reflexes 2

Question 1

what type of reflex involves an interneurone which bridges the gap between the sensory afferent and the motor efferent?

Answer 1

polysynaptic reflexes or disynaptic reflexes

NB these can be ipsilateral, contralateral or both

Question 2

what is an intrasegmental reflex?

Answer 2

a reflex arc that is restricted to one or two spinal cord segments

Question 3

what is an intersegmental reflex arc?

Answer 3

the reflex arc involves a number of spinal cord segments

Question 4

what speed can a knee jerk reflex occur at?

Answer 4

in about 20-25ms

Question 5

how many intrafusal fibres are there typically for each spindle organ?

Answer 5

8-10

Question 6

what are the two different types of intrafusal muscle fibres?

Answer 6

bag and chain

Question 7

which type of afferent nerve fibre is wrapped around the intrafusal fibres with an annulospiral ending?

Answer 7

group IA fibres

Question 8

what do group IA fibres detect?

Answer 8

change in fibre length

Question 9

what type of efferent motor fibre innervates the ends of the intrafusal muscle fibres?

Answer 9

gamma motor neuron fibres

Question 10

what do group II fibres detect?

Answer 10

overall muscle length

Question 11

what type of afferent sensory fibres innervate chain intrafusal fibres?

Answer 11

both IA and II sensory nerve fibres

Question 12

what type of afferent sensory fibres innervate bag intrafusal fibres?

Answer 12

type II only

Question 13

what happens to a antagonist muscle during a reflex response?

Answer 13

its baseline contraction is inhibited by the synapsing of an inhibitory interneurone with the afferent nerve fibre

Question 14

why do voluntary muscle contractions not cause a reflex response if the muscle is shortening?

Answer 14

when a voluntary muscle is contracted, the CNS sends signals via alpha motor neurones and gamma motor neurones so that the ends of the intrafusal muscle fibres contract and the anulospiral nerve endings do not detect any change in length