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Introduction to the Nervous System

Overview || Central || Peripheral || Overview || Related Articles
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Overview





In order to understand the nervous system we'll start with a microscopic discussion of what composes nervous tissue in the body. There are two main types of cells in the nervous system: neurons and glia.

Neurons are the information processing cells of the nervous system. They communicate with one another through electrical and chemical means. Electrical communication in the nervous system is accomplished through what are known as "action potentials". Action potentials are usually converted into a chemical message at the synapse, which is the area where two different neurons "talk" to one another.

Glia, on the other hand, are the "supporting" and nourishing cells of the nervous system. There are many types of glia with differing functions. Glia cells include ependymal cells, oligodendrocytes, astrocytes, microglia, and schwann cells.

At a macroscopic level, the nervous system is composed of various divisions that act in concert with one another to cause a specific bodily response. Generally speaking the nervous system can be broken down into central and peripheral divisions, which are themselves further subdivided.

Major sub-divisions of the nervous system:

Nervous System Main Divisions

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Central Nervous System

The central nervous system (CNS) is composed of the brain and spinal cord. The brain is further sub-divided into different parts. The main divisions are the cortex, sub-cortex, cerebellum, and brainstem.

The cortex is divided into four different lobes: frontal, parietal, occipital, and temporal. These divisions are based both on function, and anatomical location.

The other part of the central nervous system is the spinal cord. The cord receives information from the brain and then sends it to the proper body part. It also receives information from the body, which is relayed back to the brain for interpretation. The cord is surrounded by the same protective layers as the brain. It is also protected by the bony vertebrae, which provide support and structure.

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Peripheral Nervous System

Peripheral Nervous System Divisions

The peripheral nervous system has several different components. The first major division of the peripheral nevous system is the somatic system.

The somatic division refers to all the nerves that innervate skeletal muscle, as well as the sensory nerves that send information back to the central nervous system.

The second component of the peripheral nervous system is the autonomic division. The autonomic nervous system can be further divided into sympathetic and parasympathetic sub-divisions.

The sympathetic nervous system is responsible for "reving-up" the body. When your heart races, pupils dilate, or respiratory rate increases due to a stressor it is because of the sympathetic nervous system. The main hormones and neurotransmitters responsible for this effect are epinephrine (aka: adrenaline) and norepinephrine (aka: noradrenaline). The sympathetic nervous system is often humorously summarized as the "4-Fs": fight, flight, fear, and reproduction (I'll let you figure out the best "F" word for the last one).

The parasympathetic division can be thought of as the opposite of the sympathetic system. It is responsible for the "rest and digest" functions of the body. It helps slow the heart rate, decrease the respiratory rate, constrict the pupils, and aids in the control of digestive processes. The main neurotransmitter associated with parasympathetic control is acetylcholine. The parasympathetic division usually dominates the overall state of the body at rest.

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Overview

The nervous system is divided into the central and peripheral branches. The central nervous system composes the brain and spinal cord. The peripheral nervous system is composed of the somatic and the autonomic divisions. The autonomic division can be further sub-divided into the sympathetic and parasympathetic branches. Each branch of the nervous system has a specific role.

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Related Articles

- Stroke (cerebrovascular accident)

- Multiple sclerosis

- Parkinson's disease

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References and Resources

(1) Nolte J. The Human Brain: An Introduction to its Functional Anatomy. Sixth Edition. Philadelphia: Mosby, 2008.

(2) Baehr M, Frotscher M. Duus' Topical Diagnosis in Neurology: Anatomy, Physiology, Signs, Symptoms. Fourth Edition. Stuttgart: Thieme, 2005.

(3) Netter FH. Atlas of Human Anatomy: with Student Consult Access (Netter Basic Science). Fifth Edition. Philadelphia: Saunders Elsevier, 2010.

(4) Purves D, Augustine GJ, Fitzpatrick D, et al. Neuroscience. Fourth Edition. Sinauer Associates, Inc., 2007.

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