spinal reflexes

Question 1

spinal reflexes are stereotyped suggesting…..

Answer 1

‘occur the same way each time’

underlying circuitary is very simple

Question 2

spinal reflexes require stimulation (not spontaneous) suggesting…

Answer 2

they need sensory input

Question 3

spinal reflexes are automatic suggesting ….

Answer 3

little input from higher centres

Question 4

spinal reflexes are quick suggesting….

Answer 4

few synapses involved

Question 5

the stretch (myotactic) reflex- knee jerk

Answer 5

knee jerk experiment is not a repsonse to pain

the tap stretches the thigh extensor muscle and associated tendon and sets in motion a process to correct the stretching

important in maintaining body posture

Question 6

charles sherrington

Answer 6

monosynaptic relfex

simple proprioceptive feedback pathway

Question 7

muscle spindle

Answer 7

special sensory receptor that detects muscle stretch

Question 8

pouring a drink (stretch reflex)

Answer 8

1) sensory firbes sense muscle stretch and send signals to spinal cord
2) direct monosynpatc connection to motor neurone fires action potential which contract biceps

3) simultaneously, a distinct connection to an inhibitory interneruone inhibit during of motor neurones connected to triceps thus relaxing the antagonistic muscle
(reciprocal inhbition)

Question 9

where are muscle spindles found

Answer 9

in most striated muscles

and particualry in muscles in fine motor control e.g. hand

Question 10

what are muscle spindles innervated by

Answer 10

Ia sensory fibres

which provide feedback to the MN innervating the surrounding muscle (alpha motor neurons- called this because of their conduction velocity) on the amount muscles stretch that is occurring (as in knee jerk)

Question 11

the muscle spindle has muscles- they are innervated by…

Answer 11

axons from gamma (y) motor neurones

Question 12

gamma motor neurons do what

Answer 12

stimulate the intrafusal (muscle) fibres to adjust the tension in the spindle as the extrafusal (muscles) fibres of the surrounding muscle contract (so that the muscle spindle is never slack)

Question 13

Ian waterman

Answer 13

viral infection destroyed the nerve in properioceptio

also lost moving in space(kinaesthesia)

Question 14

types of proprioceptors

Answer 14

muscle spindle

golgi tendon organ

Question 15

goligi tendon organ detects

Answer 15

muscles tension due to muscle contraction (not muscle stretch)

Question 16

muscle spindle detects m

Answer 16

muscle stretch

Question 17

activation of GTO sensory (Ib) afferents leads to

Answer 17

activation of inhibitory interneurons which in turn inhibit alpha motor morons that innervate the same muscle

Question 18

the golgi tendon reflex

Answer 18

is a negative feedback circuit that regulates muscle tension and protects the muscle (and tendon) from damage when large forces are generated

Question 19

flexor (withdraw) reflex

Answer 19

quick contraction of flexor muscles to withdraw a limb from an injurious stimulus

results from the activation of nociceptors

despite speed of response it is actually a polysynaptic reflex

‘parallel after discharge circuit’

Question 20

‘parallel after discharge circuit’

Answer 20

Activation of multiple excitatory interneurons sustains the response:

Assume time taken to cross each synapse is the same.

Therefore, stimulus initiated by A will take different times to reach output neuron Z.

Result is that initial signal is sustained over extended period

Question 21

imbalance esp in leg with rapid withdrawal of limb in flexor reflex

Answer 21

there is a contralateral element to account for this

crossed extensor reflex provides postural support

Question 22

local circuits that generate the pattern of alternating flexion and extension are known as

Answer 22

central pattern generators

Question 23

as a cat walks

Answer 23

each limb has extensors and flexors alternating between active and inhbited as the cat walks

even if spinal cord connections to the brain are severed the basic alteration of acuity and the coordination between legs continues

Question 24

different neurones exhibit distinct patterns of rhythmic firing

Answer 24

also evidence in lamprey (worms)

critical feature: inhibition across the midline

Question 25

nematode worm - C. elegans

proprioception at the molecular level

Answer 25

loss of TRP-4 ‘stretch’ receptor in DVA neuron leads to ‘loopy’ swimming

DVA neuron detects body bending directly

repetitive spikes seen in swimming

DVA appears to inhibit motor neurone