in the name of allah the most beneficent the most merciful
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In The Name of Allah The Most Beneficent The Most Merciful. ECE 4552: Medical Electronics Lecture Outline: Neuro - Muscular System. Engr. Ijlal Haider University of Lahore, Lahore. Basic Systems of Human. Neuro -muscular Cardio Vascular Respiratory Digestive Reproductory Endocrine - PowerPoint PPT PresentationTRANSCRIPT
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In The Name of Allah The Most Beneficent The Most Merciful
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ECE 4552:Medical ElectronicsLecture Outline:Neuro-Muscular System
Engr. Ijlal HaiderUniversity of Lahore,
Lahore
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Basic Systems of HumanNeuro-muscularCardio VascularRespiratoryDigestiveReproductoryEndocrineLymphatic
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Nervous System Fast body controls
Majorly divided into Central Nervous System (Brain and Spinal Cord) Neuromuscular System (Peripheral Nerves,
come from the spinal cord to control the muscles of the limbs)
The junction between the peripheral nerve and the muscles is called the neuromuscular junction.
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Neuro-muscular System Two different types of nerves according
to their function: Sensory nerves: that collect sensory
information and pass onto brain via spinal cord
Motor nerves: controlling signals for muscles are sent via motor nerves from brain via spinal cord
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http://outreach.mcb.harvard.edu/animations/mcbOutreachJohnnyPreloader.swf
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Reflex Arc Some motor signals originate in Spinal
Cord itself, REFLEX ARC Muscles have reflex system If something happens suddenly, a signal
is sent from sensory nerves to spinal cord
Spinal cord have reflex arc which will give order to motor nerve and send information to the brain
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Nerves are composed of bundles of Nerve Fibers
Nerve Fibers are made of Nervous Cells called Neurons
Brain contains about 1011 neurons
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Neurons
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Neurons At birth the connection between
Neurons are not established Neurons are not regenerated Body has a cleaning system, all dead
Neurons are removed
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Nature of Pulses Control signals travel along the nerves
called “impulses”
All nerves and muscle control signals are ELECTRICAL
All nerves and muscle control signals are DIGITAL
Due to their electrical nature they are also called Nerve Potential
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Nerve Action Potential
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NAP The peak-to-peak potential remains the
same whatever the conditions may be Strength of sensation is achieved
through frequency of nerve signal pulses
Intensity of Stimulation vs. Pulse Frequency Exhibits logarithmic behavior Frequency may go 500 pps in very strong
sensations
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Nerve Conduction Velocity The speed of nerve impulses varies
enormously in different types of neuron. Fastest travel at about 250 mph, faster
than a Formula 1 racing car. Visit this link for different results on
Speed of Impulse http://www.painstudy.com/NonDrugRemedies/Pain/p10.htm
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Nerve Conduction Velocity For the impulse to travel quickly, the axon
needs to be thick and well insulated. This uses a lot of space and energy, however,
and is found only in neurons that need to transfer information urgently
Neurons that need to transmit electrical signals quickly are sheathed by a fatty substance called myelin (Schwann cells).
Myelin acts as an electrical insulator, and signals travel 20 times faster when it is present.
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Generation of a NAP A Nerve Action Potential is generated due
to movement of ions across the membrane of neurons
Mainly due to movement of Na and K ions Inside the cell: more K and less Na Outside the cell: less K and more Na Inside of the cell is negative with respect
to outside of the cells due to larger size of the K ions as compared Na ions
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Generation of NAP Semipermeable membrane ATP (Atenosine Tri Phosphate): Na+/K+
pump Na+ channels K+ channels
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Generation of NAP Resting potential: -70 mV Threshold: 5-15 mV Action potential:
Depolarization: -55 mV to 30 mV Repolarization: 30 mV to back at resting
potential Hyper polarization: -90 mV Resting potential: -70 mV
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Generation of NAP For interactive simulations
http://outreach.mcb.harvard.edu/animations/actionpotential_short.swf
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
http://www.ncbi.nlm.nih.gov/books/NBK10992/box/A1364/
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RC Equivalent of Nerve Fiber NCV of different
fibers varies Each fiber has its
own delay due to RC nature of fibers
Myelinated neurons conduct electrical impulses more swiftly
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Saltatory Conduction Type of nerve impulse conduction that allows action
potentials to propagate faster and more efficiently Occurs in myelinated nerve fibers in the human body When an NAP travels via saltatory conduction, the
electrical signal jumps from one bare segment of fiber to the next, as opposed to traversing the entire length of the nerve's axon
Saltatory conduction gets its name from the French word “saltare”, which means "to leap."
