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nervous system

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The brain and the body are constantly alive with billions of chemical and electrical signals. The nervous system has two main divisions. The central nervous system (CNS) is made up of the brain and spinal cord. Nerve fibres that branch from the CNS are referred to as the peripheral nervous system (PNS). The PNS is constantly sending information to the CNS that processes the information and then send messages back to the PNS. Diagram 1 - Systems of Nervous System Communication and Co-ordination The main job of the nervous system is to control the communication and co-ordination within the body; however the Hormonal or Endocrine system as it is sometimes referred as is also involved with the communication and co-ordination of the body. Nerves Hormones Sends fast messages around the body Sends slow messages around the body Acts for a very short time Acts for a long time Acts in a precise area Acts in a more general way Immediate reaction Longer reaction time The table above compares the hormonal system and the nervous system Neurones and Reflexes Neurones transmit electrical impulses very quickly around the body, there are three types of neurones but they are pretty much the same, they are just located in different areas of the body and connect to different tissues. ...read more.


* Several short processes called dendrites which increase the surface area available for connecting with axons of other neurones. specialised cell junctions called synapses between it's axon and other cells which allow for direct communication from one cell to another. Homeostasis Homeostasis is the active process by which an organism maintains and controls a constant internal environment despite external changes. There are two major control systems involved in homeostasis, these controls centres are: * Brain of the nervous system * Glands of the endocrine system Within the body it is important that several different factors must be regulated including: * Temperature * Heart rate * Respiratory rate * Blood pressure * Water balance * Blood sugar levels * Detoxification Activity Organs Involved Centre of Control Temperature Skin Hypothalamus Heart Rate Heart Medulla oblongata Respiratory Rate Rib and Diaphragm Medulla oblongata Blood Pressure Heart Kidneys Medulla oblongata controls: -cardiac output -arteriole resistance Hypothalamus directs the pituitary gland of the endocrine system to control water levels in the blood Water Balance Kidneys Medulla oblongata controls: -cardiac output -arteriole resistance Hypothalamus directs the pituitary gland of the endocrine system to control water levels in the blood Blood Sugar Levels Pancreas Islets of Langerhans ...read more.


A vital part is played by the hormone insulin, which reduces the level of glucose in the blood. Homeostasis also maintains a person's blood pressure, pulse rate and a person's respiratory rate. Diagram 3 - Balances and in-balances of Homeostasis Negative Feedback In animals such as ourselves, the internal environment of our bodies must have certain conditions within tolerable limits to continue the healthy functioning of us. This is done by a process called negative feedback control, where various receptors and effectors bring about a reaction to ensure that such conditions remain favourable. When a change occurs in the body, there are two general ways that the body can respond. In negative feedback, the body responds in such a way as to reverse the direction of change. Because this tends to keep things constant, it allows us to maintain homeostasis. On the other hand, positive feedback is also possible. This means that if a change occurs in some variable, the response is to change that variable even more in the same direction. This has a de-stabilizing effect, so it does not result in homeostasis. Positive feedback is used in certain situations where rapid change is desirable. The principle of negative feedback control is illustrated by the diagram below: ?? ?? ?? ?? Unit 13 Nervous System ...read more.

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