Lab 2 - Recording human nerve reflexes

Question 1

describe the stretch receptor

Answer 1

-specialized “muscle spindles” as stretch receptors monitered by gamma motor neuron
- spindles innervated by intrafusal fibers that moniter excititory sensory neurons via mechanoreceptors
-convey info about muscle legnth, tension, and pressure of extrafusal muscle fibers (monitered by alpha motor neuron) to the CNS
-maintain muscle tone via tonic control

Question 2

describe the stretch (myotatic) reflex simply

Answer 2

stretch tendon= stretch spindle = synapse on motor neuron = muscle fibers depolarize and twitch/contract
- minimal delay due to monosynaptic pathway (1 synapse from sensory neuron to motor neuron), no interneurons
-extensors inhibited, flexors contract

Question 3

what muscles are involved in the plantar and dorsiflexion of the ankle?

Answer 3

-Dorsi flexion (foot up):
tibialis anterior, extensor hallucis longus and extensor digitorum longus
-plantarflexion (foot down): gastrocnemius (connected to Achilles, contracts), plantaris, soleus, and fibularis longus

Question 4

what equipment is required for lab 2, recording human nerve reflexes

Answer 4

-laptop
-iworx case with: IXTA ROAM (record data), Power supply, and usb cable (transfer data to computer), disposable EMG electrodes, red/black/green electrode wires, alcohol for sanitizing and remocing emg electrodes, PRH-200 reflex hammer (to tap and record strength of tap)

Question 5

where are the electrodes placed for lab 2?

Answer 5

green (C/ground): on ankle
red (+1): near back of knee
black (-1): middle of calf muscle (record gastrocnemius contraction)

Question 6

What is the procedure for lab 2?

Answer 6

• subject kneels on stool with foot hanging freely
• tap wide end of reflex hammer on ankle (top of Achilles tendon)
• 30 trails in total should be done (10 with light tap, 10 with medium tap, and 10 with heavy tap)
  -record on Iworx for all

Question 7

describe the results for lab 2

Answer 7

-IWorx screen:
top pannel: EMG calf response. depolarizes then hyperpolarizes, returns to baseline
bottom pannel: hammer strike. hyperpolarizes before depolarizing and returning to baseline
-cursor placement: one just before the hyperpolarization of the bottom pannel. two just before the depolarization of the EMG channel
-Analysis window: record T2-T1 value (reflex conduction time). discard the lowest and highest values from each of the 3 strengths. average the 8 trials at each conduction time and record in table under “mean reflex conduction time”
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Question 8

describe the data analysis process for lab 2.

Answer 8

-to get “total path length”: belly of subjects calf muscle to to just above the hipbone (approx. site of synapse in spinal cord)
- convert mean reflex conduction times (m/s) for strengths 1-3 to conduction velocity (m/s) using the following equation:
CV(m/s) = (total path length mm)/(mean reflex time msec - 0.5msec)

Question 9

Does conduction velocity change with increase stimulus strength? Why or why not?

Answer 9

-YES increased strength = increased conduction velocity by approx. 1 m/s intervals
- becasue more spindle fibers (stretch receptors) are recruited and therefore more AP’s = faster transduction of signal

Question 10

besides the excitatory inputs from stretch receptors, what synaptic inputs might influence the activity of spinal motor neurons?

Answer 10

primary afferent neuron stimulates the inhibitory inter-neurons to relax/inhibit the antagonist muscles alpha motor neuron(flexor)