B7-017 Spinal Cord Reflexes

Question 1

predominant stretch receptors in muscle

Answer 1

muscle spindles

Question 2

composed of intrafusal fibers

Answer 2

muscle spindles

Question 3

muscle spindles lie in […] with extrafusal fibers

Answer 3

parallel

Question 4

the rapidly adapting (dynamic) component of muscles spindles provides info about

Answer 4

velocity of stretch

Question 5

the slowly adapting (static) component of muscles spindles provides info about

Answer 5

length

Question 6

muscle spindle innervation contributes to muscle […]

Answer 6

tone

Question 7

monitor stresses and forces at the tendon

Answer 7

golgi tendon organs

Question 8

GTOs lie in […] with extrafusal fibers

Answer 8

series

Question 9

innervated by Ib afferents only

Answer 9

GTOs

Question 10

conscious proprioception goes through the […] pathway

Answer 10

DC/ML

Question 11

unconscious proprioception goes through the […] pathway

Answer 11

spinal cord and cerebellar

Question 12

pathway the regulates balance and smoothing movements of unconscious proprioception

Answer 12

spinocerebellar

Question 13

motor units contract the muscle […] a motor neuron fires

Answer 13

every time

Question 14

have characteristic innervation ratio

Answer 14

motor units

fine control requires lower ratio than coarse control

Question 15

a lesion in one segment of the ventral horn will result in motor deficits to

Answer 15

several muscles

Question 16

2 mechanism to increase force to motor neuron

Answer 16

increase firing rate
increase number of motor units firing

Question 17

order of recruitment

Answer 17

small motor units recruited first, follwed by larger

Question 18

small slow motor units

Answer 18

type 1

Question 19

endurance motor units

Answer 19

type 1

Question 20

large fast motor units

Answer 20

type II

Question 21

motor units that convey large forces for a short time {sprint}

Answer 21

type 2

Question 22

oxidative motor unit
lots of mitochondria

Answer 22

type 1

Question 23

glycolytic motor unit
few mitochondria

Answer 23

type 2

Question 24

red motor unit

Answer 24

type 1

Question 25

white motor unit

Answer 25

type 2

Question 26

afferent coming from one muscle efferent going into same muscle

Answer 26

homonymous

Question 27

afferent coming from one muscle efferent goes to opposing muscle

Answer 27

heteronymous

Question 28

describe the sequence of events in the stretch reflex

Answer 28

1. tendon tapped, muscle is stretched 2. muscle spindle is stretched 3. Ia and II nerve ending are deformed 4. sensory nerve endings depolarized 5. increased firing of Ia and II efferents 6. excitation of alpha motor neurons 7. increased firing of alpha motor neurons 8. contraction of the muscle

Question 29

Ia afferent detects change in velocity/length of muscle and sends quick activation signal to the Ia afferent nerve

Answer 29

dynamic "knee jerk" phase of stretch reflex

Question 30

[...] phase of reflex is important to maintain muscle tone

Answer 30

tonic (cutting the Ia afferents would greatly reduce tension)

Question 31

adjust the gain (length) of the muscle spindles to continuously provide information about the length/stretch to the PNS

Answer 31

gamma motor neurons

Question 32

activated by stretching a spastic or rigid muscle contraction, then rigidity "melts away"

Answer 32

inverse stretch reflex

Question 33

inverse stretch reflex is mediated by

Answer 33

GTO/Ib afferent

Question 34

stretch reflex is mediated by

Answer 34

muscle spindles

Question 35

activated by increased stretch increasing muscle contraction

Answer 35

stretch reflex

Question 36

initiated from cutaneous stimuli to remove body from potentially damaging stimuli

Answer 36

flexion reflex

Question 37

contralateral component of the flexion reflex that helps to maintain balance

Answer 37

crossed extensor reflex (crosses the midline)

Question 38

two stages of reflexes after spinal injury

Answer 38

1. hyporeflexive due to spinal shock (1-2 weeks) 2. hyperreflexive due to loss of inhibition of LMN

Question 39

how do muscle spindles send signals to the cerebellum to create balanced, smooth movements?

Answer 39

1. muscle spindle afferent synapses at Dorsal Clarke nucleus 2. second order axons ascend via dorsal spinocerebellar tract to ipsilateral cerebellum

Question 40

striking the tendon with a reflex hammer stretches both [...] and [...] muscle fibers

Answer 40

extrafusal intrafusal

Question 41

in the stretch reflex, greater force causes greater stretch, which causes greater activation of [...] in the muscle spindle

Answer 41

Ia afferents **results in greater muscle contraction**

Question 42

causes you to extend your contralateral limb after your ipsilateral limb is flexed to try to maintain balance

Answer 42

crossed extensor reflex

Question 43

DTR is initiated by

Answer 43

stretch

Question 44

cutaneous afferents in the skin that sense somatosensory stimuli and elicit a protective response

Answer 44

flexor reflex afferents **example: Babinski's**

Question 45

examples of flexor reflex afferents [3]

Answer 45

Babinski's flexion (withdrawal) reflex corneal blink reflex

Question 46

sensory component of the inverse stretch reflex

Answer 46

GTOs

Question 47

the flexor withdrawal reflex is initiated by noxious stimuli carried on what fibers?

Answer 47

C and A-delta fibers

Question 48

conveys proprioceptive information to the ipsilateral cerebellum to smooth out movements

Answer 48

spinocerebellar

Question 49

the dorsal spinocerebellar pathway in the spinal cord conveys proprioceptive information to the [...] cerebellum the cerebellum then communicates with the [...] motor cortex to correct motor instructions to affected limb

Answer 49

ipsilateral contralateral

Question 50

carries pain and temperature information

Answer 50

spinothalamic tract

Question 51

sudden release of muscle tension when GTOs signal too much stress at the tendon

Answer 51

inverse stretch reflex

Question 52

maintaining a contraction is stimulated by [...] afferents

Answer 52

Ia

Question 53

[...] afferents inhibit the alpha motor neuron to relax the muscle

Answer 53

Ib

Question 54

force at the tendon is measured by [...] afferents in the GTO

Answer 54

Ib

Question 55

responsible for altering the length of the muscle spindle intrafusal motor fibers

Answer 55

gamma afferents

Question 56

[...] fibers mediate pain that stimulates the withdrawal reflex

Answer 56

A-delta C fibers

Question 57

number of muscle fibers innervated by a given motor axon

Answer 57

innervation ratio

Question 58

for imprecise movements requiring large force the innervation ratio is [...]

Answer 58

high (1 motor neuron activates many muscle fibers simultaneously to generate force)

Question 59

for fine, precise movements the innervation ratio is [...]

Answer 59

low (small groups of muscle fibers controlled individually for greater control)

Question 60

both firing rate and orderly recruitment by size are mechanisms for

Answer 60

increasing force

Question 61

inhibition of [...] fibers is useful to provide coordinated movements

Answer 61

heteronymous