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Description
Flashcards by sophietevans, updated more than 1 year ago
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Created by sophietevans
over 10 years ago
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| Question | Answer |
| What is the stretch reflex? | A monosynaptic reflex exhibited by all tendons/skeletal muscles in order to prevent overstretching of the muscle. |
| Describe the stretch reflex process. | Striking the tendon with a reflex hammer → stretches the main body of its attached muscle → stretches the muscle spindles contained within the muscle → activates the sensory endings of the 1a afferent fibres wrapped around the central part of the muscle spindles → action potentials travel up the 1a afferent axons → which enter the spinal cord by the dorsal roots → synapse onto the cell bodies of α-motoneurons in the ventral horn of the grey matter → stimulate action potentials which travel along the α-motoneurons, leaving the spinal cord by the ventral roots → stimulate the skeletal muscle cells of the same muscle → produce muscle action potentials (which can be recorded as EMG using surface electrodes) → muscle contraction. |
| Alongside activation of the muscle from which the stretch reflex originated, what else occurs? | Reciprocal inhibition of the antagonistic muscle, to permit only the contracting muscle to move the limb. |
| Although the stretch reflex may be tested under unnatural conditions (striking the patellar or Achilles tendon with a reflex hammer), the reflex occurs any time one uses a muscle - for what purpose? | To help to ensure that the right amount of tension is produced to match the aim of the movement. |
| How was tension taken off the Achilles tendon before measurements were taken in the lab exploring the stretch reflex? | The subject rested their weight on to their non-instrumented leg, and lifted the heel of their instrumented leg slightly. |
| What is the latency of the reflex being recorded? | The time taken for the stimuli to initiate a response. |
| What is the typical latency for the Achilles tendon/gastrocnemius stretch reflex? | ~30 ms. |
| What is the Jendrassik manoeuvre? | A technique used when pathological latencies of the stretch reflex are recorded, or when people's natural magnitudes of the reflex are 'quiet' and need to be boosted so a response can be recorded. |
| What physiological principle does the Jendrassik manoeuvre exploit? | The cells of the anterior horn are connected, as are sympathetic chain ganglia, and this arrangement allows multiple neurons to receive action potentials in order to magnify a response, if necessary. It therefore primes motor neurons and makes a response more likely. |
| How were the sympathetic chain ganglia primed in this lab? | Subjects had to hold their arms out in front of them, biceps flexed, and interlink their fingers. They would then pull against their hands to create tension in both arms, exciting the motor neurons. |
| Using a paired T-test each time, the class data showed no evidence for the Jendrassik manoeuvre affecting the latency or the magnitude of the stretch reflex before, during, or after the manoeuvre. Suggest why. | We were not accustomed to the equipment that we were using, the experimental conditions were casual, and it is unlikely that the manoeuvre was performed properly given our lack of experience. Therefore, there would not have been a significant difference between our measurements with and without the manoeuvre. |
| Using a linear regression, there was no evidence that hip-ankle length affected the latency of the stretch reflex, and only weak evidence (R^2 = 10%) that height affected stretch reflex latency. Why is this? | The data recorded may not have been accurate due to lack of experience with the technique, and somatic sensory and motor neurons are heavily myelinated and impulses travel very quickly along them (~30 m/s), so a few cm in height is not likely to make much difference when speeds are this great. |
| What can the stretch reflex be used to assess? What about the signal recorded might one be looking for? | It can be used to assess the presence and/or degree of neurological damage, and can be used to localise it. If the latency of a motor response is increased, discontinuous, or not recorded, there is likely to be a pathology. |
| How can the stretch reflex be used to localise neurological damage? | Given that nerves branch off from particular sections of the spinal cord, the damage can be localised by testing the neuromuscular responses of different muscles/limbs. |
| List some pathologies that may cause variations in the stretch reflex, and what effects they may have. | Demyelination of the nerves would increase the latency of the reflex; calcium deficiency would produce a normal latency but a delayed contraction; and nerve cell death, which would produce no response. |
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