Practical 1 Nervous System:Practical 1, Nervous System:Nervous impulse conduction: nerve d ti l it l th l fconduction velocity along the ulnar nerve of

a human subjectR fl l t t h flReflex responses: muscle stretch reflex

English Module 2nd Year, Physiology Dept., Carol Davila University of Medicine and Pharmacy

Nerve impulse conduction

Axons conduct action potentials away from the cell body of the nerve cellDendrites receive action potentials

Nervous systems use two basic strategies to improve the conduction properties of nerve fibers: (1) increasing the diameter of the axon thus decreasing the internal resistance of(1) increasing the diameter of the axon, thus decreasing the internal resistance of the cable(2) myelination, which increases the electrical insulation around the cable. As axon diameter increases, the conduction velocity of action potentials increases y pbecause the internal resistance of the axoplasm is inversely related to the internal cross-sectional area of the axon.

Saltatory conduction in a myelinated nerve can reach a very high velocity, up to 130 m/s

Local current loops during AP propagationA, The currents flow at one instant in time as a result of AP (active zone). In the adjacent inactive zones, the outward currents lead to a depolarization. If the membrane is not in an absolute refractory period and depolarization is large enough to reach threshold, the immediately adjacent

Local current loops during AP propagation

y p p g g , y jinactive zones will become active and fire their own AP. In the more distant inactive zones, the outward current is not intense enough to cause Vm to reach threshold.

B, The active zone consists of a single node of Ranvier. In a myelinated axon, the currents flow l th h th d h th i li d th d it f N + h l i hi h Thonly through the nodes, where there is no myelin and the density of Na+ channels is very high. The

high current density results in the generation of an AP at the node. Thus, the active zones jump in a "saltatory" manner from one node to another. The internodal membrane (i.e., underneath the myelin) may not ever fire an AP.

In the peripheral nervous system, nerve fibers of various diameters and functions (motor and sensory) are bundled together by connective tissue to form nerves.to o e esA 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 indicate the state of health of p p gthe nerve. Diseases that damage the myelin, destroy neurons, or constrict the whole nerve will decrease the nerve's conduction velocity. However, y ,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) f l t th ti l ti f it t t(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 Precisebetween 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 theThe ulnar nerve comes from the medial cord of the brachial plexus, and runs inferior on the medial/ posterior aspect of 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).

Ulnar Nerve

Stimulation Points:Above Elbow / Below Elbow / Wrist

Objectives 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.

The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to determine the speed of the nerve signals.

EquipmentEquipment

• PC running Windows or Macintosh computer • BIOPAC Software: Biopac Student Lab PRO p• BIOPAC Data Acquisition Unit (MP30) • BIOPAC Stimulator (BSLSTM) • BIOPAC disposable electrodes (EL503) BIOPAC disposable electrodes (EL503) • BIOPAC electrode lead set (SS2L) • BIOPAC human stimulator probe (HSTM01) • Abrasive pads (ELPAD) Abrasive pads (ELPAD) • Electrode gel (GEL1) • Ruler (cm) • Adhesive Tape (TAPE1)• Adhesive Tape (TAPE1) • Pen for marking skin

SetupH dHardware

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 on5. 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 stops7 Plug the HSTM01 human stimulator probe into the Stimulus Output port7. 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 p y ,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.

Subject - Electrode Connections5. 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 electrode7. 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 p p g ymaking sure to not cover up the metal electrode pin connections9. Clip the SS2L electrode cable to the subject’s shirt or clothes to relieve cable strainand avoid pulling on the electrodes.Normal body temperature must be maintained (low body temperature slows nerve conduction)Normal body temperature must be maintained (low body temperature slows nerve conduction).

Experimental MethodYou 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 electrodebelow. 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 Wh d th i t h ld th St t b tt i th PRO3. When ready, the experimenter should press the Start button in the PRO software window (this will begin stimulation and 200msec data 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 thistimestamp 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.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.• 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 notbeen detected, move the stimulating probe to a new position. A responseshould be detected well before the subject experiences any pain.• The recorded response on Channel 40 (blue line, bottom panel) may haveone or two upward peaks followed by a downward deflection.

5. Once you have detected a response, adjust the electrode placement to make surey p , j pthat 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 box6. Administer 3 stimuli at the S1 location and label each stimulus in the marker box as S1-1, S1-2, S1-3.

7. Now reposition the stimulating electrode at the S2 position after applying more gelto this location. Decrease the voltage to 5V less than the value for S1 and repeatthe testing process.Be sure to mark the placement of the black cathode electrode once you haveachieved a response Record 3 stimuli (label these in the marker text box) forachieved a response. Record 3 stimuli (label these in the marker text box) forthe S2 location.

