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389 lab exam > lab exam > Flashcards

lab exam Flashcards

1
Q

what is a monosynaptic reflex arc?

A
  • when a force is applied to a muscle it causes it to stretch, detected by muscle spindle
  • 1a afferent synapse to alpha motor neuron
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2
Q

what influences reflex amplitude?

how can absent reflexes sometimes brought out?

A

symmetry of limbs and whether a person is relaxed

  • reinforcement procedures like light contraction (eg Jendrassik manoeuvre)
  • helps sensitize the muscle to contraction
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3
Q

what is clonus?

A
  • repetitive vibratory contraction of the muscle that occurs in response to muscle and tendon stretch
  • sign of neurological conditions
  • can be sustained (5) or nonsustained (4)
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4
Q

what is hyperreflexia?

A
  • too strong reflexes

- signs include clonus and spreading of reflexes to muscles that are not being tested

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5
Q

how can deep tendon reflexes be diminished?

A
  • abnormalities in the muscles, sensory neurons, motor neurons or the NMJ
    eg. acute upper motor neuron lesions (stroke) and joint disease (mechanical factor)
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6
Q

what causes abnormally increased reflexes?

A
  • associated with upper MN lesions

- influenced by age, metabolic factors (thyroid, electrolytes), and anxiety

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7
Q

what is normal onset latency (b/t tendon tap and muscle reflex onset)

A
  • 38ms

- monosynaptic time for sensory input to travel and diverge to several motor neurons

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8
Q

what is the H reflex?

what does the level of the H reflex indicate?

A
  • Hoffman
  • strength of monosynaptic reflex
  • level of excitability in motor neuron pool
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9
Q

how are the M and H reflexes activated?

A
  • stimulation activates the largest 1a afferents (breaking size principle)–>stim of MNs-30ms-H-wave-monosynaptic reflex
  • motor neurons directly activated in response to greater stimulation-causes M-wave-8ms
  • as stimulation increases, H-wave decreases and M-wave grows until H disappear
  • M-wave constant amplitude reflects the same stimulation
  • changes in M-wave could be due to something moving or changes in MN pool
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10
Q

why does H wave get bigger then smaller and M wave grow w/increased stimulation

A

anti and orthodromic activation in nerves
-large MNs are hyperpolarized b/c of antidromic APs, but only a small percentage that you are stimulating so M-wave still happens

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11
Q

M/H ratio

A
  • important for knowing stimulus is at constant level
  • can combine testing w/other stimuli or in conditions when 1a info may be involved in a task to assess the strength oft the connection b/t 1as and MNs
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12
Q

what happens to T and H reflexes under height/threat of perturbation?

A
  • T reflex increase
  • steady H means motor neuron pool has the same level of excitability, so this must be due to increased muscle spindle sensitivity
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13
Q

why would cats increase spindle sensitivity on a beam?

A

to increase balance relevant afferent info

  • increase T reflex amplitudes, unchanged Hreflex amplitudes
  • since spindle stretch is unaffected by postural threat, spindles must be more activated to reflect greater sensitivity to the threat
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14
Q

what happens when subjects were asked to pay attention to passive movements?

A

lower limb firing rates increase-greater sensitivity

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15
Q

what happens when standing on an edge to T and H reflexes?

A

H is attenuated-inhibition to mute potential destabalizing effects of the stretch reflexes
T reflex facilitated

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16
Q

what happens to the T reflex w/gentle vs strong voluntary contraction of soleus/plantar flexors

A

gentle: increase in reflex: MN pool is sensitized
strong: lower reflex: MN pool being used for contraction and less available for reflex

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17
Q

what happens with other simultaneous muscular activity in the body?

A
  • eg Jendrassi maneuver
  • can bring reflex out when not present
  • inhibitory signals sent to inhibitory interneuron causes facilitation of the reflex
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18
Q

what effect does standing have on the tendon reflex?

A

slightly higher-slight soleus activation when standing

19
Q

what do we see in the antidromic response?

A

high stimulation means no time for refractory period

AP’s start propogating backward-silencing the forward info (orthodromic) and the H reflex

20
Q

what happens at 30ms latency when you slowly increase stimulation to the nerve?

A

H wave and M wave seen

21
Q

what do each of the somatosensory receptors code for?

