L25 - spinal reflexes

Question 1

reflex arc

Answer 1

a fast, predictable automatic response to a change in the environment or a stimulus

Question 2

5 functional components of a reflex arc

Answer 2

1 - receptor
2 - afferent fibre
3 - integration
4 - efferent fibre
5 - effector organ

Question 3

what receptor is involved in the myotactic stretch reflex

Answer 3

muscle spingle

Question 4

what is detected in the myotactic stretch reflex

Answer 4

stretching / changing of length within muscle

Question 5

functions of myotactic stretch reflex

Answer 5

antigravity, posture, movement

Question 6

agonist response to myotactic stretch reflex - patellar tap reflex

Answer 6

• Tap quadriceps tendon & stretch of quadriceps muscle
• Activation of the muscle spindle & increased firing of 1a afferent
• Afferent terminals synapse directly with and excite the alpha motor neurone (monosynaptic reflex)
• Increased alpha motor neurone efferent axon activity
• Contraction of the agonist homonymous muscle i.e., muscle from which afferent arose (quad)

Question 7

how does the myotactic stretch reflex travel

Answer 7

ipsilaterally

Question 8

reciprocal inhibition of antagonist muscle during the myotactic stretch reflex

Answer 8

Indirect inhibition via the 1a inhibitory interneuron of motor neurones innervating antagonist (flexor) muscle groups.
- Decreased firing on the flexor muscle

Direct excitation of motor neurones innervating agonist muscle groups (extensor) muscle groups

Question 9

myotactic stretch reflex - addition of load (arm muscles)

Answer 9

• when adding load, we want to increase contraction of agonist, to keep holding the object against the load
• Sensory muscle spindles detecting muscles shortening
• Stretch of the flexor biceps brachii and activation of the 1a afferent.
• Direct excitation of agonist (flexor) muscle groups (biceps).
• ndirect inhibition via the 1a inhibitory interneuron of antagonist (extensor) muscle groups (triceps brachii) to relax it
• decrease firing in the alpha motor neurone that go to the antagonist

Question 10

inverse myotactic (Golgi tendon) stretch reflex

Answer 10

Control the tension of an active muscle, in response to muscle contraction to avoid tendon damage

Question 11

receptors in Golgi tendon reflex

Answer 11

Golgi tendon organ

Question 12

functions of golgi tendon reflex

Answer 12

tension feedback to CNS, overload protection

Question 13

increased muscle tension feedback mechanism in Golgi tendon reflex

Answer 13

• Golgi Tendon Organ excitation
• Increased firing in 1b afferent
• Indirect inhibition via an inhibitory interneuron of the alpha motor neurone
• Decreased alpha motor neurone activity to homonymous muscle
• Relaxation/inhibition of the homonymous muscle
• indirect excitation of motor neurones innervating antagonist muscle groups

Question 14

crossed extensors / flexor withdrawal reflex

Answer 14

Noxious (harmful/unpleasant) cutaneous stimulation causes flexion withdrawal from the offending stimulus

Simultaneous extension of contralateral limb (crossed extensor) may occur for weight bearing

Question 15

functions of crossed extensor / flexor withdraws reflex

Answer 15

• Damage limitation of avoidance

- Maintained balance on limb withdrawal

Question 16

Sequence of events on activation of the cutaneous nociceptor

Answer 16

• Increased activity in A-delta & C afferents
• Polysynaptic activation of ipsilateral flexors
• Polysynaptic inhibition of ipsilateral extensors
  CROSSES THE MIDLINE
• Polysynaptic inhibition of contralateral flexors
• Polysynaptic excitation of contralateral extensors

Question 17

effect of crossed extensor reflex on ipsilateral flexors

Answer 17

excitation

Question 18

effect of crossed extensor reflex on ipsilateral extensors

Answer 18

inhibition

Question 19

effect of crossed extensor reflex on contralateral flexors

Answer 19

inhibition

Question 20

effect of crossed extensor reflex on contralateral extensors

Answer 20

excitation

Question 21

myotactic sensory afferent

Answer 21

1a

Question 22

myotactic sensory stimulus

Answer 22

change in muscle length

Question 23

inverse myotactic sensory afferent

Answer 23

1b

Question 24

inverse myotactic / Golgi tenson sensory stimulus

Answer 24

change in muscle tension

Question 25

flexor withdrawal sensory afferent

Answer 25

A-delta, C group 3/4

Question 26

flexor withdrawal sensory stimulus

Answer 26

painful or damaging stimuli