8. Finally, measure the distance in centimeters from the S1 to S2 cathode placementsRecord this distance.

9. You have completed the data collection process and may now disconnect the9. You have completed the data collection process and may now disconnect theelectrodes, turn off the stimulator and BIOPAC MP30 devices, and proceed withcleaning 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 windowBIOPAC 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 rightcorner of the displaycorner of the display.3. Use the curser to select the data from the start of the stimulus (red panel) to thepeak 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 ( k t k) l thi i th lt li dCh1 p-p (peak-to-peak) value – this is the voltage appliedCh40 p-p value – this is the magnitude of the stimulation in the ulnar nerveCh40 delta T value – this is the duration of time between the stimulus andthe nerve signal detected by the recording electrodeg y g

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 the6. Enter the delta T values for S1, S2 and your measured distance between the cathode electrodes for S1 & S2 into a data EXCEL sheet to calculate the speed of conduction using the following formula:

(Distance between S1 and S2) / (delta T for S2 - delta T for S1)(Distance between S1 and S2) / (delta T for S2 - delta T for S1)

NSC mean value ~ 60 m/sec

NCV i l d h di f h d h d f li i ( hNCV is related to the diameter of the nerve and the degree of myelination (the presence of a myelin sheath on the axon) of the nerve. Newborn infants have values that are approximately half that of adults, and adult values are normally reached by age 3 or 4.reached by age 3 or 4.

Most often, abnormal results for NCV are due to some sort of nerve damage or destruction, including:A th (d t th l ti f th ll)- Axonopathy (damage to the long portion of the nerve cell)

- Conduction block (the impulse is blocked somewhere along the nerve pathway)- Demyelination (damage and loss of the fatty insulation surrounding the nerve cell)

Reflex responses

1 - sensory transducer in the periphery, for example, a tactile sensor in the skin. 2 - the pseudounipolar sensory neuron in the circuit; its soma is physically located in a dorsal root gangliondorsal root ganglion3 - 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 is a skeletal muscle.

The withdrawal reflex (nociceptive or flexor withdrawal reflex) is a spinal reflex intended to protect the body from damaging stimuli

Reflex responses

Sensory signals enter the cord

is a spinal reflex intended to protect the body from damaging stimuli.

Sensory signals enter the cord through the sensory (posterior) roots, then 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 effectsother local effects.

(2) Another branch transmits signals to higher levels of the nervous system - to higher levels in the cord itself, to the b i t t thbrain stem, or even to the cerebral cortex

The sensation of uncomfortable heat makes it to the CNS after the motor response to withdraw your hand is initiated. In other words, you move your hand away before you "know why" you're doing it.

Reflex responsesReflex responsesStretch/ myotatic reflexes

The stretch reflexes provide information on the integrity of the central nervous system

d i h l t Thand peripheral nervous system. They are used to determine how much background excitation, or "tone," the brain is sending to the spinal cordthe spinal cord. Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central oneexaggerated reflexes a central one.

Biceps reflex (C5, C6) Brachioradialis reflex (C5, C6, C7) ( , , )Extensor digitorum reflex (C6, C7) Triceps reflex (C6, C7, C8) Patellar reflex / knee-jerk reflex (L2, L3, L4) Ankle jerk reflex (Achilles reflex) (S1, S2) Plantar reflex or Babinski reflex (L5, S1, S2)

Monosynaptic pathway allows a reflex signal to return with the shortest possible timeMonosynaptic pathway allows a reflex signal to return with the shortest possible time delay back to the muscle after excitation of the spindle.

Th d i h i ' bilit tThe damping mechanism's ability to smooth muscle contractions, even though the primary input signals to the muscle motor system may y ythemselves 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: 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 theintact; 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. );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 p y p y;contraction.

Knee Jerk / Patellarreflex

The knee jerk can be elicited by simply striking the patellar tendon with a

Animation at http://www.brainviews.com/abFiles/AniPatellar.htm

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.

The Jendrassik maneuver is a medical maneuver in which the patient flexes both sets of fingers into a hook-like form and interlocks those sets of fingers together. The tendon below the patient's knee isThe tendon below the patient s knee is then hit with a reflex hammer to elicit the patellar reflex. The elicited response is compared with the reflex result of the same action when the maneuver is not in use. Often a larger reflex response will be observed when the patient is occupied with the maneuver as the maneuver maywith the maneuver, as the maneuver may prevent the patient from consciously inhibiting or influencing his or her response to the hammer.

Van Gehuchten A. Les maladies nerveuses. Louvain: Librairie Universitaire, Uystpruyst, 1920