In The Name of Allah The Most Beneficent The Most Merciful 1

ECE 4552: Medical Electronics Lecture Outline: Neuro-Muscular System Engr. Ijlal Haider University of Lahore, Lahore 2

Basic Systems of Human  Neuro-muscular  Cardio Vascular  Respiratory  Digestive  Reproductory  Endocrine  Lymphatic 3

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. 4

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 5

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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 7

 Nerves are composed of bundles of Nerve Fibers  Nerve Fibers are made of Nervous Cells called Neurons  Brain contains about neurons 8

Neurons 9

 At birth the connection between Neurons are not established  Neurons are not regenerated  Body has a cleaning system, all dead Neurons are removed 10

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 11

Nerve Action Potential 12

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 13

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 edies/Pain/p10.htm edies/Pain/p10.htm 14

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. 15

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 16

Generation of NAP  Semipermeable membrane  ATP (Atenosine Tri Phosphate): Na+/K+ pump  Na+ channels  K+ channels 17

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 18

Generation of NAP  For interactive simulations  /actionpotential_short.swf /actionpotential_short.swf  hill.com/sites/ /student_view0/cha pter14/animation__the_nerve_impulse.html hill.com/sites/ /student_view0/cha pter14/animation__the_nerve_impulse.html  /box/A1364/ /box/A1364/ 19

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 20

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 21

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 22

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 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 23

Saltatory Conduction 24

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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 26

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 27

CAP  When a nerve is stimulated, the recorded potential is sum of potential of all NAPs  This potential is known as CAP 28

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 29

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. 30

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. 31

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. 32

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) 33

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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

 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  hill.com/sites/ /student_view0/cha pter10/animation__action_potentials_and_mu scle_contraction.html hill.com/sites/ /student_view0/cha pter10/animation__action_potentials_and_mu scle_contraction.html 37

 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. 38

 Voluntary Muscle System (Normal Muscles-under our conscious control)  Automatic Muscle System (Smooth Muscles-not under our conscious control)

 Sensory Nerves  Nerves that carry information from sensory parts to the brain  Motor Nerves  Nerves that carry information from brain to actuating parts 40

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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: volts  Pulse duration: less then 2msec  Peak current requirement near to 20 mA (max 50 mA)  Power requirement (for peak power 300x50mA)

Commonly measured  Upper limb, Median, Ulnar, Radial, Lower Limb, Common Peroneal, Tibial  Class Activity 71

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  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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Configuration of Electrodes

 EEG potentials are measured between specified electrodes on this 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: micro volts  Frequency content: 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 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 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

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 91

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 92

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 93

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 94

SSEP  For a disorder Multiple Selerosis the latencies on the both sides will be prolonged due to demyelination 95

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 96

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) 97

Parts of Brain and Functions  For interesting information on different parts of brain and their functions, visit  dpuzzles.com/brain_parts_ function.html dpuzzles.com/brain_parts_ function.html  /cgboer/genpsycerebrum. html (for Cerebrum in detail how it controls ) /cgboer/genpsycerebrum. html 98

Thank You! 99