1. The Reflex

2. Describe what is happening where…..

4. Learning Outcomes
To describe reflex actions include knee jerk reflex and blinking reflex,
Explain why and how reflex actions are associated with survival
M0.1, M0.2, M1.1, M1.2, M1.3, M1.6
PAG11
Use an appropriate number
of significant figures
Find arithmetic means
Recognise and make use
of appropriate units in
calculations
Recognise and use
expressions in decimal and standard form
Construct and interpret
frequency tables and
diagrams, bar charts and
histograms
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.
Understand the terms
mean, median and mode

5. 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

6. 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

7. 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

8. 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

9. 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)‏

10. 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)‏

15. 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

16. 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.

17. 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

18. Homework Compare Coordination by nerves and hormones
Use the following headings
Communication
Speed
Duration
Target pathway
Action