The human nervous system is a complex network of body cells and nerves whose primary function is to control, regulate and facilitate communication of the body and the external environment. It coordinates mental functions such as thinking, learning and memorizing. The system works together with the endocrine system to regulate and maintain homeostasis. The nervous system is organised into two major separate but integrated divisions; the central nervous system (CNS) and the peripheral nervous system (PNS). These two divisions of the human nervous system work together in the control of sensory input, its integration and movement of body muscles (either motor output). The current paper intends to discuss human nervous system in relation to its major characteristic and major diseases (Paxinos & Mai, 2004).
Major characteristics of the nervous system
The human nervous system has a primary role of controlling the internal and external environment by establishing a homeostatic balance. The complex human nervous system performs its mandate through two divisions; the central nervous system (CNS) and the peripheral nervous system (PNS). These two divisions of the nervous systems work together in the control of sensory input, their integration and channelling of processed information to the muscles. The CNS is composed of the brain and the spinal cord. The core function of the CNS is to integrate and process information emanating from the nerves (Paxinos & Mai, 2004).
The PNS is composed of two major systems; the somatic and autonomic. Sensory signal received by the PNS is conveyed to the CNS. The PNS also conveys information processed by the CNS to the designated body parts and muscles. The PNS performs its first role through the somatic system. The somatic system is made up of millions of receptor cells that make it possible for the PNS to receive information from internal and external environments. The receptor cells are made up of special sensory receptors with the ability to convey messages to the CNS and from the CNS to the skeletal muscles. Sympathetic and parasympathetic are subdivisions of the autonomic system. The regulation of secretions of hormones and the control of cardiac muscles performance is undertaken by the autonomic system. The sympathetic and parasympathetic segments of the autonomic system are usually working antagonistically in their functional roles. The two segments are involved in the regulation of involuntary body processes such as peristalsis and the beating of the human heart. Involuntary body processes do not necessitate the involvement of the conscious mind (Paxinos & Mai, 2004). The organization of the CNC can be summed up as shown in the chart below
Human Nervous System Tissues and Cells
Neurons and supporting cells are the major types of cells that make up the nervous system. The cells that support the neurons are called glial cells. The functional and structural foundation of the nervous system is the neurons. They are specialized to react to external environment such as physical and chemical stimuli. They also conduct electrochemical signals and release chemicals that regulate various body processes. The activity of neurons is supported by another type of cells called glial cells. Approximately, almost half of the nervous system is made of glial cells. They glial cells are more than the neurons. Collectively, glial cells nourish the neurons, remove their wastes, and defend against infection. Glial cells also provide a supporting framework for all the nervous-system tissue. The various tissues and cells the make up the human nervous system are discussed below (Nebylit︠s︡yn, 1972).
The neuroglia does not conduct impulses. Their function is to support the neurons. The neuron is made up of three body parts; soma; dendrite and axon. Soma looks like other cell types: have nucleolus and various cytoplasmic organelles. However, it does not have centrioles, thus it is amitotic (Nebylitsyn, 1972).
The dendrites are other types of cells characterised by cytoplasmic projections from the soma. These cells are also called fibres and are characterised by branching. Although the fibres naturally small, they have the ability to receive information from adjacent cells due to their increased surface area. The population of the neurons fluctuates. It is an efferent process since it transmits impulses from the cell body. In addition, there is another group of cells called the axon collaterals. These are intermittent divisions of the axon. The myelin sheath is a greasy matter that encase the axons. Fibres in the central nervous system do not regenerate because there is no neurilemma and myelin is produced by oligodendrocytes (Carvalho & Tsao, 2014; Nebylit︠s︡yn, 1972).
There are three categories of neurons based on the direction of transmission of impulse with respect to the central nervous system. The sensory of afferent neurons relay the messages emanating from sensory receptors to the CN. They are characterised by shorter axons and long dendrites. Effect neurons have longer axons and shorter dendrites. Inter-neurons are a special category of neurons found in the CNS. They link efferent and afferent neurons. The final group of human nervous system cells is called the neuroglia. These cells are not involved in the transmission of impulses. These cells feed and secure the neurons. They are mitotic, hence replaceable when one is destroyed (Nebylit︠s︡yn, 1972).
Major diseases of the nervous system
The human nervous system can be afflicted by many diseases and disorders. The diseases that afflict the nervous can be classified by their causes. Some of the major causes of the nervous system diseases include; accidents, infections, cancerous tumors, and metabolism related diseases. Accidents that result in brain injuries may affect the nervous system by causing hemorrhage, concussions and brain tumors. Disease causing pathogens may also result in the infection of the nervous system. Some of the nervous diseases that emanate from pathogen attacks include; meningitis, AIDS, TB, malaria and other parasitic infections such as syphilis and fungal infections (Brain, 1956).
The human nervous system is also affected by metabolic diseases and deficiencies in crucial elements. For example, diabetic coma is a metabolic disease that affects the CNS. Metabolic diseases are usually aggravated by extreme mental stress, liver and kidney failure and respiratory failure among others. In addition, the CNS can be afflicted by cancerous cells with adverse effect on the functionality of the CNS system. Cancerous cells may result in diseases like metastasis and meningioma. The CNS may also be affected by hormonal imbalances. Substance abuse may also result in CNS failure. For example, excessive consumption of alcohol may cause memory loss and drug induced anxiety among others (Donaghy, 2001).
It is apparent that the nervous system provides the human body with a network of specialized nerve cells and body cells that convey sensory signals from within the body and fro external environment i order to control and regulate critical functions. It coordinates mental functions such as thinking, learning and memorizing. The CNS together with the endocrine system is responsible for the regulation of the balane between the external and internal environment of the CNS. The CNS system is structured into two major categories; central nervous system (CNS) and the peripheral nervous system (PNS). These two divisions of the human nervous system work together in the control of sensory input, its integration and movement of body muscles (either motor output). The autonomic and the somatic are the two major systems that make up the PNS.. The somatic system conveys messages to the CNS and from the CNS to the skeletal muscles. The autonomic system on the other hand regulates hormonal secretions from various glands and controls the performance of cardiac muscles (Paxinos & Mai, 2004).The human CNS is afflicted by a variety of diseases emanating from a wide range of causes. Accidents, infections, cancerous tumors, and metabolism related diseases are some of the diseases that affect the CNS.
Brain, R. (1956). Diseases of the nervous system. The Journal of Nervous and Mental Disease, 123(3), 304.
Carvalho, A. & Tsao, J. (2014). The human nervous system. Journal of the Neurological Science, 343(1-2), 247-248.
Donaghy, M. (ed.). (2001). Brain’s diseases of the nervous system. New York: Oxford University Press.
Nebylit︠s︡yn, V. (1972). Fundamental properties of the human nervous system. Plenum Publishing Corporation.
Paxinos, G., & Mai, J. K. (2004). The human nervous system. Academic Press.