Saltation saves time and improves energy efficiency in the nervous system
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Myelin Sheath Myelin a whitish, electrically insulating material composed of
lipids and proteins — sheathes the length of myelinated axons
Segments of unmyelinated axon, called Node of Ranvier, interrupt the myelin sheath at intervals
Myelin sheaths wrap themselves around axons and squeeze their myelin contents out to envelope the axon
Schwann cells serve the same function in the peripheral nervous system
The Myelin sheath acts an insulator and prevents electrical charges from leaking through the axon membrane
Virtually all the voltage-gated channels in a myelinated axon concentrate at the nodes of Ranvier
These nodes are spaced approximately .04 inches (about 1 mm) apart
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Saltatory Conduction Advantages of Saltatory Conduction:
Increased conduction velocity Saltatory conduction is about 30-times faster than
continuous conduction
Improved energy efficiency By limiting electrical currents to the nodes of
Ranvier, saltatory conduction allows fewer ions to leak through the membraneThis ultimately saves metabolic energy — a significant advantage since the human nervous system typically uses about 20 percent of the body’s metabolic energy
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Saltatory Conduction
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Saltatory Conduction Myelin insulates the axon and allows the current to spread farther
before it runs out. Knowing that it takes work on the neuron's part to make the
gated channel proteins, it would be a waste of energy for the neuron to put gated channels underneath the myelin, since they could never be used.
Myelinated axons only have gated channels at their nodes. In a demyelinating disease, the myelin sheath decays... the
Schwann cells die selectively. When myelin sheath is gone, the current from the initial action
potential cannot spread far enough to affect the region of the axon where the gated channels are found.
Conductance of the action potential stops and the axon is never able to send its output (the action potential) to its axonal terminals
If this axon innervated muscle, that muscle can no longer be controlled
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Compound Action Potential Each nerve contains hundreds of axons with
different diameters, thresholds and the degree of myelination.
These are categorized as Type A, further subdivided into alpha, beta, gamma and delta- These are myelinated and have larger diameters
Type B- These are also myelinated and have smaller diameters
Type C- These are unmyelinated and smaller in size
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CAP When a nerve is stimulated, the
recorded potential is sum of potential of all NAPs
This potential is known as CAP
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CAP As stimulus strength increases, we recruit
more fibers, therefore more APs add up to produce a larger curve.
Fast fibers will contribute APs that fall towards the start of the CAP
slower fibers will contribute APs that fall towards the tail section
As we gradually increase stimulus strength, we recruit more and more fibers giving rise to a wider CAP, with longer duration
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CAP Properties The duration of the CAP
is the time from the beginning of the positive phase to the end of the negative phase of the CAP.
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CAP Properties The latency of the onset of the CAP is
the time from the onset of the stimulus artifact to the onset of the CAP.
The latency of the peak of the CAP is the time from the onset of the stimulus artifact to the peak of the CAP.
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CAP Properties The latency of the beginning of the CAP
reflects how long it takes for the fastest fibers to conduct action potentials from the stimulus source to the recording electrodes.
When the latency is measured to the peak of the CAP, we obtain the latency of an average fiber in the nerve.
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Refractory Period When neurons receive a stimulus and Na
channels are open they cannot be re stimulated until they are closed once
Absolute Refractory Period Period when another pulse cannot be
generated (during depolarization) Relative Refractory Period
Period when another pulse can be generated but only in presence of a very strong stimulation (during repolarization)
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Electrical Activities of Muscles Similar to that of nerve fibers Except that magnitude of potentials and
time duration are different Conduction velocities are less (muscle
fibers are smaller in length, so not a big issue)
Nerve fibers opens in muscles fibers through a junction
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Muscle Potential is generated in almost the same way as a Nerve Potential is generated (l.e. due to change in ionic concentrations)
Visit following link to know more about generation of muscle potential
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__action_potentials_and_muscle_contraction.html
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A wave of excitation along a muscle fiber initiated at the neuromuscular endplate; accompanied by chemical and electrical changes at the surface of the muscle fiber and by activation of the contractile elements of the muscle fiber; detectable electronically (electromyographically); and followed by a transient refractory period.
Voluntary Muscle System (Normal Muscles-under our conscious control)
Automatic Muscle System (Smooth Muscles-not under our conscious control)
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Sensory Nerves Nerves that carry information from
sensory parts to the brain Motor Nerves
Nerves that carry information from brain to actuating parts
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Vertebrate motoneuron
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Electromyogram Greek words MYOS-Muscle GRAM-Picture Picture of Electrical Activities of Muscles
Voluntary (under willful action of brain) Not good for diagnosis of muscle
disorders which has to be diagnosed early Evoked (on artificial stimulation)
Measurement of Potetial Difference How do we get a potential difference
between two points outside a muscle fiber (or a nerve fiber??)
