Spinal Reflexes Flashcards

1
Q

What is the simplest reflex?

A

The stretch reflex

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2
Q

What provides information for the stretch reflex?

A

Muscle spindles (monitor muscle length)

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3
Q

How does a muscle stretch reflex affect muscle spindles?

A

The muscle stretch causes the spindle to stretch
This activates 1a sensory nerves in the muscle spindle
This increases the number of APs in afferent nerves

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4
Q

How many connections do spindle sensory afferent fibres make?

A

3

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5
Q

How does a stretch reflex affect the stretched muscle?

A

The first connection of the afferent fibres activates the alpha-motorneuron fibres to the stretched muscle
This causes rapid contraction of the AGONIST muscle.
This is a monosynaptic reflex

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6
Q

How do afferent sensory fibres connect ot antagonist muscles?

A

spindle afferent fibres activate inhibitory interneurons
They decrease activation of alpha-motorneurons to antagonist muscles.
Tbis causes the antagonist to relax (reciprocal inhibition)

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7
Q

How do spindle afferent fibres connect to the brain?

A

They ascend in dorsal columns and connect with somatosensory cortex to tell the brain about the muscle length.

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8
Q

How does the inverse stretch reflex affect the golgi tendon organ?

A
  • Muscles contracts & shortens

- Tendon is pulled and 1b sensory nerves from GTO fire more APs

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9
Q

How does the inverse stretch reflex affect muscles?

A

The afferent nerve fibres from the GTO affect:

  • Activates inhibitory interneurones to the agonist muscle (weakens contraction)
  • Activates excitatoy interneurones to antagonist muscles
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10
Q

How does information from the inverse stretch reflex reach the brain?

A

Info about the muscle tension ascends the 1b sensory afferent fibres in dorsal columns to somatosensory cortex.

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11
Q

What is the purpose of the inverse stretch reflex?

A

Prevents muscle contracting so hard the tendon tears from the bone (think sudden release of muscle tension when losing at arm wrestling)

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12
Q

Is the inverse stretch reflex poly- or mono- synaptic?

A

Polysynaptic

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13
Q

What receptors are involed in the Flexor (withrdrawal) reflex?

A

Nociceptors or pain receptors in the skin, muscles and joints

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14
Q

Whats the purpose of the flexor (withdrawal) reflex?

A

To withdraw the body part from painful stimulus (and towards the body).

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15
Q

What does increased APs from pain receptors cause in flexor muscles?

A

Increased activity via excitatory neurons

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16
Q

What does the flexor reflex do to antagonistic extensor muscles?

A

The antagonistic extensors are inhibited.

17
Q

How do flexor reflexes cause large scale withdrawl movements?

A

The nociceptor fibres branch alot
Activate interneurons in multiple spinal segments
Activate alpha motorneurones controlling all flexor muscles of the affected limb.

18
Q

What does the flexor (withdrawal) reflex do to prevent you hurting yourself when you withdraw a limb?

A

Triggers contralateral limb extension to balance you out. (crosed extension)

19
Q

How does the flexor reflex control contralateral limb extension?

A
  • Excitatory interneurons cross the - spinal cord and excite the contralateral extensor muscles
  • Inhibitory interneuorns cross the cord and inhibit the contralateral flexor muscles.
20
Q

How does sensory info reach the brain regarding the contralateral limb extension?

A

Sensory info ascends to the brain in the contralateral spinothalamic tract

21
Q

Why is teh flexor crossed-extensor reflex slower than the stretch reflex?

A

IT involves several interneurons with a small synaptic delay

Also the nociceptor fibres are smaller in diameter than the afferent fibres from spindles/GTOs so transmit slower.

22
Q

How can we override reflexes consciously?

A

Each alpha-motorneuron receives > 10000 synapses continually integrating.
descending excitation/inhibition from the brain can overpower inhibition/excitation from the GTOs/Spindles/nociceptors.

23
Q

What do gamma-motorneurons depend on?

A

Descending pathways, no reflex APs reach tehm

24
Q

What does abnormally high gamma-motorneuron activation of muscle spindles cause?

A

The muscle spindles become resistant to passive stretch and the gamma-motorneurons triger random stretch reflexes (spastic)
This is problem with the CNS

25
Q

Whats the clinical relevance of the stretch reflex?

A
  • Useful for assessing integrity of whole spinal cord circuit
  • allows spinal level localisation of a problem (reflexes evoked above a cetain level but not below show segmental trauma to spine)
26
Q

What is facilitation?

A

Multiple small pain receptors depolarise enough to trigger depolarisation in nearby ones too which causes an exaggerated response.