Transcript In The Name of Allah The Most Beneficent The

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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
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Basic Systems of Human
 Neuro-muscular
 Cardio
Vascular
 Respiratory
 Digestive
 Reproductory
 Endocrine
 Lymphatic
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Nervous System

Fast body controls

Majorly divided into

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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/animat
ions/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/NonDrugRem
edies/Pain/p10.htm
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Nerve Conduction Velocity


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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:
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
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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.mcgrawhill.com/sites/0072495855/student_view0/cha
pter14/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



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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



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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
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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 membrane
This 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

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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

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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
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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
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
When neurons receive a stimulus and Na
channels are open they cannot be re
stimulated until they are closed once
Absolute Refractory Period
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Period when another pulse cannot be
generated (during depolarization)
Relative Refractory Period
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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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
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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.mcgrawhill.com/sites/0072495855/student_view0/cha
pter10/animation__action_potentials_and_mu
scle_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 that carry information from sensory
parts to the brain
 Motor

Nerves
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
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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

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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
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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
 EMG
Block Diagram of 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
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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
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Wrist
Elbow
 Recording

site
Thenar Muscle
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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
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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
potential
 One
pattern of many action
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/animat
ions/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
 Optic
test
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.brainhealthan
dpuzzles.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!