When Fully Polarized!! Partially Depolarized!! Fully Depolarized!!
When there is partially depolarization, ionic current start flowing which gives rise to voltage
In case of fully polarized or fully depolarized, no current flows and hence we don’t get any voltage out
Ion channel states
Voluntary EMG Measurement Using Skin Surface electrodes Using Needle electrodes
Monopolar Bipolar
Skin Surface Electrodes Compound or composite of Muscle Action Potential
from individual muscle fibers is recorded Sometime called Interference Pattern Contribution from muscle fibers will depend on the
closeness and proximity to the electrodes We cannot make out much on the origin of these
signals We can only use it to find gross muscular disorders
Which can already be felt by muscle weakness and can be visually seen as wasted muscle
Skin Surface Electrodes Surface electrodes are not very much used
for the diagnosis of muscle disorders They are used majorly for evoked potential
study in Nerve Conduction Velocity (NCV)
measurement Bio feedback study or exercise (kind of
mitigation or relaxing) Another application is Bio-feedback for stroke
recovery
Needle Electrodes Monopolar Similar to a coaxial We use instrumentation (differential)
amplifiers Requires 3 probes Active, Reference, Common Common is taken from a skin surface
electrode
Needle Electrodes Bipolar In contrast to monopolar electrodes,
bipolar have two electrodes inside and one outside
Instrument amplifiers are used All three probes are taken from the
bipolar needle electrode itself Mostly used for research purpose
Needle EMG Used for diagnosis of muscle disorders Helps in localizing a focus of disorder
As injecting a pin (needle) inside skin is painful and to diagnose properly multiple points are needed, the whole process becomes very painful
To reduce pain, insertion points are reduced and in each points the angle of pin is changed without bringing needle outside the skin (mostly 3 angles)
Analysis of EMG Analysis is done empirically by doctors
(clinical experiences) Looks for EMG patterns when the needle
is being inserted Listens to the sound produced by
feeding the muscle signal into a loud speaker
Also looks at the pattern and listens to the sound on mild voluntary contraction
Analysis of EMG Signal Processing in EMG For automated diagnosis, pattern
recognition techniques are being investigated
Old instruments used to have integrators
Analysis of EMG Simple Block Diagram of EMG
EMG Amplifiers Filter Display Integrator (signal processing unit) Audio amplifier
Measurement of NCV Using evoked potential Through artificial stimulation of nerve For example by giving a voltage of 100
volts for very short time approximately 2 msec, hand movements must be observed
--fig. evoking an action potential using surface electrodes
Nothing happens under anode (+ve electrode)
Reversal of transmembrane potential occurs under cathode (-ve electrode)
This causes generation of an action potential
Generated action potential travels along the nerves
Similar to a sprint race where a stopwatch is pressed on when runner starts and time is recorded untill he reaches the finish line and velocity is calculated from the distance travelled and time, NCV is recoded by measuring the time for nerve action potential to travel a distance “d” from stimulation point to recording point
Sensory NCV Nerve stimulator applies stimulation
through ring electrodes at fingers Median Nerve contains both sensory
and motor nerves Recording site is selected near middle of
arm
Conventions Cathode of the stimulation electrodes is kept
near the recording side, so that action potential is not perturbed by anode)
Recording electrode which is towards the stimulation side is connected to the inverting input of the amplifier
Common electrode is placed ideally at an equidistant point from both electrodes (to have min common mode voltage)
--fig. stimulation pulse --fig. recording side, stimulation artifacts
and compounded action potential Latency of the pulse is recorded SNVC=d/∆t
Motor NCV In contrast to SNCV measurement, MNCV
measurement involves stimulating at two sites and recording at one
For median nerve Stimulation sites
Wrist Elbow
Recording site Thenar Muscle
Why we stimulate on two sites? Neuromuscular junction has unknown delay Record latencies of proximal and distal
stimulation sites individually (let t1 and t2 be the latencies of both respectively)
Distance between both stimulation sites is taken
--fig. MNVC signals MNCV=d/(t2-t1)
Diagnosis and Diseases If either SNCV or MNCV is significantly
less then normal values? Is the distal latency prolonged?
