Anatomy of the Nervous System
The nervous system is the body system that carries signals between the body and the brain. It consists of the brain, the spinal cord, and all peripheral nerves. The nervous system is composed two types of cells: of various types of neurons (nerve cells) with specialized functions and different kinds of glial (support and protective) cells. A neuron is a cell in the nervous tissue that transmits electrical and chemical signals throughout the body. A neuroglia is a cell that supports and protects neurons in the central nervous system. Categories of glial cells include astrocytes, oligodendrocytes, Schwann cells, ependymal cells, microglia, and satellite cells. Neurological means pertaining to the nervous system. A neurological disease is a disease of the nervous system.
The central nervous system (CNS) is made up of the brain and spinal cord. The brain is the body's center for nerve processing and control. The brain receives messages from the body, processes them, and transmits signals out to the body. The spinal cord is the thick bundle of cells and tissues that extends from the brain through the spine. The main function of the spinal cord is to transmit signals between the brain and the nerves of the body.The peripheral nervous system (PNS) is the collection of nerves outside the brain and spinal cord that extends to the rest of the body and includes not just nerves, but also clusters of neuron cell bodies called ganglia or soma. The PNS consists of the somatic nervous system and the autonomic nervous system. The somatic nervous system receives information about the environment, transmits it to the brain, receives information from the brain, and conveys the signals for conscious actions. The autonomic nervous system controls the parts of the body outside of conscious control, such as heartbeat and digestion.
The Nervous System
Functions and Defenses of the Nervous System
The nervous system's role in the body is to receive, process, and transmit information that is used to control various body processes. The brain serves as the locus of control for all processing, receiving messages from the nerves of the body via the spinal cord.
The main defenses of the nervous system are structural. The spinal column protects the spinal cord. The spinal column is made up of 33 vertebrae, bones that form a flexible, hard shield around the more delicate soft tissues of the spinal cord. There are 24 vertebrae that remain unfused throughout a human's lifetime, including 7 cervical, 12 thoracic, and 5 lumbar vertebrae. Eight to ten sacral and coccygeal vertebrae fuse to form the sacrum and coccyx during growth between puberty and ages 25 to 30. The total number of separate vertebrae depends on a person's age. The cranium protects the brain, with its bones fused together into a thick, rigid shield in the adult.
In addition, the brain and spinal cord are surrounded by meninges, three membranes that encase the brain and spinal cord and include the dura mater, the arachnoid mater, and the pia mater. Meninges help to cushion and protect the brain. The spaces between meninges and within the brain and spinal cord are filled with cerebrospinal fluid (CSF), which lubricates and cushions the nervous tissues and aids in waste removal and homeostasis.
The nervous system is normally sterile, containing no microbes. A microglial cell is a phagocytic cell within the nervous system that seeks out and destroys any pathogens that manage to cross from the circulatory system into the nervous system. To help ensure microbes do not reach the brain, where they could cause serious damage, the body employs the blood-brain barrier. The blood-brain barrier is a network of thick-walled capillaries without pores that feeds oxygen to the brain but does not allow large molecules to pass through. It prevents pathogens from reaching the brain. However, it also prevents most medicines from reaching the brain and thus represents a major challenge for pharmaceutical researchers when investigating treatments of neurological disorders.Cerebrospinal fluid is a critical factor in the epidemiology of neurologic diseases. Epidemiology is the science that investigates the cause, transmission, timing, and distribution of infectious disease episodes, with a focus on recognizing outbreaks, controlling those outbreaks, and treating the infected. Because the cerebrospinal fluid is normally sterile, a common technique used to detect infections in the CNS is a spinal tap. In this technique a sterile needle is inserted into the spinal cord, and a sample of cerebrospinal fluid is collected. The fluid is analyzed to diagnose, or exclude from further consideration, diseases or infections. Applying antibody detection or genetic methods to cerebrospinal fluid can screen for the presence of pathogens, including bacterial, fungal, viral, and parasitic infections. Meningitis, encephalitis, and syphilis are pathogenic diseases commonly diagnosed using spinal taps. Besides pathogen detection, the pressure of cerebrospinal fluid is heightened in response to several conditions. Screening the fluid for red blood cells can indicate cerebrospinal hemorrhage, and the presence of some white blood cell types is indicative of certain infections and cancers. Despite the utility of spinal taps, headaches and pain are common side effects, and while rare, more serious complications are possible.