Nerves

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Nerves Reflexes
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The nervous system enables humans to react to
their surroundings and coordinate their behaviour.
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Receptors detect stimuli which include light,
sound, changes in position, chemicals, touch,
pressure, pain and temperature.
Where are your receptors?
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Stimulus Detected by
Pressure Receptors under skin
Pain Receptors under skin
Pleasure Receptors under skin
Temperature Receptors under skin
Light/visual Receptors in the Eye
Sound Receptors in the Ear
Taste Receptors in the Mouth
Smell Receptors in the Nose


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What are these receptors? How do they work?
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The Receptors are nerve endings. The nerves make
up your Central Nervous System along with your
spinal chord and brain.
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Retina receives the image

• The Retina is at the back of your eye.
• It is full of light receptors which are sensitive
  to Colour Light levels

Fovea
Optic Nerve
The Fovea is the main focal point and it has the
greatest density of light receptors
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Information from receptors passes along cells
(neurones) in nerves to the brain. The brain
coordinates the response.
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• Can you see
• The optic nerve bundle?
• The spinal cord?

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Nerve Cells

• Nerve cells are highly specialised.
• Their structure is directly linked to their
  function

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This picture was taken using electron microscopy.
It shows the synapses, or connections, between
two nerve fibres (in purple) and a nerve cell
(yellow). The picture is magnified 10,000 times.
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How does their structure relate to their function?

• STRUCTURE
• Long axon
• Dendrites on cell body
• Myelin sheath (fatty sheath)

• FUNCTION
• Can reach to far places in the body
• Allows nerve cells to connect with each other to
  pass on impulses (messages)
• Acts as insulation so the impulses do not cross
  over to other cells

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What do nerve cells do?

• Nerve cells connect to receptors at one end.
• Some nerves carry impulses to the brain.
• From here the brain will decide what response is
  necessary.
• Once it has decided what to do, the brain will
  send another impulse through another nerve cell.
• These nerves connect to a muscle or gland at the
  other end.
• The muscle or gland carries out the job required

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Stimulus? receptor ? nerve ? brain ? nerve ?
muscle/gland ? response

• As you can see there are 2 nerves involved in
  this chain. We can give these nerves special
  names according to the jobs they do
• We call the first nerve in the chain the SENSORY
  NERVE. This is because it is involved in the
  sensing of the stimulus.
• We call the second nerve the MOTOR NEURONE. This
  one is involved in bringing about the response to
  the stimulus.
• We can also call the muscle/gland the EFFECTOR.
  This is easier as it is only one word and can
  mean either muscle or gland. It is the part
  actually doing something.
• So our chain can now look like this

Stimulus? receptor?sensory nerve? brain? motor
neurone? effector?response
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• Working example
• See your friend ? receptors in eye ? sensory
  nerve ? brain ? motor neurone ? arm muscles ?
  wave
• Try and think of your own example and write it
  down

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Reflex actions
Reflex actions are automatic and rapid. They
often involve sensory, relay and motor
neurones. You need to know the role of
receptors, sensory neurones, motor neurones,
relay neurones, synapses and effectors in simple
reflex actions.
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Reflexes

• Some responses need to be really, really quick.
  We need to be able to do this without thinking.
• If we are in danger of harming ourselves we would
  need to act without thinking about what to do.
• We call this a reflex. It is like an action that
  is already programmed into our nervous systems
  it happens automatically.
• With reflexes the sensory nerves do not travel
  all the way to the brain. This would take too
  long if we were in danger.
• Instead the impulses are taken to the spinal cord
  as it is closer.
• Look at the next diagram and label your own.

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Motor Neurone
Effector (muscle)
Relay Neurone
Sensory Neurone
Spinal Cord
Receptor
Stimulus (heat)
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Activity

• Write down as many reflex actions as you can
  think of..
• Write out the chain of events for a reflex like
  the chain we went through before. Pick a specific
  type of reflex from your list and write out the
  chain.

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Questions

• 1) What do these words mean
• - stimulus
• - response
• - effector
• 2) What is the special name given to the nerve
  that carries the impulse from the receptor to the
  brain or spinal cord?
• 3) What is the special name given to the nerve
  that carries the impulse from the brain or spinal
  cord to the effector?
• 4) What is the name given to the brain and spinal
  cord together?
• 5) Write the chain of events for the following
  scenario
• A silly year 11 boy has just thrown a pen
  towards a year 7 boys face. What does the year 7
  boy do?

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Link to past paper questions
Link to answers