Causes of low NCV Demyelination Conduction block Axonopathy
Disorders Peripheral Neurotherapy Carpel Tunnel Syndrome (Wrist) GB Syndrome Cervical Spondylosis (Neck) Lumbo-Sacral Spondylosis (Waist)
Nerve Stimulator For a single pulse: Monostable Multi-vibrator For repetitive pulses: Astable Multi-vibrator
Amplitude required: 100-200 volts Pulse duration: less then 2msec
Peak current requirement near to 20 mA (max 50 mA)
Power requirement (for peak power 300x50mA)
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Commonly measured Upper limb, Median, Ulnar, Radial, Lower
Limb, Common Peroneal, Tibial
Class Activity
Electro Encephalo Gram Greek words Encephalo (Brain) Gram (Picture)
Picture of electrical activities of Brain
EEG Interference pattern of many action
potential
One nearer to electrode will dominate Diagnosis are based on Empirical Study
i.e. doing by reasoning
Configuration of Electrodes Needs a standard configuration of
electrodes on the brain 10-20 system is accepted worldwide The top of head is divided into grids of
20%, 20% and 10% from the center to the sides
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http://outreach.mcb.harvard.edu/animations/brainanatomy.swf
Configuration of Electrodes
Configuration of Electrodes EEG potentials are measured between
specified electrodes on this 10-20 grid Usually look for symmetry between right
and left brain, this is useful in diagnosis of Brain Tumor
Look for abnormally large signals to detect Epilepsy
Epilepsy (Petit Mal and Grand Mal)
Typical EEG Signal Normal EEG signal Amplitude: 10-50 micro volts Frequency content: 0.1-30 Hz
Typical EEG Signal Compared to amplitude when awake,
amplitude increases when a person is dozing
It is because of the nature of the interference
When awake more probability of cancellation of phase (more destructive)
When dozing less probability of cancellation (constructive)
Diagnosis
Electrodes are placed on both sides of brain
Activities are measured If both are not symmetrical then there
may be something happening inside e.g. tumor
Diagnosis Epilepsy (seizure) Hyper activity of brain To stimulate seizure, flashes of light are
used (normally for 10-15 min)
Diagnosis Hearing test
Optic nerve test
Evoked EEG EEG response obtained through
stimulations
Audio (Ears) Visual (Eyes) Somatosensory (Nerves)
Audio Evoked Potentials (AEP) Audio Stimulations or Audio Evoked
Potentials (AEP) Slow vertex response (SVR) Brain stem electric response (BSER)
Audio Evoked Potentials (AEP) Used for tests of hearing when subject is
unable to give feedback or where there is possibilities of intentional misinformation
Objective hearing test In contrast to subjective tests where
subject’s feedback is used
Audio Evoked Potentials Give click sound stimulation (pulses) to
the ear through headphones in isolated environment preferably
Record response from the brain In SVR or BSER configuration
Audio Evoked Potentials (AEP) SVR Active electrode at top of head Reference electrode near the ear
(mastoid bone) Common electrode on forehead
Audio Evoked Potentials (AEP) BSER Active electrode at back of brain Reference electrode near the ear
(mastoid bone) Common electrode on forehead
Audio Evoked Potentials (AEP) Latency of SVR: approx. 300 ms Amplitude; few microvolts Needs approx. 50 averages
Latency of BSER: approx. 10 ms Amplitude: < 1 microvolt Needs approx. 1000 averages
Hearing Test Hearing test Usually level of stimulation is reduced
from a high value till there is no evoked response
This gives the threshold of hearing
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Visual Evoked Potential (VEP) Give different pattern of visual
stimulation and record evoked potential from the “visual cortex” at the back of brain.
Reference and common electrodes are at ear and at forehead
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Visual Evoked Potential (VEP) Applications Detect condition of optic nerve for each
age separately If there is tumor pressing on optic nerve,
the latency of the response for the affected side will be prolonged
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Somato Sensory Evoked Potential (SSEP) Stimulate a sensory nerve and record
from brain at the respective area Commonly Median nerve at wrist and
Tibial nerve at the ankle is stimulated
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SSEP Time it takes for nerve fibers to relay a
stimulus from the point of stimulation (wrist or ankle) to a detection site on the scalp, neck or back can be analyzed
By analyzing the SSEP pattern, condition of sensory nerves can be detected
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SSEP For a disorder Multiple Selerosis the
latencies on the both sides will be prolonged due to demyelination
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SNR Improvement Due to low amplitude signals of EEG,
noise can effect the signal measurements
In order to get better Signal to Noise Ratio, a number of samples are recorded and averaged
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Parts of Brain and Functions 3 Major Parts
The Medulla Oblongata helps in control of Autonomic Functions, Relay of Nerve Signals Between the Brain and Spinal Cord Coordination of Body Movements
The Cerebellum is involved in the coordination of voluntary motor movement, balance and equilibrium
The Cerebrum is the newest (evolutionarily) and largest part of the brain as a whole. It is here that things like perception, imagination, thought, judgment, and decision occur (consists of many lobes, links on next slide)
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Parts of Brain and Functions
For interesting information on different parts of brain and their functions, visit
http://www.brainhealthandpuzzles.com/brain_parts_function.html
http://webspace.ship.edu/cgboer/genpsycerebrum.html (for Cerebrum in detail how it controls )
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Thank You!