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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!