Crayfish
Crayfish belong to the phylum
Arthropoda, and the sub-phylum Crustacea. They look a lot like little
lobsters, which makes sense, since lobsters and crayfish belong to the same
sub-phylum. This means that they are related to each other (It might help
if you think of them as cousins. They are not as close as brothers and sisters
are, but they are still family.). Crayfish can be found almost anywhere in
the world, except in Africa. Most live in freshwater ponds, rivers, and streams,
but some can even live in saltwater (like the ocean). Crayfish are usually
3-4 inches long, and can be many different colors, like red, brownish green,
and even white! Crayfish like to eat tiny fish, shrimp, tadpoles, worms,
and organic matter (which is stuff that contains an important element,
called carbon). Crayfish like to hide under rocks and logs, and most only
come out at night, or on cloudy days. They usually live for about two years.
In some parts of the world, like Louisiana, Missisippi, and Europe,
people even eat crayfish!
Crayfish have a hard skeleton on the outside
of their body, called an exoskeleton. Their body is divided
into two parts, called the cephalothorax and the abdomen. They
have 10 pairs of legs, and a tail, called a telson. They use their antennae
and antennules to sense things (just like our fingers help us to touch things,
and our tongue helps us to taste things). They have many different eyes on
stalks, which stick straight out in front of them. Some crayfish have as
many as 7,000-30,000 eyes on each eyestalk (imagine trying to pass a note
to your friend in class if your teacher had 30,000 eyes to look around the
room with)!
It can be hard to understand what the inside of a crayfish looks like. Their
organs are organized very differently than yours or mine. Above is a picture
of the inside of a crayfish. For this experiment, we only need to worry
about where the heart is. As you can see in the picture, the heart is located
on the top, or the dorsal, part of
the body. It is right behind, or caudal, to the stomachs and the
brain.
(The author would like to thank the following
sites for the information and images contained above:
http://www.shrimpcrabsandcrayfish.co.uk/Shrimp.htm?crayfishamerica.html~mainFrame
http://www.jordan.palo-alto.ca.us/staff/gtsuruda/public/zoids.html)
Earthworms
The earthworm belongs to the phylum Annelida. To say that something belongs to a phylum means that it shares some common features with other members of that same phylum. One common type of earthworm is the Canadian night crawler (its scientific name is Lumbricus terrestris). Worms can be found all over the world. They live in the soil, where there is plenty of food, oxygen, and water, and where the temperature is just right. In one acre of land, there can be more than a million earthworms! In fact, there are 2,700 species of earthworms! Earthworms range from 90-300 mm long, but they can be much longer sometimes. They are usually pinkish brown, or beige, in color. Worms are important because they help the soil. They churn up the soil, which helps to mix it and move water through it, and they secrete a slime that has a nutrient called nitrogen in it. Nitrogen helps plants to grow and stay healthy. This earthworm slime also helps hold the soil together. Earthworms eat organic matter, that they find in the soil, vegetable and fruit peelings, grain, and even dead animals. Earthworms must be kept wet, or they'll die. Since they like water so much, they usually come to the surface on rainy days. This is why you see them when it's nice and wet outside. Most earthworms live for about a year, although some can live longer. If you cut a worm in half, it's end portion (posterior part) will grow back from the front portion (anterior part)! Believe it or not, some people eat worms, just like they do crayfish!
The earthworm has many different body parts. It has a head (its anterior part), and a tail (its posterior part). Its body is a round tube, divided into little rings, called segments. The earthworm can have 120-170 segments. On each segment are four pairs of bristly hairs, called setae, that help the worm to move. The earthworm does not have any bones, and its body is soft, wet, and slimy. It has a large bump in the front of its body (in the anterior part). This bump is called the clitellum, and it's important for mating, and making the cocoons that it keeps its babies in. The worm doesn't have any eyes, but it does have cells that are very sensitive to light. This helps it to tell the difference between night and day, and light and dark. This is important for its survival.
The internal anatomy of the earthworm can be hard to understand. Like the crayfish, its insides look a lot different from yours or mine. The picture above is what the inside of an earthworm looks like. For this experiment, we only need to worry about the location of the hearts. As we can see in the picture below, the hearts are in the head, or anterior, part of the earthworm. The earthworm has five hearts. These hearts are important for moving blood through the body of the earthworm.
