Reflexes

Question 1

What basic properties do nociceptive withdrawal reflexes show?

Answer 1

1. Spatial and temporal summation

2. Local sign

Question 2

What is spatial and temporal summation?

Answer 2

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

Question 3

What is local sign?

Answer 3

Different reflexes are evoked at different locations

Question 4

What are proprioceptors?

Answer 4

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

Question 5

What are exteroceptors?

Answer 5

Cutaneous receptors on the surface of the body

Question 6

What are teloceptors?

Answer 6

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

Question 7

What is proprioception?

Answer 7

The sense of position and movement of the body

Involves proprioceptors, exteroceptors and teloceptors

Question 8

What are the three major groups of proprioceptors?

Answer 8

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

Question 9

What are the two types of intrafusal fibres?

Answer 9

1. Bag fibres

2. Chain fibres

Question 10

What are bag fibres?

Answer 10

Swollen central region containing many nuclei

Contractile ends

Question 11

What are chain fibres?

Answer 11

Uniform in diameter

Uniformly contractile

Question 12

What are primary group Ia spindle afferents?

Answer 12

Very large

Very fast conducting

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

Signal static and dynamic components

Question 13

What are secondary group II spindle afferents?

Answer 13

Small

Slower conducting

End adjacent to central region of intrafusal muscle fibres

Question 14

What are intrafusal muscle fibres?

Answer 14

Specialised muscle fibres within the muscle spindle

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

Question 15

What kind of motorneuron innervates intrafusal muscle fibres?

Answer 15

α-motorneurons in primitive amphibians/reptiles

γ-motorneurons in mammals

These are small and slower conducting motorneurons

Question 16

What do chain fibres signal?

Answer 16

Muscle length

Approx linearly

Static response

Question 17

What do bag fibres signal?

Answer 17

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

Question 18

How is intrafusal muscle fibre sensitivity adjusted?

Answer 18

Stretching of central region of fibre changes sensitivity

Allows muscle spindle to operate at different starting muscle lengths

This is a form of adaptation

Question 19

What generates a change in muscle spindle afferent firing?

Answer 19

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

Usually both

Question 20

What is an efference copy?

Answer 20

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

Question 21

What is a golgi tendon organ?

Answer 21

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

Question 22

What is the knee jerk reflex?

Answer 22

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

Question 23

What is a stretch reflex?

Answer 23

Homeostatic reflex

Maintains muscle length in the face of an imposed stretch

Particularly useful in postural control

Question 24

What is the only known monosynaptic reflex?

Answer 24

Monosynaptic stretch reflex

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

Question 25

Which muscles do not have a stretch reflex?

Answer 25

1. Tongue | 2. Eye muscles

Question 26

What occurs to synergistic muscles in the stretch reflex?

Answer 26

Muscle spindle fibres also excite synergistic muscles

Question 27

What is reciprocal inhibition?

Answer 27

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

Question 28

What is the role of the stretch reflex?

Answer 28

Negative feedback control Compensate for unexpected loads that stretch a muscle

Question 29

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

Answer 29

It is exaggerated Oscillation may be seen as myoclonus following a muscle stretch

Question 30

What is recurrent inhibition?

Answer 30

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

Question 31

What are Renshaw cells?

Answer 31

Inhibitory interneuron Regulate timing of motorneuron firing Prevent synchrony

Question 32

What is a tendon organ reflex?

Answer 32

Context dependent Static/resting position: activation produces inhibition of parent muscle Dynamic/moving: activation produces excitation of parent muscle

Question 33

Give three examples of neonatal reflexes

Answer 33

1. Grasp reflex 2. Babinski's sign (plantar reflex) 3. Reflex stepping

Question 34

When might you see neonatal reflexes?

Answer 34

They are found in neonates and are lost over the first few years of life They may be regained following motor cortex damage

Question 35

Give three examples of pathological reflexes

Answer 35

1. Spasticity - exaggerated stretch reflex, oscillation, clonus 2. Babinski's sign 3. Clasp-knife reflex

Question 36

What is Babinski's sign?

Answer 36

Toes turn up in plantar stimulation instead of down

Question 37

What is the clasp-knife reflex?

Answer 37

Limbs snap into extension or flexion

Question 38

What is a central pattern generator?

Answer 38

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

Question 39

What is encephalisation?

Answer 39

Dominance of motor cortex over spinal cord