A

spindles: velocity and length of muscle
skin: length and velocity of skin stretch, onset of movement, acceleration
GTOs: tension/force
joint: pressure, contraction sensitivity

22
Q

for fast movements, muscle spindles in the agonist are unloaded, why?
what could code for limb movement in this case?

A
  • extrafusal fibers shorten faster than 2 resting lengths per second and spindles go quiet b/c gamma discharge is not sufficient to maintain it’s length
  • antagonist muscle is being stretched–ie spindles are sensitive
23
Q

what did the Inglis and Frank study (1990) show?

A
  • vibration of only the antagonist muscle caused errors to the movement (overshoot in perception of movement)
  • magnitude of overshoot was the same for the 3 distances of targets
  • but agonist vibration did not effect movement accuracy
24
Q

what does vibration do to the muscle?

A

causes increased spindle firing-which tells us the muscle is lengthening

25
Q

what did vibration of the antagonist muscle lead to?

A

significant overestimation of the vibrated limb position (6-13 degrees)

26
Q

what could the CNS be using to decode spindle afference if it codes for more than just length?

A

-corollary discharge-copy of the command-(would take into account both alpha and gamma inputs from supraspinal levels w/varying loads on the muscle)
OR
-derives position sense and movement from antagonist-which is being stretched

27
Q

how is matching limb accuracy explained despite undershoot of target in vibrated limb?

A
  1. L arm movement controlled independently of R arm and so moved to target distance b/c subject believes the vibrated arm is there too
  2. more likely (variations in individual performance b/t arms support this) is that afferent info from antagonist spindles in vibrated limb are monitored and since they say greater stretch, matching arm gets to target when vibrated arm doesn’t
28
Q

what is electromyography

A

-electrodes record electric activity of striated muscle potentials through skin of muscle AP’s beneath

29
Q

what type of electrode is best for experiments involving walking?

A

electrodes w/two pickups encased in plastic with pre-amplifier

30
Q

what is the benefit of a pre-amplifier?

A

ensures signal conducted to main amplifier is large enough and free from electrical interference

31
Q

what is the purpose of an amplifier?

A

allows small voltages to be picked up

32
Q

what is an A/D converter?

A

analogue to digital

converts stream to series of discrete digital points that the computer can process into programs like labchart and excel

33
Q

what is gain

A

output/input-what magnitude to amplify by

-ie 1000x

34
Q

what is adequate gain for surface emg?

A

500-`1000x

  • for things like tendon reflex (large contraction), 500 is adequate
  • for small activity need larger multiplier
35
Q

why is sampling rate important + what’s appropriate for surface EMG?

A

1000 to 2000hz
need to sample at high enough frequency to catch all the events
ie 1. frequency of event is important and 2. detail of signal (eg ECG: not frequent enough would give you a not very detailed shape of the wave-could miss top of R wave for example)

36
Q

two examples of internal perturbations (postural threats)

A
  1. voluntary limb movement that changes COM (eg lifting a weight in front of you)
  2. voluntarily changing the base of support (eg lifting one leg requires weight shift onto the other)
37
Q

what is an APA

A

anticipatory postural adjustment

feed-forward, pre movement signal to postural muscles to maintain posture during movement

38
Q

what are two balance challenges that highlight the importance of APA’s?

A
  1. back and heels against wall-fall forward when you try to touch toes b/c can’t make hip shift APA backward (limb movement)
  2. standing with a doorway in front of you-rising up on toes makes you fall back b/c can’t shift COM forward onto balls of feet (changing base of support)
39
Q

what happens in focal and postural muscles when pulling on a bar in front of you?

A
  1. postural-limb/trunk muscles activated before actual movement so that it doesn’t pull you forward
  2. focal movement-arms pulling forward
40
Q

which lower leg muscle is activated first when rapidly moving to toes and why?

A

TA produces forward lean of body so that contraction of calf muscles doesn’t loss of balance backward

41
Q

what decreases the preparatory TA activity?

A

COM further forward in front of malleoli

42
Q

describe TA/soleus activation timing

A
  • tonic discharge in soleus is normally observed and disappears 100-150ms after movement start
  • TA activation coupled with pre motor silent period in soleus`
43
Q

when is tonic soleus activity larger?

A

on a decline (subjects unintentionally leaning back to stay upright with forward force)

44
Q

what happens on an incline?

A

TA amplitude and duration increases

389 lab exam (1 decks)

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