Reflexes

Question 1

what is the knee jerk relfex also known as

Answer 1

monosynaptic stretch reflex

Question 2

what is the knee jerk reflex mediated by

Answer 2

muscle spindles

Question 3

where does the knee jerk reflex occur

Answer 3

at the level of the spinal cord

Question 4

how long does the knee jerk reflex take

Answer 4

20-25 ms from force applied to reflex

Question 5

what is the process of the knee jerk reflex (7)

Answer 5

1. tendon tap rapidly lengthens the quad
2. stretch lengthens causing muscle spindle to fire APs
3. spindle afferents enter the dorsal horn and synape onto and excite aMN
4. excitation of aMN causes reflex contraction of quad
5. sensory afferent also synapses onto inhibitory interneuron which inhibits the aMN of antagonist muscle
6. hamstring is inhibited
7. leg straightens

Question 6

what is reciprocal inhibition

Answer 6

muscle spindle inputs excite aMN of agonist muscle and excite inhibitory interneurons in the spinal cord that inhibit aMN of antagonist muscle

Question 7

what is the stretch reflex - activation of synergists

Answer 7

stretch of agonist muscle produces reflex contraction of agonist and synergists
- combined with inhibition of antagonists

Question 8

what is the difference in responses to the stretch reflex in healthy vs deafferented (dorsal roots cut)

Answer 8

healthy
- applied force = rapid muscle stretch
- force generation begins shortly after muscle is stretched

deafferented
- reflex response is muted
- basic reflex function is impaired when there is no sensory info from the periphery

Question 9

what is another name for the GTO reflex

Answer 9

autogenic inhibition

Question 10

what is the purpose of autogenic inhibition

Answer 10

protective feedback mechanism to control the tension in active muscle
- relaxes msucle before tension levels are high enough to damage it or the tendon

Question 11

what is the process of autogenic inhibition (4)

Answer 11

1. GTOs detect tension in tendon
2. sensory neurons conduct APs to the spinal cord
3. sensory neurons synpase with inhibitory interneurons that synapse with aMNs
4. inhibiton of aMNs cause muscle relaxation relieving the tension

Question 12

why is the inhibitory interneuron required in the GTO reflex

Answer 12

aMN can only send excitatory NTs and it needs to switch to inhibitory