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Nervous System.
Lesson Structure
• Lesson 1
– Nervous system and the reflex arc.
– Reaction time practical.
• Lesson 2
– Hearing and waves.
– Worksheets
– Senses movie.
Lesson Objectives.
1. List the sense organs and their receptors.
2. Describe the difference between a
controlled reaction and a reflex action.
3. Label and explain the reflex arc.
The Nervous System.
•The nervous system is composed of 5 sense organs, neurones, brain and
spinal cord.
•Sense organs detect stimuli and the Central Nervous System (CNS)
coordinates a response.
Sense organ
Receptors
Eyes
Light
Ears
Sound and Balance
Nose
Smell
Tongue
Taste
Skin
Pressure and Pain
The CNS (central nervous system) consists of the brain and
spinal cord.
Controlled Actions.
Stimulus
Receptor
Cells
Sensory
Neuron
Spinal
Cord
• This is the way we usually respond to changes in the
world around us.
• The process takes about 0.7 seconds.
Neurons:
• Sensory neurons – Carry electrical impulses from
the receptors to the CNS
• Relay Neurons – carry electrical impulses from
sensory neurons to the motor neurons (Only found
in CNS)
• Motor neurons – carry impulses from the CNS to
the effectors.
Motor
Neuron
Brain
Effector
Response
Effectors can be
muscles or glands:
They produce a
response.
Reflex Actions.
Stimulus
Receptor
Cells
Sensory
Neuron
Spinal
Cord
• Reflex actions are automatic, they happen without you
thinking about them.
• They do not involve the brain, therefore they are much
quicker (around 0.2 seconds)
• They are usually used to avoid damage.
Motor
Neuron
Effector
Response
Reflex Arc.
1. Stimulus is detected
by receptor.
2. Sensory neurone to
relay neurone to
motor neurone.
3. Effector produces a
response.
Synapse
Receptor
Sensory
Neuron
Relayneurone.
Neuron
Relay
Muscles responds by
contracting.
Gland responds by
secreting.
Motor Neuron
Effector (e.g. Muscle)
The Eye.
Very bright light can damage your eye – so you have a reflex to
protect it.
• In bright light,
circular muscles
contract to make
pupil smaller (Lets
less light in)
• In dim light,
radial muscles
contract making
pupil larger (Lets
more light in).
The Eye.
• Focusing the eye, another reflex:
The eye focuses by changing the shape of the lens, this is
called accommodation.
Binocular Vision.
Bi = two
Ocular = vision
• Having two
eyes which
work together is
known as
binocular vision.
• This allows us
to judge speed
and distances.
• Handy for
crossing the
road!
• It’s only
binocular if your
eyes are on the
front of your
head.
Summary Questions.
• Match the statements:
Part of the nervous system
Function
Receptor cells
Cause a response
Effectors
Carry electrical impulses
Neurons
Decides on a response.
Brain
Detects changes in your environment.
Are the following reactions controlled or reflex?
1.
2.
3.
4.
Pupils in your eyes shrinking in bright light. _______________________
Tying your show lace.
__________________
Signing your name.
__________________
Taking your hand of a hot plate.
_____________________
Hearing and Waves.
Lesson Objectives
• Describe how
sound travels in
longitudinal
waves.
• Understand how
excessive sound
can affect hearing.
•When a drum is
hit, it vibrates.
•The vibrations
make the air
molecules parallel
to the drum
vibrate.
•The vibrating air
molecules cause
neighbouring
particles to also
vibrate
•This continues
out ward from the
drum in a
longitudinal
wave.
Sound can travel anywhere there is a particles;
through solids, gasses and liquids.
Therefore sound cannot travel through space
as it is a vacuum.
Rarefaction
Compression
As the vibration passes, some particles are squashed together. This
is called a compression..
In other places particles spread out. This is called rarefaction.
• We measure how quickly something vibrates
(it’s frequency) in hertz.
• 1 cycle per second = 1 hertz.
• Humans can only hear between 20 and 20,000
hertz.
• Noise levels are measured in decibels.
• For ever 10 decibel increase the sound is 10x
louder. i.e. 60 decibels is ten times louder than 50
decibels.
Prolonged exposure to loud sounds damages your hearing.
• Tinnitus (High pitched ringing in the ears).
• You can lose the ability to hear certain frequencies (common to lose the ability
to hear conversations).
Summary Questions
1. Complete these sentences by choosing the
right word.
a) Sound waves travel as
Longitudinal/electromagnetic waves.
b) With Longitudinal waves, particles vibrate
parallel/at right angles to the way the energy
travels.
Explain why sounds cannot travel through space.
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