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NHB > Reflexes > Flashcards

Reflexes Flashcards

1
Q

What basic properties do nociceptive withdrawal reflexes show?

A
  1. Spatial and temporal summation

2. Local sign

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2
Q

What is spatial and temporal summation?

A

Noxious stimuli at adjacent sites or close together in time summate to give a greater response

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3
Q

What is local sign?

A

Different reflexes are evoked at different locations

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4
Q

What are proprioceptors?

A

Receptors that provide sensory signals as to the state of muscles, tendons and joints

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5
Q

What are exteroceptors?

A

Cutaneous receptors on the surface of the body

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6
Q

What are teloceptors?

A

Sense environment at a distance, eg. sight, sound, smell

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7
Q

What is proprioception?

A

The sense of position and movement of the body

Involves proprioceptors, exteroceptors and teloceptors

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8
Q

What are the three major groups of proprioceptors?

A
  1. Muscle spindle afferents are muscle stretch receptors
  2. Golgi tendon organ afferents are muscle tension receptors
  3. Joint receptors signal joint position and movement, especially at extremes
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9
Q

What are the two types of intrafusal fibres?

A
  1. Bag fibres

2. Chain fibres

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10
Q

What are bag fibres?

A

Swollen central region containing many nuclei

Contractile ends

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11
Q

What are chain fibres?

A

Uniform in diameter

Uniformly contractile

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12
Q

What are primary group Ia spindle afferents?

A

Very large

Very fast conducting

Annulospiral endings that coil around the central region of intrafusal muscle fibres

Signal static and dynamic components

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13
Q

What are secondary group II spindle afferents?

A

Small

Slower conducting

End adjacent to central region of intrafusal muscle fibres

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14
Q

What are intrafusal muscle fibres?

A

Specialised muscle fibres within the muscle spindle

Motorneurons innervate the contractile ends of the intrafusal muscle fibre, away from sensory regions in the centre

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15
Q

What kind of motorneuron innervates intrafusal muscle fibres?

A

α-motorneurons in primitive amphibians/reptiles

γ-motorneurons in mammals

These are small and slower conducting motorneurons

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16
Q

What do chain fibres signal?

A

Muscle length

Approx linearly

Static response

17
Q

What do bag fibres signal?

A

Muscle length

Central region is elastic, not contractile, so stretches at onset of muscle contraction but relieved as visco-elastic contractile ends elongate

Dynamic response

Rapidly adapting response to length change

18
Q

How is intrafusal muscle fibre sensitivity adjusted?

A

Stretching of central region of fibre changes sensitivity

Allows muscle spindle to operate at different starting muscle lengths

This is a form of adaptation

19
Q

What generates a change in muscle spindle afferent firing?

A
  1. Change in muscle length
  2. Altered γ-motorneuron activity

Usually both

20
Q

What is an efference copy?

A

Copy of command to γ-motorneurons sent back to the brain to be able to interpret muscle spindle afferent activity unambiguously

21
Q

What is a golgi tendon organ?

A

Located in tendons

Activated by tension in the tendon

Signal active tension generated when joint is moved by contracting muscle, NOT passive movement

Signal strongly proportional to load on muscle

22
Q

What is the knee jerk reflex?

A
  1. Tap patellar tendon
  2. Stretch muscle spindles in quadriceps
  3. Reflex contraction of quadriceps
  4. Knee jerk
23
Q

What is a stretch reflex?

A

Homeostatic reflex

Maintains muscle length in the face of an imposed stretch

Particularly useful in postural control

24
Q

What is the only known monosynaptic reflex?

A

Monosynaptic stretch reflex

Axons of muscle spindle afferents onto α- motorneurons that innervate the same muscle

25
Q

Which muscles do not have a stretch reflex?

A
  1. Tongue

2. Eye muscles

26
Q

What occurs to synergistic muscles in the stretch reflex?

A

Muscle spindle fibres also excite synergistic muscles

27
Q

What is reciprocal inhibition?

A

Muscle spindle fibres excite glycinergic spinal interneurons, which inhibit antagonist muscles

This prevents further stretch

These effects are mediated by group Ia inhibitory interneurons associated with each motorneuron pool

28
Q

What is the role of the stretch reflex?

A

Negative feedback control

Compensate for unexpected loads that stretch a muscle

29
Q

What occurs to the stretch reflex when descending pathways are pathologically damaged?

A

It is exaggerated

Oscillation may be seen as myoclonus following a muscle stretch

30
Q

What is recurrent inhibition?

A

Motorneuron axons have recurrent collateral branches within the spinal cord that innervate Renshaw cells

31
Q

What are Renshaw cells?

A

Inhibitory interneuron

Regulate timing of motorneuron firing

Prevent synchrony

32
Q

What is a tendon organ reflex?

A

Context dependent

Static/resting position: activation produces inhibition of parent muscle

Dynamic/moving: activation produces excitation of parent muscle

33
Q

Give three examples of neonatal reflexes

A
  1. Grasp reflex
  2. Babinski’s sign (plantar reflex)
  3. Reflex stepping
34
Q

When might you see neonatal reflexes?

A

They are found in neonates and are lost over the first few years of life

They may be regained following motor cortex damage

35
Q

Give three examples of pathological reflexes

A
  1. Spasticity - exaggerated stretch reflex, oscillation, clonus
  2. Babinski’s sign
  3. Clasp-knife reflex
36
Q

What is Babinski’s sign?

A

Toes turn up in plantar stimulation instead of down

37
Q

What is the clasp-knife reflex?

A

Limbs snap into extension or flexion

38
Q

What is a central pattern generator?

A

Spinal circuit with capacity to generate a detailed motor pattern without needing input from brain

Locomotion is spinally generated in most vertebrates, including many mammals, but not humans

39
Q

What is encephalisation?

A

Dominance of motor cortex over spinal cord

NHB (17 decks)

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