Nervous System

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NERVOUS SYSTEM

The human body’s activities are regulated by two systems – the nervous system and the endocrine system. Although both systems control body functions, their methods differ.

The nervous system is the body's information gatherer, storage center and control system. Its primary function is to collect information about the external conditions in relation to the body's external state, to analyze this information, and to initiate appropriate responses to satisfy certain needs; the most significant of these needs is survival. Nervous system structures vary in the animal kingdom. In lower forms of animals, we can see different types of nervous systems. Cnidarians have a network of loosely arranged nerve cells throughout their bodies, forming a nerve net. Flatworms such as planarians exhibit a rudimentary brain with nerve cords traversing the length of their bodies. Mammals have highly evolved nervous systems. They have large brains which process information and sense organs located near the brain. The human nervous system is made up of nerves, the brain, and the spinal cord. The nerves themselves do not form one single system, but several which are interrelated. Some of these are physically separate while others are different from one another in function only. The brain and spinal cord make up the central nervous system (CNS). The peripheral nervous (PNS) is made up of nerves which transmit information back to the brain; this system is responsible for the bodily functions which are not under conscious control, like the heartbeat or the digestive system. The smooth operation of the peripheral nervous system is achieved by dividing it into sympathetic and parasympathetic systems. These are opposing actions and create a check and balance system. The nervous system uses electrical impulses to communicate external conditions to the brain; the electrical impulses travel along the length of the neurons (the nervous system's primary network of cells) and other nervous system cells. These cells process information from the sensory nerves and initiate an action within milliseconds. These impulses travel at up to 250 miles per hour, while other systems, such as the endocrine system, may take many hours to respond with the appropriate hormones.

The Central Nervous System
The CNS is composed of the brain and the spinal cord. It is protected by two sets of bones: the brain is protected by the skull and the spinal cord is protected by the vertebral column. Both the brain and the spinal cord are enclosed within three layers of membranes known as the meninges. The Brain. The brain is the anterior end of the spinal cord. It is where responses received from the sensory receptors are interpreted. The spaces within the brain are called ventricles. They are filled with cerebrospinal fluid. The brain is made up of two parts:

1. Brain stem – functions below the level of consciousness and thus called the unconscious brain. It controls involuntary actions such as heartbeat, breathing, swallowing, sneezing, digestion and action of the blood vessels. It has two distinct regions:

* Hypothalamus – concerned with homeostasis. It controls the pituitary gland – a gland of the endocrine system – thereby creating a link between the nervous system and the endocrine system. It receives all the sensory impulses from other parts of the spinal cord and the brain. * Thalamus – most prominent part of the forebrain. It sorts out information coming from all the senses and sends it to the appropriate centers in the brain where it is interpreted. Components of the brain stem:

* Cerebellum – it is located at the back of the medulla oblongata which is also part of the brain stem. It coordinates movements of the voluntary muscles and maintains muscle vigor and body balance. * Medulla oblongata – has control centers for breathing, heart and blood vessel activity, digestion, vomiting, and swallowing. * Pons – it participates in the...
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