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The Reflex
Describe what is happening where…..
Learning Outcomes
 To describe reflex actions include knee jerk reflex and blinking reflex,
 Explain why and how reflex actions are associated with survival
Recognise and
make use
of appropriate units
in
calculations
Recognise and use
expressions in
decimal and
standard form
 M0.1, M0.2, M1.1, M1.2, M1.3, M1.6
 PAG11
Select and use a
statistical
test
-the chi squared test (χ2) to test the
significance of the difference
between observed and expected
results
-the Student’s t-test
-the Spearman’s rank correlation
coefficient.
Use an appropriate
number
of significant figures
Find arithmetic
means
Construct and
interpret
frequency tables
and
diagrams, bar charts
and
histograms
Understand the terms
mean, median and
mode
Proprioceptors and the Control of
Movement
 Proprioceptors – specialized receptors found in tendons, muscles,
and joints
 Provide sensory information about the state of muscle contraction, the
position of limbs, and body posture and balance
 This feedback is provided primarily by afferent (sensory) input from two
sensory receptors:
 tendon organs and muscle spindles
Golgi Tendon Organs (Tension Reflex)
 Sensory receptors that terminate where tendons joint to
muscle fibres
 Since they are aligned with muscle, any stretching of
the muscle also stretches the GTO
 The job of GTO is to detect increased tension exerted
on the tendon
 When a change in tension is detected an impulse is sent
along afferent (sensory) neurons to the CNS
 The efferent (motor) neurons transmit an impulse
causing the muscle to relax
 This prevents injury
Muscle Spindles
 Lie parallel to the muscle
fibre
 Send constant signals to the
spinal cord
 Help maintain muscle
tension
 They are sensitive to
changes in muscle length.
 Responds to changes in
length by sending a
message to the spinal cord
The Stretch Reflex
 Simplest spinal reflex
 Depends only on the single
connection between
primary afferent fibres and
motor neurons of the same
muscle
 i.e. Knee-jerk test
 1. The receptor muscle senses the action of the
hammer against the patella ligament through the
muscle spindle's sensory neuron
 2. The message is transmitted along the afferent
(sensory) nerve axon to the spinal cord
 3. The afferent neuron synapses with the efferent
pathway (motor neuron) of the same muscle
 4. An impulse is transmitted along the efferent
pathway (motor neuron) to the muscle
 5. The motor units contract (knee-jerk to
accomodate additional stretch)
Reciprocal Inhibition
During a reflex, the
opposing muscle
group is simultaneously
stimulated
In a knee-jerk reflex the
quadriceps contract to
extend the knee while
the hamstrings are
inhibited in a slightly
delayed response
(they do not flex)
Categorising reflexes
 Knee jerk reflex is a spinal reflex.
 The pathway consists of only two neurones: sensory and
motor neurone.
 There is no relay or interneurone.
 This means that there is only ONE synapse – therefore it is
a very fast response.
 This also means that because there is no relay neurone –
the brain cannot inhibit the reflex - (the inhibition would
have to be provided by inhibitory synapses before the
motor neurone is depolarised).
 The pain withdrawal reflex is a multisynaptic spinal reflex
Categorising reflexes
 The blink reflex is a
cranial reflex. It is a reflex
arc because the
receptor and effector
are in the same place.
 The corneal reflex –
stimulated by touching
the cornea – has two
synapses and so can be
overridden by inhibitory
signals from the cerebral
cortex.
Questions
 Explain why higher reasoning or conscious thought are
not necessary for reflex behaviours.
 Distinguish between a spinal reflex and a cranial reflex
and give an example of each.
 Describe the survival value of the following reflexes:
Knee-jerk
Corneal blink reflex
Grasp reflex
Pupillary light reflex
Homework
 Compare Coordination by nerves and hormones
 Use the following headings
 Communication
 Speed
 Duration
 Target pathway
 Action