1. The document discusses the somatosensory and skeletal motor nerve axes of the nervous system and how they relate to muscle stretch reflexes and nerve conduction. 2. It provides details on the muscle stretch reflex pathway and how sensory signals from muscle spindles are transmitted to the spinal cord to elicit reflexive muscle contractions in response to changes in muscle length. 3. The document describes experiments measuring nerve conduction velocity along the ulnar nerve and the equipment, electrode placements, stimulation procedures, and data analysis methods used.

1. Nervous impulse conduction.
Reflex responses: muscle stretch reflex
Practical 1 for Nervous System
Somatosensory axis of the nervous system:
Inform what is the length of the muscle, what is
Skeletal motor nerve axis of the nervous
its instantaneous tension, and how rapidly is its
system: excitation of the muscle by spinal cord
length or tension changing.
anterior motor neurons

2. Sensory signals enter th cord th
S i l t the d through th sensory (
h the (posterior) roots.
t i ) t
After entering the cord, every sensory signal travels to two separate
destinations: (1) One branch of the sensory nerve terminates almost
immediately in the gray matter of the cord and elicits local segmental
cord reflexes and other local effects. (2) Another branch transmits
signals to higher levels of the nervous system - to higher levels in the
cord itself, to the brain stem, or even to the cerebral cortex
1 - sensory transducer in the periphery for example a Pacinian corpuscle or other
periphery, example,
tactile sensor in the skin.
2 - the pseudounipolar sensory neuron in the circuit. Its soma is physically located in a
dorsal root ganglion
3 - an interconnector neuron, whose soma is found in the CNS.
4 - motor neuron whose soma is in the ventral horn of the gray H of the spinal cord.
5 - the effector organ, which in the case of this type of arc, will always be skeletal
muscle.

3. Somatic arc reflex:
how the system works?
1. Something impinges on the transducer, which causes the afferent
fiber of the pseudounipolar sensory neuron to fire.
2. That signal is transmitted via the sensory neuron efferent fiber into the
CNS, specifically into a synapse with an interconnector neuron in the
dorsal horn of the gray H.
3. That neuron then sends a signal to a synapse with the motor neuron
in the ventral horn.
4. The axon of the motor neuron - which may actually be several meters
in length - l
i l th leaves th CNS and t
the d terminates at a motor end plate on
i t t t d l t
some myofiber. When it fires it initiates contraction.
! This loop is completely independent; it's not necessary to have
CNS involvement beyond the "relay" at the interconnector neuron.
Ex: What happens when you inadvertently put your hand on a hot
stove burner….
Axons conduct action potentials away from the cell
body of the nerve cell
Dendrites receive action potentials

4. Nerve Conduction
Nerve Conduction Velocity Along the Ulnar Nerve of a
Human Subject
The nerve impulse is a wave of depolarization immediately followed by a
wave of repolarization, collectively called an action potential, occurring on
the plasma membrane of a nerve fiber. Changes in ion conductances
across the nerve fiber membrane are responsible for the initiation and
propagation of the action potential. Experimentally, these changes can be
the result of electrical current applied through electrodes. Once initiated,
an action potential is usually propagated without decrement in amplitude
or velocity along the plasma membrane of a nerve fiber.
The velocity or speed of the propagated (conducted) nerve impulse is directly
related t the diameter of th nerve fib and th presence of a myelin
l t d to th di t f the fiber d the f li
sheath.
• The fastest nerve fibers have large diameters and are myelinated (motor
nerve fibers for skeletal mm).
• The slowest nerve fibers have small diameters and are unmyelinated
(sensory nerve fibers).

5. In the peripheral nervous system, nerve fibers of various diameters and
functions (motor and sensory) are bundled together by connective tissue
to form nerves. A compound action potential is the sum of all the
action potentials occurring in the individual neurons of the whole nerve.
The velocity of the compound action potential signal can be a measure
and can indicate the state of health of the nerve. Diseases that damage
the
th myelin, destroy neurons, or constrict the whole nerve will d
li d t t i t th h l ill decrease
the nerve's conduction velocity. However, the nerve conduction velocity
may remain normal until late in a disease process as long as a few
normal neurons survive, In addition, the nerve conduction velocity
reflects conduction of the fastest nerve fibers, usually motor neurons.
The nerve conduction velocity is determined by recording the motor
(EMG) response of a muscle to the stimulation of its motor nerve at
two or more points along the nerve course. The time between
stimulation and response is measured and compared to the distance
between the point of stimulation and point of response. Precise
parameters of measurement have been developed for the ulnar nerve
and the motor response is measured over the abductor digiti minimi.
The ulnar nerve comes from the medial
cord of the brachial plexus, and runs
inferior on the medial/posterior aspect of
/p p
the humerus down the arm, going behind
the medial epicondyle, through the
cubital tunnel, at the elbow (where it is
exposed for a few centimeters, just above
the joint).

