Reflexes Flashcards
Explain how the patella tendon knee jerk works?
Tap on the inelastic tendon causes the muscle fibres to stretch activating the sensory nerves in the muscle spindle. This increases the number of action potentials that are sent through the afferent neurone into the dorsal horn of the spinal cord
What is a reflex that doesn’t involve any interneurones called?
Monosynaptic
What are the three fates of the spindle sensory afferents?
Activates the alpha motoneurone pool of the agonist muscle causing rapid contraction.
Actives inhibitory interneurone which decreases the activation of alpha interneurones in the antagonist muscle, causing it to relax. This is called reciprocal inhibition.
Spindle afferents also ascend dorsal columns to the somatosensory cortex to tell the brain about the length of the muscle.
What causes the inverse stretch reflex?
The golgi tendon organ
When the muscle contracts and activates the inverse stretch reflex, what do the action potentials fired from the GTO cause?
Causes the activation of the inhibitory neurones to the agonist muscle causing the contraction strength to decrease
Activates exitatory interneurones causing the antagonist muscle to contract.
Information about muscle tension ascends through the dorsal route to the somatosensory cortex.
How is the golgi tendon reflex protective?
Prevents the muscle contracting so hard that the tendon insertion is torn away from the bone.
Where do flexor reflexes get their information?
Nociceptors - muscles flex TOWARDS the body
They are polysynaptic and protective.
What is the result of activation of the flexor reflex on agonist and antagonist muscles?
The increased number of action potentials in the nociceptor causes the flexor muscle to contract by activation of excitatory interneurones.
Antagonist extensors are inhibited by a number of inhibitory and excitatory interneurones
What type of flexion is the flexor reflex?
Ipsilateral flexion
What stops you from falling over if the flexor reflex is activated?
Contralateral extensor muscles are activated
Excitatory interneurones which cross the spinal cord excite contralateral extensors
Inhibition of contralateral flexor muscles
Where does this sensory information travel to activate contralateral flexors?
Contralateral spinothalamic tract
Why is the withdrawal flexor crossed extensor reflex much slower than the stretch reflex?
nociceptor fibres are much smaller diameter and narrower than spindle fibre afferents, meaning they conduct much slower
How can inhibition of the GTO be overidden?
Voluntary excitation of alpha motoneurones
Why are subjects distracted when testing reflexes?
Prevents voluntary effects on the reflex response
What is the clinical relevance of reflexes?
Assesses the integrity of the whole spinal cord unit, allows spinal level localisation of a problem
