eis 23: the nervous system
The whole point of the nervous system is to send messages fast. Like, really fast. If you have your hand on a hot stove, you’re going to want to pull that off as quickly as possible so you don’t burn your hand too badly. If you’re being chased by a bear (as I am on a regular basis), you want your motor neurons to be pretty much constantly telling your muscles to go, go, go if you want to have any chance of surviving.
Compare this type of communication to the other main method your body uses: hormones. Hormones are great. They can cause more permanent changes, and they can have more global effects (whereas nerves pretty much just act on one or a few cells). But, they are slow. It could take minutes, hours, or even years for a hormone to show its full function. If you’re being chased by a bear, you are going to want some hormones to keep you running fast over long distances and to get the rest of your body on board with this whole “life or death” situation. But hormones alone are not going to be enough to tell your muscles to move as quickly as they need to.
The nervous system is fast because it uses electrical signals (using ions), not unlike turning on a lightswitch. They have their own private highways in the body called axons, which are the parts of neurons (nerve cells) that transmit electrical impulses. The proper name for these electrical impulses is action potentials.
Reflexes are an especially fast type of neural communication because they don’t have to go through the brain: the spinal cord can handle them on their own. So, the sensory input (say, someone throwing a ball at your face) comes in, gets sent to the spinal cord via a sensory nerve, gets turned right back around by the spinal cord and sent back to the body via a motor nerve (which tells your muscles to do something, like DUCK!). This process is called a reflex arc. All this happens before the signal even gets sent to your brain to cognitively tell you to duck, or you even realize that you are ducking.
In this activity, you’ll be testing a few different reflexes and reaction time tests to show off the speed of your nervous system.
Compare this type of communication to the other main method your body uses: hormones. Hormones are great. They can cause more permanent changes, and they can have more global effects (whereas nerves pretty much just act on one or a few cells). But, they are slow. It could take minutes, hours, or even years for a hormone to show its full function. If you’re being chased by a bear, you are going to want some hormones to keep you running fast over long distances and to get the rest of your body on board with this whole “life or death” situation. But hormones alone are not going to be enough to tell your muscles to move as quickly as they need to.
The nervous system is fast because it uses electrical signals (using ions), not unlike turning on a lightswitch. They have their own private highways in the body called axons, which are the parts of neurons (nerve cells) that transmit electrical impulses. The proper name for these electrical impulses is action potentials.
Reflexes are an especially fast type of neural communication because they don’t have to go through the brain: the spinal cord can handle them on their own. So, the sensory input (say, someone throwing a ball at your face) comes in, gets sent to the spinal cord via a sensory nerve, gets turned right back around by the spinal cord and sent back to the body via a motor nerve (which tells your muscles to do something, like DUCK!). This process is called a reflex arc. All this happens before the signal even gets sent to your brain to cognitively tell you to duck, or you even realize that you are ducking.
In this activity, you’ll be testing a few different reflexes and reaction time tests to show off the speed of your nervous system.
materials
A partner: friend, family member, or anyone else you trust
A ruler or dollar bill
A flashlight or pen light
A ruler or dollar bill
A flashlight or pen light
Activity 1: Knee Jerk Reflex
You are probably familiar with the knee flex or knee jerk reflex. This is where you hit your knee in just the right spot and it kicks out. This type of reflex is extra fast because it is monosynaptic. So monosynaptic means there’s only one synapse or connection between nerves (two nerves).
Let’s try it! Have your partner sit with their leg dangling. Then, find their patellar tendon. This will feel like a springy connector between the kneecap and the top of the shin. Then, hold your hand in a karate-chop position and hit their patellar tendon. This should be firm but not painful. If you hit the right spot, their leg should kick out!
Let’s try it! Have your partner sit with their leg dangling. Then, find their patellar tendon. This will feel like a springy connector between the kneecap and the top of the shin. Then, hold your hand in a karate-chop position and hit their patellar tendon. This should be firm but not painful. If you hit the right spot, their leg should kick out!
Activity 2: Blink Reflex
When you are surprised or think something is coming at your face, you blink. This is to protect your eyes if something really is coming at your face.
You can easily observe the blink reflexes in others. Simply act like you’re coming at their face (do not actually hit them). Try this a few times. See if telling them it’s coming stops the reflex.
You can easily observe the blink reflexes in others. Simply act like you’re coming at their face (do not actually hit them). Try this a few times. See if telling them it’s coming stops the reflex.
Activity 3: Pupillary Reflex
You may already know that your pupils change sizes in response to light. This is another reflex.
Look into your partner’s eyes. Note the size of their pupils. Then, quickly shine a light in one eye and then the other one. Do you notice the change? You can also try this on yourself in the mirror.
Look into your partner’s eyes. Note the size of their pupils. Then, quickly shine a light in one eye and then the other one. Do you notice the change? You can also try this on yourself in the mirror.
Activity 4: Cognitive Reaction Time 1
Reflexes are so fast because they don’t go through the brain. But, some tasks do require you to think (at least a little). Let’s see how fast your cognitive reaction time is.
Have your partner drop a ruler or dollar bill. Be sure to start the drop at 0 inches or at one end of the dollar bill. Then, see how fast you’re able to catch it (if you can at all)! If you’re using a ruler, you can measure the distance that it fell before you were able to catch it.
Have your partner drop a ruler or dollar bill. Be sure to start the drop at 0 inches or at one end of the dollar bill. Then, see how fast you’re able to catch it (if you can at all)! If you’re using a ruler, you can measure the distance that it fell before you were able to catch it.
Activity 5: Cognitive Reaction Time 2
Do you have the reaction time that it takes to safely drive a car? Do you want to know how your reaction time compares to, say, a 70 year old? Try this online quiz! It will have you hit your space bar when a stop sign pops up.
If you’re having fun, we want to see it! If you have an Instagram and the permission of your relevant responsible adult, share with us @eons_learning, #ReflexEonsEdu
If you’re having fun, we want to see it! If you have an Instagram and the permission of your relevant responsible adult, share with us @eons_learning, #ReflexEonsEdu
Longitudinal Activity: Making a Model of the Human Body
Add the following to your model of the human body:
You may choose to label them somehow, but this is not required.
- Cerebrum
- Cerebellum
- Hypothalamus
- Brainstem
- Spinal Cord
- One or two peripheral nerves (or more, if you like)
You may choose to label them somehow, but this is not required.