6. Objectives
1.
1 To record a charge from the stimulus electrodes to recording
electrodes.
2. To observe the Threshold, Maximal and Supra-Maximal
response levels.
3. To determine nerve conduction velocity along the ulnar nerve.
Equipment
• PC running Windows or Macintosh computer
• BIOPAC Software: Biopac Student Lab PRO
• BIOPAC Data Acquisition Unit (MP30)
• BIOPAC Stimulator (BSLSTM)
• BIOPAC disposable electrodes (EL503)
• BIOPAC electrode lead set (SS2L)
• BIOPAC human stimulator probe (HSTM01)
• Abrasive pads (ELPAD)
• Electrode gel (GEL1)
• Ruler (cm)
• Adhesive Tape (TAPE1)
• Pen for marking skin

7. Setup
Hardware
1. Plug the BSLSTM Trigger cable into the Analog Out port on the back
panel of the MP 30 Unit.
2. Plug the BSLSTM Reference Output cable into CH1 on the front of the
MP30 unit.
3. Plug the SS2L electrode lead into CH2 on the front of the MP30 Unit.
4. Turn the MP30 Data Acquisition Unit on.
5. Turn the BSLSTM Stimulating Unit on.
6. Set the BSLSTM Range to "0-100V" and Level to "0" by turning the Level
knob counterclockwise until it stops
7. Plug the HSTM01 human stimulator probe into the Stimulus Output port
on the front of the BSLSTM Unit.
Setup
Software
1. Turn the computer on.
2. Launch the BSL PRO software on the host computer. The program should
create a new "Untitled1" window. You may close this window, you will not
need it.
3. Open the Nerve Conduction Velocity template by choosing File menu >
Open >
Then change the FILE TYPE to: Graph Template (*GTL) and locate the File
Name:
h03.gtl on the desktop of the computer. This should open a data acquisition
window and the Stimulator control window, as shown below.
4. Click on the Display menu, then select Show and select Markers. This will
add a white text box directly above the top data collection panel. This is
where you can type notes about each stimulus that you administer.

8. Subject - Electrode Connections
5. Remove any jewelry or watches on your wrist.
6. Clean skin with an alcohol prep and allow to air dry before proceeding.
7. Apply a very small drop of electrode gel (GEL1) in the center of each electrode.
8. Place three EL503 disposable recording electrodes on the subject's hand as
follows and attach the appropriate colored electrode leads to each of the electrode
sites; use the cloth tape provided to secure each electrode tightly to the skin
making sure to not cover up the metal electrode pin connections
9. Clip the SS2L electrode cable to the subject’s shirt or clothes to relieve cable strain
and avoid pulling on the electrodes.

9. Experimental Method
You will record the stimulation of the ulnar nerve at two points
along the forearm. Note the stimulation points on the figure
below. You may have to move around and adjust the electrode
placement to find the optimal placement.
NOTE: The white anode electrode is always further
from the hand and the black cathode electrode is
always closest to the hand.
(we will not use the S3 stimulation position)
Experimental Method
1. The subject should hold the HSTM01 stimulating probe at position S1 and
depress and hold the red button down for stimulation to occur.
2. Increase the level setting on the BSLSTM unit to 5V.
3. When ready, the experimenter should press the Start button in the PRO
software indo
soft are window (this will begin stim lation and 200msec data acq isition) E er
ill stimulation acquisition). Every
time that you administer a stimulus by pressing the start button, a marker with a
timestamp will be automatically inserted for you. You may add notes to this
timestamp.
4. Increase the level setting on the BSLSTM unit by 5V increments until a
response is detected.
• A response may be indicated by involuntary twitching of the fingers.
• A response typically occurs between stimulus levels of 25 to 40 volts.
p yp y
• Move the probe around a little if no response occurs by 45 volts.
• If the subject experiences pain with the finger twitch, and a response has not
been detected, move the stimulating probe to a new position. A response
should be detected well before the subject experiences any pain.
• The recorded response on Channel 40 (blue line, bottom panel) may have
one or two upward peaks followed by a downward deflection.

