The Brain and the Nervous System
There are several things that all organisms (living things) have in common. One of those characteristics is that they respond to their environment by sensing things that happen in their surroundings and reacting to them. The parts of your body that control your physical reactions to the environment are called the nervous system. The nervous system consists of your brain, spinal cord, and nerves. The nervous system is an elaborate communication system that collects information and sends messages throughout your body. Your brain alone contains more than 100 billion nerve cells. Nerves are special cells that communicate using electrochemical impulses. An electrochemical impulse is a process that uses chemicals to create an electrical impulse. Nerve cells do not touch each other, but meet at a synapse, a small gap where the electrochemical impulse releases a chemical messenger that transfers the impulse from one nerve cell to the next.
Sensory nerves collect information from your environment such as hot, cold, touch, pressure, and pain. They send this information to your brain, which decides how to react. The brain and spinal cord are collections of interneurons, nerves that link other nerves within the body. Once your brain decides on the appropriate response, it sends messages to other nerves called motor nerves, which direct your muscles to move.
Sometimes you respond to what is happening around you and at other times you respond to what is happening inside of you. For instance, you hear a friend call your name and you turn and say hello. A mosquito lands on your skin and again you respond, but this time your response is different. You try to slap the mosquito. When you get hungry, you eat, and so on.
The activities in this chapter will help you investigate how your brain and nervous system keep you in contact with your environment by telling you what is happening and deciding how to act on that information.
I'm sure you are a good reader, and that you can easily identify the colors red, blue, and green. But is it possible to confuse your mind so that it mixes up the words and colors that you see? Try this activity to find out.
6 different colored felt-tip pens paper
1. Use the felt-tip pens to make a list of the names of six colors. Write out each color's name with a different colored pen, but don't use the color of pen that matches the name. For example, don't use the green pen to write out the word "GREEN."
2. Read the words on the list out loud as fast as you can.
3. Read the list again, only this time say the color that the word is written in. What happens? Which is easier to do?
You should have little trouble reading the words on the page, but you will find it takes longer to say the color that the word is written in.
Different areas of the brain have different responsibilities. For example, the area of the brain responsible for vision is located near the back of your brain, while your knowledge of colors is located in the front of your brain. The area responsible for speaking is located along the left side of your brain, and language understanding is further back along the left side. When you first learned to read, you were taught to speak and read words. For this reason, there are many nerves that connect the areas of your brain responsible for speaking with those responsible for language understanding. You were taught to recognize colors by sight, so you developed connections between the vision area and the color knowledge area of your brain. When you try to see the color of a word that is spelling out a different color, your brain gets confused. It sees both the word and its color, and sends the information to two different parts of the brain. The dominant part of your brain, however, is the part that understands language, so your first impulse is to name the color that the word spells out. It takes a while for you to say what color the word is written in.
THINK FAST, ACT FASTER
It takes time for your body to react to messages from the brain. But how long does it take? Try this activity to find out.
1. Hold the 12-inch (30-cm) end of the ruler vertically at arm's length as high as possible, with the 1-inch (2.5-cm) end toward the ground.
2. Have a helper stand facing you so that his or her thumb and index finger of one hand are on the sides of the bottom of the ruler. The thumb and index finger should be close to the ruler, but not touching it.
3. Drop the ruler at any time. With his or her hand held steady, your helper should try to catch the ruler as quickly as possible between the thumb and index finger.
4. Calculate the distance the ruler fell before it was caught, using the inch mark covered by your helper's finger.
The ruler will fall a short distance and your helper will catch it between his thumb and index finger. The distance the ruler falls can be used to determine your helper's reaction time. Reaction time is the amount of time it takes for a message to travel from the brain to the muscles in the body and cause a movement.
When the ruler drops, the motor cortex of the brain sends an electrochemical message to the fingers. The motor cortex is the area of the brain responsible for creating and sending the messages that cause movement. The message travels along the thick bundles of nerve cells-the spinal cord-that are inside the bones of the spine. Then the message travels to the finger muscles through the smaller bundles of motor nerves that branch from the spinal cord. The finger muscles get the message and close, catching the ruler.
