Lab 2: Recording Human Nerve Reflexes Flashcards
What can you get out of studying stretch reflexes?
-strech receptors
-nerve conduction velocity
-electromyograms (EMG)
-motor control
What is the objective of this lab?
-to record human nerve reflex impulses, and to determine it’s speed
How do the specialized receptors in the muscle respond to stretching of a tendon?
The stretching of the tendon attached to the muscle sends a signal to motor neurons through a single synapse.
What is the response to the incoming impulse from the motor neuron?
The muscle fibre depolarizes and twitch (contract)
What do the specialize receptors in skeletal muscles give info about?
-muscle length
-muscle tension
-muscle pressure to the central nervous system
What is the name of the sensory receptor responsible for providing info about length or rate of change of the length of a muscle?
muscle spindles
How do muscle spindles work?
they are in parallel with muscle fibres and when the muscle is stretched by an external force, that is when the spindles are stretched.
Muscle spindles are composed of and play a role in…
contain a small bundle of intrafusal fibres that regulate the excitability of the sensory afferent spindle nerves
How do muscle spindles regulate the excitability of spindle nerves?
by mechanically deforming the receptors
How do receptors deform?
by being inverted by gamma motor neurons
What are sensory afferent spindle nerves?
specialized nerve fibers the convey muscle info from muscle spindles to the CNS
What do the sensory receptors play a significant role in?
-developing antigravity reflexes
-maintaining muscle tone
Describe the strech (myotic) refelx
when a muscle is stretched and the excitation of it’s muscle spindles causes a reflex contraction of the muscle
Is there a minimal delay between the muscle stretching and reflex contraction or is it an immediate response?
there is a minimal delay
What is the reason that causes the minimal delay?
due to the fact that it is a monosynaptic pathway
What does it mean a pathway is monosynaptic?
there are no interneurons meaning the sensory afferent nerves from the spindles synapse DIRECTLY with motor neurons.
What is the shortest possible reflex arch?
a monosynaptic stretch reflex arch
For example: the reflex response that occurs when a person jumps from a low stool to the floor…
the extensor (straightening) muscles of the legs are stretched on landing which causes their muscle spindles to lengthen. The discharge of the muscle spindles is conveyed to the CNS through fast conducting axons. These sensory axons enter the spinal cord through the dorsal root and synapse with the motor neurons of the same extensor muscle. The motor neurons then trigger the contraction of the extensor muscle to oppose the stretch that is produced by landing. (this reflex is why you keep your balance and don’t fall when you change body positions)
What is being recorded in this lab?
-electromyograms (EMG)
-summation of asynchronous electrical activity (muscle action potential) in the multiple fibers in the muscle
-determine the time between the stretch of the tendon and arrival of the motor impulse at the muscle (using action potential)
Which tendon was tested on in this experiment?
Achilles tendon
What is being measured?
-the effect of varying the strength of the strike on the reflex response
-conduction times and nerve velocities
Equipment required:
-laptop
-black iWork case containing:
~IXTA ROAM data acquisition unit + power supply + USB cable
~iWire-B3G harness and red, green and black electrode lead wires
~disposable EMG electrode
~PRH-200 reflex hammer
Follow IXTA ROAM setup with…
-plug the PRH-200 reflex hammer to the A3 channel on the IXTA ROAM
-apply the electrodes to the following places of the subject’s leg:
~red (+1): lead wire, to the back of the knee
~black (-1): lead wire, near the back of the knee
~green (C): functions as the ground, on the ankle
What software is used for this lab?
LabScribe23
What do you open once LabScribe has been opened?
go to settings, select human nerve folder and find the setting file “StrechReceptorReflex-iWireB3G”, this will bring a blank file to appear
Exercise 1: Achilles Tendon Reflex
What is the goal of this exercise?
to determine conduction time from tendon tap to response of the gastrocnemius muscle in the Achilles tendon reflex arch.
Exercise 1: Achilles Tendon Reflex
Procedure
- Have subject sit so their calves hang freely OR to kneel on chair with their ankles/feet hanging over the edge
- Tap the tendon with the hammer in order to locate the point in the tendon which produces a contraction of the gastrocnemius muscle and the foot moving in a downward direction
- Click record and instruct the subject to move their foot up and down and click autoscale
- Use the mark button and label the part of the experiment that was just conducted.
- Start the experiment by informing the subject it has started
- Tap the subject’s Achilles tendon and record a total of 10 trials using the same tapping force but at different times without the subject being aware.
- Press Stop recording once all 10 trials have been complete
- Select Save As for the file and save it in the appropriate location under the appropriate name
- Repeat this on the subject with 3 different amounts of force
Where is the Achilles tendon located?
above the heel which connect the gastrocnemius muscle to the tarsal bone (ankle/foot region)
What side of the hammer do you hit the tendon with?
the wide side
Which direction should the subject’s foot move when the gastrocnemius muscle is contracted?
plantar flexion (downward)
What is the opposite of a plantar flexion?
dorsiflexion (upward)
Why does the subject have to move their foot up and down and record it before preforming the test?
to demonstrate the type of EMG that occurs plantar flexion and dorsiflexion
How do you use the mark button?
type <Subject’s name> in the mark box located to the right of the mark button and press the enter key and keep recording
What sound the file type be saved as?
.iwxdata
How do you view the signal made by tapping the tendon and the EMG response on the same screen?
clicking the display time button
OR
placing one cursor before the beginning of the signal from the tendon tap and the second cursor after the subject’s EMG response and zoom in between the cursors to see the complete reaction time
What button do you click to analyze the results?
click the analysis icon in the tool bar
Where does the mathematical function T2-T1 show up?
the function table which is above the display of the EMG results in the analysis window
What does the T2-T1 function tell you?
the mean reflex conducted time (ms)
The analysis window is divided into two, what does the top window tell you and what does the bottom one tell you?
top: EMG activity
bottom: when the tendon is tapped
Where can you save the results you got from the lab?
in the Journal
Where is the total path length measured?
from the top of the hip bone to the middle of the calf (thickest part)
What is the total length of the nerve path?
the path length multiplied by 2
Conduction velocity equation (m/sec)
total path length (mm) / (Mean reflex time (msec)- 0.5msec)
Why do you subtract 0.5 msec from the mean reflex time?
because the monosynaptic reflex includes the neuromuscular synapse (NMJ), we assume the synaptic transmission takes about 0.5msec
What muscle groups are involved in plantar flexion and in dorsiflexion of the ankle?
-plantar flexion: gastrocnemius, soleus and tibialis
-dorsiflexion: tibialis anterior, extensor digitorum longus and extensor hallucis longus
Expected results:
as the strength of the tap increases, the mean reflex conduction time will decrease and the reflex condition velocity will increase
Why does the time decrease with the increasing strength?
because the muscle spindles are stimulated more intensely causing a faster reflex response
Besides excitatory inputs from stretch receptors, what synaptic inputs might influence the activity of spindle motor neurons?
various synaptic inputs such as inhibitory inputs.
How do you calculate mean reflex time?
you take the average of the 10 trials T2-T1 results