10. 5. Once you have detected a response, adjust the electrode placement to make sure
that you had the optimal placement. Then mark with a small ink dot the location of
the black cathode electrode.
6. Administer 3 stimuli at the S1 location and label each stimulus in the marker box
as S1-1 S1-2 S1-3
S1 1, S1 2, S1 3.
7. Now reposition the stimulating electrode at the S2 position after applying more gel
to this location. Decrease the voltage to 5V less than the value for S1 and repeat
the testing process.
Be sure to mark the placement of the black cathode electrode once you have
achieved a response. Record 3 stimuli (label these in the marker text box) for
the S2 location.
8. Finally, measure the distance in centimeters from the S1 to S2 cathode
placements
Record this distance.
9. You have completed the data collection process and may now disconnect the
electrodes, turn off the stimulator and BIOPAC MP30 devices, and proceed with
cleaning up the equipment and subject.
Data Analysis
At the conclusion of your recording session you may want to make your data
collection measurements or you can return at a later date to collect your data. The
data collection measurements should already be appropriately selected for you in the
BIOPAC window.
1. Scroll through the data until you locate your first stimulus for S1. By clicking on the
inverted triangle markers located above the data window you can view the marker text
associated with each marker position.
2. Once you find your Threshold stimuli, you will need to change from the “arrow”
cursor to the I-beam curser by selecting the I-beam button in the bottom right
corner of the display.
3. Use the curser to select the data from the start of the stimulus (red panel) to the
peak of the response (blue panel) as shown in the example figure above.
4. These data variables are already set-up for you in the boxes above the data signal:
Ch1 p-p (peak-to-peak) value – this is the voltage applied
Ch40 p-p value – this is the magnitude of the stimulation in the ulnar nerve
Ch40 delta T value – this is the duration of time between the stimulus and
the nerve signal detected by the recording electrode

11. 5. Record the Ch40 delta T value from the onset of the voltage (red panel) to the
peak of the ulnar nerve stimulation (blue panel) for each of the S1 stimuli. You
may need to zoom in using the magnifying glass tool in order to see the data
in enough detail to accurately measure the time.
6. Enter the delta T values for S1, S2 and your measured distance between the
cathode electrodes for S1 & S2 into a data EXCEL sheet found on the lab web
site. The excel sheet will calculate the speed of conduction using the following
formula:
(Distance between S1 and S2) / (delta T for S2 - delta T for S1)
7. You
7 Y need t i
d to input th speed of conduction values ( h
t the d f d ti l (shown i red t t i th E
in d text in the Excel
l
sheet) into the group data sheet found on the desktop of the computer.

12. Muscle stretch reflex
Monosynaptic pathway that allows a reflex
signal to return with the shortest possible time
delay back to the muscle after excitation of the
spindle
Neuronal circuit of the muscle stretch reflex - the simplest
manifestation of muscle spindle function.
Whenever a muscle is stretched suddenly, excitation of the spindles
causes reflex contraction of the large skeletal muscle fibers of the
stretched muscle and also of closely allied synergistic muscles.

13. The dynamic stretch reflex is elicited by the potent dynamic signal
transmitted from the primary sensory endings of the muscle spindles,
caused by rapid stretch or unstretch. That is, when a muscle is
suddenly stretched or unstretched, a strong signal is transmitted to the
spinal cord; thi causes an i t t
i l d this instantaneous strong reflex contraction
t fl t ti
(or decrease in contraction) of the same muscle from which the signal
originated.
Thus, the reflex functions to oppose sudden changes in muscle
length.
The dynamic stretch reflex is over within a fraction of a second after the
muscle has been stretched (or unstretched) to its new length, but then a
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weaker static stretch reflex continues for a prolonged period
thereafter. This reflex is elicited by the continuous static receptor
signals transmitted by both primary and secondary endings.
This static stretch reflex causes the degree of muscle contraction to
remain reasonably constant, except when the person's nervous
system specifically wills otherwise.
Muscle Sensory Receptors: Muscle Spindles and Golgi Tendon Organs
Muscle function requires not only excitation of the muscle by spinal cord anterior
motor neurons but also continuous feedback of sensory information from each
muscle to the spinal cord, indicating the functional status of each muscle at each
instant (length of the muscle, instantaneous tension, how rapidly is its length or
( g p y g
tension changing).
Muscles and their tendons are supplied abundantly with two special types of sensory
receptors:
(1) muscle spindles, which are distributed throughout the muscle and send information
to the nervous system about muscle length or rate of change of length,
(2) Golgi tendon organs, which are located in the muscle tendons and transmit
information about tendon tension or rate of change of tension.
The signals from these two receptors are almost entirely for the purpose of intrinsic
muscle control. They operate almost completely at a subconscious level and
transmit information not only to the spinal cord but also to the cerebellum and even
to the cerebral cortex, helping to the control of muscle contraction.

