Nerves+and+Hormones+Nathan

__**Hormones Are Chemical Messages Are Sent In The Blood.**__


 * 1) Hormones are chemical relesed directly into the blood.
 * 2) They're carried in the blood to other parts of the body.
 * 3) Hormones only affect particular cells in particular places (called target cells).
 * 4) Hormones are produced in (and secreted by) various glands.

__Hormones and Nerves Do Similar Jobs, but There Are Differences. __

__Nerves; __
 * 1) Very FAST action.
 * 2) Act for a very SHORT TIME.
 * 3) Act on a very PRECISE AREA.

__Hormones;__
 * 1) SLOWER action.
 * 2) Act for a long time.
 * 3) Act in a more GENERAL way..........

One of the functions of blood is to transport dissolved substances, including hormones, around the body. Hormones are chemical substances that help to regulate processes in the body. Insulin is one such hormone, regulating the level of glucose in the blood. Oestrogen and progesterone are two hormones involved in the female menstrual cycle.

Plasma
Plasma is a straw-coloured liquid. It transports dissolved substances around the body, including:
 * hormones
 * nutrients, such as water, glucose, amino acids, minerals and vitamins
 * waste substances, such as carbon dioxide and urea

Red blood cells
Red blood cells contain a protein called haemoglobin. This sticks to oxygen, allowing it to be carried round the circulatory system.

The nervous system allows the body to respond, through effectors, to changes in the environment detected by receptors. The process involves neurones, and is usually coordinated by the brain. A reflex action is an extra-rapid response to a stimulus, and this process also involves the nervous system, but it bypasses the brain. The iris of the eye is a receptor, which adjusts itself according to the amount of light entering the eye. Accommodation is the ability of the eye to bring objects into focus. The brain can be damaged by accidents or illness, such as strokes and Parkinson's disease. =Receptors and effectors=

Receptors
Receptors are groups of specialised cells. They can detect changes in the environment, which are called **stimuli**, and turn them into electrical impulses. Receptors are often located in the **sense organs**, such as the ear, eye and skin. Each organ has receptors sensitive to particular kinds of stimulus.

Different receptors
The central nervous system (CNS) in humans consists of the brain and spinal cord. When a receptor is stimulated, it sends a signal along the nerve cells - neurones - to the brain. The brain then co-ordinates the response.
 * ~ sense organs ||~ receptors sensitive to ||
 * [[image:http://www.bbc.co.uk/schools/gcsebitesize/science/images/baby_hand.jpg width="226" height="248" caption="A baby holding its mother's finger"]]Skin || touch, pressure, pain and temperature ||
 * [[image:http://www.bbc.co.uk/schools/gcsebitesize/science/images/women_tongue.jpg width="226" height="248" caption="A womens tongue "]]Tongue || chemicals in food ||
 * [[image:http://www.bbc.co.uk/schools/gcsebitesize/science/images/nose.jpg width="226" height="248"]]Nose || chemicals in the air ||
 * [[image:http://www.bbc.co.uk/schools/gcsebitesize/science/images/women_eyes.jpg width="226" height="248"]]Eyes || light ||
 * [[image:http://www.bbc.co.uk/schools/gcsebitesize/science/images/man_ear.jpg width="226" height="248"]]Ears || sound and position of the head ||

Effectors
An effector is any part of the body that produces the response. Here are some examples of effectors:
 * a muscle contracting to move the arm
 * a muscle squeezing saliva from the salivary gland
 * a gland releasing a hormone into the blood.