Much of the time it takes you to react to the ruler dropping is the time it takes electrical signals to travel along your nerves. Moving at about metres per second, a signal telling a finger to move has to travel from your brain down your spinal cord and into your arm. Signals for muscle control generally move faster than other ones. Pain signals for example, move very slowly, often less than one metre per second.
Describe how the nervous system responds to a stimulus. Per Student Pair: copy of reaction timer template printed onto stiff card or attached to a ruler with tape. How fast is your reaction time?
What had to happen in your body for you to catch the ruler? How can reaction time be improved? Does your reaction time improve with practice?
Why was the ruler caught in the middle after a lag period rather than at the end instantaneously? What causes this hesitation? This happens almost instantaneously. How fast it actually happens is called the reaction time. When comparing hands, students will usually find that their dominant hand is faster. Because the dominant hand is used more often every day, the neurons that carry messages between that hand and the brain are faster at transmitting electro-chemical signals.
They are communicating along well-worn pathways. By running the same messages along the same pathway repeatedly, students can improve their motor skills. Details Activity Length 20 mins. How fast can you react? This is a recommended pre-visit activity to Science World. Objectives Describe how the nervous system responds to a stimulus. The knee reflex arc is a spinal reflex, and the circuit is drawn above.
This picture shows how the sensory afferent neuron sends information through the dorsal root ganglion into the spinal cord; where the signal splits into two different paths. The first is the motor neuron efferent leading back to the quadriceps. When your quad muscle's motor neuron receives the information it fires and causes your lower leg to spring forward up in the air. The second signal from the sensory neuron travels to an interneuron which sends a signal to the motor neuron efferent leading to the hamstring.
This signal tells your hamstring to relax so there is no negative force acting on the quadriceps muscle when it contracts. Both signals work together and all of this happens in the spinal cord without going to the brain. It never needs the brain. You may be asking how a knee reflex arc and a soccer player dealing with an oncoming ball are different.
Are both not reflexes? While it may seem that a soccer player negotiating an oncoming ball is a simple fast reflex, it is actually a symphony of hundreds of thousands of neurons working together to produce a conscious decision. Does the player catch, dodge, or bat away the ball? This choice is what makes a reaction. When a soccer player realizes the ball is blistering towards him, there is visual information that has to be processed and decisions regarding a correct course of action.
The brain then needs to send many signals to various muscles. Feet begin to move, hands might travel in front of the face, and eyes may close shut, along with many more processes. This is the work of many neurons as well as numerous systems and circuits in the brain, and what's more, and you can train and enhance your skill through practice.
This is how you get better at sports over time. Like all science, the history of the reaction time discovery is peculiar. Dutch physiologist F. Donders in began to think about human reaction time and if it was measurable.
Prior to his studies scientists thought that human mental processes were too fast to be measured. This assumption was proved incorrect with the help of Charles Wheatstone, an English scientist and inventor. In Wheatstone invented a device, much like his early telegraph system invention, that recorded the velocity of artillery shells. Donders used that device to measure the time it took from when a shock occurred on a patient's foot until when that patient pressed a button.
The button had to be pressed by the left or right hand matching the left or right foot that was shocked. Again, have students record their reaction time data on the Reaction Time Data Sheet , as well as answer the accompanying analysis question. After all students have tested their reaction time by catching the ruler, ask these questions:. To get at this point, ask students this question:. Again, students should realize the importance of practice, and understand that practicing this activity over and over would most likely lead to even better reaction times.
Follow this lesson with the second lesson in the reaction time series: Reaction Time 2: Zap! Students could revisit the Exploratorium's Fastball Reaction Time and design and conduct their own tests of human response time. For example, do students have a faster response time using the hand that they write with, or the opposite hand? Are students' times the same when they listen to music?
This activity tests how fast students respond to different colors, and allows students to explore how their reaction times vary with different colors. Students could go to Explorescience.
Sound Reflexes , where they'll respond to visual and auditory cues to determine when response time is quicker. See the Tool. See the Collection. See the Lesson. Related Resources Nutrition 3: Got Broccoli? Did you find this resource helpful? Have you tried this lesson? Share your tips. Other Lessons in This Series 1.
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