The Reflex Arc
Starter: Why does our body have to feel
pain?
Our learning objectives
 Describe the role of the nervous system
 Describe the structures involved in a pain withdrawal reflex arc
 Explain the pathway taken in a pain withdrawal reflex
https://www.youtube.com/watch?v=UtEqmmLJstg
We met these words last lesson, can you
match the definition to the word?
A) Receptor
1) A name for a nerve cell
B) Effector
2) A muscle or organ that
brings about a change
C) Coordination
Centre
3) Receives information from the
receptors and organises the
response e.g. brain or spinal cord
D) Neurone
4) Detects changes in the
environment (known as stimuli)
We met these words last lesson, can you
match the definition to the word?
A) Receptor
1) A name for a nerve cell
B) Effector
2) A muscle or organ that
brings about a change
C) Coordination
Centre
3) Receives information from the
receptors and organises the
response e.g. brain or spinal cord
D) Neurone
4) Detects changes in the
environment (known as stimuli)
Think of some famous arches…
A reflex arc follows a very similar shape
There are various types
of neurones:
1)Sensory neurons
2)Relay neurones
(interneurons)
3)Motor neurones
https://www.youtube.com/watch?v=nKPEW-ao2Wg
Name the 5 senses…
Sensory neurones carry the information from receptors which can tell if there is
a change in one of senses that can be detected (these stimulate the receptor).
The 5 main senses are:
 Touch
 Sight
 Hearing
 Taste
 Smell
Relay neurone
 Passes message on from sensory neurone
 Because they are not directly connected, a
chemical is released across the junction (or
synapse)
Motor neurone
 The motor neurone goes from the relay neurone to the effector
(the muscle or gland)
Now you’re going to test some basic
reflexes as well
You will have just 3 minutes with each reflex.
With reflex you should:
 Write down what the stimulus is (what is being sensed?) Light,
touch etc.
 What does the reflex protect you from?
Reflex arcs
Reflex
Knee-jerk
Iris (muscles in eye)
Gag reflex
The ‘Startle’ Reflex
Stimulus (what change is
detected?)
What does this protect?
Tendons below knee cap are
stretched
Balance
Reflex arcs
Reflex
Stimulus (what change is
detected?)
What does this protect?
Knee-jerk
Tendons below knee cap are
stretched
Balance
Iris (muscles in eye)
Light intensity (level of light)
Stops eye damage
Gag reflex
Touching back of
throat/tongue
Choking
The ‘Startle’ Reflex
Loud noise
Potential danger
Plenary – whiteboards ready
1.
How would you describe a reflex arc?
a)
Slow and voluntary b) Fast and voluntary
c) Fast and automatic
2. Where are responses coordinated during a reflex arc?
a)
Brain
b) Spinal Cord
c) Pancreas
3. What is the correct order that impulses are sent through neurones?
a) Sensory, Relay, Motor
b) Motor, Relay, Sensory
c) Sensory, Motor, Relay
4. What happens at the junction where one neurone meets another?
a) The neurones are connected
b) A chemical signal is released
c) The impulse stops
Plenary – whiteboards ready
1.
How would you describe a reflex arc?
a)
Slow and voluntary b) Fast and voluntary
c) Fast and automatic
2. Where are responses coordinated during a reflex arc?
a)
Brain
b) Spinal Cord
c) Pancreas
3. What is the correct order that impulses are sent through neurones?
a) Sensory, Relay, Motor
b) Motor, Relay, Sensory
c) Sensory, Motor, Relay
4. What happens at the junction where one neurone meets another (synapse)?
a) The neurones are connected
stops
b) A chemical signal is released
c) The impulse