Week 12 - reflexes

Question 1

simple reflexes

Answer 1

sensory neurons make synapses with spinal cord motor neurons to mediate simple reflexes. this is the simplest form of motor control.

Question 2

central pattern generators

Answer 2

Networks of interneurons in the spinal cord and brainstem coordinate the interaction of many different motor groups (locomotion, respiration)

Question 3

complex/volitional movement

Answer 3

motor output that is planned an refined by the motor cortex, basal ganglia and cerebellum

Question 4

monosynaptic reflex

Answer 4

single synapse between afferent and efferent neurons

Question 5

polysynaptic reflex

Answer 5

they have two or more synapses. this somatic motor reflex has both synapses in the CNS.

Question 6

stretch reflex

Answer 6

it operates at a conscious level
stimulus: passive stretch of a muscle by applies load or contraction of antagonist muscle
response: active contraction of muscle e.g. patellar tendon reflex
it is very fast and sensitive due to muscle spindle afferents and monosynaptic connection to motorneurons

Question 7

example of stretch reflex

Answer 7

1. load is placed in hand
2. load will activate muscle spindle (direct connection with the motorneuron)
3. the motorneuron is also activated, there will be contraction of the same muscle that was strecthed.

Question 8

what is the stretch reflex essential for

Answer 8

stabilizing, reflex strongest in postural muscles

Question 9

wha tis the latencies of strecth reflex in forearm muscles and ankle extensors

Answer 9

forearm muscles - 25 ms
ankle extensors - 37 ms

Question 10

stretch reflex paths

Answer 10

parallel multisynaptic paths through spinal cord (it branches up to somatosensory cortex s well)

Question 11

which is strecth relfex supressed

Answer 11

during movement

Question 12

golgi tendon reflex

Answer 12

Golgi tendon organ afferents synapse on interneurons in intermediate zone of spinal cord. Interneurons inhibit motorneurons of same muscle
Stimulus: Active tension in muscle
}Reponse: relaxation or reduction of tension

Question 13

golgi tendon reflex mechanism explanation

Answer 13

regulate the level of activity - complementary to stretch reflect
over extortion of the muscle > golgi tendon organ activated > interneurons activated
the intrneurons inhibit motorneuron (reduce contraction) - to regulate the amount of force

Question 14

golgi tendon reflex example

Answer 14

when there is excessive load the muscle relaxes. the load is dropped but the muscle is saved.
neuron from golgi tendon firs, motor neurons is inhibited, muscle relaxes and the load is dropped.

Question 15

golgi tendon reflex properties

Answer 15

1. it prevents movement
2. acts in concert with stretch reflect to stabilize posture
3. suppressed when net motion is desired

Question 16

stretch and golgi tendon reflexes

Answer 16

overactivation of biceps > golgi tendon reflex > reduced activity in biceps - occurs via feedback from GTO which synapses with interneurons, generally inhibitory

overactivation of biceps > stretch of triceps (antagonistic muscle) > stretch reflex > contraction of triceps

Question 17

flexion withdrawal relfex

Answer 17

stimulus: noxious injury of limb
response: flexion of joints proximal to stimulus (extension distal to stimulus)
nociceptor afferents synapse on interneurons in superficial dorsal horn - slowly conduction afferents
multi-synaptic path to motorneurons

Question 18

how does the flexion withdrawal reflex work

Answer 18

activate pain receptor in forearm > flexion of the proximal joiny and extension of the distal joint

Question 19

what happens if we prick our finger

Answer 19

all flexion

Question 20

recirprocal inhibition

Answer 20

activation of one motor nucleus is coupled to inhibition of antagonistic motor nucleus
eg. activation of flexor motorneurons elicits inhibition of antagonist extensors
when co-contraction of antagonists desires (for join stiffness) this circuit is suppressed

Question 21

patellar tendon reflex

Answer 21

tap on patellar tendon > stretch quads > contraction of quads
simultaneously inhibit hamstrings contraction

Question 22

cross exension reflex

Answer 22

Full extension of the flexion withdrawal reflex involves contralateral extension for increased postural support > mainly seen in legs
Commissural interneurons carry signals to contralateral spinal cord

Question 23

extensor thrust reflex

Answer 23

stimulus: pressure on sole of foot
response: activation of leg extensors
Mechanoreceptors project to intermediate zone interneurons > extensor motorneurons
reflex operates only during stance

Question 24

Babinski sign

Answer 24

extensor thrust reflex is influences by corticospinal tract
can be elicited at rest (in toes) bby vigorous stroking of sole of the foot
if corticospinal tract is damages (stroke, spinal injury), the reflex pattern is switched to flexion withdrawal

Question 25

vestibulo spinal reflex

Answer 25

stimulus: downward deviation of head on one side – activates otolith afferents
response: downhill limbs extend
otolith afferents activate lateral vestibule spinal tract: ipsilateral projection to extensor (antigravity) motor nuclei }
postural reflex - reflex latency in legs about 80ms