Use the Reaction Time table below to convert the distance the ruler falls into reaction time.
HEAT TO TOE
Science in Action
In some sports, fast reaction times are very important. Sprinters must react quickly to the start signal. Baseball players also need to be able to react very fast. A good pitcher in the major leagues can throw a ball at a speed of between 90 and 100 miles per hour (144 and 160 km/h). What does that mean to a batter? The ball will take between 0.46 and 0.41 seconds to travel from a pitcher's hand to the plate. If you figure it takes about 0.3 seconds to actually swing, the batter may have only 0.1 to 0.2 seconds to decide when and where to swing and get the message to the arm and hand muscles. It's truly amazing that the human body can perform at this speed.
TEACH A DOG NEW TRICKS
You have learned a lot of things in your life, such as how to walk and talk, and to read and write. What is the best way to learn a new task? Try this activity to learn more about how the brain learns new things.
broom 2-by-12-by-24-inch (5-by-30-by-60-cm) wooden plank stopwatch or watch with a second hand helper
1. Lay the broom flat on the floor.
2. Center the wooden plank across the broom handle so that the longest side of the plank is perpendicular to the handle.
3. Have your helper step on the plank so that one foot is placed near each end of the plank.
4. Time your helper for 5 minutes while he or she tries to learn to balance the plank on the broom handle so that neither end of the plank is touching the floor.
5. After your helper has had 5 minutes to learn to balance, it's your turn. You will also have 5 minutes to learn this new task, but you will spread your 5 minutes out over the day. Practice for 1 minute at a time, then stop for several hours. Your total practice time should be no more than 5 minutes.
6. The next day, both you and your helper should try again to balance on the plank. Who has learned to balance better?
You both had the same amount of practice time, but because you spread out your practice over a longer period, you learned to balance better than your helper who tried to learn all at once.
Although no one is exactly sure how the brain learns, the most common theory is that it needs consolidation time to learn a new task well. Consolidation time is the time your brain needs to store in a more permanent way the information about how to do a new task. When you first learn a new task, whether it is how to balance on a plank or how to do a new math problem, the information is stored temporarily as an electrical code within the brain. This electrical code is not stable, so you will quickly lose the information when you stop doing the task. However, if the task is practiced over a longer time, the electrical code is changed and stored in a more permanent, stable chemical code. Memory stored as a chemical is remembered better in the long term, which lets you perform the task better the next time you try it.
The brain is amazing because it both registers what you see and interprets the information. But sometimes the brain can be fooled into seeing something that isn't there. Try this activity to trick your brain.
scissors Styrofoam plate helper
1. Cut the rim off half the plate.
2. Cut the piece of rim approximately in half so you can lay one half over the other.
3. Trim the edges of both pieces at the same time to make sure that they are exactly the same length.
4. Place the 2 pieces on the table so that they are facing the same direction.
5. Ask your helper which piece is bigger.
Your helper will have a difficult time telling which piece of the plate rim is larger when indeed both are the same length. Odds are, he or she will think that the left piece of the rim is longer.
There are different reasons for optical illusions. An optical illusion is a picture or image that results in a false impression. Some illusions occur when your brain sees something and incorrectly interprets it to be something you've seen before. You assume something looks one way because you have seen something similar before.
Optical illusions also occur when your brain compares two different, but similar, objects. With the plate pieces, the inner arc of the right piece is next to the longer outer arc of the left piece, which makes the right piece seem shorter.
THROUGH THE LOOKING GLASS
Your sense of direction is something that you often take for granted. Up or down and left or right seem easy to tell apart. But what if your sense of direction became mixed up? Try this activity to see how you would react if everything seemed backward.
pencil paper stopwatch or watch with a second hand hand mirror helper
1. Make a copy of the two mazes shown below, either using a copy machine or tracing them on another piece of paper.
2. Draw a path through the first maze without lifting your pencil. Have a helper time how long it takes you to complete the task.
