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GCSE  Core:  Student  Task  Sheet  

Reflex:  Acting  Without  Thinking  
 
Imagine  that  you  jump  in  response  to  a  loud  noise  while  
watching  a  scary  movie,  Use  diagrams  and  a  flow  chart  to  show  
what  happens  in  the  body  when  it  reacts  suddenly
...
 Body  temperature  and  hunger  are  also  controlled  by  parts  of  the  
brain  stem
...
   
 
The  Central  Nervous  System  allows  the  body  to  respond,  through  effectors,  to  
changes  in  the  environment  detected  by  receptors
...
 They  can  detect  changes  in  the  environment,  which  are  called  
stimuli,  and  turn  them  into  electrical  impulses
...
 Each  organ  has  receptors  sensitive  to  
particular  kinds  of  stimulus
...
 The  brain  then  co-­‐ordinates  the  
response
...
 The  spinal  cord  is  a  bundle  of  nerves  
and  tissue  enclosed  in  the  spine
...
   
 
The  peripheral  nervous  system  (PNS)  is  the  part  of  the  nervous  system  that  
consists  of  the  nerves  and  ganglia  outside  of  the  brain  and  spinal  cord
...
 
 
 
{https://simple
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org/wiki/Brain  
https://en
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org/wiki/Central_nervous_system  
http://www
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co
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shtml  
https://en
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org/wiki/Peripheral_nervous_system}  
 
 
 
 
 

  
 
Use  a  detailed  flow  diagram  of  the  reflex  arc  for  this  situation:  
 
Brain  
 
 
 
 
 
 
 
 
 

Receptor  

Stimulus  

 
 

Sensory  Neuron  

 

Relay  
Neuron  

 
 
Response  

 
Effector  

Motor  Neuron  

 
 
 
 
 
 
Explain  the  Reflex  Arc  in  detail,  explaining  the  role  of  the  main  neurons,  
synapse  receptor  and  effectors:  
 
First  the  receptor  detects  a  stimulus,  a  change  in  the  environment
...
 Next,  the  motor  neuron  
sends  signal  to  the  effector
...
 
 
For  example,  if  your  hand  touched  the  flame  of  a  candle,  the  flame  would  be  the  
stimulus
...
 The  signal  would  be  passed  
alone  the  relay  neuron  and  sent  to  the  brain
...
 Of  
course,  this  happens  extremely  quickly!  
 
A  synapse  is  a  junction  between  two  nerve  cells,  consisting  of  a  minute  gap  
across  which  impulses  pass  by  diffusion  of  a  neurotransmitter
...
google
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uk/search?q=what+is+a+synapse&ie=utf-­‐8&oe=utf-­‐
8&gws_rd=cr&ei=AqqiVdKnBtTQ7Aa4vp_YBA  
http://www
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co
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shtml  

https://www
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 Instead,  it  triggers  the  neuron  to  release  a  
chemical  neurotransmitter
...
 
 
A  nucleus  is  surrounded  by  cytoplasm
...
 This  is  called  an  axon
...
 The  fatty  sheath  increases  the  speed  at  which  the  
nerve  impulse  is  transmitted
...
 
 

 
 
Two  neurons  do  not  make  direct  contact
...
 The  impulse  needs  to  cross  this  gap  to  continue  on  its  
journey  to,  or  from,  the  CNS
...
 
 
{http://www
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Explain  why  the  reflex  arc  happens  so  quickly:  
 
Pulling  your  hand  away  from  a  hot  object,  blinking  because  it's  very  bright  or  
kicking  when  someone  taps  the  tendon  below  your  kneecap  -­‐  these  are  all  innate  
reflex  actions
...
 

 

  
Most  reflexes  don't  have  to  travel  up  to  your  brain  to  be  processed,  which  is  why  
they  take  place  so  quickly
...
 
A  reflex  arc  starts  off  with  receptors  being  excited
...
 As  a  result,  one  of  your  muscles  or  glands  is  stimulated
...
bbc
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uk/science/humanbody/body/factfiles/reflexes/reflexes

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