14. Muscle spindles are distributed throughout the belly of the muscle, send information to the
NS about muscle length or rate of change of length; both motor and sensory innervation.
Each spindle is 3 ‐ 10 mm long. It is built around 3 ‐ 12 very small intrafusal muscle fibers that
are pointed at their ends and attached to the glycocalyx of the surrounding large extrafusal
skeletal muscle fibers
fibers.
Each intrafusal muscle fiber is a very small skeletal muscle fiber, with:
‐ a central region with few or no actin and myosin filaments (does not contract when the ends
do), that functions as a sensory receptor.
‐the end portions that do contract and are excited by small gamma motor /efferent fibers that
originate from small type A gamma motor neurons in the anterior horns of the spinal cord.
Extrafusal skeletal muscle is innervated by large alpha efferent fibers (type A alpha nerve
fibers), that branch many times after they enter the muscle and innervate from three to
several hundred skeletal muscle fibers of the same motor unit.
Nerve connections from the nuclear bag & nuclear chain muscle spindle fibers.
Muscle spindle receptor can be excited in two ways:
- Lengthening the whole muscle stretches the midportion of the
spindle and, therefore, excites the receptor.
- Even if the length of the entire muscle does not change,
contraction of the end portions of the spindle's intrafusal fibers
stretches the midportion of the spindle and therefore excites the
receptor.

15. Golgi tendon organ helps control muscle tension:
encapsulated sensory receptor through which muscle tendon fibers pass.
About 10 ‐ 15 muscle fibers are usually connected to each Golgi tendon organ, and
the organ is stimulated when this small bundle of muscle fibers is "tensed" by
tensed
contracting or stretching the muscle. Thus, the major difference in excitation of the
Golgi tendon organ versus the muscle spindle is that the spindle detects muscle
length and changes in muscle length, whereas the tendon organ detects muscle
tension as reflected by the tension in itself.
Motor units

16. REFLEX RESPONSE
"Damping" Function of the Dynamic and Static Stretch Reflexes
Stretch reflex is able to prevent oscillation or jerkiness of body movements
movements.
This is a damping, or smoothing function.
Damping mechanism in smoothing muscle contraction. Signals from the
spinal cord are often transmitted to a muscle in an unsmooth form, increasing
in intensity for a few milliseconds, then decreasing in intensity, then changing
to another intensity level, and so forth. When the muscle spindle apparatus is
not functioning satisfactorily, the muscle contraction is jerky during the course
of such a signal.

17. The damping mechanism's ability to
smooth muscle contractions, even
though the primary input signals to
the muscle motor system may
themselves be jerky. This effect can
also be called a signal averaging
function of the muscle spindle reflex.
Muscle contraction caused by a spinal cord signal under two conditions:
curve A, in a normal muscle (the muscle spindle reflex of the excited muscle is
intact; the contraction is relatively smooth, even though the motor nerve to the
muscle is excited at a slow frequency of only 8 signals per second. ), and
curve B, in a muscle whose muscle spindles were denervated by section of
the posterior roots of the cord 82 days previously; note the unsmooth muscle
contraction.
Clinical Applications of the Stretch Reflex
Almost every time a clinician performs a physical examination on a patient, he or she
elicits multiple stretch reflexes. The purpose is to determine how much background
excitation, or "tone," the brain is sending to the spinal cord. This reflex is elicited as
follows.
follows
Knee Jerk and Other Muscle Jerks.
Clinically, a method used to determine the sensitivity of the stretch reflexes is to elicit
the knee jerk and other muscle jerks.
The knee jerk can be elicited by simply striking the patellar tendon with a reflex
hammer; this instantaneously stretches the quadriceps muscle and excites a dynamic
stretch reflex that causes the lower leg to "jerk" forward.
myogram from the quadriceps muscle recorded during a knee jerk.
Similar reflexes can be obtained from almost any muscle of the body either by striking
the tendon of the muscle or by striking the belly of the muscle itself. In other words,
sudden stretch of muscle spindles is all that is required to elicit a dynamic stretch reflex.

18. Myograms recorded from the quadriceps muscle during elicitation of the knee jerk (above) and
from the gastrocnemius muscle during ankle clonus (below).
The muscle jerks are used by neurologists to assess the degree of facilitation of spinal cord
j y g g p
centers. When large numbers of facilitatory impulses are being transmitted from the upper
regions of the central nervous system into the cord, the muscle jerks are greatly exaggerated.
Conversely, if the facilitatory impulses are depressed or abrogated, the muscle jerks are
considerably weakened or absent. These reflexes are used most frequently in determining the
presence or absence of muscle spasticity caused by lesions in the motor areas of the brain or
diseases that excite the bulboreticular facilitatory area of the brain stem. Ordinarily, large lesions
in the motor areas of the cerebral cortex but not in the lower motor control areas (especially
lesions caused by strokes or brain tumors) cause greatly exaggerated muscle jerks in the muscles
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