Conduction Velocity and Determining the Site and Extent of Spinal Cord Injuries based on Sensory Deficits The proximity of the Ulnar nerve near the surface at elbow and wrist makes it well suited for studying action potential conduction velocity ID: 724797
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Slide1
Measuring Action Potential
Conduction Velocity
and
Determining the Site and Extent of Spinal Cord Injuries
based on Sensory DeficitsSlide2
The proximity of the Ulnar nerve near the surface at elbow and wrist makes it
well suited for studying action potential conduction velocity.Slide3
The ulnar nerve has both efferent (motor) and afferent (sensory) axons.Slide4
Stimulating the ulnar nerve at the elbow or wrist will produce
s
ensations and contractions of muscles in the hand.
What types of sensory axons are in the ulnar nerve and what will you feel when action potentials are induced in those axons?Slide5
Neuromuscular Junctions (NMJs) and Synaptic Delay
Action potentials in efferent axons arrive at NMJ
Release of neurotransmitter (Acetylcholine)
Depolarization of muscle cell membrane
Appearance of action potential in muscle cells
Muscle contractionSlide6
Choir = a muscle consisting of individual muscle cells (each singer)
Choir output = sum of individual voices
Electromyogram = sum of action potentials for all active muscle cells
Single stimulus (command from conductor) produces Compound Muscle Action PotentialSlide7
Peripheral nerve with afferent and efferent axons
The Neuromuscular Junction and
Synaptic Delay
Cars = action potentials conducted along axons (lanes)
Distance1/time1
Distance2/time2
Distance1-Distance2-/time1-time2 = highway speed = conduction velocity in axons!Slide8
An excellent resource on discriminating between the various causes of muscle weakness demonstrating the diagnostic power of transcutaneous electrical stimulation and recording compound muscle action potentials.
Website
Remember to measure the two distances!Slide9
-
+
Ground
on dorsum
of hand
orSlide10
PowerLab
Scope 4.1 Settings:
Input B = Off, Input A = Ch 3, BioAmp
range
10 mV or 5 mV or as necessary to see Compound Muscle Action Potential
Timebase
= 50 ms
Samples = 2560 (40KHz) Setup/ Stimulator:
Check
Isolated, mode = pulse, delay = 10
ms
, duration =
200
us, Amplitude = 20 mA.
Display:
Overlay stimulator to Input A,
Set up:
Sampling = Sweep
=
Multiple,
32 sweeps
Source= User, 0.5 sec delay,
Display/Overlay All.To examine individual recording, select Display/Overlay None.Use M (Marker) to measure times.
Measure latency from stimulus to first positive or negative peak of Compound Muscle Action Potential from Wrist and from Elbow. Exit Scope software.
Load LabChart software, then exit.Reload Scope program.Slide11
Action Potential Conduction Velocity in Human Ulnar Nerve
Arm
Domin
distance
time
distance
time
Conduction
Tested
Arm
Sex
Athletic
Elbow to Palm
Elbow to Palm
Wrist to Palm
Wrist to Palm
Velocity
L or R
L or R
M or F
Y or N
Subject
E to P mm
E to P ms
W to P mm
W to P ms
CV m/s
tested
dom
sex
Athletic
Enter your data into the Spreadsheet on the Side Bench Computer
Which arm to test is determined randomly by last digit of SSN:
Even number test Right Arm
Odd number test Left Arm.Slide12
Role of Neurophysiologic Evaluation in Diagnosis
Journal of the American Academy of
Orthopaedic Surgeons May/June 200 Vol 8 No. 3 p 190-199
Lawrence R. Robinson
, MD
Dr. Robinson is Professor of Rehabilitation Medicine, University of Washington School of Medicine, Seattle, and Chief of Rehabilitation Medicine and Director,
Electrodiagnostic Medicine Laboratory, Harborview Medical Center, Seattle.
Reprint requests: Dr. Robinson, Rehabilitation Medicine, Harborview Medical Center, Box 359740, 325 Ninth Avenue, Seattle, WA 98104. AbstractThe
electrodiagnostic
evaluation assesses the integrity of the lower-motor-neuron unit (i.e., peripheral nerves, neuromuscular junction, and muscle). Sensory- and motor-nerve conduction studies measure compound action potentials from nerve or muscle and are useful for assessing possible axon loss and/or
demyelination
. Needle electromyography measures electrical activity directly from muscle and provides information about the integrity of the motor unit; it can be used to detect loss of axons (
denervation
) as well as
reinnervation
. The
electrodiagnostic
examination is a useful tool for first detecting abnormalities and then distinguishing problems that affect the peripheral nervous system. In evaluating the patient with extremity trauma, it can differentiate
neurapraxia
from axonal
transection
and can be helpful in following the clinical course. In patients with complex physical findings, it is a useful adjunct that can help discriminate motor neuron disease from
polyneuropathy or
myeloradiculopathy due to spondylosis.Link to the abstract.
This paper describes the various clinical applications of the techniquewere using today! Could be a useful reference for some abstracts.Slide13
source
How are stimuli delivered to one side of the body
processed on the opposite (contralateral) side of the brain?
Right side
Left side
Right side
Left sideSlide14
Right side of body
Left side of body
Left side of brainSlide15
Source
Diagnosis the level and extent of spinal cord injury based on sensory deficits.Slide16
sourceSlide17
For simplicity, all our cases will involve injury either at high cervical levels (which produce sensory deficits in hands and feet) or mid-thoracic levels (which do not affect hands.)Slide18Slide19
Case # 4
All sensations normal except loss of pain and temperature from the right foot.Slide20Slide21Slide22
Body-sense sensations
Proprioceptors are receptors that give information about body position.
These receptors are located in muscles, tendons, ligaments, joints and skin.
Somesthetic
sensations (senses associated with the surface of the body). Mechanoreceptors
detect pressure, force and vibration. These include: Merkel's disks and Meissner's
corpuscles
in the superficial layer of the skin and,
hair follicle receptors,
Pacinian
corpuscles
and
Ruffini's
endings
in deeper layers.
Thermoreceptors
respond to temperature of receptor endings themselves.
Warm receptors
respond to temperature between 30
o
C and 45o C with action potentials increasing as temperature increases. Cold receptors
respond to temperatures between 35o C and 20o C with action potentials increasing as the temperature falls. Both warm and cold receptors respond rapidly to temperature changes and show rapid adaptation. The brain uses the relative changes in the responses of hot and cold receptors to interpret the temperature of the environment.
Nociceptors transduce harmful stimuli that we perceive as pain. These consist of free nerve endings. There are three types of
nociceptors: Mechanical - respond to intense mechanical stimuli. Thermal -
respond to intense heat. Polymodal - respond to a variety of stimuli including mechanical, intense heat and chemicals released from damaged tissue. Slide23Slide24Slide25Slide26Slide27Slide28Slide29
sourceSlide30Slide31
SourceSlide32
Source