Week 12 - Scientific Investigation and Medical Applications

1 Sensory Awareness

Lesson 13

Science in Action 8
Pages 146-151

ScienceFocus 8
Pages 151-152


Lesson 13: Sensory Awareness
Your nervous system, with the help of all the other body systems we have studied, tries to keep your body stable. For example, the ideal body temperature for humans is 37 degrees Celsius. But throughout the day you may have times of strenuous exercise and times of sitting quietly. The temperature regulating region of your brain ( the hypothalamus) coordinates the behavior of you're your skin, blood vessels and muscles to ensure your body maintains its ideal temperature. The brain tries to maintain this stability in, and between, all body systems.

Background Information
Stimulus / Response

A stimulus is anything that causes an organism to react. A response is a reaction to a stimulus. A stimulus can come from outside the body and be received by your five senses, or it can arise internally. An internal stimulus might cause a response to breath faster.

You have external sensory organs that constantly monitor your external environment. Do you remember what they are?
Monitoring Internal Body Systems

We all know that it is very important that we get enough oxygen and so we assume that our body monitors the amount of oxygen we receive. But interestingly, it doesn't work that way. Our body monitors the build up of carbon dioxide in our blood stream not oxygen. So we breath faster when the carbon dioxide levels rise - usually due to exercise
Did You Know? Swimming under water can be fun but dangerous.

Never hyperventilate before you swim under water!
Knowing that the body monitors carbon dioxide, not oxygen, is important for swimmers. I'm sure we've all seen kids playing around lakes or pools. Sometimes they compete with each other to see who can swim the farthest underwater. You might see them take many deep breaths before they dive. This is called hyperventilating and is very dangerous. The children think that they are building up reserves of oxygen for their swim, but actually they are dramatically lowering their carbon dioxide levels without really changing the oxygen levels. This means they don't feel the need to breath even though they are running short of oxygen. Every year children drown because they blacked out under water when they ran out of oxygen.

The Nervous System

The nervous system is composed of specialized cells called neurons . Neurons receive a message at one end through structures called dendrites. The message travels through the cell body and then through very long extensions called axons. The axons relay the message on to the next neuron.

Nervous System Organization

The nervous system can be divided into two basic divisions. The central nervous system is made up of the brain and spinal chord . All the nerves that radiate from the central nervous system are considered to be part of the peripheral nervous system .

The Central Nervous System

Your brain receives all the incoming sensory information and decides how to deal with it. Once a response is decided on, it sends out instructions to the appropriate muscles and organs. The brain can be divided into three major parts: the cerebrum, the cerebellum and brain stem (medulla). The cerebrum receives sensory information and does the decision-making. You could also think of it as the thinking , feeling part of your brain. The cerebellum coordinates muscle movements. For example, do you remember when you first learned to ride a bike ? For a while you were probably all over the place. But as cerebellum learned to coordinate your muscles and balance, you got better and better. Your brain stem looks after organ system functions like breathing and digestion, so you don't have to consciously think about all the things that go on inside you - thank goodness!

The spinal cord 's job is to connect the brain to all the peripheral nerves. Think of it as a highway for all the sensory and motor nerve messages traveling throughout your body.

The Peripheral Nervous System

Peripheral nerves connect the muscles and organs throughout your body to the spinal chord. Nerves that carry sensory information to your central nervous system are called sensory neurons . Instructions from the brain back to organs and muscles are called motor neurons .

The peripheral nervous system can be further divided into automatic responses and those that you consciously decide to carry out. The autonomic nervous system deals with automatic responses which include: your blood pressure, heart rate, breath rate and rate of peristalsis in the digestive tract. Somatic nerves carry voluntary responses such as reaching for a piece of pizza or turning or head to follow a sound.
Exercise 4.1: Measuring Your Reaction Time

© 2002 Alberta Online Consortium