part of the cortical portion of the limbic system and the center of memory (Bidelman, 2018). The amygdala receives signals from the hippocampus, hypothalamus, cerebral cortex, and olfactory cortex and plays a key responsibility in relaying emotions like fear and decision making. The two neurotransmitters in the nigrostriatal region include dopamine from the substantia nigra pars compacta and GABA (gamma-aminobutyric acid) from the substantial nigra par reticulata.
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A glial cell refers to a type of cell in the nervous system that protects, supports, and nourishes other neurons (Allen & Lyons, 2018). Examples of glial cells in the CNS include the astrocytes, oligodendrocytes, ependymal cells, and microglia. Astrocytes support other neurons or offer "scaffolding." Oligodendrocytes play the role of myelination of the axons of neurons in the CNS, thus facilitating a quick impulse transmission. Ependymal cells play a key role in the absorption of CSF fluid, and a variant of ependymal cells known as choroid plexus and generates CSF (Allen & Lyons, 2018). On the other hand, microglia are phagocytic cells that get activated to respond to damage in CNS tissue.
The synapse is the space between the axon terminal of one neuron and the dendrites of another neuron, and it is these parts of the neuron that communicate with each other. Typically, an impulse travel from the dendrites to the cell body, then to the axon, and finally to its axon terminal (Shin et al., 2019). The impulses then reach the synapse, where the dendrites of another neuron are found and stimulated. This action denotes the direction of the electrical impulses from the dendrites to the axon terminal and synapse.
The concept of neuroplasticity means the ability of the brain to form new neural connections and reorganize itself (Price & Duman, 2020). Neuroplasticity enables the brain to adjust its activities to respond to the environment. It also enables the brain to compensate for any neuronal injury. Again, neuroplasticity often enables the human brain to develop from infancy throughout adulthood. This concept is mostly applicable among patients that recover from a stroke. For instance, if the portion of the brain affected by the stroke is the portion responsible for moving the left arm, the intact neurons in the other portions of the brain may be "taught" to take over such function (Price & Duman, 2020). Therefore, new connections between the intact neurons can be formed via rehabilitation and repetitive activities. Another example of neuroplasticity is when an aged individual learns a new task or a new language.
References
Allen, N. J., & Lyons, D. A. (2018). Glia as architects of central nervous system formation and function. Science, 362(6411), 181-185.
Bidelman, G. M. (2018). Subcortical sources dominate the neuroelectric auditory frequency-following response to speech. Neuroimage, 175, 56-69.
Price, R. B., & Duman, R. (2020). Neuroplasticity in cognitive and psychological mechanisms of depression: an integrative model. Molecular psychiatry, 25(3), 530-543.
Shin, M., Wang, Y., Borgus, J. R., & Venton, B. J. (2019). Electrochemistry at the Synapse. Annual Review of Analytical Chemistry, 12, 297-321.
Vergnolle, N., & Cirillo, C. (2018). Neurons and glia in the enteric nervous system and epithelial barrier function. Physiology, 33(4), 269-280.
