You are going to try to find out how fast impulses travel through someone by measuring the time it takes for someone to feel a squeeze in one elbow and pass the squeeze on to a neighbour.
Prediction
1 a How fast do you think the ‘squeezing message’ will take to go through someone?
b Why do you think this?
Apparatus
stopwatchtape measure
Method
AGet all the members of your group to stand in a circle. Each person should hold their neighbour’s right elbow with their left hand.
BGet one person to hold a stopwatch in their right hand.
C The person with the stopwatch squeezes the elbow of the person to the left of them at the same time as starting the stopwatch.
DAs soon as the next person feels their elbow being squeezed, they should squeeze the elbow of the person on their left.
EWhen the person with the stopwatch feels their elbow being squeezed they should stop the stopwatch and record the time.
F Divide the time taken by the number of people in the circle. This will give you the time it takes for the impulses to travel through one person.
GNow measure the route an impulse must take from the right elbow to the brain and then to the left hand. This will give you the distance the impulse has travelled.
HDivide the distance (in metres) by the time taken (in seconds), and this will give you the speed of the impulses (in m/s).
I Repeat the experiment several times and record all your results.
Recording your results
2 Write up your results neatly in a table.
Considering your results/conclusions
3 Work out the mean speed of an impulse (Hint: Add up the speeds you calculated in step H for all the times you did the experiment, and divide by the number of times you did the experiment).
4 a How does this compare with your prediction?
bWhy do you think it is different from your prediction?
5Why is it important that neurones carry impulses quickly?
Evaluation
6 a Which variables did you keep the same to try to make this a fair test?
b Which variables could you not keep the same?
7 a Which do you think was your least good result?
bWhy do you think this result was not as good as the others?
8How would you change the experiment to get better quality data?
© Pearson Education 2010. Edexcel GCSE Science Activity Pack
This document may have been altered from the original.
1 Look at the sentences and then fill in the table.
aTony sees in a TV guide that there is something good on TV. He switches on the TV with the remote control.
bAnnabel turned the CD player off when she realised she was listening to one of her father’s CDs.
Sentence / What is the stimulus? / Where are the receptor cells for this stimulus? / What is the response? / Where are the effector cells for this response?a
b
2Draw lines to connect the following cells to the drawing of the neurone they send impulses to or receive impulses from.
aa cell in the retina of the eye
ba muscle cell
can adrenal gland cell
da ‘touch receptor’ in the skin
3 aOn the diagram draw a line (with an arrow) to show how the brain senses that you have touched a pen with a finger. Label this pathway A.
b On the diagram draw a line (with an arrow) to show how impulses are sent from the brain to the finger. Label the pathway B.
Feeling a pen and then picking it up is an example of a coordinated response. Other responses are automatic and occur very quickly.
cWhat are these quick automatic responses called?
dWhat is the name of the short pathway of neurones that impulses in an automatic response follow?
© Pearson Education 2010. Edexcel GCSE Science Activity Pack
This document may have been altered from the original.
You do not need to remember the details on this sheet for your exam but you could be asked to apply your knowledge to unfamiliar situations.
Inside all your muscles are muscle spindles that contain receptor cells. The muscle spindles are stretched when a muscle is stretched. When this happens an impulse is generated, which is sent along a sensory neurone. The impulse is transmitted through a reflex arc, causing the muscle to contract (or contract even more). Even if you are standing still, minute variations in position are occurring all the time, and these are detected by muscle spindles and cause reflexes that automatically make slight alterations to muscle tensions, so that you stay upright.
The knee jerk reflex (or patellar reflex) is one of these reflexes and it occurs using a monosynaptic (single synapse) reflex arc. However, it’s not quite as simple as that!
Another sensory neurone runs from a receptor called the Golgi tendon organ. As the quadriceps muscle contracts it pulls on the tendon and stretches it. If the quadriceps muscle contracts too much, and there is a danger that the tendon could be damaged, the Golgi tendon organ sends impulses to a relay neurone which connects to the motor neurone going to the quadriceps. This relay neurone uses a neurotransmitter called glycine in its synapse with the motor neurone, and this inhibits (decreases the chances of) an impulse being generated in the motor neurone. Most synapses use a neurotransmitter that stimulates (increases the chances of) impulses being generated.
1 What is a monosynaptic reflex arc?
2What part of a muscle detects stretching?
3 aWhat is the effect on the quadriceps muscle when the tendon is stretched too much?
bWhy is this useful?
cWeightlifters have been known to inject themselves with local anaesthetic near their Golgi tendon organs. Why do you think they do this?
4 aName each type of neurone labelled P to U in the diagram.
bState whether each neurone is inhibitory or stimulatory.
5 Describe, in as much detail as you can, what happens when the muscle spindle is stretched.
6Why are reflex arcs useful for the body?
Extra challenge
7If a bacterium called Clostridium tetani gets into humans it can produce a poison that causes a serious condition called tetanus. The poison blocks the release of glycine into synapses. What do you think the symptoms of tetanus are? Explain your reasoning.
© Pearson Education 2010. Edexcel GCSE Science Activity Pack
This document may have been altered from the original.