(The author would like to thank the following site: http://www.urbanext.uiuc.edu/worms/index.html for the information and photos above.)
Now that we've learned a little about invertebrates, we'll start talking a little bit about neuroscience. Neuroscience is the study of the brain, and all of its different parts and functions. Neuroscientists study the brains of many different species, from crayfish and earthworms, to gorillas and humans. Neuroscientists must study for a long time: they go to high school, then to college, and then to graduate or professional school. While in these programs, they study to become researchers, doctors, teachers, and much more. Neuroscience is an exciting field to be in, because it changes everyday. There are several important things that every neuroscientist must know. We'll talk about each of them a little.
Neurons
Neurons are the cells of the nervous system. Our brains have 100 billion neurons! They carry messages from the brain to other parts of the body, and carry information from other parts of the body to the brain. Without neurons, we wouldn't be able to move, speak, or sense anything. We wouldn't even be able to learn! Neurons communicate with each other by generating things called action potentials. Neurons also send molecules called neurotransmitters from one neuron to another. Below is a picture of some real neurons.
Neurons are a lot like other cells. They have a cell membrane, and a nucleus, along with other organelles. Neurons are different than other cells because they have axons, which help carry messages away from the cell body, or soma. They also have dendrites which help bring information to the cell body, or soma. Neurons are the oldest and longest cells in the body.
Neurotransmitters
Neurotransmitters are the messengers that neurons use to communicate with each other. They are special chemicals that are released from the end of one neuron, called the pre-synaptic element, to the beginning of another neuron, called the post-synaptic element. They are made in the cell body, or the soma, and move down the axon, where they are stored in vesicles. When it is time for them to be released, the vesicle attaches to the place where the neurotransmitters are released from. The neurotransmitters are released, and move across a small space, called a synapse. They then attach to the receptors of the receiving neuron, or the post-synaptic element. Each neurotransmitter can bind only with a certain receptor site, just like a key can only fit a certain lock.
There are many different kinds of neurotransmitters. The first neurotransmitter, acetylcholine, was discovered in 1921 by Otto Loewi. He found that acetylcholine makes the heart of a frog slow down. In this experiment, we will be using acetylcholine and atropine, a neurotransmitter that works just like epinephrine. The way to make acetylcholine and epinephrine is shown in the pictures above. For our experiment, you just have to know that adding acetylcholine to the heart makes the heart beat slower, and that adding atropine to the heart makes the heart beat faster.
(The author would like to thank the following sites for the information contained above: http://faculty.washington.edu/chudler/cells.html and http://faculty.washington.edu/chudler/chnt1.html )
Experiment
In this experiment, we're going to see exactly how neurotransmitters are used for communication. We will study how neurotransmitters affect the heart of two common invertebrates. First, though, we will look at how a signal moves from one neuron to another.
Materials:
-Earthworms
-Crayfish
-Acetylcholine
-Atropine
-Microscope
-Dissecting kit
-Foil
-Bottle with dropper
-Ball
Procedure
1. Line up in two equal groups, and have each group join hands to form a chain. Leave a space between groups.
2. Hand ball from the beginning to the end of one chain. When the ball reaches the end of the chain, have the last person in the chain toss the ball across to the cupped hands of the beginning of the second chain. Hand the ball from the beginning to the end of the second chain. This represents how a signal travels down one neuron, across a synapse, and down a second neuron.
3. Next, have an adult mix up the neurotransmitters atropine and acetylcholine. Place in dropper bottle, and wrap in foil. Place in fridge.
4. Dissect to the hearts of a live crayfish/worm. Examine appearance of normal heart under microscope.
5. Drip acetylcholine on the heart. Examine how the heart slows down under the microscope.
6. Drip atropine on the heart. Examine how the heart speeds up under the microscope.
7. Clean up.
For more information on Neuroscience for Kids, please visit the following sites: http://faculty.washington.edu/chudler/neurok.html
http://www.beemnet.com/dana/kidlinks.html
http://www.cartage.org.lb/en/kids/science/Biology%20Cells/Nervous%20System/introb.html