Reflexes Flashcards

1
Q

Explain how the patella tendon knee jerk works?

A

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

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2
Q

What is a reflex that doesn’t involve any interneurones called?

A

Monosynaptic

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3
Q

What are the three fates of the spindle sensory afferents?

A

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.

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4
Q

What causes the inverse stretch reflex?

A

The golgi tendon organ

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5
Q

When the muscle contracts and activates the inverse stretch reflex, what do the action potentials fired from the GTO cause?

A

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.

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6
Q

How is the golgi tendon reflex protective?

A

Prevents the muscle contracting so hard that the tendon insertion is torn away from the bone.

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7
Q

Where do flexor reflexes get their information?

A

Nociceptors - muscles flex TOWARDS the body

They are polysynaptic and protective.

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8
Q

What is the result of activation of the flexor reflex on agonist and antagonist muscles?

A

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

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9
Q

What type of flexion is the flexor reflex?

A

Ipsilateral flexion

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10
Q

What stops you from falling over if the flexor reflex is activated?

A

Contralateral extensor muscles are activated

Excitatory interneurones which cross the spinal cord excite contralateral extensors

Inhibition of contralateral flexor muscles

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11
Q

Where does this sensory information travel to activate contralateral flexors?

A

Contralateral spinothalamic tract

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12
Q

Why is the flexor crossed extensor reflex much slower than the stretch reflex?

A

nociceptor fibres are much slower narrower than spindle fibre afferents, meaning they conduct much slower

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13
Q

How can inhibition of the GTO be overidden?

A

Voluntary excitation of alpha motoneurones

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14
Q

Why are subjects distracted when testing reflexes?

A

Prevents voluntary effects on the reflex response

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15
Q

What is the clinical relevance of reflexes?

A

Assesses the integrity of the whole spinal cord unit, allows spinal level localisation of a problem

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16
Q

What is the result of a larger pain stimulus on the response?

A

Pain fibre input spreads through several spinal segments (unlike the stretch reflex which is highly localised). The greater the stimulus means a greater spinal spread and a larger response e.g retracting your entire arm instead of just hand

17
Q

What is the effect of facillitation?

A

Increases the effects of sensory inputs

Examples include activation of several pain fibres which are similar
Pain fibres maintain alpha motorneurones in a more depolarised state - FACILITATING the action of muscle spindles = a stretch reflex would be greatly exaggerated