1. It's all under control

2. Getting the message H umans (and all other organisms)need to respond to changes that occur both inside and outside their bodies. If they don©t, their lives can be under threat.The brain is the control centre of the human body. It receives information from the sense organs Ð the eyes, ears, nose,tongue and skin. It processes the information received and sends messages to different parts of your body. information is carried to and from the brain through a system of nerves. The centre of this system is your spinal cord, which starts at the base of your brain. Messages are sent through your nervous system at speeds of up to 350 kilometres per hour. So, it©s not surprising that you can respond to changes in your environment very quickly. Response times are often very important Ð especially in life or death situations

3. 1 Which of your sense organs is involved in helping you keep your balance when riding a bike? 2 Think of some situations in which you have to respond quickly to changes in your surroundings in order to prevent injury or death. 3 How are messages sent through your nervous system? 4 What activities does your body carry out without you even thinking about them?

4. Map the external regions of the brain

5. Responding to external changes Have you ever wondered how you can hear, see and duck a ball speeding towards you all within just a fraction of a second? Have you felt the pain when you've ducked too slowly? Detecting changes in our environment requires use of our sense organs. Your eyes, ears, nose, tongue and skin detect minor changes in your surroundings. If your organs don't sense a change, you can't respond, no matter how fast your nervous system sends messages.

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9. inner ear

10. The human sense organs are supplied with neurons (nerve cells) to detect and respond to changes that occur both inside and outside our bodies. The neurons that detect changes are called sensory neurons. The parts of the sensory neuron that actually detect the change are called receptor sites. Each sensory neuron responds to changes by sending messages to the spinal cord and (usually) the brain to interpret and decide what the body should do about the change. Messages carried through nerve cells are called nervous impulses, or just impulses. Neurons in the eyes, ears, nose and tongue respond to very specific stimuli. For example, the neurons in the eye respond to light; those in the ear respond to sound and gravity; and those in the nose and tongue respond to chemicals. Different types of neuron in skin respond to temperature, pressure, touch and pain.

12. Did you know? Does it hurt?

13. Different kinds of sensory neuron S ensory neurons are named according to the stimuli that make them respond. For example: ·· Chemoreceptors respond to chemicals. ·· Photoreceptors respond to light. ·· Mechanoreceptors respond to movement. ·· Thermoreceptors respond to changes in temperature.

14. REMEMBER 1. What are neurons? 2. What one name is given to all of the neurons that detect change in your sense organs? 3. What is a receptor site? 4. What does a receptor do when it detects a change? 5. What is a nervous impulse? 6. Copy and complete the table below.