3. Have your helper hold the hand mirror so that you can see the second maze in the mirror. Draw a path through the maze while watching the path you make in the mirror. Do not look directly at the paper or pencil. Have your helper time how long it takes you to complete the task this time. Which way of drawing a path through the maze takes less time? Which way is more accurate?
It will be more difficult and will take longer to draw a line through the maze when you are looking at it in the mirror.
The eyes send a message to the brain, telling it where the pencil is and where the pencil should move next. Over time, your body has learned to coordinate these motions, so when your brain sees that the path goes left, it tells your hand to move left. When you try to draw the maze while looking in the mirror, the task becomes more difficult because everything is backward. Your eyes look at the maze and send a message to your brain, which sees that the pencil mark has to go left. However, your brain knows that the mirror has reversed the image, so it has to tell your hand to move right instead of left. The brain is confused between doing what the eyes are showing it and what it understands it should do.
It's easy to figure out which hand is your dominant one. It's usually the hand that you use to write with. But did you know that you also have a dominant eye? Try this activity to find out more.
pencil paper tape
1. Draw a spot about the size of a quarter on the paper.
2. Tape the paper on a wall.
3. Stand on the opposite side of the room facing the paper.
4. Extend your arms in front of you, palms facing the paper. Make a small peephole between your hands with your thumbs and fingers of each hand.
5. Look at the spot on the paper through the peephole with both eyes open.
6. Without moving your hands or your head, first close your right eye and look for the spot. Then open your right eye and close your left. Which eye still sees the spot?
The spot will be seen by only one eye, either the right or the left. The eye you see the spot with is your dominant eye. Your dominant eye is your favored eye, which usually sees an object slightly better than your nondominant eye. This isn't related to whether you are right- or left-handed. But in the same way that you have a dominant hand, you also have a dominant eye.
HEAD TO TOE
Science in Action
Your dominant eye doesn't affect your everyday life too much, but it does affect how you move when you play sports. To allow your body to use its dominant eye more, you will slightly turn your head right or left to let the dominant eye get a better view of what you're looking at. Some coaches have found that a gymnast who has a dominant right eye will make left turns better because the gymnast's head naturally turns that way to let the right eye get a better view. The same applies to a dominant left eye and right turns.
SPIN LIKE A TOP
Your inner ear helps your body know whether you are right side up or upside down. In other words, it helps you balance. Try this activity to learn more.
swivel chair scarf that can be used as a blindfold timer or watch that counts seconds helper
1. Place the chair in the center of the room. Make sure you have enough space for the chair to turn in circles without stopping.
2. Have your helper sit in the chair, feet off the floor. Use the scarf to blindfold your helper.
3. Turn the chair slowly in one direction. Time the turns so that you make one complete turn every 2 to 3 seconds, turning at a constant speed. How does your helper feel after one or two turns?
4. After 1 minute, stop turning the chair. How does your helper feel now?
When the chair first begins to spin, your helper should sense the turning motion. After about 30 seconds, however, your helper won't feel the turning at all. After 1 minute, when you stop turning the chair, your helper will feel that he or she is turning in the opposite direction.
Your sense of balance is controlled by granules in two fluid-filled sacs that detect direction up and down and three fluid-filled semicircular canals that detect motion. These loop-shaped structures are located in your inner ear. The inner ear contains the semicircular canals along with the cochlea and the auditory nerve. The cochlea and auditory nerve will be discussed later, in chapter 2. The movement of the fluid in the semicircular canals sends messages of movement to your brain. When you turn your helper initially, the fluid in the canals of his or her ears moves. At first the fluid resists movement because of inertia (the tendency of an object to remain at rest or continue moving unless acted on by an outside force). Your helper's brain registers movement in the direction of the spin. But as the spinning continues, the fluid flows in the direction of the spin and your helper no longer feels the movement. When the chair stops turning, the fluid resists the stopping motion and incorrectly sends signals to your helper's brain that he or she is turning in the opposite direction.
Excerpted from Head to Toe Science by Jim Wiese Copyright © 2000 by Jim Wiese. Excerpted by permission.
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