lab exam

Question 1

what is a monosynaptic reflex arc?

Answer 1

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

Question 2

what influences reflex amplitude?

how can absent reflexes sometimes brought out?

Answer 2

symmetry of limbs and whether a person is relaxed

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

Question 3

what is clonus?

Answer 3

• 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)

Question 4

what is hyperreflexia?

Answer 4

• too strong reflexes

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

Question 5

how can deep tendon reflexes be diminished?

Answer 5

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

Question 6

what causes abnormally increased reflexes?

Answer 6

• associated with upper MN lesions

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

Question 7

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

Answer 7

• 38ms

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

Question 8

what is the H reflex?

what does the level of the H reflex indicate?

Answer 8

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

Question 9

how are the M and H reflexes activated?

Answer 9

• 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

Question 10

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

Answer 10

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

Question 11

M/H ratio

Answer 11

• 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

Question 12

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

Answer 12

• 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

Question 13

why would cats increase spindle sensitivity on a beam?

Answer 13

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

Question 14

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

Answer 14

lower limb firing rates increase-greater sensitivity

Question 15

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

Answer 15

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

Question 16

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

Answer 16

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

Question 17

what happens with other simultaneous muscular activity in the body?

Answer 17

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

Question 18

what effect does standing have on the tendon reflex?

Answer 18

slightly higher-slight soleus activation when standing

Question 19

what do we see in the antidromic response?

Answer 19

high stimulation means no time for refractory period

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

Question 20

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

Answer 20

H wave and M wave seen

Question 21

what do each of the somatosensory receptors code for?

Answer 21

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

Question 22

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

Answer 22

• 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

Question 23

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

Answer 23

• 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

Question 24

what does vibration do to the muscle?

Answer 24

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

Question 25

what did vibration of the antagonist muscle lead to?

Answer 25

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

Question 26

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

Answer 26

-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

Question 27

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

Answer 27

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

Question 28

what is electromyography

Answer 28

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

Question 29

what type of electrode is best for experiments involving walking?

Answer 29

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

Question 30

what is the benefit of a pre-amplifier?

Answer 30

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

Question 31

what is the purpose of an amplifier?

Answer 31

allows small voltages to be picked up

Question 32

what is an A/D converter?

Answer 32

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

Question 33

what is gain

Answer 33

output/input-what magnitude to amplify by | -ie 1000x

Question 34

what is adequate gain for surface emg?

Answer 34

500-`1000x - for things like tendon reflex (large contraction), 500 is adequate - for small activity need larger multiplier

Question 35

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

Answer 35

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)

Question 36

two examples of internal perturbations (postural threats)

Answer 36

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)

Question 37

what is an APA

Answer 37

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

Question 38

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

Answer 38

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)

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

what decreases the preparatory TA activity?

Answer 41

COM further forward in front of malleoli

Question 42

describe TA/soleus activation timing

Answer 42

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

Question 43

when is tonic soleus activity larger?

Answer 43

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

Question 44

what happens on an incline?

Answer 44

TA amplitude and duration increases